# Patent

## Title
Sample preparation on a solid support

## Abstract

Presented are methods and compositions for using immobilized transposase and a transposon end for generating an immobilized library of 5′-tagged double-stranded target DNA on a surface. The methods are useful for generating 5′- and 3′-tagged DNA fragments for use in a variety of processes, including massively parallel DNA sequencing.

## Background
RELATED APPLICATIONS
This application claims priority to U.S. Provisional Application No. 61/750,682, filed on Jan. 9, 2013, which is hereby incorporated by reference in its entirety.


BACKGROUND
There are a variety of methods and applications for which it is desirable to generate a library of fragmented and tagged DNA molecules from double-stranded DNA (dsDNA) target molecules. Often, the purpose is to generate smaller DNA molecules (e.g., DNA fragments) from larger dsDNA molecules for use as templates in DNA sequencing reactions.
Many of the methods currently used for fragmentation and tagging of double-stranded DNA for use in next-generation sequencing are wasteful of the DNA, require expensive instruments for fragmentation, and the procedures for fragmentation, tagging and recovering tagged DNA fragments are difficult, tedious, laborious, time-consuming, inefficient, costly, require relatively large amounts of sample nucleic acids. In addition, many of these methods generate tagged DNA fragments that are not fully representative of the sequences contained in the sample nucleic acids from which they were generated. Thus, what is needed in the art are methods that provide speed and ease of use when generating libraries of tagged DNA fragments from target DNA and which can be easily applied to nucleic acid analysis methods such as next-generation sequencing and amplification methods.
BRIEF SUMMARY
Presented herein are methods and compositions for nucleic acid sample preparation on a solid support. The methods and compositions especially relate to methods and compositions for fragmenting and tagging DNA using transposon compositions immobilized to a solid support. The methods and compositions presented herein are useful, for example, for generating libraries of tagged DNA fragments for use, e.g., in next generation sequencing methods, and the like. In some preferred embodiments, the present invention relates to preparation of linear ssDNA fragments on a solid support from target DNA comprising any dsDNA of interest (including double-stranded cDNA prepared from RNA), from any source, for genomic, subgenomic, transcriptomic, or metagenomic analysis, or analysis of RNA expression.
Accordingly, presented herein are methods of preparing an immobilized library of tagged DNA fragments comprising: (a) providing a solid support having transposome complexes immobilized thereon, wherein the transposome complexes comprise a transposase bound to a first polynucleotide, the first polynucleotide comprising (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain; and (b) applying a target DNA to the solid support under conditions whereby the target DNA is fragmented by the transposome complexes, and the 3′ transposon end sequence of the first polynucleotide is transferred to a 5′ end of at least one strand of the fragments; thereby producing an immobilized library of double-stranded fragments wherein at least one strand is 5′-tagged with the first tag. In some embodiments, the transposome complexes comprise a second polynucleotide comprising a region complementary to said transposon end sequence. The methods can further comprise (c) providing transposome complexes in solution and contacting the transposome complexes with the immobilized fragments under conditions whereby the target DNA is fragmented by the transposome complexes in solution; thereby obtaining immobilized nucleic acid fragments having one end in solution. In some embodiments, the transposome complexes in solution can comprise a second tag, such that the method generates immobilized nucleic acid fragments having a second tag, the second tag in solution. The first and second tags can be different or the same.
Also presented herein are solid supports having a library of tagged DNA fragments immobilized thereon prepared according to the above methods or other methods. For example, presented herein are solid supports having transposome complexes immobilized thereon, wherein the transposome complexes comprise a transposase bound to a first polynucleotide, the polynucleotide comprising (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain.
Also presented herein are methods of generating a flowcell, comprising immobilizing a plurality of transposome complexes to a solid support, the transposome complexes comprising a transposase bound to a first polynucleotide, the first polynucleotide comprising (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain.
The methods can further comprise providing a solid support having a plurality the first polynucleotides immobilized thereon, and contacting the solid support with transposase holoenzyme and a second polynucleotide, the second polynucleotide comprising a region complementary to the transposon end sequence. In some embodiments of the methods, immobilizing comprises (a) providing a solid support having amplification primers coupled thereto; (b) hybridizing a second polynucleotide to one of the amplification primers, the second oligonucleotide comprising a region complementary to a transposon end sequence and a region complementary to the first tag; (c) extending the amplification primer using a polymerase to generate a duplex comprising the first polynucleotide hybridized to the second polynucleotide, the first polynucleotide immobilized directly to the solid support; and (d) contacting the solid support with transposase holoenzyme, thereby assembling a transposome complex on the solid support.
Also presented herein is a population of microparticles having transposome complexes immobilized thereto, the transposome complexes comprising a transposase bound to a first polynucleotide and a second polynucleotide; wherein the first polynucleotide is immobilized at its 5′ end to the surface of the microparticle and the second polynucleotide is hybridized to the 3′ end of the first polynucleotide; and wherein the first polynucleotide comprises: (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain. Also presented herein are methods of producing an immobilized library of tagged DNA fragments comprising contacting a target DNA with the above population of microparticles to generate immobilized tagged DNA fragments.
Also presented herein are methods of generating a library of tagged DNA fragments for index-directed assembly into a longer sequence read, the method comprising: providing a population of microparticles having transposome complexes immobilized thereto, the transposome complexes comprising a transposase bound to a first polynucleotide comprising an index domain associated with the microparticle and a second polynucleotide; applying a target DNA to the population of microparticles, thereby generating immobilized DNA fragments that are tagged with the index domain. In certain embodiments of the above methods, the first polynucleotide is immobilized at its 5′ end to the surface of the microparticle and the second polynucleotide is hybridized to the 3′ end of the first polynucleotide; and wherein the first polynucleotide comprises: (i) a 3′ portion comprising a transposon end sequence, and (ii) the index domain; and wherein the population of microparticles comprises at least a plurality of index domains, and wherein the first polynucleotides on an individual microparticle share the same index domain.
Also presented herein is a method for sequencing a plurality of target DNA molecules, comprising: applying a plurality of target DNA to a solid support having transposome complexes immobilized thereon under conditions whereby the target DNA is fragmented by the transposome complexes; thereby producing an immobilized library of double-stranded fragments, wherein a first portion of each target DNA is attached to said solid support at a first location on said solid support and a second portion of each target DNA is attached to said solid support at a second location on said solid support; and mapping said immobilized library of double-stranded fragments to generate a set of locations that are linked by each target DNA; determining the sequences of said first and second portions of the target DNA; and correlating said set of locations to determine which first and second portions are linked by said target DNA and to determine the sequence of the target DNA molecules.
In some embodiments of the methods and compositions presented herein, the transposome complexes are present on the solid support at a density of at least 103, 104, 105, 106 complexes per mm2. In some embodiments, the transposome complex comprises a hyperactive transposase, such as Tn5 transposase.
In some embodiments of the methods and compositions presented herein, the tag domain can comprise, for example, a region for cluster amplification. In some embodiments, the tag domain can comprise a region for priming a sequencing reaction.
In some embodiments of the methods and compositions presented herein, the solid support can comprise, for example, microparticles, a patterned surface, wells and the like. In some embodiments, the transposome complexes are randomly distributed upon the solid support. In some embodiments, the transposome complexes are distributed on a patterned surface.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a shows the general concept according to one embodiment. FIG. 1b shows the general concept according to one embodiment.
FIG. 2a is a schematic illustrating a tagmentation reaction.
FIG. 2b is a schematic with the resulting bridge redrawn to clarify the nature of the resulting bridge.
FIG. 3a illustrates an embodiment where two forms of transposome are assembled on the surface of a flowcell. Addition of DNA to the flowcell results in tagmentation and coupling of the DNA to the transposomes. Also shown in FIG. 3a are different types of resulting clusters: P7:P7, P5:P5, and P5:P7 clusters. 3b illustrates an embodiment where two forms of transposome are assembled on the surface of a flowcell.
FIG. 4a illustrates another embodiment. In FIG. 4a, only one form of surface bound transposome (e.g. P5 transposome) is present, resulting in bridges having the same tag sequence at each end. Additional transposomes are added to further fragment the bridge structures and incorporate an additional tag sequence (P7).
FIG. 4b shows amplification to generate pairs of clusters resulting from each transposome stump which represent two adjacent fragments in the original intact DNA sample (FIG. 4b).
FIGS. 5a, 5b, 5c and 5d illustrate different methods for assembling surface bound transposome complexes. FIG. 5a shows one embodiment of this method for assembling the surface bound transposome complexes. FIG. 5b shows transposome complexes are assembled in solution and immobilizing comprises a further step of ligating the first polynucleotide to a splint oligonucleotide coupled to the solid support. FIG. 5c shows a transposome dimer is assembled by hybridizing a looped oligonucleotide to an immobilized first polynucleotide. FIG. 5d shows transposome complexes can be assembled on a standard paired end flow cell with amplification primers immobilized thereto.
FIG. 6a sets forth the design for an experiment set forth as Example 1. FIG. 6b sets forth the design for an experiment set forth as Example 1.
FIG. 7 sets forth representative data obtained in an experiment conducted according to the design set forth in Example 1.
FIG. 8 sets forth representative data obtained in an experiment conducted according to the design set forth in Example 1.
FIG. 9 is an illustration of assembly of bead-bound transposomes and subsequent tagmentation according to one embodiment.
FIG. 10 is an illustration of assembly of bead-bound transposomes and subsequent tagmentation according to one embodiment.
FIG. 11 is an illustration of assembly of bead-bound transposomes and subsequent tagmentation according to one embodiment.
FIG. 12 is an illustration of assembly of bead-bound transposomes and subsequent tagmentation according to one embodiment.
FIG. 13 is an illustration of surface bound transposomes according to one embodiment.
FIG. 14 is an illustration of tagmentation performed on bead-bound transposomes according to one embodiment.
FIG. 15 is an illustration of tagmentation and barcoding of sub-fragments performed on bead-bound transposomes according to one embodiment.
FIG. 16 is an illustration of tagmentation and barcoding of sub-fragments performed on bead-bound transposomes according to one embodiment.
FIG. 17 is an illustration of transposome assembly as described in Example 3.
FIG. 18a is an illustration of transposome assembly as described in Example 3.
FIG. 18b sets forth results using transposome assembly as described in Example 3.



DETAILED DESCRIPTION
Current protocols for sequencing nucleic acid samples routinely employ a sample preparation process that converts DNA or RNA into a library of templates. These methods can result in loss of DNA sample and often require expensive instruments for fragmentation. In addition, the sample preparation methods are often difficult, tedious, and inefficient.
In standard sample preparation methods, each template contains an adaptor at either end of the insert and often a number of steps are required to both modify the DNA or RNA and to purify the desired products of the modification reactions. These steps are performed in solution prior to the addition of the adapted fragments to a flowcell where they are coupled to the surface by a primer extension reaction that copies the hybridized fragment onto the end of a primer covalently attached to the surface. These ‘seeding’ templates then give rise to monoclonal clusters of copied templates through several cycles of amplification.
The number of steps required to transform DNA into adaptor-modified templates in solution ready for cluster formation and sequencing can be minimized by the use of transposase mediated fragmentation and tagging. This process, referred to herein as ‘tagmentation,’ often involves the modification of DNA by a transposome complex comprising transposase enzyme complexed with adaptors comprising transposon end sequence. Tagmentation results in the simultaneous fragmentation of the DNA and ligation of the adaptors to the 5′ ends of both strands of duplex fragments. Following a purification step to remove the transposase enzyme, additional sequences are added to the ends of the adapted fragments by PCR.
Solution-based tagmentation has drawbacks and requires several labor-intensive steps. Additionally, bias can be introduced during PCR amplification steps. The methods and compositions presented herein overcome those drawbacks and allow unbiased sample preparation, cluster formation and sequencing to occur on a single solid support with minimal requirements for sample manipulation or transfer.
The present disclosure relates to the surprising discovery that transposome complexes pre-coupled to the surface of a flowcell can effectively fragment, tag and immobilize intact DNA within the flowcell. In specific embodiments, one or more of the strands that comprise the transposome adaptors are attached to the surface of the flowcell via their 5′ end. When intact DNA is pumped onto the flowcell, the tagmentation reaction occurs in the same manner as occurs in solution-based tagmentation reactions, but the resulting product fragments are physically attached to the surface of the flowcell by their ends. The transposome adaptor sequences can contain sequences that enable subsequent cluster generation and sequencing.
The methods and compositions presented herein provide several advantages over solution-based tagmentation methods. For example, purified, partially purified or even unpurified intact DNA template can be loaded directly onto a flowcell for generation of clusters, without prior sample preparation. In addition, the contiguity of sequence information in the original intact DNA can be physically preserved by the juxtaposition of tagmented fragments on the surface of the flowcell. As a further advantage, DNA is physically linked to the surface of the flowcell so purification of reagents following further manipulation of the DNA can be achieved by flow-through buffer exchange in the flowcell channel.
Tagmentation on a Solid Support
In accordance with the above, presented herein are methods of preparing an immobilized library of tagged DNA fragments. In some embodiments, the methods can comprise: (a) providing a solid support having transposome complexes immobilized thereon, wherein the transposome complexes comprise a transposase bound to a first polynucleotide, the first polynucleotide comprising (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain; and (b) applying a target DNA to the solid support under conditions whereby the target DNA is fragmented by the transposome complexes, and the 3′ transposon end sequence of the first polynucleotide is transferred to a 5′ end of at least one strand of the fragments; thereby producing an immobilized library of double-stranded fragments wherein at least one strand is 5′-tagged with the first tag.
As used herein, the term “transposome complex” refers generally to a transposase enzyme non-covalently bound to a double stranded nucleic acid. For example, the complex can be a transposase enzyme preincubated with double-stranded transposon DNA under conditions that support non-covalent complex formation. Double-stranded transposon DNA can include, without limitation, Tn5 DNA, a portion of Tn5 DNA, a transposon end composition, a mixture of transposon end compositions or other double-stranded DNAs capable of interacting with a transposase such as the hyperactive Tn5 transposase.
A “transposase” means an enzyme that is capable of forming a functional complex with a transposon end-containing composition (e.g., transposons, transposon ends, transposon end compositions) and catalyzing insertion or transposition of the transposon end-containing composition into the double-stranded target DNA with which it is incubated, for example, in an in vitro transposition reaction. A transposase as presented herein can also include integrases from retrotransposons and retroviruses. Transposases, transposomes and transposome complexes are generally known to those of skill in the art, as exemplified by the disclosure of US 2010/0120098, the content of which is incorporated herein by reference in its entirety. Although many embodiments described herein refer to Tn5 transposase and/or hyperactive Tn5 transposase, it will be appreciated that any transposition system that is capable of inserting a transposon end with sufficient efficiency to 5′-tag and fragment a target DNA for its intended purpose can be used in the present invention. In particular embodiments, a preferred transposition system is capable of inserting the transposon end in a random or in an almost random manner to 5′-tag and fragment the target DNA.
The term “transposon end” refers to a double-stranded nucleic acid DNA that exhibits only the nucleotide sequences (the “transposon end sequences”) that are necessary to form the complex with the transposase or integrase enzyme that is functional in an in vitro transposition reaction. In some embodiments, a transposon end is capable of forming a functional complex with the transposase in a transposition reaction. As non-limiting examples, transposon ends can include the 19-bp outer end (“OE”) transposon end, inner end (“IE”) transposon end, or “mosaic end” (“ME”) transposon end recognized by a wild-type or mutant Tn5 transposase, or the R1 and R2 transposon end as set forth in the disclosure of US 2010/0120098, the content of which is incorporated herein by reference in its entirety. Transposon ends can comprise any nucleic acid or nucleic acid analogue suitable for forming a functional complex with the transposase or integrase enzyme in an in vitro transposition reaction. For example, the transposon end can comprise DNA, RNA, modified bases, non-natural bases, modified backbone, and can comprise nicks in one or both strands. Although the term “DNA” is used throughout the present disclosure in connection with the composition of transposon ends, it should be understood that any suitable nucleic acid or nucleic acid analogue can be utilized in a transposon end.
The term “transferred strand” refers to the transferred portion of both transposon ends. Similarly, the term “non-transferred strand” refers to the non-transferred portion of both “transposon ends.” The 3′-end of a transferred strand is joined or transferred to target DNA in an in vitro transposition reaction. The non-transferred strand, which exhibits a transposon end sequence that is complementary to the transferred transposon end sequence, is not joined or transferred to the target DNA in an in vitro transposition reaction.
In some embodiments, the transferred strand and non-transferred strand are covalently joined. For example, in some embodiments, the transferred and non-transferred strand sequences are provided on a single oligonucleotide, e.g., in a hairpin configuration. As such, although the free end of the non-transferred strand is not joined to the target DNA directly by the transposition reaction, the non-transferred strand becomes attached to the DNA fragment indirectly, because the non-transferred strand is linked to the transferred strand by the loop of the hairpin structure. Additional examples of transposome structure and methods of preparing and using transposomes can be found in the disclosure of US 2010/0120098, the content of which is incorporated herein by reference in its entirety.
The terms “tag” and “tag domain” as used herein refer to a portion or domain of a polynucleotide that exhibits a sequence for a desired intended purpose or application. Some embodiments presented herein include a transposome complex comprising a polynucleotide having a 3′ portion comprising a transposon end sequence, and tag comprising a tag domain. Tag domains can comprise any sequence provided for any desired purpose. For example, in some embodiments, a tag domain comprises one or more restriction endonuclease recognition sites. In some embodiments, a tag domain comprises one or more regions suitable for hybridization with a primer for a cluster amplification reaction. In some embodiments, a tag domain comprises one or more regions suitable for hybridization with a primer for a sequencing reaction. It will be appreciated that any other suitable feature can be incorporated into a tag domain. In some embodiments, the tag domain comprises a sequence having a length between 5 and 200 bp. In some embodiments, the tag domain comprises a sequence having a length between 10 and 100 bp. In some embodiments, the tag domain comprises a sequence having a length between 20 and 50 bp. In some embodiments, the tag domain comprises a sequence having a length between 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150 and 200 bp.
In the methods and compositions presented herein, transposome complexes are immobilized to the solid support. In some embodiments, the transposome complexes are immobilized to the support via one or more polynucleotides, such as a polynucleotide comprising a transposon end sequence. In some embodiments, the transposome complex may be immobilized via a linker molecule coupling the transposase enzyme to the solid support. In some embodiments, both the transposase enzyme and the polynucleotide are immobilized to the solid support. When referring to immobilization of molecules (e.g. nucleic acids) to a solid support, the terms “immobilized” and “attached” are used interchangeably herein and both terms are intended to encompass direct or indirect, covalent or non-covalent attachment, unless indicated otherwise, either explicitly or by context. In certain embodiments of the invention covalent attachment may be preferred, but generally all that is required is that the molecules (e.g. nucleic acids) remain immobilized or attached to the support under the conditions in which it is intended to use the support, for example in applications requiring nucleic acid amplification and/or sequencing.
Certain embodiments of the invention may make use of solid supports comprised of an inert substrate or matrix (e.g. glass slides, polymer beads etc.) which has been functionalized, for example by application of a layer or coating of an intermediate material comprising reactive groups which permit covalent attachment to biomolecules, such as polynucleotides. Examples of such supports include, but are not limited to, polyacrylamide hydrogels supported on an inert substrate such as glass, particularly polyacrylamide hydrogels as described in WO 2005/065814 and US 2008/0280773, the contents of which are incorporated herein in their entirety by reference. In such embodiments, the biomolecules (e.g. polynucleotides) may be directly covalently attached to the intermediate material (e.g. the hydrogel) but the intermediate material may itself be non-covalently attached to the substrate or matrix (e.g. the glass substrate). The term “covalent attachment to a solid support” is to be interpreted accordingly as encompassing this type of arrangement.
The terms “solid surface,” “solid support” and other grammatical equivalents herein refer to any material that is appropriate for or can be modified to be appropriate for the attachment of the transposome complexes. As will be appreciated by those in the art, the number of possible substrates is very large. Possible substrates include, but are not limited to, glass and modified or functionalized glass, plastics (including acrylics, polystyrene and copolymers of styrene and other materials, polypropylene, polyethylene, polybutylene, polyurethanes, TeflonTM, etc.), polysaccharides, nylon or nitrocellulose, ceramics, resins, silica or silica-based materials including silicon and modified silicon, carbon, metals, inorganic glasses, plastics, optical fiber bundles, and a variety of other polymers. Particularly useful solid supports and solid surfaces for some embodiments are located within a flow cell apparatus. Exemplary flow cells are set forth in further detail below.
In some embodiments, the solid support comprises a patterned surface suitable for immobilization of transposome complexes in an ordered pattern. A “patterned surface” refers to an arrangement of different regions in or on an exposed layer of a solid support. For example, one or more of the regions can be features where one or more transposome complexes are present. The features can be separated by interstitial regions where transposome complexes are not present. In some embodiments, the pattern can be an x-y format of features that are in rows and columns. In some embodiments, the pattern can be a repeating arrangement of features and/or interstitial regions. In some embodiments, the pattern can be a random arrangement of features and/or interstitial regions. In some embodiments, the transposome complexes are randomly distributed upon the solid support. In some embodiments, the transposome complexes are distributed on a patterned surface. Exemplary patterned surfaces that can be used in the methods and compositions set forth herein are described in U.S. Ser. No. 13/661,524 or US Pat. App. Publ. No. 2012/0316086 A1, each of which is incorporated herein by reference.
In some embodiments, the solid support comprises an array of wells or depressions in a surface. This may be fabricated as is generally known in the art using a variety of techniques, including, but not limited to, photolithography, stamping techniques, molding techniques and microetching techniques. As will be appreciated by those in the art, the technique used will depend on the composition and shape of the array substrate.
The composition and geometry of the solid support can vary with its use. In some embodiments, the solid support is a planar structure such as a slide, chip, microchip and/or array. As such, the surface of a substrate can be in the form of a planar layer. In some embodiments, the solid support comprises one or more surfaces of a flowcell. The term “flowcell” as used herein refers to a chamber comprising a solid surface across which one or more fluid reagents can be flowed. Examples of flowcells and related fluidic systems and detection platforms that can be readily used in the methods of the present disclosure are described, for example, in Bentley et al., Nature 456:53-59 (2008), WO 04/018497; U.S. Pat. No. 7,057,026; WO 91/06678; WO 07/123744; U.S. Pat. No. 7,329,492; U.S. Pat. No. 7,211,414; U.S. Pat. No. 7,315,019; U.S. Pat. No. 7,405,281, and US 2008/0108082, each of which is incorporated herein by reference.
In some embodiments, the solid support or its surface is non-planar, such as the inner or outer surface of a tube or vessel. In some embodiments, the solid support comprises microspheres or beads. By “microspheres” or “beads” or “particles” or grammatical equivalents herein is meant small discrete particles. Suitable bead compositions include, but are not limited to, plastics, ceramics, glass, polystyrene, methylstyrene, acrylic polymers, paramagnetic materials, thoria sol, carbon graphite, titanium dioxide, latex or cross-linked dextrans such as Sepharose, cellulose, nylon, cross-linked micelles and teflon, as well as any other materials outlined herein for solid supports may all be used. “Microsphere Detection Guide” from Bangs Laboratories, Fishers Ind. is a helpful guide. In certain embodiments, the microspheres are magnetic microspheres or beads.
The beads need not be spherical; irregular particles may be used. Alternatively or additionally, the beads may be porous. The bead sizes range from nanometers, i.e. 100 nm, to millimeters, i.e. 1 mm, with beads from about 0.2 micron to about 200 microns being preferred, and from about 0.5 to about 5 micron being particularly preferred, although in some embodiments smaller or larger beads may be used.
FIGS. 1a and 1b generally illustrate the method according to one embodiment. A solid support coated with grafted oligonucleotides is shown, some of which contain the ME sequences, will form active transposome complexes that are physically coupled to the solid support in the presence of Tn5. The density of these surface bound transposomes can be modulated by varying the density of the grafted oligonucleotides containing the ME sequence or by the amount of transposase added to the solid support. For example, in some embodiments, the transposome complexes are present on the solid support at a density of at least 103, 104, 105, or at least 106 complexes per mm2.
When double stranded DNA is added to the solid support, the transposome complexes will tagment added DNA, thus generating ds fragments coupled at both ends to the surface. In some embodiments, the length of bridged fragments can be varied by changing the density of the transposome complexes on the surface. In certain embodiments, the length of the resulting bridged fragments is less than 100 bp, 200 bp, 300 bp, 400 bp, 500 bp, 600 bp, 700 bp, 800 bp, 900 bp, 1000 bp, 1100 bp, 1200 bp, 1300 bp, 1400 bp, 1500 bp, 1600 bp, 1700 bp, 1800 bp, 1900 bp, 2000 bp, 2100 bp, 2200 bp, 2300 bp, 2400 bp, 2500 bp, 2600 bp, 2700 bp, 2800 bp, 2900 bp, 3000 bp, 3100 bp, 3200 bp, 3300 bp, 3400 bp, 3500 bp, 3600 bp, 3700 bp, 3800 bp, 3900 bp, 4000 bp, 4100 bp, 4200 bp, 4300 bp, 4400 bp, 4500 bp, 4600 bp, 4700 bp, 4800 bp, 4900 bp, 5000 bp, 10000 bp, 30000 bp or less than 100,000 bp. In such embodiments, the bridged fragments can then be amplified into clusters using standard cluster chemistry, as exemplified by the disclosure of U.S. Pat. Nos. 7,985,565 and 7,115,400, the contents of each of which is incorporated herein by reference in its entirety.
In some embodiments, the length of the templates is longer than what can be suitably amplified using standard cluster chemistry. For example, in some embodiments, the length of templates is longer than 100 bp, 200 bp, 300 bp, 400 bp, 500 bp, 600 bp, 700 bp, 800 bp, 900 bp, 1000 bp, 1100 bp, 1200 bp, 1300 bp, 1400 bp, 1500 bp, 1600 bp, 1700 bp, 1800 bp, 1900 bp, 2000 bp, 2100 bp, 2200 bp, 2300 bp, 2400 bp, 2500 bp, 2600 bp, 2700 bp, 2800 bp, 2900 bp, 3000 bp, 3100 bp, 3200 bp, 3300 bp, 3400 bp, 3500 bp, 3600 bp, 3700 bp, 3800 bp, 3900 bp, 4000 bp, 4100 bp, 4200 bp, 4300 bp, 4400 bp, 4500 bp, 4600 bp, 4700 bp, 4800 bp, 4900 bp, 5000 bp, 10000 bp, 30000 bp or longer than 100,000 bp. In such embodiments, then a second tagmentation reaction can be performed by adding transposomes from solution that further fragment the bridges, as illustrated, for example, in FIG. 4a. The second tagmentation reaction can thus remove the internal span of the bridges, leaving short stumps anchored to the surface that can converted into clusters ready for further sequencing steps. In particular embodiments, the length of the template can be within a range defined by an upper and lower limit selected from those exemplified above.
In certain embodiments, prior to cluster generation, the DNA immobilized by surface tagmentation can imaged. For example, the immobilized DNA can be stained with an interchelating dye and imaged to preserve a record of the position of the backbone of the DNA molecule on the surface. Following cluster generation and sequencing, the coordinates of clusters can be associated with their position on the original backbone, thus assisting in alignment of reads along a molecule and genome assembly.
In some embodiments, the step of applying a target DNA comprises adding a biological sample to said solid support. The biological sample can be any type that comprises DNA and which can be deposited onto the solid surface for tagmentation. For example, the sample can comprise DNA in a variety of states of purification, including purified DNA. However, the sample need not be completely purified, and can comprise, for example, DNA mixed with protein, other nucleic acid species, other cellular components and/or any other contaminant. As demonstrated in Example 2 below, in some embodiments, the biological sample comprises a mixture of DNA, protein, other nucleic acid species, other cellular components and/or any other contaminant present in approximately the same proportion as found in vivo. For example, in some embodiments, the components are found in the same proportion as found in an intact cell. In some embodiments, the biological sample has a 260/280 ratio of less than 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, or less than 0.60. In some embodiments, the biological sample has a 260/280 ratio of at least 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, or at least 0.60. Because the methods provided herein allow DNA to be bound to a solid support, other contaminants can be removed merely by washing the solid support after surface bound tagmentation occurs. The biological sample can comprise, for example, a crude cell lysate or whole cells. For example, a crude cell lysate that is applied to a solid support in a method set forth herein, need not have been subjected to one or more of the separation steps that are traditionally used to isolate nucleic acids from other cellular components. Exemplary separation steps are set forth in Maniatis et al., Molecular Cloning: A Laboratory Manual, 2d Edition, 1989, and Short Protocols in Molecular Biology, ed. Ausubel, et al, hereby incorporated by reference.
Thus, in some embodiments, the biological sample can comprise, for example, blood, plasma, serum, lymph, mucus, sputum, urine, semen, cerebrospinal fluid, bronchial aspirate, feces, and macerated tissue, or a lysate thereof, or any other biological specimen comprising DNA. One advantage of the methods and compositions presented herein that a biological sample can be added to the flowcell and subsequent lysis and purification steps can all occur in the flowcell without further transfer or handling steps, simply by flowing the necessary reagents into the flowcell. Examples 1 and 2 below demonstrate successful application of crude cell lysates to the methods and compositions provided herein.
FIGS. 2a and 2b further illustrate the tagmentation reaction according to one embodiment. As shown in FIG. 2a, transposomes comprise a dimer of Tn5 with each monomer binding a double stranded molecule, i.e. the ME adaptor. One strand of the ME adaptor is covalently attached to the surface of a flowcell. Transposomes bind target DNA and generate two nicks in the DNA backbone, 9 bases apart on either strand. Although FIG. 2a shows a 9 bp gap between nicks, in other embodiments, the transposome can generate a gap of 7, 8, 9, 10, 11, or 12 bp between nicks. Only one of the two strands of each ME adaptor is ligated to the 5′ strand at each nick position. This strand ‘the transferred strand’ is grafted to the surface of the flowcell via its 5′ end. The resulting bridge of the surface tagmentation is redrawn in FIG. 2b to clarify the nature of the resulting bridge.
FIGS. 3a and 3b illustrate an example of the invention put into practice. Two forms of transposome are assembled on the surface of a flowcell. The first form comprises a P7 transposome in which the ‘transfer strand’ of the ME adaptor comprises an extended oligonucleotide sequence linking the transposome to the surface including an amplification domain (P7) and a sequencing primer (S2). The second form comprises a P5 transposome in which the ‘transfer strand’ of the ME adaptor comprises an extended oligonucleotide sequence linking the transposome to the surface including an amplification domain (P5) and a sequencing primer (S1). Addition of DNA to the flowcell results in tagmentation and coupling of the DNA to the transposomes. Three types of bridges result: P5-P5, P7-P7 and P5-P7. Following cluster formation and linearization (FIG. 3b), either P5-P5 or P7-P7 clusters are removed (depending on linearization). As shown in FIG. 3b, if linearization happens via P5, then only the P5-P7 and P7-P7 bridges remain. P7-P7 clusters are not linearized by this reaction and therefore will not sequence. P7-P7 clusters are subsequently removed during Read 2 linearization for sequencing.
The method presented herein can further comprise an additional step of providing transposome complexes in solution and contacting the solution-phase transposome complexes with the immobilized fragments under conditions whereby the target DNA is fragmented by the transposome complexes solution; thereby obtaining immobilized nucleic acid fragments having one end in solution. In some embodiments, the transposome complexes in solution can comprise a second tag, such that the method generates immobilized nucleic acid fragments having a second tag, the second tag in solution. The first and second tags can be different or the same.
In some embodiments, one form of surface bound transposome is predominantly present on the solid support. For example, in some embodiments, at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or at least 99% of the tags present on said solid support comprise the same tag domain. In such embodiments, after an initial tagmentation reaction with surface bound transposomes, at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or at least 99% of the bridge structures comprise the same tag domain at each end of the bridge. A second tagmentation reaction can be performed by adding transposomes from solution that further fragment the bridges. In some embodiments, most or all of the solution phase transposomes comprise a tag domain that differs from the tag domain present on the bridge structures generated in the first tagmentation reaction. For example, in some embodiments, at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or at least 99% of the tags present in the solution phase transposomes comprise the a tag domain that differs from the tag domain present on the bridge structures generated in the first tagmentation reaction.
FIGS. 4a and 4b illustrate this embodiment. The solid support shown in FIG. 4a comprises only surface bound transposome comprising a single type of tag sequence (e.g. P5 transposome). In this instance, all tagmented bridges are P5-P5 bridges. A P7 transposome is added from solution and tagments into the bridges making all surface bound molecules P5-P7 templates. The surface bound fragments can be subsequently converted into clusters (see, for example, FIG. 4b). Furthermore, a pair of clusters will result from each transposome stump which represent the two adjacent fragments in the original intact DNA sample (FIG. 4b).
Also presented herein are solid supports having a library of tagged DNA fragments immobilized thereon prepared according to the above methods.
Physical Maps of Immobilized Polynucleotide Molecules
Also presented herein are methods of generating a physical map of immobilized polynucleotides. The methods can advantageously be exploited to identify clusters likely to contain linked sequences (i.e., the first and second portions from the same target polynucleotide molecule). The relative proximity of any two clusters resulting from an immobilized polynucleotide thus provides information useful for alignment of sequence information obtained from the two clusters. Specifically, the distance between any two given clusters on a solid surface is positively correlated with the probability that the two clusters are from the same target polynucleotide molecule, as described in greater detail in WO 2012/025250, which is incorporated herein by reference in its entirety.
As an example, in some embodiments, long dsDNA molecules stretching out over the surface of a flowcell are tagmented in situ, resulting in a line of connected dsDNA bridges across the surface of the flowcell. Further, a physical map of the immobilized DNA can then be generated. The physical map thus correlates the physical relationship of clusters after immobilized DNA is amplified. Specifically, the physical map is used to calculate the probability that sequence data obtained from any two clusters are linked, as described in the incorporated materials of WO 2012/025250.
In some embodiments, the physical map is generated by imaging the DNA to establish the location of the immobilized DNA molecules across a solid surface. In some embodiments, the immobilized DNA is imaged by adding an imaging agent to the solid support and detecting a signal from the imaging agent. In some embodiments, the imaging agent is a detectable label. Suitable detectable labels, include, but are not limited to, protons, haptens, radionuclides, enzymes, fluorescent labels, chemiluminescent labels, and/or chromogenic agents. For example, in some embodiments, the imaging agent is an intercalating dye or non-intercalating DNA binding agent. Any suitable intercalating dye or non-intercalating DNA binding agent as are known in the art can be used, including, but not limited to those set forth in U.S. 2012/0282617, which is incorporated herein by reference in its entirety.
In some embodiments, the immobilized double stranded fragments are further fragmented to liberate a free end (see FIG. 4a) prior to cluster generation (FIG. 4b). Cleaving bridged structures can be performed using any suitable methodology as is known in the art, as exemplified by the incorporated materials of WO 2012/025250. For example, cleavage can occur by incorporation of a modified nucleotide, such as uracil as described in WO 2012/025250, by incorporation of a restriction endonuclease site, or by applying solution-phase transposome complexes to the bridged DNA structures, as described elsewhere herein.
In certain embodiments, a plurality of target DNA molecules is flowed onto a flowcell comprising a plurality of nano-channels, the nano-channel having a plurality of transposome complexes immobilized thereto. As used herein, the term nano-channel refers to a narrow channel into which a long linear DNA molecule is flown. In some embodiments, no more than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900 or no more than 1000 individual long strands of target DNA are flowed into each nano-channel. In some embodiments the individual nano-channels are separated by a physical barrier which prevents individual long strands of target DNA from interacting with multiple nano-channels. In some embodiments, the solid support comprises at least 10, 50, 100, 200, 500, 1000, 3000, 5000, 10000, 30000, 50000, 80000 or at least 100000 nano-channels. In some embodiments, transposomes bound to the surface of a nano-channel tagment the DNA. Contiguity mapping can then be performed, for example, by following the clusters down the length of one of these channels. In some embodiments, the long strand of target DNA can be at least 0.1 kb, 1 kb, 2 kb, 3 kb, 4 kb, 5 kb, 6 kb, 7 kb, 8 kb, 9 kb, 10 kb, 15 kb, 20 kb, 25 kb, 30 kb, 35 kb, 40 kb, 45 kb, 50 kb, 55 kb, 60 kb, 65 kb, 70 kb, 75 kb, 80 kb, 85 kb, 90 kb, 95 kb, 100 kb, 150 kb, 200 kb, 250 kb, 300 kb, 350 kb, 400 kb, 450 kb, 500 kb, 550 kb, 600 kb, 650 kb, 700 kb, 750 kb, 800 kb, 850 kb, 900 kb, 950 kb, 1000 kb, 5000 kb, 10000 kb, 20000 kb, 30000 kb, or at least 50000 kb in length. In some embodiments, the long strand of target DNA is no more than 0.1 kb, 1 kb, 2 kb, 3 kb, 4 kb, 5 kb, 6 kb, 7 kb, 8 kb, 9 kb, 10 kb, 15 kb, 20 kb, 25 kb, 30 kb, 35 kb, 40 kb, 45 kb, 50 kb, 55 kb, 60 kb, 65 kb, 70 kb, 75 kb, 80 kb, 85 kb, 90 kb, 95 kb, 100 kb, 150 kb, 200 kb, 250 kb, 300 kb, 350 kb, 400 kb, 450 kb, 500 kb, 550 kb, 600 kb, 650 kb, 700 kb, 750 kb, 800 kb, 850 kb, 900 kb, 950 kb, or no more than 1000 kb in length. As an example, a flowcell having 1000 or more nano-channels with mapped immobilized tagmentation products in the nano-channels can be used to sequence the genome of an organism with short ‘positioned’ reads. In some embodiments, mapped immobilized tagmentation products in the nano-channels can be used resolve haplotypes. In some embodiments, mapped immobilized tagmentation products in the nano-channels can be used to resolve phasing issues.
Amplification and Sequencing Immobilized DNA Fragments
Amplification.
The present disclosure further relates to amplification of the immobilized DNA fragments produced according to the methods provided herein. The immobilized DNA fragments produced by surface bound transposome mediated tagmentation can be amplified according to any suitable amplification methodology known in the art. In some embodiments, the immobilized DNA fragments are amplified on a solid support. In some embodiments, the solid support is the same solid support upon which the surface bound tagmentation occurs. In such embodiments, the methods and compositions provided herein allow sample preparation to proceed on the same solid support from the initial sample introduction step through amplification and optionally through a sequencing step.
For example, in some embodiments, the immobilized DNA fragments are amplified using cluster amplification methodologies as exemplified by the disclosures of U.S. Pat. Nos. 7,985,565 and 7,115,400, the contents of each of which is incorporated herein by reference in its entirety. The incorporated materials of U.S. Pat. Nos. 7,985,565 and 7,115,400 describe methods of solid-phase nucleic acid amplification which allow amplification products to be immobilized on a solid support in order to form arrays comprised of clusters or “colonies” of immobilized nucleic acid molecules. Each cluster or colony on such an array is formed from a plurality of identical immobilized polynucleotide strands and a plurality of identical immobilized complementary polynucleotide strands. The arrays so-formed are generally referred to herein as “clustered arrays”. The products of solid-phase amplification reactions such as those described in U.S. Pat. Nos. 7,985,565 and 7,115,400 are so-called “bridged” structures formed by annealing of pairs of immobilized polynucleotide strands and immobilized complementary strands, both strands being immobilized on the solid support at the 5′ end, preferably via a covalent attachment. Cluster amplification methodologies are examples of methods wherein an immobilized nucleic acid template is used to produce immobilized amplicons. Other suitable methodologies can also be used to produce immobilized amplicons from immobilized DNA fragments produced according to the methods provided herein. For example one or more clusters or colonies can be formed via solid-phase PCR whether one or both primers of each pair of amplification primers are immobilized.
In other embodiments, the immobilized DNA fragments are amplified in solution. For example, in some embodiments, the immobilized DNA fragments are cleaved or otherwise liberated from the solid support and amplification primers are then hybridized in solution to the liberated molecules. In other embodiments, amplification primers are hybridized to the immobilized DNA fragments for one or more initial amplification steps, followed by subsequent amplification steps in solution. Thus, in some embodiments an immobilized nucleic acid template can be used to produce solution-phase amplicons.
It will be appreciated that any of the amplification methodologies described herein or generally known in the art can be utilized with universal or target-specific primers to amplify immobilized DNA fragments. Suitable methods for amplification include, but are not limited to, the polymerase chain reaction (PCR), strand displacement amplification (SDA), transcription mediated amplification (TMA) and nucleic acid sequence based amplification (NASBA), as described in U.S. Pat. No. 8,003,354, which is incorporated herein by reference in its entirety. The above amplification methods can be employed to amplify one or more nucleic acids of interest. For example, PCR, including multiplex PCR, SDA, TMA, NASBA and the like can be utilized to amplify immobilized DNA fragments. In some embodiments, primers directed specifically to the nucleic acid of interest are included in the amplification reaction.
Other suitable methods for amplification of nucleic acids can include oligonucleotide extension and ligation, rolling circle amplification (RCA) (Lizardi et al., Nat. Genet. 19:225-232 (1998), which is incorporated herein by reference) and oligonucleotide ligation assay (OLA) (See generally U.S. Pat. Nos. 7,582,420, 5,185,243, 5,679,524 and 5,573,907; EP 0 320 308 B1; EP 0 336 731 B1; EP 0 439 182 B1; WO 90/01069; WO 89/12696; and WO 89/09835, all of which are incorporated by reference) technologies. It will be appreciated that these amplification methodologies can be designed to amplify immobilized DNA fragments. For example, in some embodiments, the amplification method can include ligation probe amplification or oligonucleotide ligation assay (OLA) reactions that contain primers directed specifically to the nucleic acid of interest. In some embodiments, the amplification method can include a primer extension-ligation reaction that contains primers directed specifically to the nucleic acid of interest. As a non-limiting example of primer extension and ligation primers that can be specifically designed to amplify a nucleic acid of interest, the amplification can include primers used for the GoldenGate assay (Illumina, Inc., San Diego, Calif.) as exemplified by U.S. Pat. Nos. 7,582,420 and 7,611,869, each of which is incorporated herein by reference in its entirety.
Exemplary isothermal amplification methods that can be used in a method of the present disclosure include, but are not limited to, Multiple Displacement Amplification (MDA) as exemplified by, for example Dean et al., Proc. Natl. Acad. Sci. USA 99:5261-66 (2002) or isothermal strand displacement nucleic acid amplification exemplified by, for example U.S. Pat. No. 6,214,587, each of which is incorporated herein by reference in its entirety. Other non-PCR-based methods that can be used in the present disclosure include, for example, strand displacement amplification (SDA) which is described in, for example Walker et al., Molecular Methods for Virus Detection, Academic Press, Inc., 1995; U.S. Pat. Nos. 5,455,166, and 5,130,238, and Walker et al., Nucl. Acids Res. 20:1691-96 (1992) or hyperbranched strand displacement amplification which is described in, for example Lage et al., Genome Research 13:294-307 (2003), each of which is incorporated herein by reference in its entirety. Isothermal amplification methods can be used with the strand-displacing Phi 29 polymerase or Bst DNA polymerase large fragment, 5′→3′ exo− for random primer amplification of genomic DNA. The use of these polymerases takes advantage of their high processivity and strand displacing activity. High processivity allows the polymerases to produce fragments that are 10-20 kb in length. As set forth above, smaller fragments can be produced under isothermal conditions using polymerases having low processivity and strand-displacing activity such as Klenow polymerase. Additional description of amplification reactions, conditions and components are set forth in detail in the disclosure of U.S. Pat. No. 7,670,810, which is incorporated herein by reference in its entirety.
Another nucleic acid amplification method that is useful in the present disclosure is Tagged PCR which uses a population of two-domain primers having a constant 5′ region followed by a random 3′ region as described, for example, in Grothues et al. Nucleic Acids Res. 21(5):1321-2 (1993), incorporated herein by reference in its entirety. The first rounds of amplification are carried out to allow a multitude of initiations on heat denatured DNA based on individual hybridization from the randomly-synthesized 3′ region. Due to the nature of the 3′ region, the sites of initiation are contemplated to be random throughout the genome. Thereafter, the unbound primers can be removed and further replication can take place using primers complementary to the constant 5′ region.
Sequencing.
The present disclosure further relates to sequencing of the immobilized DNA fragments produced according to the methods provided herein. The immobilized DNA fragments produced by surface bound transposome mediated tagmentation can be sequenced according to any suitable sequencing methodology, such as direct sequencing, including sequencing by synthesis, sequencing by ligation, sequencing by hybridization, nanopore sequencing and the like. In some embodiments, the immobilized DNA fragments are sequenced on a solid support. In some embodiments, the solid support for sequencing is the same solid support upon which the surface bound tagmentation occurs. In some embodiments, the solid support for sequencing is the same solid support upon which the amplification occurs.
One preferred sequencing methodology is sequencing-by-synthesis (SBS). In SBS, extension of a nucleic acid primer along a nucleic acid template (e.g. a target nucleic acid or amplicon thereof) is monitored to determine the sequence of nucleotides in the template. The underlying chemical process can be polymerization (e.g. as catalyzed by a polymerase enzyme). In a particular polymerase-based SBS embodiment, fluorescently labeled nucleotides are added to a primer (thereby extending the primer) in a template dependent fashion such that detection of the order and type of nucleotides added to the primer can be used to determine the sequence of the template.
Flow cells provide a convenient solid support for housing amplified DNA fragments produced by the methods of the present disclosure. One or more amplified DNA fragments in such a format can be subjected to an SBS or other detection technique that involves repeated delivery of reagents in cycles. For example, to initiate a first SBS cycle, one or more labeled nucleotides, DNA polymerase, etc., can be flowed into/through a flow cell that houses one or more amplified nucleic acid molecules. Those sites where primer extension causes a labeled nucleotide to be incorporated can be detected. Optionally, the nucleotides can further include a reversible termination property that terminates further primer extension once a nucleotide has been added to a primer. For example, a nucleotide analog having a reversible terminator moiety can be added to a primer such that subsequent extension cannot occur until a deblocking agent is delivered to remove the moiety. Thus, for embodiments that use reversible termination, a deblocking reagent can be delivered to the flow cell (before or after detection occurs). Washes can be carried out between the various delivery steps. The cycle can then be repeated n times to extend the primer by n nucleotides, thereby detecting a sequence of length n. Exemplary SBS procedures, fluidic systems and detection platforms that can be readily adapted for use with amplicons produced by the methods of the present disclosure are described, for example, in Bentley et al., Nature 456:53-59 (2008), WO 04/018497; U.S. Pat. No. 7,057,026; WO 91/06678; WO 07/123744; U.S. Pat. No. 7,329,492; U.S. Pat. No. 7,211,414; U.S. Pat. No. 7,315,019; U.S. Pat. No. 7,405,281, and US 2008/0108082, each of which is incorporated herein by reference.
Other sequencing procedures that use cyclic reactions can be used, such as pyrosequencing. Pyrosequencing detects the release of inorganic pyrophosphate (PPi) as particular nucleotides are incorporated into a nascent nucleic acid strand (Ronaghi, et al., Analytical Biochemistry 242(1), 84-9 (1996); Ronaghi, Genome Res. 11(1), 3-11 (2001); Ronaghi et al. Science 281(5375), 363 (1998); U.S. Pat. No. 6,210,891; U.S. Pat. No. 6,258,568 and U.S. Pat. No. 6,274,320, each of which is incorporated herein by reference). In pyrosequencing, released PPi can be detected by being immediately converted to adenosine triphosphate (ATP) by ATP sulfurylase, and the level of ATP generated can be detected via luciferase-produced photons. Thus, the sequencing reaction can be monitored via a luminescence detection system. Excitation radiation sources used for fluorescence based detection systems are not necessary for pyrosequencing procedures. Useful fluidic systems, detectors and procedures that can be adapted for application of pyrosequencing to amplicons produced according to the present disclosure are described, for example, in WIPO Pat. App. Ser. No. PCT/US11/57111, US 2005/0191698 A1, U.S. Pat. No. 7,595,883, and U.S. Pat. No. 7,244,559, each of which is incorporated herein by reference.
Some embodiments can utilize methods involving the real-time monitoring of DNA polymerase activity. For example, nucleotide incorporations can be detected through fluorescence resonance energy transfer (FRET) interactions between a fluorophore-bearing polymerase and γ-phosphate-labeled nucleotides, or with zeromode waveguides (ZMWs). Techniques and reagents for FRET-based sequencing are described, for example, in Levene et al. Science 299, 682-686 (2003); Lundquist et al. Opt. Lett. 33, 1026-1028 (2008); Korlach et al. Proc. Natl. Acad. Sci. USA 105, 1176-1181 (2008), the disclosures of which are incorporated herein by reference.
Some SBS embodiments include detection of a proton released upon incorporation of a nucleotide into an extension product. For example, sequencing based on detection of released protons can use an electrical detector and associated techniques that are commercially available from Ion Torrent (Guilford, Conn., a Life Technologies subsidiary) or sequencing methods and systems described in US 2009/0026082 A1; US 2009/0127589 A1; US 2010/0137143 A1; or US 2010/0282617 A1, each of which is incorporated herein by reference. Methods set forth herein for amplifying target nucleic acids using kinetic exclusion can be readily applied to substrates used for detecting protons. More specifically, methods set forth herein can be used to produce clonal populations of amplicons that are used to detect protons.
Another useful sequencing technique is nanopore sequencing (see, for example, Deamer et al. Trends Biotechnol. 18, 147-151 (2000); Deamer et al. Acc. Chem. Res. 35:817-825 (2002); Li et al. Nat. Mater. 2:611-615 (2003), the disclosures of which are incorporated herein by reference). In some nanopore embodiments, the target nucleic acid or individual nucleotides removed from a target nucleic acid pass through a nanopore. As the nucleic acid or nucleotide passes through the nanopore, each nucleotide type can be identified by measuring fluctuations in the electrical conductance of the pore. (U.S. Pat. No. 7,001,792; Soni et al. Clin. Chem. 53, 1996-2001 (2007); Healy, Nanomed. 2, 459-481 (2007); Cockroft et al. J. Am. Chem. Soc. 130, 818-820 (2008), the disclosures of which are incorporated herein by reference).
Exemplary methods for array-based expression and genotyping analysis that can be applied to detection according to the present disclosure are described in U.S. Pat. No. 7,582,420; 6,890,741; 6,913,884 or 6,355,431 or US Pat. Pub. Nos. 2005/0053980 A1; 2009/0186349 A1 or US 2005/0181440 A1, each of which is incorporated herein by reference.
An advantage of the methods set forth herein is that they provide for rapid and efficient detection of a plurality of target nucleic acid in parallel. Accordingly the present disclosure provides integrated systems capable of preparing and detecting nucleic acids using techniques known in the art such as those exemplified above. Thus, an integrated system of the present disclosure can include fluidic components capable of delivering amplification reagents and/or sequencing reagents to one or more immobilized DNA fragments, the system comprising components such as pumps, valves, reservoirs, fluidic lines and the like. A flow cell can be configured and/or used in an integrated system for detection of target nucleic acids. Exemplary flow cells are described, for example, in US 2010/0111768 A1 and U.S. Ser. No. 13/273,666, each of which is incorporated herein by reference. As exemplified for flow cells, one or more of the fluidic components of an integrated system can be used for an amplification method and for a detection method. Taking a nucleic acid sequencing embodiment as an example, one or more of the fluidic components of an integrated system can be used for an amplification method set forth herein and for the delivery of sequencing reagents in a sequencing method such as those exemplified above. Alternatively, an integrated system can include separate fluidic systems to carry out amplification methods and to carry out detection methods. Examples of integrated sequencing systems that are capable of creating amplified nucleic acids and also determining the sequence of the nucleic acids include, without limitation, the MiSegTM platform (Illumina, Inc., San Diego, Calif.) and devices described in U.S. Ser. No. 13/273,666, which is incorporated herein by reference.
Solid Supports with Immobilized Transposomes and Methods of Preparation
Other embodiments presented herein include solid supports, such as flowcells, having transposome complexes immobilized thereon. In certain embodiments, the transposome complexes comprise a transposase bound to a first polynucleotide, the polynucleotide comprising (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain. The density of these surface bound transposomes can vary. For example, in some embodiments, the transposome complexes are present on the solid support at a density of at least 103, 104, 105, or at least 106 complexes per mm2.
Also presented herein are methods of generating a flowcell for tagmentation. The methods can comprise, for example, immobilizing a plurality of transposome complexes to a solid support, the transposome complexes comprising a transposase bound to a first polynucleotide, the first polynucleotide comprising (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain.
Transposome complexes can be immobilized to a solid support in a variety of methods, which will be appreciated by one of skill in the art. In one embodiment, the method comprises providing a solid support having a plurality of first polynucleotides immobilized thereon, and contacting the solid support with transposase holoenzyme and a second polynucleotide, the second polynucleotide comprising a region complementary to the transposon end sequence. In some embodiments, the second polynucleotide is hybridized to the immobilized first polynucleotide before the transposase holoenzyme is added. In some embodiments, the second polynucleotide and the transposase holoenzyme are provided together. FIG. 5a shows one embodiment of this method for assembling the surface bound transposome complexes. In one method, transposase holoenzyme is added along with the non-transferred strand of the ME adaptor to a flowcell containing oligonucleotides comprising from the 5′ surface grafted end: a cluster amplification primer (A.pr) and sequencing primer (S.pr) and the ME sequence (FIG. 5a). Alternatively, the non-transferred ME′ strand can hybridized to the surface grafted ME strand first and then the transposase added to the flowcell.
In some embodiments, the transposome complexes are assembled in solution and immobilizing comprises a further step of ligating the first polynucleotide to a splint oligonucleotide coupled to the solid support. This embodiment is illustrated in FIG. 5b. In some embodiments, the splint oligonucleotide can be extended using a polymerase before a ligating step occurs.
In some embodiments, transposome dimer is assembled by hybridizing a looped oligonucleotide to an immobilized first polynucleotide. For example, a looped oligonucleotide can comprise a first end and a second end, with the first end being complementary to the transposon end sequence of the first polynucleotide. The second end of the looped oligonucleotide can be complementary to a second transposon end sequence. The second transposon end sequence can be, for example, part of a solution-phase first polynucleotide. In some embodiments, the immobilized first polynucleotide and the solution-phase first polynucleotide can comprise dissimilar transposon end sequences or complements thereof. In some such embodiments, the looped oligonucleotide comprises sequences complementary to each of the dissimilar transposon end sequences at the first and second ends. An illustration of this embodiment is shown in FIG. 5c. As shown in FIG. 5c, a contiguous adaptor pair is generated by hybridizing two oligonucleotides to the surface bound oligonucleotide. This can be achieved by employing two dissimilar transposon end sequences (ME1 and ME2). Addition of transposase holoenzyme reconstitutes an active ‘looped’ transposome complex, where only one of the two adaptors of each transposome is coupled to the surface FIG. 5c. 
In another embodiment, transposome complexes can be assembled on a standard paired end flow cell with amplification primers immobilized thereto (e.g. a HiSeq flow cell or MiSeq flow cell sold by Illumina Inc, San Diego, Calif.). This can be accomplished by, for example, hybridization of a ‘splint’ oligonucleotide that anneals to one or both species of surface grafted amplification primer. The splint acts as a template to then extend the grafted surface primer with a polymerase and dNTPs to form an oligonucleotide duplex that contains a surface amplification primer, a sequencing primer and the transposon end sequences of the transposase. Addition of transposase assembles a transposome of the surface. This embodiment is illustrated in FIG. 5d. 
In any of the embodiments provided herein, transposome complexes may be homodimers, or heterodimers. For example, as illustrated in FIG. 11, a homodimeric transposome would comprise two P5-ME adaptors at both sites or alternatively, two P7-ME adaptors. Similarly, a heterodimeric transposome complex would comprise both P5-ME and P7-ME adaptors, as shown in FIG. 11.
Tagmentation Using Transposome Beads
One embodiment presented herein is a population of microparticles having transposome complexes immobilized thereto. The use of a solid support such as beads can provide several advantages over solution-based tagmentation. For example, in standard solution-based tagmentation, it is difficult to control the final fragment size of the tagmentation reaction. Fragment size is a function of the ratio of transposomes to the amount and size of DNA and to the duration of the reaction. Even if these parameters are controlled, size selection fractionation is commonly required as an additional step to remove excess small fragments shorter than the combined paired-read lengths. The methods provided herein avoid those disadvantages. Specifically, bead-immobilized transposomes allow for selection of final fragment size as a function of the spatial separation of the bound transposomes, independent of the quantity of transposome beads added to the tagmentation reaction. An additional limitation of solution-based tagmentation is that it is typically necessary to do some form of purification of the products of the tagmentation reaction both before and after PCR amplification. This typically necessitates some transfer of reactions from tube to tube. In contrast, tagmentation products on the bead based transposomes can be washed and later released for amplification or other downstream processing, thus avoiding the need for sample transfer. For example, in embodiments where transposomes are assembled on paramagnetic beads, purification of the tagmentation reaction products can easily be achieved by immobilizing the beads with a magnets and washing. Thus, in some embodiments, tagmentation and other downstream processing such as PCR amplification can all be performed in a single tube, vessel, droplet or other container. In some embodiments, tagmentation and downstream processing of samples takes place on a microfluidic droplet based device, as exemplified in the disclosure of U.S. Application Ser. No. 13/670,318, filed on Nov. 6, 2012 entitled “INTEGRATED SEQUENCING APPARATUSES AND METHODS OF USE” which is incorporated herein by reference in its entirety. For example, in a microfluidic droplet based device, a droplet containing target nucleic acid, wash buffer or other reagents may be passed over a surface comprising immobilized transposome complexes. Likewise, a droplet comprising beads having transposomes immobilized thereon may be contacted with target nucleic acid, wash buffer or other reagents in a microfluidic droplet based device.
In some embodiments, the immobilized transposome complexes comprise a transposase bound to a first polynucleotide and a second polynucleotide; wherein the first polynucleotide is immobilized at its 5′ end to the surface of the microparticle and the second polynucleotide is hybridized to the 3′ end of the first polynucleotide; and wherein the first polynucleotide comprises: (i) a 3′ portion comprising a transposon end sequence, and (ii) a first tag comprising a first tag domain.
FIGS. 9-12 provide an illustration of transposomes assembled on the surface of paramagnetic beads. FIG. 9 shows a bead surface with two different first polynucleotides immobilized thereto. The first polynucleotides that are shown comprise a transposon end sequence (ME). One of the first polynucleotides shown in comprises a tag domain comprising an amplification primer sequence (P5) and a sequencing primer sequence (Read 1). The other polynucleotide shown in FIG. 9 comprises a different amplification primer sequence (P7) and a sequencing primer sequence (Read 2). The first polynucleotides may also comprise an index tag. The index tag may be unique to the bead, or it may be shared with one or more other beads in the population. A single bead may have only a single index tag immobilized thereto, or it may have a plurality of index tags immobilized thereto.
FIG. 10 shows a second polynucleotide hybridized to each first polynucleotide. The second polynucleotide comprises a region complementary to the transposon end sequence of the first polynucleotide. In some embodiments, the second polynucleotide is 15 bp in length. In some embodiments, the second polynucleotide can be approximately 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 bp or more than 20 bp in length. In some embodiments, the second polynucleotide is phosphorylated at its 5′ end.
FIG. 11 illustrates assembly of transposomes on the surface of the bead, where transposase enzyme is contacted with the immobilized oligonucleotides. As shown in FIG. 11, when the transposase is added to the beads, three types of transposome complexes are formed: a P5:P5, a P7:P7, and a P5:P7 complex (FIG. 11).
When the transposome beads are added to a solution of target DNA in a tagmentation buffer, tagmentation takes place, linking the DNA to the surface of the beads. An immobilized library of tagged DNA fragments is generated.
FIG. 12 illustrates an embodiment where successive tagmentation into the DNA results in bridged molecules between transposomes. Where three types of transposomes are present (as in FIG. 11), three types of bridge complexes result: a P5:P5, P7:P7 and P5:P7 complex in a ratio of 25:25:50, respectively.
In some embodiments, the length of the bridged fragments can be dictated by the density of the transposomes on the surface of the bead. This density is tunable via the amount of oligonucleotide on the surface, the amount of duplex transposon end complexes on the surface and the amount of transposase enzyme added during the transposome assembly. Once tagmentation is complete, the P5:P7 tagmentation products can be liberated from the surface of the bead using any suitable method. In some embodiments, the tagmentation products are liberated from the beads using an amplification method such as suppression PCR, step-out PCR and the like. In some embodiments, the tagmentation products are liberated from the beads by cleavage. The cleavage can be, for example, chemical, enzymatic, photochemical or a combination thereof. It will be appreciated that any suitable method for releasing one or more tagmentation products from a solid support can be utilized in the methods provided herein.
DNA can be efficiently contacted with surface bound transposomes using any suitable method for increasing the probability of contact. For example, in some embodiments, precipitation of DNA onto the solid surface can be utilized to increase contact between the target DNA and the transposome complexes on the solid surface. Any one of a number of methods that are known in the art for contacting DNA with a solid support can be utilized, as exemplified by the disclosure of WO 2010/115122, which is incorporated by reference in its entirety. As will be appreciated by one of skill in the art, DNA can be precipitated onto a solid support by the addition of PEG, ethanol or any one of a variety of other agents known to precipitate DNA onto surfaces, including, for example, any one of a number of buffers used in solid phase reversible immobilization (SPRI) technology.
In some embodiments, a population of beads bearing immobilized transposome complexes can be mixed with an excess of beads that bear no transposomes or oligonucleotides, thereby reducing the likelihood of tagmentation across two or more different beads. Another method to reduce the likelihood of tagmentation across two or more different beads includes immobilizing beads so contact between beads is minimized. Immobilization of beads can be accomplished by any of a number of techniques known in the art, including, for example, immobilizing the beads via magnetism to the sides of a solid surface such as a microcentrifuge tube, or any other immobilization technique as exemplified by the incorporated materials of WO 2010/115122.
Methods of Assembling Long Reads Using Barcodes on Immobilized Transposomes
Barcode-assisted assembly of DNA fragments enables isolation of individual long DNA molecules within a population of DNA molecules and conversion of each molecule into a uniquely barcoded sub-fragment library. When the entire population of sub-fragmented DNA molecules is sequenced, the subfragments can be assembled back into their original long molecule by reference to the barcodes they contain.
Various methods of barcoding individual DNA molecules are known. For example, the ‘dilution method,’ isolates individual long molecules by extreme dilution and aliquoting into separate compartments (e.g., wells of a plate), such that each well contains only one or just a few molecules of DNA. Because each well is physically separate, a library preparation can be done in each well with a unique barcode. Thereafter the contents of the wells are pooled and sequenced. Another method employs an emulsion wherein each droplet contains long DNA molecules, library preparation reagents and a barcode unique to each droplet. Another approach uses a large library of indexed looped transposome complexes to insert multiple twin barcodes along the length of the DNA while preserving the intactness of the molecule. Subsequent cleavage between the barcode ‘twins’ yields fragments that can be sequenced and reassembled by matching up the twin barcodes. Each of the above-mentioned barcoding methods carries with it disadvantages that are overcome by the barcoding methods presented herein.
Presented herein are alternative methods to the above described ways of isolating and barcoding individual long molecules. The methods presented herein achieve advantages of physical isolation similar to the emulsion method without using emulsions, and at the same time provide a complexity that is much greater than that provided by the large number of ‘wells’ used in the dilution method. The unique barcodes of the present methods are in some ways analogous to the ‘wells’ of the dilution method except that the number of beads in the bead-based method can often be much higher than the number of wells in the dilution method. An additional advantage over the emulsion methods is that in the bead-based method, the barcodes are deterministically distributed (i.e., one barcode per bead) and not random (i.e. Poisson distributed). The methods presented herein also achieve the same initial preservation of molecule intactness and contiguity but without the need for looped transposome complexes as used in some other methods. Additionally, the methods presented herein do not require as large a code space as used in some other methods.
Accordingly, in some embodiments presented herein, barcoding method comprise providing a population of microparticles having transposome complexes immobilized thereto, the transposome complexes comprising a transposase bound to a first polynucleotide and second polynucleotide. In some embodiments, the first polynucleotide comprises an index domain associated with the microparticle. In some embodiments, the index domain can be unique to the microparticle. In some embodiments, the population of microparticles comprises at least a plurality of index domains. In some embodiments, the index domain is present on more than one microparticle in the population of microparticles. In some embodiments, a microparticle in the population of microparticles comprises more than one index domain.
The barcoding methods presented herein further comprise applying a target DNA to the population of microparticles, thereby generating immobilized DNA fragments that are tagged with the index domain. DNA can be efficiently contacted with surface bound transposomes using any suitable method for increasing the probability of contact as discussed hereinabove, as exemplified by the incorporated materials of WO 2010/115122.
The methods can be performed using any one of a variety of known formats, for example, with a combination of tagmentation reagents and a bead array for the library preparation, followed by an indexed sequencing run and bespoke data analysis. Any other suitable method that maintains beads in static separation from one another can be used for surface tagmentation and indexing of samples. For example, physical configurations such as wells or small depressions in the substrate that can retain the beads, such that a microsphere can rest in the well, or the use of other forces (magnetic or compressive), or chemically altered or active sites, such as chemically functionalized sites, electrostatically altered sites, hydrophobically and/or hydrophilically functionalized sites, or spots of adhesive.
In some embodiments, the microspheres are non-covalently associated in the wells, although the wells may additionally be chemically functionalized as is generally described below, cross-linking agents may be used, or a physical barrier may be used, e.g., a film or membrane over the beads.
In certain embodiments, the surface of the substrate is modified to contain chemically modified sites that can be used to attach, either covalently or non-covalently, the microspheres of the invention to the discrete sites or locations on the substrate. “Chemically modified sites” in this context includes, but is not limited to, the addition of a pattern of chemical functional groups including amino groups, carboxy groups, oxo groups and thiol groups, that can be used to covalently attach microspheres, which generally also contain corresponding reactive functional groups; the addition of a pattern of adhesive that can be used to bind the microspheres (either by prior chemical functionalization for the addition of the adhesive or direct addition of the adhesive); the addition of a pattern of charged groups (similar to the chemical functionalities) for the electrostatic attachment of the microspheres, e.g., when the microspheres comprise charged groups opposite to the sites; the addition of a pattern of chemical functional groups that renders the sites differentially hydrophobic or hydrophilic, such that the addition of similarly hydrophobic or hydrophilic microspheres under suitable experimental conditions will result in association of the microspheres to the sites on the basis of hydroaffinity. For example, the use of hydrophobic sites with hydrophobic beads, in an aqueous system, drives the association of the beads preferentially onto the sites. As outlined above, “pattern” in this sense includes the use of a uniform treatment of the surface to allow attachment of the beads at discrete sites, as well as treatment of the surface resulting in discrete sites. As will be appreciated by those in the art, this may be accomplished in a variety of ways.
In certain embodiments, a multitude of beads comprising surface bound transposomes are generated, wherein each bead contains many transposomes but all transposomes on any given bead all contain the same barcode. The generation of a population of monoclonal barcoded transposome oligonucleotides on beads can be performed according to any one of a number of techniques as is known in the art, as exemplified by the disclosure of U.S. Pat. No. 5,604,097, which is incorporated by reference in its entirety.
FIG. 13 illustrates one embodiment, where a surface bound transposome contains long oligonucleotides attached to the surface via their 5′ end. As set forth in FIG. 13, the 3′ end of the oligonucleotide comprises the Mosaic End (METS) sequences of the Tn5 transposase enzyme. Upstream of this sequence (closer to the 5′ end) is a barcode sequence of typically 6-8 bases in length. Further upstream is a primer sequence. Additionally, the oligonucleotide can further comprise a cleavage site to enable the oligonucleotide to be cleaved off the surface: its presence in the oligonucleotide is optional to the overall method. A second short oligonucleotide (the non-transferred strand, MENTS) is hybridized to the METS sequence at the 3′ end of the long surface grafted oligonucleotide. Finally, a transposase dimer is assembled at the 3′ end of the oligonucleotides to form a functional transposome.
FIG. 14 illustrates barcoding on beads in an array of wells. As shown in FIG. 14, when long molecules of dsDNA are added to an array of bead-immobilized transposomes, a given molecule encounters a bead and gets tagmented many times by the transposomes on the bead. Each fragment becomes immobilized to the bead and tagged with the barcode associated with that bead. In the particular embodiment shown in FIG. 14, the physical separation of beads in the array chip prevents a DNA molecule from reaching between two beads. In other embodiments, the beads are in close contact and one or more DNA molecules may stretch between two or more beads. In some embodiments, more than one DNA molecule can be tagmented per bead. The probability of two alleles being tagmented onto the same bead is low and is a function of the concentration of the DNA added, the number of beads and the number of barcodes. For example, to avoid two alleles occurring in the same well, 0.1× haplome equivalents (50,000 genomes equivalents) would need to be loaded to 1 million beads each with a unique barcode.
FIG. 15 illustrates transfer of barcoded tagged molecules to a sequencing reaction. As shown in FIG. 15, once the tagmentation is complete the DNA is transferred from the bead surface to solution so that individual fragments can be pooled and prepared for sequencing. Sequencing and assembly by reference to the barcodes enables the sequence of the original long tagmented DNA molecules to be re-created, thus enabling long or pseudo-long reads and phasing of SNPs.
Release of the barcoded surface tagmented fragments to the solutions can be achieved using any suitable methodology as is known in the art. For example, in some embodiments, the tagmented molecules can be cleaved off the surface of the beads via a cleavage moiety present at the 5′ end of the surface bound oligonucleotides (see FIG. 13). The cleavage moiety can be any moiety suitable for cleavage of a nucleic acid strand from a solid support. Examples of methods that utilize a cleavage moiety include, but are not limited to, restriction endonuclease cleavage, chemical cleavage, RNase cleavage, photochemical cleavage, and the like, including those cleavage methods and cleavage moieties set forth in WO 2006/064199, which is incorporated by reference in its entirety.
Cleavage using a cleavage moiety yields a molecule having the following format:

    
    
        5′-Primer-Barcode-ME-Insert-ME-Barcode-Primer-3′
    
    


The “Primer” regions can be used as hybridization points to hybridize PCR step-out primers that enable additional sequences to be added such as amplification and sequencing primers. For example, amplification primers P5 and P7 can be added. Once added, suppression PCR can be used, for example, to enrich for molecules that have P5 adaptors on one end and P7 on the other.
In some embodiments, amplification can be performed directly off the beads with step-out primers that add P5 and P7 adaptor sequences by suppression PCR. In another embodiment, each bead can have two types of surface grafted oligonucleotides where the primer sequence (as in FIG. 13) is either P5-Read1 sequencing primer or P7-Read 2 sequencing primer. This will result in mixed P5-P7 transposomes. These can either be cleaved off the beads and followed by suppression PCR to enrich the P5/P7 molecules or amplified directly off the beads, as described above.
In some embodiments, a single transposome type (e.g. P5-Read 1-barcode) may be present on the surface of the bead. Once surface tagmentation is complete, a second transposome bearing a different amplification and/or sequencing primer can be added in solution to cleave the bridged molecules. This yields all molecules with the same adaptor format that can either be cleaved or amplified off the bead surface. An additional sample-specific barcode could be added to the solution transposome such that multiple samples can be pooled by the method. FIG. 16 is an illustration of this embodiment. As shown in FIG. 16, solution-phase transposomes bearing a P7 amplification primer sequence are added to a bead with immobilized bridged tagmentation products. The immobilized fragments are tagged with a polynucleotide sequence comprising a P5 amplification primer sequence and an barcode index tag (i9) that is unique to the bead. As shown in FIG. 16, after the second tagmentation reaction, each fragment has a free end bearing a P7 primer sequence and an immobilized end bearing a P5 primer sequence.
Example 1
Surface Tagmentation on a Flowcell
This example describes an experiment confirming the embodiment illustrated in FIGS. 4a and 4b (surface tagmentation followed by solution tagmentation).
An experiment on an 8 lane flowcell was carried out using a list of conditions and controls as shown in FIGS. 6a and 6b. Lane 6 indicates the complete end to end exposition of the method: unfragmented E. coli genomic DNA was added to a flowcell where upon it was tagmented by the surface bound transposomes. Next heat was applied to the flowcell to selectively dehybridize the naked ME sequences thus abolishing them as a target for a second tagmentation reaction when transposome was next added from solution. Following the second tagmentation reaction, clusters were generated and ‘paired-end’ sequenced (2×36 base reads) was performed. Sequencing metrics are given in slide 7 which show that in lane 6, 73.14% of clusters passed filters and 74.69 of these aligned. This provides enough data to yield a gap size plot of the inserts and an estimation of library diversity (see FIG. 8).
Other lanes included controls which are listed below:
Lane 1 comprises PhiX DNA as a positive control to ensure everything has been pumping correctly and cluster generation and sequencing works as expected.
Lane 2 is another control lane and illustrates tagmentation into surface bound transposons in the absence of target DNA. The flowcell (FC) comprises a standard paired end FC onto which an oligonucleotide containing the tagmentation primer sequence and ME′ sequence (non-transferred ME′ strand) was hybridized to the P7 surface oligonucleotide. This oligonucleotide was added at a saturating concentration. First extension resulted in a double stranded transposon with ME ends. A P5 transposome was assembled in solution and flowed onto the FC (6.25 nM/lane). The P5 transposome tagments the double stranded surface bound transposons. The tagmentation products are subsequently converted into clusters.
Lane 3 illustrates tagmentation into surface bound transposons in the absence of target DNA, only in this instance the FC has been heated to 75° C. in order to convert the ds surface bound transposons into single stranded oligonucleotides prior to the addition of the P5 Transposome from solution in order to prevent tagmentation into these constructs, as this was interfering with the tagmentation of the target DNA.
Lane 4 illustrates the addition of a surface bound transposome to the lane 3 conditions. In this lane an oligonucleotide containing the tagmentation primer sequence and ME′ sequence was hybridized to the P7 surface oligonucleotide. First extension results in a double stranded transposon with ME ends. Following this a P7 transposome was assembled on the surface of the FC by adding Tn5 enzyme to the lane at 50× concentration and incubating at 30° C. for 30 minutes. The FC was then heated to 75° C. prior to adding P5 Transposome from solution.
Lane 5 comprises the same conditions as lane 4, only in this case instead of adding P5 Transposome from solution, an E. coli 900 bp library (with P5/P7 ends) was added to determine whether the P7 surface bound transposome remains active after the heating step.
Lane 6 illustrates an example of the invention put into practice. In this instance the FC comprises of a standard paired end FC onto which an oligonucleotide containing the tagmentation primer sequence and ME′ sequence was hybridized to the P7 surface oligonucleotide. First extension results in double stranded transposons with ME ends. P7 transposomes are assembled on the surface of the FC by adding Tn5 enzyme to the lane at 50× concentration and incubating at 30° C. for 30 minutes. Target DNA (300 ng of unfragmented E. coli genomic DNA) was added onto the FC lane and an incubation step of 15 min at 55° C. was carried out in order for tagmentation to take place. The P7 surface bound transposome was washed off using PBI (Qiagen) and the FC was then heated to 75° C. prior to adding P5 transposome from solution. Following addition of P5 transposome from solution and an incubation step of 15 min at 55° C., a stand displacement extension reaction was carried out in order to fill in the 9-bp gaps generated in the DNA backbone by the transposition reaction. The stand displacement extension reaction comprises of the addition of a Bst and dNTP mix and incubation at 65° C. for 5 min. The P5 transposome was washed off in the final step. At this point all surface bound molecules should be P5-P7 templates and can therefore be converted into clusters.
Lane 7 comprises of the same conditions as lane 6, only in this instance the heat step has been left out in order to highlight the effect of heat on the cluster number and % align.
Lane 8 comprises a negative control where the P7 transposome has been assembled on the surface at 50× concentration in the presence of a saturating concentration of ds surface bound transposons, however, no target DNA has been added. This allows an assessment of whether the surface bound P7 transposome tagments into its neighboring ds surface bound transposons.
Example 2
Surface Bound Sample Preparation from an E. coli Scrape
An E. coli sample (5 mm by 2 mm scrape from a lawn on an agar plate) was scraped and resuspended in a tube containing water and glass beads. The suspended cells and beads were mixed using a vortex mixer to break open the cells and then centrifuged to pellet cellular debris. The supernatant (containing the cell lysate, including proteins and nucleic acids) was removed and added to a Genome Analyzer flowcell (Illumina, Inc., San Diego, Calif.) having immobilized transposomes according to the protocol described in Example 1.
Cluster generation was performed on the flowcell using a Cluster Station sample preparation device (Illumina, Inc., San Diego, Calif.). After cluster generation, a paired-end sequencing run was performed with reads of 36 bases in each direction.
For Read 1, 58.99% of clusters passed filters and 92.16 of these aligned. For Read 2, 58.99% of clusters passed filters and 55.08 of these aligned. These data confirm that unpurified cell lysates can be added directly to a flowcell having immobilized transposomes with surprisingly robust sequencing results.
Example 3
This example describes methods to avoid tagmentation of surface-bound oligonucleotide duplexes when solution phase transposomes are added to a flowcell. One method for assembling transposomes on the surface of a flow cell is to take a standard paired end flow cell, hybridize a ‘splint’ oligonucleotide against the P5 and/or P7 surface grafted oligonucleotides forming an extendable overhang that can be extended with a polymerase to make a duplex containing a double stranded ME sequence. At this stage transposase enzyme can be added to form a functional surface bound transposome (FIG. 5d). If only a portion of the duplexes form a transposome, remaining ‘naked’ ME duplexes may subsequently become targets for tagmentation by either nearby surface-bound transposomes or transposomes added from solution. Furthermore, fully assembled surface transposomes contain dsDNA portions upstream of the ME sequences that can also become targets for tagmentation by nearby surface-bound transposomes or transposomes added from solution. This undesired tagmentation manifests itself in a reduction of the percentage of clusters passing purity filters that align to the target genome.
An example of this effect can be seen by comparing lanes 4 and 5 versus lanes 6 and 7 in FIG. 18b. In lanes 6 and 7 transposomes were assembled as described above with the long splint oligonucleotides that, after extension and transposome assembly, produced surface bound duplexes that have at least 50 double stranded bases. Upon use in a surface tagmentation reaction (FIG. 18a) and subsequent sequencing, only 22.59 and 15.52% of clusters aligned to the target E. coli respectively (FIG. 18b).
To avoid producing a population of clusters that contain sequences that do not align to the target genomic DNA, transposome assembly was done as indicated in FIG. 17. A ‘splint’ oligonucleotide was first hybridized against the P5 and/or P7 surface grafted oligonucleotides forming an extendable overhang that could be extended with a polymerase to make a duplex containing a double stranded ME sequence. Next, the splint oligonucleotide was removed by de-annealing and washing away, and then was replaced by hybridizing a shorter oligonucleotide as little as 12 bases long but preferably 16 bases long to the 3′ end of the surface attached ME oligonucleotide. Transposase was added to assemble a transposome that did not contain any exposed dsDNA. Any ‘naked’ duplexes that did not contain a bound transposase were removed by incubating the flow cell at 60° C. and washing under flow conditions to selectively de-anneal and remove the short duplex DNA.
The beneficial effect of this approach to assembling transposomes can be seen in Lanes 4 and 5 where the surface bound transposomes were assembled by this method and used in a surface tagmentation reaction (FIG. 18a). The percentage of clusters that aligned to E. coli increases from 22.59 and 15.52% for lane 6 and 7 respectively, to 96.47 and 96.41 for lanes 4 and 5 respectively (FIG. 18b).
Throughout this application various publications, patents and/or patent applications have been referenced. The disclosure of these publications in their entireties is hereby incorporated by reference in this application.
The term comprising is intended herein to be open-ended, including not only the recited elements, but further encompassing any additional elements.
A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the following claims.

## Claims

1. A method of preparing an immobilized library of tagged DNA fragments comprising:
(a) providing a solid support having transposome complexes immobilized thereon, wherein said transposome complexes comprise a transposase bound to a first polynucleotide, said first polynucleotide comprising
(i) a 3′ portion comprising a transposon end sequence, and
(ii) a first tag comprising a first tag domain;
(b) providing a sample comprising target DNA, proteins and other cellular components from an in vivo source;
(c) applying said sample to the solid support under conditions wherein said target DNA, proteins and other cellular components are present at the same proportion as in said in vivo source, whereby the target DNA is fragmented by the transposome complexes, and the 3′ transposon end sequence of the first polynucleotide is transferred to a 5′ end of at least one strand of the fragments; thereby producing an immobilized library of double-stranded fragments wherein at least one strand is 5′-tagged with the first tag.

2. The method of claim 1, wherein said first polynucleotide is immobilized to said solid support.

3. The method of claim 1, wherein said transposome complexes comprise a second polynucleotide comprising a region complementary to said transposon end sequence.

4. The method of claim 1, further comprising washing the solid support to remove any unbound nucleic acids.

5. The method of claim 1, wherein the transposome complexes are present on the solid support at a density of at least 103, 104, 105, or 106 complexes per mm2.

6. The method of claim 1, wherein said transposome complex comprises a hyperactive Tn5 transposase.

7. The method of claim 1, wherein the lengths of the double-stranded fragments in said immobilized library are adjusted by increasing or decreasing the density of transposome complexes present on said solid support.

8. The method of claim 1, wherein at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% of the tags present on said solid support comprise the same tag domain.

9. The method of claim 1, further comprising:
(d) providing transposome complexes in solution and contacting said transposome complexes in solution with the immobilized fragments under conditions whereby the target DNA is further fragmented by the transposome complexes in solution; thereby obtaining immobilized nucleic acid fragments having one end in solution.

10. The method of claim 9, wherein the transposome complexes in solution comprise a second tag, thereby generating immobilized nucleic acid fragments having a second tag in solution.

11. The method of claim 10, wherein the first and second tags are different.

12. The method of claim 9, wherein at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% of said transposome complexes in solution comprise a second tag comprising a second tag domain.

13. The method of claim 9, further comprising amplifying the fragments on said solid support by providing a polymerase and an amplification primer corresponding to a portion of the first polynucleotide.

14. The method of claim 1, wherein said tag domain comprises a region for cluster amplification.

15. The method of claim 1, wherein said tag domain comprises a region for priming a sequencing reaction.

16. The method of claim 1, wherein the solid support comprises microparticles.

17. The method of claim 1, wherein the solid support comprises a patterned surface.

18. The method of claim 1, wherein the solid support comprises wells.

19. The method of claim 1, wherein said target DNA is double stranded, wherein said transposition reaction and introduction of tags into said target DNA results in double stranded bridged structures across said solid support.

20. The method of claim 19, wherein the length of the bridged fragments is between 100 base pairs and 1500 base pairs.

21. The method of claim 1, wherein said sample that is applied to said solid support is blood.

22. The method of claim 1, wherein the solid support is inner or outer surface of a tube.

23. The method of claim 1, wherein said sample that is applied to said solid support is a cell lysate.

24. The method of claim 23, wherein said cell lysate is a crude cell lysate.

25. The method of claim 1, wherein said sample that is applied to said solid support has a 260/280 absorbance ratio that is less than 1.7.

26. The method of claim 1, further comprising lysing cells in said sample after applying said sample to said solid support.

27. A solid support having a library of tagged DNA fragments immobilized thereon prepared according to the method of claim 1.