a prokaryote is a unicellular organism that lacks a membrane-bound nucleus ( karyon ) , mitochondria , or any other membrane-bound organelle .

the word prokaryote comes from the greek πρό ( pro ) " before " and κάρυον ( karyon ) " nut or kernel " .

prokaryotes can be divided into two domains , archaea and bacteria .

in contrast , species with nuclei and organelles are placed in the domain eukaryota .

in the prokaryotes , all the intracellular water-soluble components ( proteins , dna and metabolites ) are located together in the cytoplasm enclosed by the cell membrane , rather than in separate cellular compartments .

bacteria , however , do possess protein-based bacterial microcompartments , which are thought to act as primitive organelles enclosed in protein shells .

some prokaryotes , such as cyanobacteria may form large colonies .

others , such as myxobacteria , have multicellular stages in their life cycles .

molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species .

eukaryotes are organisms , including humans , whose cells have a well defined membrane-bound nucleus ( containing chromosomal dna ) and organelles .

the division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization .

distinctive types of prokaryotes include extremophiles and methanogens ; these are common in some extreme environments .

prokaryote

a prokaryote is a single - celled organism that doesn ' t have a nucleus . bacteria are one familiar type of prokaryote .
prokaryote - eukaryote relationship and the amino acid sequence of plastocyanin from anabaena variabilis .
brown jr , doolittle wf . archaea and the prokaryote - to - eukaryote transition .
' candidatus magnetoglobus multicellularis ' , a multicellular , magnetotactic prokaryote from a hypersaline environment .
poole am , phillips mj , penny d ( 2003 ) prokaryote and eukaryote evolvability .
cell adhesion , multicellular morphology , and magnetosome distribution in the multicellular magnetotactic prokaryote candidatus magnetoglobus multicellularis .
a prokaryote is a cell without a distinct nucleus . bacteria and some other simple organisms are prokaryotic . the genome of a prokaryote is in the form of a single dna molecule , like a single chromosome .
' candidatus magnetoglobus multicellularis ' , a multicellular , magnetotactic prokaryote from a hypersaline environment . - pubmed - ncbi
dagan t , martin w . ancestral genome sizes specify the minimum rate of lateral gene transfer during prokaryote evolution .
genetic variation within prokaryotic organisms is accomplished through recombination . in recombination , genes from one prokaryote are incorporated into the genome of another prokaryote . recombination is accomplished in bacterial reproduction by the processes of conjugation , transformation , or transduction .
) had counterpart segments with a significant level of sequence homology in the mt genomes of a minimum of nine of the ten examined green plants and one or both of the two prokaryote genomes , supporting the interpretation of their prokaryote origin .
prokaryote . provided by : wikipedia . located at : urltoken . license : cc by - sa : attribution - sharealike
prokaryote . provided by : wiktionary . located at : urltoken . license : cc by - sa : attribution - sharealike
] - it is possible to constrain some nodes in the prokaryote timescale , but only in a coarse sense . however , most information on the timescale of prokaryote evolution has come from analysis of dna and amino acid sequence data with molecular clocks [
cell adhesion , multicellular morphology , and magnetosome distribution in the multicellular magnetotactic prokaryote candidatus magnetoglobus multic . . . - pubmed - ncbi
dagan t , artzy - randrup y , martin w . modular networks and cumulative impact of lateral transfer in prokaryote genome evolution .
) branch basally in the tree . these groups and relationships are similar to those found previously with analyses of prokaryote genome sequences [
doolittle rf , feng df , anderson kl , alberro mr . a naturally occurring horizontal gene transfer from a eukaryote to a prokaryote .
transformation is a type of prokaryotic reproduction in which a prokaryote can take up dna found within the environment that has originated from other prokaryotes .
a ) five green plant and a prokaryote species were used in the analysis : oryza sativa ( monocotyledon ) , arabidopsis thaliana ( dicotyledon ) , cycas taitungensis ( gymnosperm ) , physcomitrella patens ( bryophyte ) , chlorokybus atmophyticus ( green alga ) , and prochlorococcus marinus ( prokaryote ) .
what made you want to look up prokaryote ? please tell us where you read or heard it ( including the quote , if possible ) .
transduction is a type of prokaryotic reproduction in which a prokaryote is infected by a virus which injects short pieces of chromosomal dna from one bacterium to another .
the tnt score heat maps for different functional classes of gene from the 100 analyzed prokaryote species . the order of and numbering of the species are as in
three mechanisms for the origin of ctdna - homologous mtdna segments : ( 1 ) vertical transmission of a prokaryote dna segment ( orthology ) , ( 2 ) interorganellar dna transfer from the ct to mt genome ( xenology ) and ( 3 ) amplification of an orthologous or xenologous dna segment in the mitochondrion ( paralogy ) . circle : prokaryote genome and plant organellar genome . thick arc on dna molecule : homologous dna segment descended from the prokaryote genome or by xenology or paralogy .
] . the detection of evolutionary patterns in metabolic innovations , as a consequence of a phylogeny not dominated by hgt events , allows more detailed constraints on a prokaryote timescale .
slesarev ai , stetter ko , lake ja , gellert m , krah r , kozyavkin sa . dna topoisomerase v is a relative of eukaryotic topoisomerase i from a hyperthermophilic prokaryote .
binary fission is a type of reproduction in which the chromosome is replicated and the resultant prokaryote is an exact copy of the parental prokaryate , thus leaving no opportunity for genetic diversity .
all prokaryote and eukaryote cells also have cytoplasm ( or cytosol ) , a semiliquid substance that composes the volume of a cell . essentially , cytoplasm is the gel - like material enclosed by the plasma membrane .
. we assume that present day bacteria were derived from a single ancestral prokaryote . in addition , the diagram assumes that the ct and mt genomes of green plants originated from a cyanobacterium and an α - proteobacterium , respectively .
temporal information concerning prokaryote evolution has come from diverse sources . for eukaryotes , the fossil record provides an abundant source of such data , but this has not been true for prokaryotes , which are difficult to identify as fossils [
dion p . ( 2008 ) extreme views on prokaryote evolution . in : dion p . , nautiyal c . s . ( eds ) microbiology of extreme soils . soil biology , vol 13 . springer , berlin , heidelberg
these example sentences are selected automatically from various online news sources to reflect current usage of the word ' prokaryote . ' views expressed in the examples do not represent the opinion of merriam - webster or its editors . send us feedback .
doolittle rf , anderson kl , feng d - f ( 1989 ) estimating the prokaryote - eukaryote divergence time from protein sequences . in : fernholm b , bremer k , jornvall h ( eds ) the hierarchy of life . elsevier , amsterdam , pp 73–85
a search of the distribution of ctdna - homologous mtdna sequences among the mt genomes of a wide range of green plants , including the reference prokaryote genomes , will provide insights into the phylogenetic origin of ctdna transfer in plant evolution . for this purpose , the mtdnas of 10 green plant species of diverse taxa and the two prokaryote reference genomes were blast searched for sequences with homology to the 52 wheat mtdna segments of orthologous or xenologous origin . to confirm the validity of the present method , the presence of homologous sequences to the wheat ct -
reproduction in prokaryotes is asexual and usually takes place by binary fission . the dna of a prokaryote exists as as a single , circular chromosome . prokaryotes do not undergo mitosis ; rather the chromosome is replicated and the two resulting copies separate from one another , due to the growth of the cell . the prokaryote , now enlarged , is pinched inward at its equator and the two resulting cells , which are clones , separate . binary fission does not provide an opportunity for genetic recombination or genetic diversity , but prokaryotes can share genes by three other mechanisms .
the genome fluidity statistic ϕ as a function of synonymous core genome nucleotide variation π for 90 free - living prokaryote species on a ln - ln scale . white dots : proteobacteria , black dots : terrabacteria ( actinobacteria , firmicutes and cyanobacteria ) , grey dots : other taxa .
prokaryote , any organism that lacks a distinct nucleus and other organelles due to the absence of internal membranes . bacteria are among the best - known prokaryotic organisms . the lack of internal membranes in prokaryotes distinguishes them from eukaryotes . the prokaryotic cell membrane is made up of phospholipids and constitutes…
] . the following settings were used : numsamp ( 10 , 000 ) , burnin ( 100 , 000 ) , and sampfreq ( 100 ) . this method permitted rates to vary on different branches , which was necessary given the known rate variation among prokaryote and eukaryote nuclear protein sequences [
modes of prokaryote reproduction : besides binary fission , there are three other mechanisms by which prokaryotes can exchange dna . in ( a ) transformation , the cell takes up prokaryotic dna directly from the environment . the dna may remain separate as plasmid dna or be incorporated into the host genome . in ( b ) transduction , a bacteriophage injects dna into the cell that contains a small fragment of dna from a different prokaryote . in ( c ) conjugation , dna is transferred from one cell to another via a mating bridge that connects the two cells after the pilus draws the two bacteria close enough to form the bridge .
bacteria and radiation tolerance : deinococcus radiodurans , visualized in this false color transmission electron micrograph , is a prokaryote that can tolerate very high doses of ionizing radiation . it has developed dna repair mechanisms that allow it to reconstruct its chromosome even if it has been broken into hundreds of pieces by radiation or heat .
genes , respectively ; both genes encode an nadh dehydrogenase subunit . neither of the two prokaryote genomes had sequences with significant homology to the no . 22 segment , indicating the non - orthologous origin of these segments in the mt and ct genomes . homologues of the no . 22 mtdna segment were found only in the monocotyledon species ( ref . table
the evolution of the eukaryote cell was probably spurred by the benefits that the engulfed bacteria provided . if an anaerobic prokaryote engulfed an aerobic bacteria , it would have acquired the ability to generate energy from nutrients and oxygen . a prokaryote that took up a cyanobacteria would acquire the ability to make energy utilizing sunlight . the engulfed aerobic bacteria and cyanobacteria would benefit from the protection and nutrients supplied by the host cell . the extra energy produced by the bacteria may have allowed the primitive eukaryotic cell to enlarge and acquire other bacteria , resulting in a more complex cell . without the extra energy provided by the bacterial organelles , the primitive eukaryotic cell may not have been able to develop into a multicellular organism .
a timescale of prokaryote evolution . letters indicate nodes discussed in the text . the last common ancestor was arbitrarily placed at 4 . 25 ga in the tree , although this placement was not part of the analyses . the grey rectangle shows the time prior to the initial rise in oxygen ( presumably anaerobic conditions ) . mtb : methanothermobacter , tab : thermoanaerobacter , tsc : thermosynechococcus .
in transformation , the prokaryote takes in dna found in its environment that is shed by other prokaryotes . if a nonpathogenic bacterium takes up dna for a toxin gene from a pathogen and incorporates the new dna into its own chromosome , it , too , may become pathogenic . in transduction , bacteriophages , the viruses that infect bacteria , sometimes also move short pieces of chromosomal dna from one bacterium to another . transduction results in a recombinant organism . archaea are not affected by bacteriophages , but instead have their own viruses that translocate genetic material from one individual to another . in conjugation , dna is transferred from one prokaryote to another by means of a pilus , which brings the organisms into contact with one another . the dna transferred can be in the form of a plasmid or as a hybrid , containing both plasmid and chromosomal dna .
if you take a biology class , you ' re likely to learn about prokaryotes , tiny organisms without a distinct nucleus bound by a membrane , like most other living things . prokaryotes are often contrasted with the single - celled or multicellular eukaryotes , which do have a nucleus . the word prokaryote is rooted in greek — it combines the word pro ,
before ,
with karyon ,
nut or kernel .
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membranes , energetics , and evolution across the prokaryote - eukaryote divide
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phylogenetic trees of individual genes of prokaryotes ( archaea and bacteria ) generally have different topologies , largely owing to extensive horizontal gene transfer ( hgt ) , suggesting that the tree of life ( tol ) should be replaced by a “net of life” as the paradigm of prokaryote evolution . however , trees remain the natural representation of the histories of individual genes given the fundamentally bifurcating process of gene replication . therefore , although no single tree can fully represent the evolution of prokaryote genomes , the complete picture of evolution will necessarily combine trees and nets . a quantitative measure of the signals of tree and net evolution is derived from an analysis of all quartets of species in all trees of the “forest of life” ( fol ) , which consists of approximately 7 , 000 phylogenetic trees for prokaryote genes including approximately 100 nearly universal trees ( nuts ) . although diverse routes of net - like evolution collectively dominate the fol , the pattern of tree - like evolution that reflects the consistent topologies of the nuts is the most prominent coherent trend . we show that the contributions of tree - like and net - like evolutionary processes substantially differ across bacterial and archaeal lineages and between functional classes of genes . evolutionary simulations indicate that the central tree - like signal cannot be realistically explained by a self - reinforcing pattern of biased hgt .
the concept of evolvability covers a broad spectrum of , often contradictory , ideas . at one end of the spectrum it is equivalent to the statement that evolution is possible , at the other end are untestable post hoc explanations , such as the suggestion that current evolutionary theory cannot explain the evolution of evolvability . we examine similarities and differences in eukaryote and prokaryote evolvability , and look for explanations that are compatible with a wide range of observations . differences in genome organisation between eukaryotes and prokaryotes meets this criterion . the single origin of replication in prokaryote chromosomes ( versus multiple origins in eukaryotes ) accounts for many differences because the time to replicate a prokaryote genome limits its size ( and the accumulation of junk dna ) . both prokaryotes and eukaryotes appear to switch from genetic stability to genetic change in response to stress . we examine a range of stress responses , and discuss how these impact on evolvability , particularly in unicellular organisms versus complex multicellular ones . evolvability is also limited by environmental interactions ( including competition ) and we describe a model that places limits on potential evolvability . examples are given of its application to predator competition and limits to lateral gene transfer . we suggest that unicellular organisms evolve largely through a process of metabolic change , resulting in biochemical diversity . multicellular organisms evolve largely through morphological changes , not through extensive changes to cellular biochemistry .
one of the mechanisms that produced homology between the ct and mtdna segments is the vertical transmission of an ancestral prokaryote dna segment ( or gene ) to both the ct and mt genomes via a cyanobacterium or an α - proteobacterium , respectively ( “orthology” ) . the second mechanism is interorganellar dna transfer between the ct and mt genomes ( “xenology” ) . 32 ) the third mechanism is amplification of a dna segment of orthologous or xenologous origin in an organelle ( “paralogy” ) .
recently , we reported a comparative analysis of approximately 7 , 000 phylogenetic trees for prokaryote genes that jointly constitute the “forest of life” ( fol ) and showed that the fol does gravitate to a single - tree topology . this statistically significant trend was particularly prominent among nearly universal trees ( nuts ) , that is , trees for highly conserved genes that are represented in all or almost all prokaryote genomes ( puigbo et al . 2009 ) . here , we describe a quantitative measure of the tree and net signals in evolution that is derived from an analysis of all quartets of species in all trees of the fol . we find that , although diverse routes of net - like evolution jointly dominate the fol , the pattern of tree - like evolution that recapitulates the consensus topology of the nuts is the single most prominent coherent trend . evolutionary simulations suggest that the central tree - like signal cannot be realistically explained by a self - reinforcing pattern of biased hgt .
) . these observations support my conclusion on the orthology of the 16 wheat mtdna segments and their ctdna counterparts . orthology of two other mtdna segments , nos . 24 and 31 , was not supported by the presence of orthologous gene sequences . however , they did show high sequence homology to the wheat ct genome and to one or other of the prokaryote genomes . they also had significant and high sequence homology to the mtdnas of the 10 green plant species examined later ( ref . table
the timescale of prokaryote evolution has been difficult to reconstruct because of a limited fossil record and complexities associated with molecular clocks and deep divergences . however , the relatively large number of genome sequences currently available has provided a better opportunity to control for potential biases such as horizontal gene transfer and rate differences among lineages . we assembled a data set of sequences from 32 proteins ( ~ 7600 amino acids ) common to 72 species and estimated phylogenetic relationships and divergence times with a local clock method .
certain prokaryotes move independently by using flagella , long structures that rotate in a propeller - like fashion . prokaryotic flagella consist of intertwined fibrils ( small fibers ) of the protein flagellin . a prokaryote may have a single flagellum , a group of flagella at one or both poles of the cell , or may be covered with flagella . many species of prokaryotes also have pili ( singular , pilus ) slender , hairlike extensions used for attachment to soil , rocks , teeth , or other structures .
cocci ( the plural of coccus , from the greek kokkus = berry ) are round bacteria . spherical is a safe shape since it gives the maximum surface area for a given volume . however , spherical doesn’t necessarily mean small . thiomargarita namibiensis is a spherical bacterium , but it is the second largest prokaryote we know of . if an e . coli cell was the size of a tic tac , t . namibiensis would have a diameter a bit larger than the barringer meteor crater in arizona ( see picture above ) .
eleven mtdna segments showed high sequence homology ( ca . 70 % or higher ) to sequences in all genomes of wheat ct , pm and pu . additionally , five mtdna segments , nos . 2 , 18 , 28 , 40 and 51 , showed high sequence homologies ( ca . 60 % or higher ) to ct sequences and also to either pm or pu sequences . in addition to their high sequence homologies , most of the wheat mtdna segments and their corresponding wheat ct and prokaryote dna segments included complete or partial sequences of orthologous genes ( table
all prokaryote and eukaryote cells have plasma membranes . the plasma membrane ( also known as the cell membrane ) is the outermost cell surface , which separates the cell from the external environment . the plasma membrane is composed primarily of proteins and lipids , especially phospholipids . the lipids occur in two layers ( a bilayer ) . proteins embedded in the bilayer appear to float within the lipid , so the membrane is constantly in flux . the membrane is therefore referred to as a fluid mosaic structure . within the fluid mosaic structure , proteins carry out most of the membrane’s functions .
the aims and materials of the present investigation were very similar to those of wang et al . 41 ) with the following exceptions : ( 1 ) i surveyed sequence homologies between all the ct and mtdna segments , irrespective of the presence / absence of genes , to obtain an entire picture of ctdna transfers ; ( 2 ) the ctdna - homologous mtdna segments were classified with respect to origin as orthologous ( prokaryote origin ) , xenologous ( ctdna origin ) and paralogous ( amplification of orthologs or xenologs ) using prokaryotic genome sequences as a reference ; ( 3 ) the dynamics of recurrent ct - to - mt transfers were analyzed in detail with respect to the transfer of ctdna segments in the same ct genome region to different sites of the mt genome , in order to assess directionality of the transfer ; and ( 4 ) the evolutionary timing of transfer of most of the xenologs to the mt genome was estimated , based on the results of a homology search between the ctdna - derived wheat mtdna segments and the mt genomes of ten green plant species and two reference prokaryote genomes . these analyses identified new aspects of the dynamics and phylogenetic origins of interorganellar dna transfers .
the analyses presented here are based on the assumption , still under debate , that historical information ( phylogenies and divergence times ) can be retrieved from genes in the prokaryote genome that have not been affected by horizontal gene transfer . our prokaryotic timeline shows deep divergences within both the eubacterial and archaebacterial domains indicating a long evolutionary history . the early evolution of life ( > 4 . 1 ga ) and early origin of several important metabolic pathways ( phototrophy , methanogenesis ; but not oxygenic photosynthesis ) suggests that organisms have influenced the earth ' s environment since early in the history of the planet ( fig .
in contrast , the dna of prokaryotic cells is distributed loosely around the cytoplasm , along with the protein synthesis machinery . this closeness allows prokaryotic cells to rapidly respond to environmental change by quickly altering the types and amount of proteins they manufacture . note that eukaryotic cells likely evolved from a symbiotic relationship between two prokaryotic cells , whereby one set of prokaryotic dna eventually became separated by a nuclear envelope and formed a nucleus . over time , portions of the dna from the other prokaryote remaining in the cytoplasmic part of the cell may or may not have been incoporated into the new eukaryotic nucleus ( figure 3 ) .
differences in the mechanisms of inheritance across the prokaryote–eukaryote divide generate , over long time frames , different patterns of variation . in both prokaryotes and eukaryotes , there are clonally propagating species that seem never to undergo recombination . because mutation is inevitable ( 45 ) , prokaryotic or eukaryotic species that never undergo recombination will continuously accumulate sublethal mutations , which they cannot purge from their genomes . this process continuously increases genetic load , for which reason they will eventually go extinct , a process known as muller ' s ratchet ( 46 – 49 ) . recombination has an important role in evolution in that it rescues genomes from muller’s ratchet .
notwithstanding the ubiquity of hgt , trees remain the natural representation of the histories of individual genes given the fundamentally bifurcating character of gene replication and the low frequency of intragenic recombination compared with intergenic recombination at long evolutionary distances ( koonin and wolf 2009 ; koonin , wolf , and puigbo 2009 ) . therefore , although no single tree can fully represent the evolution of prokaryote genomes , the complete picture of evolution will necessarily combine trees and nets ( gogarten et al . 2002 ; koonin and wolf 2008 ) . taken together , the results of the present analysis reveal a complex landscape of tree - like and net - like evolution of prokaryotes . the signals from these two types of evolution are distributed in a highly nonrandom fashion among lineages of archaea and bacteria and among functional classes of genes . overall , within the fol , the net - like signal is quantitatively dominant , vindicating the concepts of “lateral genomics” or net of life ( hilario and gogarten 1993 ; doolittle 1999a , 2009 ; gogarten et al . 2002 ; gogarten and townsend 2005 ; doolittle and bapteste 2007 ; koonin and wolf 2008 ) . by no account , are these results compatible with the representation of prokaryote evolution as a tol adorned with thin , random “cobwebs” of hgt ( kurland et al . 2003 ; ge et al . 2005 ; kunin et al . 2005 ) . however , the tree - like signal compatible with the consensus topology of the nuts is also unmistakably detectable and strong as by our measurement up to 40 % of the evolution in the prokaryote world conforms with the “statistical tol . ” the reality of prokaryote evolution appears to be that , although net - like processes are quantitatively dominant , the single strongest trend is the tree - like evolution characteristic of the nuts that also partially recapitulates the rrna tree ( pace 1997 ; puigbo et al . 2009 ) . of course , the tree - like and net - like processes of evolution are entangled : when we consider a “tree - like” signal , we actually mean the topology of the supertree of the nuts that is affected not only by the coherent central trend but also biased routes of hgt . however , the strong coherence between the topologies of the nuts , the quasi - random distribution of hgt events in this set of trees , and the substantial topological similarity between the nuts and a large fraction of the trees in the fol , taken together , seem to justify the use of the supertree as the best available standard of tree - like evolution .
the early eukaryote cell evolved more than a billion years ago . the endosymbiosis theory of the evolution of eukaryotes was first proposed by biologist lynn margulis in the 1960s . over the years , many scientists have gathered evidence in support of endosymbiosis . the endosymbiosis theory states that the eukaryotic cell developed from a larger prokaryotic cell engulfing a smaller prokaryotic cell without digesting it . the smaller prokaryotic cell or bacteria lived on in the larger prokaryote , providing it with extra energy , while the larger cell protected the small bacteria , allowing it to survive . engulfed aerobic bacteria eventually developed into mitochondria , while photosynthetic bacteria became the chloroplasts of eukaryotic cells .
the majority ( 81 % ) of the 32 proteins that were used are classified in the
information storage and processes
functional category of the cog . the other categories represented are
cellular processes
( 10 % ) ,
metabolism
( 3 % ) , and
information storage and processing
+
metabolism
( proteins with combined functions ; 6 % ) . other studies that have analyzed prokaryote genome sequence data for phylogeny have found a similar high proportion of proteins in the
information storage and processes
functional category , presumably because hgt is more difficult with such genes that are vital for the survival of the cell [
in principle , the fol encompasses the complete set of phylogenetic trees for all genes from all genomes . however , a comprehensive analysis of the entire fol is computationally prohibitive , so a representative subset of the trees needs to be selected and analyzed . previously ( puigbo , wolf , and koonin 2009 ) , we defined such a subset by selecting 100 archaeal and bacterial genomes representative of all major prokaryote groups and building 6 , 901 ml trees for all sufficiently conserved genes in this set of genomes ; for brevity , we refer to this set of trees as the fol ( see details in supplementary materials and methods and supplementary fig . s1 , supplementary material online ) .
many prokaryote species are known to have fluid genomes , with different strains varying markedly in accessory gene content through the combined action of gene loss , gene gain via lateral transfer , as well as gene duplication . however , the evolutionary forces determining genome fluidity are not yet well understood . we here for the first time systematically analyse the degree to which this distinctive genomic feature differs between bacterial species . we find that genome fluidity is positively correlated with synonymous nucleotide diversity of the core genome , a measure of effective population size n e . no effects of genome size , phylogeny or homologous recombination rate on genome fluidity were found . our findings are consistent with a scenario where accessory gene content turnover is for a large part dictated by neutral evolution .
a prokaryotic host cell incorporates another prokaryotic cell . each prokaryote has its own set of dna molecules ( a genome ) . the genome of the incorporated cell remains separate ( curved blue line ) from the host cell genome ( curved purple line ) . the incorporated cell may continue to replicate as it exists within the host cell . over time , during errors of replication or perhaps when the incorporated cell lyses and loses its membrane separation from the host , genetic material becomes separated from the incorporated cell and merges with the host cell genome . eventually , the host genome becomes a mixture of both genomes , and it ultimately becomes enclosed in an endomembrane , a membrane within the cell that creates a separate compartment . this compartment eventually evolves into a nucleus .
the tnt score heatmaps for the 100 analyzed prokaryote species . ( a ) the 102 nuts . ( b ) the fol without the nuts ( 6 , 799 trees ) . the tnt increases from red ( slow tnt score , close to random , an indication of net - like evolution ) to green ( high tnt score , close to the supertree topology , an indication of tree - like evolution ) . the species are ordered in accord with the topology of the supertree of the 102 nuts . in ( a ) , the major groups of archaea and bacteria are denoted . the complete species names are given in the supplementary table s1 ( supplementary material online ) . for additional tnt heatmaps , see supplementary figs . s12 , s13 , and s24 ( supplementary material online ) .
many bacterial species have been shown to exhibit extensive variation in gene repertoires , where a set of core genes shared by all strains are supplemented with a set of accessory genes that are only present in a subset of strains ( ochman et al . , 2000 ; gogarten et al . , 2002 ; tettelin et al . , 2005 ) . although accessory genome analyses are routinely performed in prokaryote genomics studies , whether certain genome characteristics are associated with particularly low or high genome fluidity has not been systematically tested . we here make use of the increasing availability of whole - genome sequences to , for the first time , perform a meta - analysis to ( 1 ) gauge the extent to which genome fluidity varies among different species and ( 2 ) test which genome characteristics best explain genome fluidity .
naturally occurring horizontal gene transfers between nonviral organisms are difficult to prove . only with the availability of sequence data from a wide variety of organisms can a convincing case be made . in the case of putative gene transfers between prokaryotes and eukaryotes , the minimum requirements for inferring such an event include ( 1 ) sequences of the transferred gene or its product from several appropriately divergent eukaryotes and several prokaryotes , and ( 2 ) a similar set of sequences from the same ( or closely related organisms ) for another gene or genes . given these criteria , we believe that a strong case can be made for escherichia coli having acquired a second glyceraldehyde - 3 - phosphate dehydrogenase gene from some eukaryotic host . ancillary observations on the general rate of change and the time of the prokaryote - eukaryote divergence support the notion .
since there are no fossil records on the evolution of eukaryotes , most of the evidence is based on the study of present - day cells . evidence for endosymbiosis comes from dna sequencing and the comparison of bacterial , mitochondrial and chloroplast characteristics . dna analysis reveals that eukaryotes contain many bacterial genes . mitochondria and chloroplasts are similar to bacteria in size and divide independently of the eukaryote host cell by a process called binary fission . bacteria also replicate by binary fission , while eukaryotes multiply by mitosis or meiosis . mitochondria and chloroplasts inside the eukaryotic cell have single , circular dna molecules just like bacteria . the inner membrane of bacteria , mitochondria and chloroplasts contains the electron transport chain , which provides chemical energy . mitochondria and chloroplasts also have a second membrane surrounding their inner membrane , which is thought to have arisen from the host cell membrane indenting and surrounding the early prokaryote to take it up .
phylogenetic analysis and phenotypic characterization were used to assign a multicellular magnetotactic prokaryote the name ' candidatus magnetoglobus multicellularis ' . ' candidatus magnetoglobus multicellularis ' lives in a large hypersaline coastal lagoon from brazil and has properties that are unique among prokaryotes . it consists of a compact assembly or aggregate of flagellated bacterial cells , highly organized in a sphere , that swim in either helical or straight trajectories . the life cycle of ' candidatus magnetoglobus multicellularis ' is completely multicellular , in which one aggregate grows by enlarging the size of its cells and approximately doubling the volume of the whole organism . cells then divide synchronously , maintaining the spherical arrangement ; finally the cells separate into two identical aggregates . phylogenetic 16s rrna gene sequence analysis showed that ' candidatus magnetoglobus multicellularis ' is related to the dissimilatory sulfate - reducing bacteria within the deltaproteobacteria and to other previously described , but not yet well characterized , multicellular magnetotactic prokaryotes .
although a few basic trends stand out ( e . g . , that motile cells are usually rods ) , we know exceedingly few morphological rules . this means that , except for the simplest cases , it is difficult or impossible to answer the question , “why does a bacterium have a particular shape ? ” consider , for example , the bacterium pelagibacter ubique , which constitutes ~ 25 % of all ocean microorganisms and is possibly the most successful , most numerous single prokaryote on earth [ 49 ] . even for such a plain bacterium in a relatively uncomplicated environment , we have no clue as to why it is a tiny curved rod instead of a small straight rod ; and beyond this , everything else is even more uncertain . in short , at our present level of understanding , when given an organism’s environment we cannot predict its shape , nor when given its shape can we confidently infer the characteristics of its environment [ 5 ] .
biology of termites : a modern synthesis ( bignell de , roisin y , lo n , ( editors ) , springer , dordrecht , 576pp , isbn 978 - 90 - 481 - 3976 - 7 , e - isbn 978 - 90 - 481 - 3977 - 4 , doi 10 . 1007 / 978 - 90 - 481 - 3977 - 4 ) was published in 2011 . with the agreement of the publishers , we give a taxonomic index of the book comprising 494 termite entries , 103 entries of other multicellular animal species mentioned as associates or predators of termites , with 9 fungal , 60 protist , and 64 prokaryote identities , which are listed as termite symbionts ( sensu stricto ) . in addition , we add descriptive authorities for living ( and some fossil ) termite genera and species . higher taxonomic groupings for termites are indicated by 25 code numbers . microorganisms ( prokaryotes , protists , and fungi ) are listed separately , using broad modern taxonomic affiliations from the contemporary literature of bacteriology , protozoology , and mycology .
candidatus magnetoglobus multicellularis is an uncultured magnetotactic multicellular prokaryote composed of 17 - 40 gram - negative cells that are capable of synthesizing organelles known as magnetosomes . the magnetosomes of ca . m . multicellularis are composed of greigite and are organized in chains that are responsible for the microorganism ' s orientation along magnetic field lines . the characteristics of the microorganism , including its multicellular life cycle , magnetic field orientation , and swimming behavior , and the lack of viability of individual cells detached from the whole assembly , are considered strong evidence for the existence of a unique multicellular life cycle among prokaryotes . it has been proposed that the position of each cell within the aggregate is fundamental for the maintenance of its distinctive morphology and magnetic field orientation . however , the cellular organization of the whole organism has never been studied in detail . here , we investigated the magnetosome organization within a cell , its distribution within the microorganism , and the intercellular relationships that might be responsible for maintaining the cells in the proper position within the microorganism , which is essential for determining the magnetic properties of ca . m . multicellularis during its life cycle . the results indicate that cellular interactions are essential for the determination of individual cell shape and the magnetic properties of the organism and are likely directly associated with the morphological changes that occur during the multicellular life cycle of this species .
when these endosymbiotic events occured is subject to much debate , but it must have been early in life ' s history , perhaps as early as the archean eon more than 2500 million years ago . the heterotrophic prokaryote used cellular respiration to intake oxygen and convert organic molecules to energy . the prokaryotic cells that were too small to be digested continued to live inside the host eukaryote , eventually becoming dependent on the host cell for organic molecules and inorganic compounds . importantly , the host cell could have acquired , by the addition of the aerobic function , an increased output of atp for cellular activities , leading to its improved selective advantage . was the
engulfer
a eubacteria or an archaean - yes - it depends on which of competing theories you choose ? other theories hold that the prokaryotes that gave rise to early eukaryotes were probably from the domain archaea , both because of several key characteristics and because dna sequence comparison suggest that archaeans are more closely related to the eukaryotes than are eubacteria . this is the so - called serial endosymbiosis theory of a monophyletic origin of the mitochondrion from a eubacterial ancestor . that fact that mitochondria have their own dna , rna , and ribosomes , supports the endosymbiosis theory , as does the existence of the amoeba , a eukaryotic organism that lacks mitochondria and therefore requires a symbiotic relationship with an aerobic bacterium .
a second development is the recognition that the origin of the roughly 2 , 000 gene families that underpinned the origin of eukaryotic - specific traits in the eukaryote ancestor required the biochemical power of internalized bioenergetic membranes that mitochondria provided ( 3 ) . mitochondria , not oxygen , made the energetic difference that separates eukaryotes from prokaryotes . that is because anaerobic mitochondria generate about five atp per glucose and fermentations in eukaryotes generate two to four atp per glucose ( 11 ) , such that the meager 5 - to 10 - fold increase in atp yield per glucose conferred by oxygen respiration is dwarfed by the 10 4 to 10 5 increase in atp yield per gene manifest in cells with mitochondria ( 3 ) . the key to the orders of magnitude increase in energy available for evolutionary invention that mitochondria conferred is the eukaryotic configuration of internal , compartmentalized bioenergetic membranes relative to genes ( 3 , 5 ) . after all , had oxygen been the key to eukaryote complexity , escherichia coli would have become eukaryotic for the same reason . furthermore , eukaryotic aerobes and anaerobes interleave across eukaryote phylogeny ( 11 ) , and bioenergetics point to a mitochondrion ancestor with a facultatively anaerobic lifestyle ( 12 ) . only those cells became complex that experienced the increased energy per gene afforded by mitochondria , and the long puzzling lack of true intermediates in the prokaryote–eukaryote transition has a bioenergetic cause ( 3 ) .
the ϕ estimate only provides a general indication of genome fluidity as it ignores genome rearrangements or plasmids , and we cannot exclude the fact that elevated or decreased levels of genome fluidity are associated with some of the many phyla that could not be included in this analysis due to a lack of data . these caveats aside , the positive relationship of genome fluidity with synonymous diversity is highly significant . the synonymous nucleotide diversity equals two times the product of the mutation rate μ and effective population size n e for haploid species . as variation in prokaryote mutation rate is believed to be relatively small ( lynch , 2010 ) , π syn can be taken as a proxy for n e . large effective population size is expected to result in generally higher levels of genetic diversity due to neutral evolution ( kimura , 1984 ) . the result of our cross - species meta - analysis is therefore consistent with the expectation that large n e species exhibit greater accessory genome variation . a variety of studies have suggested that many gene content changes have only minor effects on fitness and are effectively neutral ( gogarten and townsend , 2005 ; baumdicker et al . , 2012 ; haegeman and weitz , 2012 ; knöppel et al . , 2014 ) , although it is clear that a proportion of gene gains and losses will be significantly deleterious or beneficial . to gain a full understanding of selection on the accessory genome , it will be vital to collect data on the distribution of fitness effects of gene content changes ( vos et al . , 2015 ) .
two mtdna segments , nos . 52 and 53a , maintained a high level of sequence homology to the mtdna segments of all 10 green plants , with no or a low level of homology to prokaryote genomes . this finding indicated that these two mtdna segments were transferred from the ct genome at an early stage of green plant evolution . four wheat mtdna segments , nos . 16 , 29 , 36 and 37 , appeared to have been transferred at an early stage of angiosperm evolution , because their homologues were found in almost all of the monocotyledons and dicotyledons examined , but not in the lower plant taxa , including the gymnosperm . three other mtdna segments , nos . 17 , 22 and 34 , showed highly significant sequence homology to all monocotyledons examined , but not to other plant taxa , suggesting they were transferred at an early stage of monocotyledon evolution . nine mtdna segments , nos . 3 , 4 , 21 , 33 , 35 , 38 , 39 , 42 and 49 , showed highly significant homology to the mtdnas in various combinations of two or three monocotyledons , including wheat , suggesting their transfer occurred during divergence of the cereal species . our previous phylogenetic studies on the organellar genomes indicated that genetic distances between the organellar genomes of wheat , rice and maize were similar , suggesting that the phylogenetic divergence of their organellar genomes occurred at almost the same time . 31 ) as a result , i could not conclude with any certainty whether the observed ctdna transfer occurred in a common ancestor of the two to three cereal species or if it occurred independently in these species . transfer of eight mtdna segments , nos . 5 , 6 , 7 , 9 , 15 , 32 , 50 and 54 , undoubtedly occurred only once in the wheat lineage .
using the logic germane to supernumerary phylobiont inference , the findings in dataset s1 and figs . s2 and s3 would be interpreted as evidence that neither the mitochondrion nor the plastid arose via endosymbiosis ; rather , each would be the product of 43 and 124 independent gene transfers , respectively , from different donors , thus one at a time , to the eukaryotic ancestor and the archaeplastidan ancestor , but the transfers would have to be directed to some kind of preexisting compartment , not dissimilar to gray ' s premitochondrion , where rrna operons and trnas also became donated , enabling the result of such transfer to morph into a bioenergetic organelle , but only mimicking a bona fide endosymbiotic origin , the real mechanism being lgt : so say the single - gene trees . we say : that scenario cannot possibly be true . however , why can it not be true ? it cannot be true because exactly the same kinds of transfers—one at a time and from independent donors—for exactly the right kinds of genes to support the function of the bioenergetic membrane in mitochondria and the bioenergetic membrane in plastids ( in addition to the other biochemical and physiological functions of the organelles ) would have to be going on to the nucleus as well , the crux being that , until the whole organelle is assembled through such imaginary lgt , none of the transferred genes have a selectable function . without selection for function , they would all become pseudogenes , and no organelle would emerge at all . a free - living prokaryote brings along the complete and selectable functional unit , which can then be transferred a chunk at a time to the host , but from a continuously selected and replicating functional source . there is something very wrong with the supernumerary phylobiont stories , and the core of the problem is rooted in trees .
like eukaryotes , the origin of sex also counts as one of the major evolutionary transitions ( 1 ) and remains one of evolutionary biology’s toughest problems . existing theories seek the origin of sex in a haploid cell with fully fledged eukaryotic mitosis ( 104 ) , but it is more likely that mitosis and sex arose in a cell that had a mitochondrion ( 3 , 5 ) . during the prokaryote - to - eukaryote transition , eukaryotes seem to have lost the standard mechanisms that prokaryotes use to escape muller’s ratchet—transduction , transformation , and conjugation—because they are lacking in all eukaryotic groups . had eukaryotes retained one or all three of those mechanisms , it seems unlikely that they would have evolved sex on top of them , and , indeed , cells that never had mitochondria ( prokaryotes ) never evolved sex . the machinery involved in eukaryotic recombination was surely present at the time of mitochondrial symbiosis because the main enzymes involved are homologous to their prokaryotic counterparts : spo11 , mre11 , dmc1 , rad51 , mlh1 , and pms1 ( 105 , 106 ) . did a simple form of eukaryotic recombination , catalyzed by enzymes that are homologous to the enzymes of prokaryotic recombination , rescue nascent eukaryotes from muller’s ratchet ? the basic machinery required might have been a property of the host . it is a curiously underpublicized observation that various archaea can fuse their cells ( 55 , 107 ) and that , in some haloarchaea , fusion is accompanied by recombination ( 108 ) whereas , in others , only recombination is observed ( 109 ) . one needs to be careful not to ( over - ) state that “archaea have sex , ” but , in some rare documented examples , they do undergo outright cell fusion ( an otherwise curious property of gametes ) and , in some rarer cases , recombination and fusion are observed ( 108 ) .
1 center for biofilm engineering , montana state university , bozeman , mt 59717 , usa .
2 department of microbiology , university of iowa , iowa city , ia 52242 , usa .
science 21 may 1999 : vol . 284 , issue 5418 , pp . 1318 - 1322 doi : 10 . 1126 / science . 284 . 5418 . 1318
center for biofilm engineering , montana state university , bozeman , mt 59717 , usa .
department of microbiology , university of iowa , iowa city , ia 52242 , usa .
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bacteria that attach to surfaces aggregate in a hydrated polymeric matrix of their own synthesis to form biofilms . formation of these sessile communities and their inherent resistance to antimicrobial agents are at the root of many persistent and chronic bacterial infections . studies of biofilms have revealed differentiated , structured groups of cells with community properties . recent advances in our understanding of the genetic and molecular basis of bacterial community behavior point to therapeutic targets that may provide a means for the control of biofilm infections .
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bornella anguilla is a species of sea slug , a nudibranch , a marine gastropod mollusk in the family bornellidae .

this species is widely distributed throughout the tropical waters of the indo-west pacific .

this species can grow up to a length of 8 cm .

bornella anguilla

bornella anguilla from reunion is . from : yves coze , july 31 , 2003
worms - world register of marine species - bornella anguilla s . johnson , 1984
its name ( anguilla = eel ) refers to its method of swimming . while most species of
relatively large species of bornella , growing up to 80mm . it has a very characteristic mosaic - like colour pattern . its name [ anguilla = eel ] refers to its method of swimming . while most species of bornella can swim by a lateral flexion of their body , in b . anguilla a muscular wave travels down the body to produce an eel - like motion . it is reported by johnson to feed on the hydroid plumularia .
the rhinophores are on long stalks which bear a ring of long pointed papillae . the oral tentacles are very elaborate sensory appendage , shaped like a hand with long fingers . the name
anguilla
meaning eel , refers to its method of swimming . most species of bornella can swim by a lateral flexion of their body . b . anguilla uses a muscular wave that travels down the body to produce an eel - like swimming motion .
. i looked up
anguilla
and discovered that it means
eel .
this had to be it . i also noticed it was described by johnson in 1985 . i emailed scott and he answered right away :
johnson , scott . 1984 . a new indo - west pacific species of the dendronotacean nudibranch bornella ( mollusca : opisthobranchia ) with anguilliform swimming behaviour . micronesica , 19 ( 1 ) : 17 - 26 .
johnson , s . ( 1984 ) . a new indo - west pacific species of the dendronotacean nudibranch bornella ( mollusca : opisthobranchia with anguilliform swimming behavior . micronesica . 19 , 17 - 26 . [ details ]
reference : • johnson , s . ( 1984 ) a new indo - west pacific species of the dendronotacean nudibranch bornella ( mollusca : opisthobranchia ) with anguilliform swimming behaviour . micronesica , 19 ( 1 ) : 17 - 26 . [ for 1983 ]
a key diagnostic for this species is the characteristic mosaic - like color pattern on the body . this relatively large species of bornella , grows up to 80mm in length . this species is found throughout the indo - pacific being reported from south africa to australia , including myranmar , indonesia and fiji .
the genus bornella belongs to the dendronotina . the genus has many similarities in shape and natural history to members of the aeolids . members have a series of cerata - like structures on each side of its elongate body and they feed on hydroids . the cerata - like gills do not carry nematocysts like most aeolids .
johnson , s . ( 1984 ) a new indo - west pacific species of the dendronotacean nudibranch bornella ( mollusca : opisthobranchia ) with anguilliform swimming behaviour . micronesica , 19 ( 1 ) : 17 - 26 . [ for 1983 ] yonow , n . and hayward , p . j . ( 1991 ) . opistobranches de l ' île maurice , avec la description de deux espèces nouvelles ( mollusca : opistobranchia ) revue française d ' aquariologie herpétologie , 18 ( 1 ) , 1 - 30
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urltoken
it has a very characteristic mosaic - like colour pattern with orange , yellow and white spots .
a muscular wave travels down the body to produce an eel - like motion . when disrupted , it swims with a sideways ondulation of its entire body .
the anus opens on the right side just below and between the first and second cerata .
the reproductive opening is further forward on the right side , below and between the rhinophore and the first cerata .
) , 18 october 1985 , size : 45 mm . one other from belle mare (
) , 27 february 1990 , size : 49 mm . and one other from trou aux biches (
a muscular wave travels down the body to produce an eel - like motion .
scottburgh - 20m - south coast kwazulu - natal , south africa . 21 may 2000 . size : 80mm . photo of head . photo : valda fraser
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the color pattern of this impressive dendronotid is a mosaic of orange , brown and white spots against a black reticulate background . each of the six pairs of cerata , as well as the rhinophoral sheaths , possess a distinctive flap shaped like a rabbit ear with black , white and orange streaks .
is a rare species , having been reported only twice . it was found in highly exposed locations , both times during the day . one of those occasions was on a basalt cliff at 6 m ( 20 ft ) . though other bornellids can swim using a side - to - side flapping motion ,
this species was first recorded in hawaii from south point , big island by john hoover in july , 1998 . it was named for its eel - like swimming motion . it ' s referred to as the
eel nudibranch
in hoover , 1998 & 2006 .
pola , m . ; rudman , w . b . ; gosliner , t . m . ( 2009 ) . systematics and preliminary phylogeny of bornellidae ( mollusca : nudibranchia : dendronotina ) based on morphological characters with description of four new species . zootaxa . 1975 : 1 - 57 . page ( s ) : 26 [ details ] available for editors [ request ]
yonow n . ( 2017 ) . results of the rumphius biohistorical expedition to ambon ( 1990 ) . part 16 . the nudibranchia - dendronotina , arminina , aeolidina , and doridina ( mollusca : gastropoda : heterobranchia ) . archiv für molluskenkunde . 146 ( 1 ) : 135 - 172 . [ details ]
gosliner t . m . , behrens d . w . & valdés a . ( 2008 ) indo - pacific nudibranchs and sea slugs . sea challengers natural history books and california academy of sciences . 426 pp . page ( s ) : 320 [ details ]
to biodiversity heritage library ( 1 publication ) to biological information system for marine life ( bismal ) to encyclopedia of life to genbank ( 2 nucleotides ; 2 proteins ) to sea slug forum ( via archive . org )
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how would you greet this
trick - or - treater
if it came to your door this halloween ? man – i think i’d just die . this amazing species looks like something you would see at a chinese new year parade . just look at the facial expression . makes you wonder whos behind that mask .
john greenamyer has been diving some twenty - four years with a macro u / w photography pursuit using both still photography and video . his favorite diving areas are png and indonesia with an emphasis on png , especially the milne bay region so popularized for its
muck
photographic opportunities . as of late he has been keeping company with roger steene and neville coleman on his travels to png and will be diving with them again in the next couple of weeks .
alan grant and myself took a sunday off in august to travel up to visit john and immerse ourselves in some four hours of still and video photography of branchs . john has some outsanding macro video footage of branchs that hopefully will appear in the near future on a sister site this webmaster is in the process of setting up for streaming video .
when he ' s not diving , john and his wife reside in running springs , california , in the los angeles area . he has his own graphic arts business in cerritos , california .
© the slug site , michael d . miller 2004 . all rights reserved .
while diving at south point on the island of hawai ` i ( the southernmost point of land in the u . s . a . ) , i noticed this unusual nudibranch on the basalt cliffs at a depth of about 20 ft . ( 7 m . ) patterned somewhat like a giraffe , with paddle - like cerata protruding from its back . not recognizing it , i popped it into a clear ziplock bag for a later photography session in anticipation of a new record for hawai ` i .
immediately the animal began swimming actively against the side of the bag with the fluid wriggling motions of a tiny eel . confused , i thought for a moment that it was actually a strange fish that mimicked a nudibranch . yet the animal definitely possessed a molluscan foot ; it had to be a slug after all . after taking pictures i let it go . regretfully , there was no way to bring it home to o ` ahu alive . i could only hope that the pictures came out .
i sent a slide to hawaii ' s reigning nudibranch queen , pauline fiene - severns , and she confirmed the id and also confirmed that it was indeed a new record for hawai ` i .
although scott states that it is primarily a nocturnal species , the specimen i found was out in the open in broad daylight .
lives in honolulu . he has published two books on marine life of the hawaiian islands . his third , a field guide to the marine invertebrates of the hawaii , will be available approximately february 1999 . with over 600 photographs , it will cover 500 species , including 66 of hawaii ' s most colorful and interesting opisthobranchs .
© the slug site , michael d . miller 1998 . all rights reserved .
the nudibranch , flabellina exoptata , is often found on hydroids and is known to feed on them . the nematocysts from hydroids are transfered and stored in cerata , which , when disturbed , are able to release these nematocysts for defense .
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