Patent Publication Number: US-10308972-B2

Title: Whole-cell system for cytochrome P450 monooxygenases biocatalysis

Description:
This application is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/EP2014/062749, filed Jun. 17, 2014, which claims the benefit of European Patent Application No. EP 13305814.9, filed Jun. 17, 2013, the disclosures of each of which are explicitly incorporated by reference herein. 
     The subject of the present invention is a whole-cell catalysis process for converting substrates of cytochrome P450 monooxygenases of eukaryotic origin into valuable biotechnological products. The subject of the present invention is also microorganisms genetically engineered to achieve those biotransformations with high rates and processes to prepare these microorganism strains. 
     BACKGROUND OF THE INVENTION 
     Cytochrome P450 monooxygenases (P450s) play an important role in the metabolism of a variety of hydrophobic compounds. They are involved in the synthesis of steroids, fatty acids, vitamins, and other biological processes like the detoxification of xenobiotics (Maurer et al, 2003; Urlacher et Girhard, 2012). P450s catalyze a wide variety of reactions including hydroxylations, N-oxidations, N-, O- and S-dealkylations, sulfoxidations, deaminations, desulfurations, dehalogenations, peroxidations, N-oxide reductions, rearrangement reactions, C—C and C—O phenol couplings, cleavage of C—C bonds and others (Bernhardt et al, 1996; Bernhardt et al, 2006;). 
     The ability of P450s to catalyze the regio-, chemo- and stereospecific oxidation of a vast number of substrates reflects their biological roles and makes them important candidates for biotechnological applications. 
     Particularly, steroid hormones are widely used as anti-inflammatory, contraceptive and antiproliferative drugs. In mammals, the synthesis of these steroids starts with the side-chain cleaving reaction of cholesterol to pregnenolone. Pregnenolone serves as a basis for the production of further steroid hormones such as hydrocortisone (Szczebara et al, 2003) and great interests are associated with its industrial large scale conversion from low-priced substrates such as cholesterol and its plant-derived analogs. 
     However, side-chain cleaving reaction of cholesterol to pregnenolone is a limiting step in steroids overall process. In mammals, it is catalyzed by a membrane-bound CYP11A1 enzyme using adrenodoxin and adrenodoxin reductase as electron carriers. 
     Great efforts have been spent in order to reconstitute a sterol side-chain cleaving enzyme system in recombinant microorganisms such as  Escherichia coli  (Sakamoto et al., EP2386634) but it remains difficult to obtain a satisfactory level of enzymatic activity mainly because of the fact that CYP11A1 of mammalian origin is an insoluble membrane-associated enzyme and that CYP11A1 does not seem to properly fold in prokaryotic hosts. 
     A plasmidless derivative of  B. megaterium  DSM319 has proven to be a valuable host for co-expressing the prokaryotic cytochrome P450 CYP106A2 from  B. megaterium  ATCC 13368 with bovine adrenodoxin reductase (AdR), and adrenodoxin (Adx); it has been applied for the whole-cell conversion of hydrophobic acids with terpene structure such as the antiinflammatory pentacyclic triterpene 11-Keto-β-boswellic acid (KBA). In this work, the recombinant  B. megaterium  system was investigated in comparison with the naturally CYP106A2-expressing  B. megaterium  strain ATCC 13368 and an  E. coli  whole-cell system. The prokaryotic cytochrome P450 CYP106A2 from  B. megaterium  ATCC 13368 is one of only a few cloned bacterial steroid hydroxylases. It was recently identified as the first reported bacterial P450 diterpene hydroxylase, which is able to carry out a one-step regioselective allylitic hydroxylation of abietic acid (Bleif et al 2012). 
     However, a microorganism which allows, as a whole-cell catalyst, to express and catalyze at high rates the bioconversion of substrates from cytochrome P450 monooxygenases of eukaryotic origin, such as the side-chain cleaving reaction of cholesterol to pregnenolone by insoluble CYP11A1, is still needed. 
     SUMMARY OF THE INVENTION 
     Surprisingly, the inventors have found that it was possible to express and catalyze the bioconversion of substrates from cytochrome P450 monooxygenases of eukaryotic origin at high rates, by using a microorganism as a whole-cell catalyst and by increasing its storage capacity dependent of polyhydroxyalkanoate granules. 
     Especially, the inventors achieved a high rate conversion of cholesterol, cholesterol analogs and derivatives into pregnenolone, hydroxylated cholesterol analogs and secosteroids, by co-expressing into  B. megaterium  MS941 the insoluble CYP11A1 of bovine origin, bovine adrenodoxin reductase (AdR), and bovine adrenodoxin (Adx). 
     Therefore, a first aspect of the present invention is a genetically engineered microorganism capable of converting cholesterol, cholesterol analogs and derivatives thereof into steroid hormones precursors or derivatives wherein said microorganism comprises at least one DNA sequence encoding a cytochrome P450 of eukaryotic origin, an exogenous DNA sequence encoding Adx and an exogenous DNA sequence encoding AdR. 
     A second aspect of the present invention is a method for producing steroid hormones precursors, comprising the steps of:
         Providing a microorganism as described above,   Culturing said microorganism under conditions allowing the expression of exogenous DNA sequences,   Contacting said microorganism culture with a substrate selected from the group consisting of cholesterol, cholesterol analogs and derivatives, and   Recovering steroid hormones precursors or derivatives.       

     A third aspect of the present invention is a method of preparing recombinant strains which are improved with respect to the conversion of cholesterol, cholesterol analogs and derivatives into steroid hormones precursors or derivatives, comprising the steps of:
         Providing a microorganism,   Introducing by means of genetic engineering techniques into said microorganism at least one DNA sequence encoding a cytochrome P450 of eukaryotic origin, an exogenous DNA sequence encoding Adx, and an exogenous DNA sequence encoding AdR.       

     A fourth aspect of the present invention is a method for increasing the storage capacity of a microorganism for hydrophobic or hydrophilic compounds comprising the steps of:
         Providing a microorganism comprising a functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies (PHA-bodies); and   Modulating by means of genetic engineering techniques into said microorganism, the expression of at least one gene involved in the building of PHA-bodies,
 
thereby obtaining a microorganism with increased storage capacity for hydrophobic or hydrophilic compounds.
       

     These and other features and advantages of the disclosed microorganisms and methods will be more fully understood from the following detailed description taken together with the accompanying claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     1. Genetically Engineered Microorganisms According to the Invention 
     Surprisingly, the inventors have found that it was possible to express and catalyze the bioconversion of substrates from cytochrome P450 monooxygenases of eukaryotic origin at high rates, by using a microorganism as a whole-cell catalyst. 
     Especially, the inventors achieved a high rate conversion of cholesterol, cholesterol analogs and derivatives into pregnenolone by co-expressing into  B. megaterium  MS941 the insoluble CYP11A1 of bovine origin, bovine adrenodoxin reductase (AdR), and adrenodoxin (Adx) as described in example 2 and  FIGS. 2-12 . 
     Therefore, the present invention pertains to a genetically engineered microorganism capable of converting cholesterol, cholesterol analogs and derivatives thereof into steroid hormones precursors, wherein said microorganism comprises at least one DNA sequence encoding a cytochrome P450 of eukaryotic origin, an exogenous DNA sequence encoding Adx and an exogenous DNA sequence encoding AdR. 
     By “genetically engineered” microorganism is meant any microorganism according to the present invention which has been modified by genetic engineering techniques known in the field by the skilled in the art. 
     Those techniques are conventional techniques, unless otherwise indicated, in the fields of bioinformatics, cell biology, cell culture, molecular biology, transgenic biology, microbiology, recombinant DNA, and immunology, which are within the skill of the art. Such techniques are explained fully in the literature. See, for example, Current Protocols in Molecular Biology (Frederick M. AUSUBEL, 2000, Wiley and son Inc, Library of Congress, USA); Molecular Cloning: A Laboratory Manual, Third Edition, (Sambrook et al, 2001, Cold Spring Harbor, New York: Cold Spring Harbor Laboratory Press); Oligonucleotide Synthesis (M. J. Gait ed., 1984); Mullis et al. U.S. Pat. No. 4,683,195; Nucleic Acid Hybridization (B. D. Harries &amp; S. J. Higgins eds. 1984); Transcription And Translation (B. D. Hames &amp; S. J. Higgins eds. 1984); Culture Of Animal Cells (R. I. Freshney, Alan R. Liss, Inc., 1987); Immobilized Cells And Enzymes (IRL Press, 1986); B. Perbal, A Practical Guide To Molecular Cloning (1984); the series, Methods In ENZYMOLOGY (J. Abelson and M. Simon, eds.—in-chief, Academic Press, Inc., New York), specifically, Vols. 154 and 155 (Wu et al. eds.) and Vol. 185, “Gene Expression Technology” (D. Goeddel, ed.); Gene Transfer Vectors For Mammalian Cells (J. H. Miller and M. P. Calos eds., 1987, Cold Spring Harbor Laboratory); Immunochemical Methods In Cell And Molecular Biology (Mayer and Walker, eds., Academic Press, London, 1987); Handbook Of Experimental Immunology, Volumes I-IV (D. M. Weir and C. C. Blackwell, eds., 1986); and Manipulating the Mouse Embryo, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1986). 
     Those techniques according to the present invention relates to technologies allowing the modulation of gene expression known in the field by the skilled in the art. By “modulation of gene expression” or “modulating one gene by means of genetic engineering techniques” or “genetically engineered microorganism wherein one gene is modulated” are encompassed technologies allowing to overexpress one gene of interest or otherwise to down regulate or to suppress the expression of one gene of interest. By “overexpress” or “down regulate” one gene of interest is meant reaching an expression level of said gene above or under its normal level of expression, respectively. The overexpression of a gene of interest can be achieved as a non-limiting example by introducing into a cell or a microorganism an exogenous DNA sequence encoding for such gene of interest. The down regulation of a gene of interest can be achieved by using gene silencing technologies known by the skilled in the art such as antisense and RNA interference technologies known as gene knockdown technologies. The suppression of a gene can be achieved, as non-limiting example, by a gene replacement experiment of a targeted gene of interest by replacing such gene by a non-functional copy of said gene (as described in example 4 for phaC gene deletion) or by a knock-out experiment deleting one part or all the gene by using specific endonucleases as non-limiting examples. 
     By “introducing into a cell or a microorganism one DNA sequence by means of genetic engineering techniques” is meant the action of transforming said cell or microorganism with a DNA sequence of interest by any transformation technologies known by the skilled in the art such as a non-limiting example the PEG-mediated protoplast transformation technic used in example 1 (Barg H. et. al (2005). 
     By “exogenous DNA sequence(s)” is meant nucleic acid sequence(s) non originally and/or naturally express in the considered microorganism or the way it is in the natural strain of microorganism (in term of expression level for example), and which have been used to transform said microorganism in order to obtain a genetically engineered microorganism as referred above. In a specific embodiment, the exogenous DNA sequence originates from another species than the considered microorganism (e.g. another species of microorganism or organism). In another specific embodiment, exogenous sequence originates from the same microorganism. 
     The term “nucleic acid” will generally refer to at least one molecule or strand of DNA, RNA, or a derivative or mimic thereof, comprising at least one nucleobase, such as, for example, a naturally occurring purine or pyrimidine base found in DNA (e.g., adenine “A,” guanine “G,” thymine “T,” and cytosine “C”) or RNA (e.g. A, G, uracil “U,” and C). A nucleic acid may be made by any technique known to one of ordinary skill in the art (see above and for example, Sambrook et al. 2000). 
     In another specific embodiment, said exogenous DNA sequences have been introduced into said microorganism by means of genetic engineering techniques. Any techniques known by the skilled in the art can be used to introduce those sequences such as a non-limiting example the PEG-mediated protoplast transformation technic used in example 1 (Barg H. et. al (2005)). 
     Said exogenous DNA sequence(s) may encode proteins of interest such as cytochrome P450 and redox partners AdR and Adx and the expression “exogenous DNA” can designate each individual sequence or encompasses a whole sequence comprising each individual sequences. As a non-limiting example, said microorganism has been transformed with one plasmid comprising said exogenous DNA sequences as described in example 1. As another non-limiting example, said exogenous DNA sequences are integrated into the genome of said microorganism by techniques known in the field such as homologous recombination for example. 
     By “microorganism” is meant the microorganism used to construct said genetically engineered microorganism according to the present invention. In the frame of the present invention, the microorganism can for instance be selected from the list consisting of  Escherichia coli, Bacillus licheniformis, Bacillus megaterium, Bacillus subtilis, Kluyveromyces lactis, Saccharomyces cerevisiae  and  Schizosaccharomyces pombe.    
     In a specific embodiment according to the invention, the microorganism is  Bacillus megaterium . In another specific embodiment according to the invention, the microorganism is a  Bacillus megaterium  strain chosen from the group consisting of strains deposited with Deutsche Stammsammlung von Mikroorganismen and Zellkulturen, hereinafter abbreviated as “DSM”, having accession numbers DSM 1517, DSM 1668, DSM 1669, DSM 1670, DSM 1671, DSM 1804, DSM 2894, DSM 30587, DSM 30601, DSM 30782, DSM 30787, DSM 30897, DSM 319, DSM 32, DSM 321, DSM 322, DSM 3228, DSM 333, DSM 337, DSM 339, DSM 344, DSM 3641, DSM 509, DSM 510, DSM 786 and DSM 90 strain. 
     In a specific embodiment according to the invention, the microorganism is  Bacillus megaterium  DSM 319 strain. In a specific embodiment according to the invention, the microorganism is a  Bacillus megaterium  strain which cannot express the major extracellular protease gene nprM (e.g. a strain of which the major extracellular protease gene nprM is deleted or silenced). In a specific embodiment according to the invention, the microorganism is  Bacillus megaterium  referred to as  Bacillus megaterium  MS941. By  Bacillus megaterium  MS941 strain is meant the strain as referenced in Wittchen K. D. and Meinhardt F., (1995) and in Jingwen Z. and al (2012) and derived from wild-type DSM319 strain by knocking out the major extracellular protease gene nprM. 
     One aspect of the present invention pertains to a genetically engineered microorganism capable of converting cholesterol, cholesterol analogs and derivatives thereof into steroid hormones precursors or derivatives, wherein said microorganism comprises at least one DNA sequence encoding a cytochrome P450 of eukaryotic origin, an exogenous DNA sequence encoding Adx and an exogenous DNA sequence encoding AdR. 
     By “cytochrome P450” is meant monooxygenases which are capable of catalyzing numbers of reactions (as reviewed in Van Bogaert, I. N. et al (2011) or in Urlacher V. B. and Girhard M. (2011) or at http://dmelson.uthsc.edu/CytochromeP450.html). Cytochrome P450 of the present invention is membrane-bound (insoluble) or cytoplasmic (soluble) in their respective original hosts. 
     In a specific embodiment, said cytochrome P450 of the present invention is selected from the group consisting of CYP11A1 (EC: 1.14.15.6 according to the Enzyme Commission number), CYP17A1 (EC: 1.14.99.9 or 4.1.2.30), CYP21A1, CYP11B1 (EC: 1.14.15.4), CYP11B2, CYP3A4, CYP46A1, CYP27A1 and CYP21A2 (EC: 1.14.99.10). 
     In the frame of the present invention, the cytochrome P450 introduced into the microorganism is of eukaryotic origin, as may be the exogenous AdR and Adx. By the expression “of eukaryotic origin” is meant a protein originally expressed in an (i.e. originating from) eukaryotic organism of the genus  Homo, Rattus, Mus, Sus, Bos, Gallus, Taeniopygia, Ovis, Macacamulatta, Capra, Odontesthes, Trichoplax, Alligator, Eublepharis, Macaca, Papio, Callithrix, Oryctolagus, Mesocricetus, Canis, Rana, Glandirana, Oncorhynchus, Epinephelus, Acanthopagrus, Tautogolabrus, Pimephales, Carassius, Gobiocypris, Anguilla, Dasyatis, Felis  and  Equus  as non-limiting examples, or in cell lines derived from these organisms for in vitro cultures or primary cells taken directly from living tissue and established for in vitro culture. In a specific embodiment, said cytochrome P450 of the present invention is a protein originally expressed in an eukaryotic organism of a species selected from the group consisting of  Homo sapiens, Mus musculus, Rattus norvegicus, Sus scrofa, Bos taurus, Gallus gallus, Taeniopygia guttata, Ovis aries, Taeniopygia guttata, Macaca mulatta, Capra hircus, Equus caballus, Odontesthes bonariensis, Trichoplax adhaerens, Alligator mississippiensis, Eublepharis macularius, Macaca fascicularis, Papio ursinus, Callithrix jacchus, Oryctolagus cuniculus, Mesocricetus auratus, Canis lupus familiaris, Rana catesbeiana, Glandirana rugosa, Oncorhynchus mykiss, Epinephelus coioides, Acanthopagrus schlegelii, Tautogolabrus adspersus, Pimephales promelas, Carassius auratus, Gobiocypris rarus, Anguilla japonica  and  Dasyatis Americana.    
     In a specific embodiment, the cytochrome P450 introduced into the microorganism is a cytochrome P450 from Bos Taurus. In another specific embodiment, said cytochrome P450 is CYP11A1 from Bos Taurus (referenced as P00189 in UniProtKB/Swiss-Prot) and catalyzes the side-chain cleavage reaction of cholesterol, cholesterol analogs and derivatives thereof to pregnenolone or other steroid hormones precursors and derivatives as a non-limiting example. In another specific embodiment, said cytochrome P450 catalyzes the hydroxylation of vitamin D2 to 20-hydroxyvitamin D2, 17,20-dihydroxyvitamin D2 and 17,20,24-trihydroxyvitamin D2 (Nguyen M. N. et al. 2009), the hydroxylation of vitamin D3 to 20-hydroxyvitamin D3, 20,23-dihydroxyvitamin D3 and 17,20,23-trihydroxyvitamin D3 (Tuckey R. C. et al. 2008). In another specific embodiment, said cytochrome P450 catalyzes the the oxidation of ergosterol to 17,24-dihydroxyergosterol, 20-hydroxy-22,23-epoxy-22,23-dihydroergosterol and 22-keto-23-hydroxy-22,23-dihydroergosterol (Tuckey R. C. et al. 2012), as other non-limiting examples. In another specific embodiment, the protein sequence of said cytochrome P450 is SEQ ID NO: 2. In another specific embodiment, the protein sequence of said cytochrome P450 is a variant of SEQ ID NO: 2, provided it retains its biological activity. Said microorganism according to the invention comprises at least one DNA sequence encoding a cytochrome P450 of eukaryotic origin or a variant of said cytochrome P450. The encoded cytochrome P450 of eukaryotic origin or the variant thereof according to the invention is not a fusion protein. 
     By “AdR” is meant Adrenodoxin reductase (EC: 1.18.1.6) or Adrenodoxin-NADP+ reductase, the enzyme which is known as the first component in the mitochondrial Cytochrome P450 electron transfer system and which is involved in the biosynthesis of all steroid hormones. 
     In a specific embodiment, said AdR enzyme is selected from the group consisting of AR (NADPH:adrenodoxin oxidoreductase (EC=1.18.1.6) encoded by arh1 gene) from  Schizosaccharomyces pombe  or from  Saccharomyces cerevisiae  and FNR (Ferredoxin-NADP reductase (EC=1.18.1.2) encoded by fpr gene) from  Escherichia coli.    
     In a specific embodiment, the AdR enzyme which is introduced into the microorganism is AdR from Bos Taurus (referenced as P08165 in UniProtKB/Swiss-Prot). In another specific embodiment, the protein sequence of said AdR is SEQ ID NO: 3. In another specific embodiment, the protein sequence of said AdR is a variant of SEQ ID NO: 3, provided it retains its biological activity. 
     By “Adx” is meant Adrenodoxin or Ferredoxin 1, the protein which is known for its activity of transferring electrons from Adrenodoxin reductase to CYPA11. 
     In a specific embodiment, said Adx enzyme is selected from the group consisting of Fdx from mammalian origin, Etp1fd from  Schizosaccharomyces pombe , Yah1 from  Saccharomyces cerevisiae.    
     In a specific embodiment, the Adx enzyme which is introduced into the microorganism is Adx from Bos Taurus as a non-limiting example (referenced as P00257 in UniProtKB/Swiss-Prot). In another specific embodiment, the protein sequence of said Adx is SEQ ID NO: 4. In another specific embodiment, the protein sequence of said Adx is a variant of SEQ ID NO: 4, provided it retains its biological activity. 
     Said genetically engineered microorganism according to the present invention further comprises a functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies. 
     By “functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies” is meant a PHA synthase regulon system or an equivalent system with respect to microorganism species which allows said microorganism to produce polyhydroxyalkanoate bodies (PHA-Bodies) or polyhydroxyalkanoate granules or equivalent with respect to considered microorganism species such as polyhydroxybutyrate bodies (PHB-Bodies) or polyhydroxybutyrate granules as non-limiting examples. In a specific embodiment, genetically engineered microorganism according to the present invention is capable of producing polyhydroxyalkanoate bodies (PHA-Bodies) or polyhydroxyalkanoate granules. In another specific embodiment, said genetically engineered microorganism according to the present invention is capable of producing polyhydroxybutyrate bodies (PHB-Bodies) or polyhydroxybutyrate granules. 
     By PHA synthase regulon system is meant a collection of genes encoding key enzymes of the polyhydroxyalkanoate biosynthesis, which allow the covalent linkage of activated precursors such as (R)-3-hydroxyacyl-coenzyme A thioester with chain length between 3-14 C-atoms, which are substrates of pha-synthase. More than 59 pha-synthase genes with high homology from more than 45 bacterial species have been isolated showing a broad specificity (as described in http://mibi1.unimuenster.de/Biologie.IMMB.Steinbuechel/Forschung/PHA.hta and in Steinbüchel A. and Valentin H. E. 1995, Stubbe J. and Tian J. 2003, Sudesh K. et al. 2000, Liebergesell, M. et al., 1994). 
     The activity of said polymerase system capable of building polyhydroxyalkanoate bodies according to the present invention can be measured by staining with nile red or nile blue and fluorescence microscopy (As shown in Ostle A. G. and Holt J. G., 1982; Spierkemann P. et al. 1999; Der-Shyan S. et al. 2000) or as mentioned in example 4. 
     In the expression “functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies” is encompassed the case where the capacity of building polyhydroxyalkanoate bodies is not detectable by regular measurement of activity as mentioned above but where genes of such an endogenous polymerase system are detectable by genomic methods and susceptible to form detectable polyhydroxyalkanoate bodies under particular conditions such as when another pha-synthase gene is overexpressed as a non-limiting example. 
     In another embodiment, said genetically engineered microorganism according to the present invention further comprises at least one gene involved in the building of PHA-bodies wherein said gene expression is “modulated” as described above. In a specific embodiment, said gene is overexpressed. In another specific embodiment, said gene is down-regulated. In another specific embodiment, said gene is knocked out. In another specific embodiment, said gene is one of the pha-synthase genes as mentioned in the references above. In another specific embodiment, said gene is selected from the group consisting of PhaR (pha synthase), PhaP (Phasin), PhaC (pha synthase), PhaE (Pha synthase), PhaQ (poly-beta-hydroxybutyrate-responsive repressor), PhaB (Acetoacetyl-CoA reductase) and PhaA (3-Ketothiolase). In another specific embodiment, said genetically engineered microorganism according to the present invention comprises overexpressed PhaC (pha synthase). In another specific embodiment, said genetically engineered microorganism according to the present invention comprises overexpressed PhaP (phasin). In another specific embodiment, said genetically engineered microorganism according to the present invention comprises overexpressed PhaA (3-Ketothiolase). In another specific embodiment, said genetically engineered microorganism according to the present invention is knocked out for the Pha depolymerase genes (PhaZ, poly(3-hydroxyalkanoic acid) depolymerase, PhaZ1, PhaZ2 and PhaZ3). 
     In another embodiment, said genetically engineered microorganism according to the present invention comprises more than one gene involved in the building of PHA-bodies wherein said genes expression are “modulated”, such as two, three, four, five, six, seven, eight, nine, ten or more than ten genes. 
     In another embodiment, said genetically engineered microorganism according to the present invention is modified by overexpressing at least one gene selected in the group consisting of PhaR, PhaP, PhaC, PhaE, PhaB and PhaA and/or down regulating or inactivating at least one gene selected in the group consisting of PhaZ and PhaQ. 
     In another specific embodiment, said genetically engineered microorganism according to the present invention comprises all together overexpressed PhaA (3-Ketothiolase), PhaB (Acetoacetyl-CoA reductase), PhaC (pha synthase) and PhaR (pha synthase). 
     In another specific embodiment, said genetically engineered microorganism according to the present invention comprises overexpressed PhaC (pha synthase) and PhaR (pha synthase) as subunits of a same pha polymerase class IV. 
     In another specific embodiment, said genetically engineered microorganism according to the present invention comprises overexpressed PhaC (pha synthase) and PhaE (pha synthase) as subunits of a same pha polymerase class III. 
     In another embodiment, said overexpressed genes within genetically engineered microorganism according to the present invention are genes originated from the same microorganism species. In another embodiment, said overexpressed genes within genetically engineered microorganism according to the present invention are genes from other microorganisms species. As non-limiting examples, those genes belong to pha gene system from  Ralstonia eutropha, Pseudomonas aeruginosa , and  Allochromatium vinosum.    
     In another specific embodiment, said microorganism of the present invention is  Bacillus megaterium . In another specific embodiment, said microorganism of the present invention is  Bacillus megaterium  of strain MS941. 
     Within substrates which the genetically engineered microorganism of the present invention is capable of converting are encompassed phytosterol derivated from cycloartenol and lanosterol. Amongst these substrates, by “cholesterol, cholesterol analogs and derivatives thereof” is meant a list of substrates selected from the group consisting of cholesterol, brassicasterol, campesterol, ergostadienol such as ergosta 5, 22 dienol, ergosta 5, 24 (28) dienol, ergosta 5, 24 (25) dienol, ergostatrienol such as ergosta 5, 22, 24 (25) trienol, ergosta 5, 22, 24 (28) trienol, ergosta 5, 7, 22 trienol, ergostatetrenol such as ergosta 5, 7, 22, 24 (25) ou ergosta 5, 7, 22, 24 (28), desmosterol, beta-sitosterol, generol, a mixture of oxysterols, stigmasterol, vitamin D, 7-Dehydrocholesterol and ergosterol as illustrated in examples 3-5 and in  FIGS. 2-12 . Sterol mixes currently used in industrial processes are also encompassed in this definition of substrates, such as generol 100 and ADM90 (comprising brassicasterol+campesterol+stigmasterol+β-sitosterol at different ratios). 
     By “variant(s)” is meant protein and nucleic acid variants. Variant proteins may be naturally occurring variants, such as splice variants, alleles and isoforms. Variations in amino acid sequence may be introduced by substitution, deletion or insertion of one or more codons into the nucleic acid sequence encoding the protein that results in a change in the amino acid sequence of the protein. Variant proteins may be a protein having a conservative or non-conservative substitution. For example, a variant of SEQ ID NO: 2, SEQ ID NO: 3 or SEQ ID NO: 4 may be a polypeptide having at least one substitution at a particular amino acid residue. Variant proteins may include proteins that have at least about 80% amino acid sequence identity with a polypeptide sequence disclosed herein. Preferably, a variant protein will have at least about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% amino acid sequence identity to a full-length polypeptide sequence or a fragment of a polypeptide sequence as disclosed herein. Amino acid sequence identity is defined as the percentage of amino acid residues in the variant sequence that are identical with the amino acid residues in the reference sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity, and not considering any conservative substitutions as part of the sequence identity. Sequence identity may be determined over the full length of the variant sequence, the full length of the reference sequence, or both. The percentage of identity for protein sequences may be calculated by performing a pairwise global alignment based on the Needleman-Wunsch alignment algorithm to find the optimum alignment (including gaps) of two sequences along their entire length, for instance using Needle, and using the BLOSUM62 matrix with a gap opening penalty of 10 and a gap extension penalty of 0.5. 
     Variant nucleic acid sequences may include nucleic acid sequences that have at least about 80% nucleic acid sequence identity with a nucleic acid sequence disclosed herein. Preferably, a variant nucleic acid sequence will have at least about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% nucleic acid sequence identity to a full-length nucleic acid sequence or a fragment of a nucleic acid sequence as disclosed herein. Nucleic acid sequence identity can be calculated by methods well-known to one of skill in the art. The percentage of identity may be calculated by performing a pairwise global alignment based on the Needleman-Wunsch alignment algorithm to find the optimum alignment (including gaps) of two sequences along their entire length, for instance using Needle, and using the DNAFULL matrix with a gap opening penalty of 10 and a gap extension penalty of 0.5. Examples of nucleic acid variants can be variants of nucleic acid encoding for proteins of SEQ ID NO: 2, SEQ ID NO: 3 and SEQ ID NO: 4 and variants of nucleic acid encoding pha system genes. 
     As used herein, “amino acid” refers to the 20 standard alpha-amino acids as well as naturally occurring and synthetic derivatives. A polypeptide may contain L or D amino acids or a combination thereof. 
     2. Methods of Producing Steroid Hormones According to the Invention 
     The inventors achieved a high rate conversion of cholesterol, cholesterol analogs and derivatives into pregnenolone, hydroxylated cholesterol analogs and secosteroids, by co-expressing into  B. megaterium  MS941 the insoluble CYP11A1 of bovine origin, bovine adrenodoxin reductase (AdR), and adrenodoxin (Adx) as shown in examples 3-5 and  FIGS. 2-12 . 
     Therefore, a second aspect of the present invention pertains to a method for producing steroid hormones precursors and derivatives, comprising the steps of:
         Providing a microorganism as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”,   Culturing said microorganism under conditions allowing the expression of said exogenous DNA sequences,   Contacting said microorganism culture with a substrate, and   Recovering steroid hormones precursors and derivatives.       

     In a specific embodiment, said “steroid hormones precursors and derivatives” are selected from the group consisting of pregnenolone, 7-Dehydropregnenolone, Hydroxyergosterol, and Hydroxystigmasterol. In another specific embodiment, said steroid hormones precursors and derivatives are selected from the group of hydroxylated cholesterol analogs and secosteroids (such as vitamins D2 and D3 as derivatives of the cholesterol analogs 7-dehydrocholesterol and ergosterol). 
     By “culturing said microorganism under conditions allowing the expression of said exogenous DNA sequences” is meant any well-known culturing and inducing methods in the biotechnology field. As an illustrative example, culture conditions of a microorganism according to the present invention are given in examples 1 and 2. 
     By “substrates” which the genetically engineered microorganism of the present invention is able to convert are encompassed phytosterol derivated from cycloartenol and lanosterol. 
     In a specific embodiment, the present invention pertains to a method for producing steroid hormones precursors and derivatives, comprising the steps of:
         Providing a microorganism as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”,   Culturing said microorganism under conditions allowing the expression of said exogenous DNA sequences,   Contacting said microorganism culture with a substrate selected from the group consisting of cholesterol, cholesterol analogs and derivatives, and   Recovering steroid hormones precursors and derivatives.       

     By “cholesterol, cholesterol analogs and derivatives thereof” is meant a list of compounds selected from the group consisting of cholesterol, brassicasterol, campesterol, ergostadienol such as ergosta 5, 22 dienol, ergosta 5, 24 (28) dienol, ergosta 5, 24 (25) dienol, ergostatrienol such as ergosta 5, 22, 24 (25) trienol, ergosta 5, 22, 24 (28) trienol, ergosta 5, 7, 22 trienol, ergostatetrenol such as ergosta 5, 7, 22, 24 (25) or ergosta 5, 7, 22, 24 (28), desmosterol, beta-sitosterol, generol, generol 100, sterol ADM90, a mixture of oxysterols, stigmasterol, vitamin D, 7-Dehydrocholesterol and ergosterol as illustrated in examples 3-5 and in  FIGS. 2-12 . 
     In a specific embodiment, the present invention pertains to a method for producing steroid hormones precursors and derivatives, comprising the steps of:
         Providing a microorganism as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”,   Culturing said microorganism under conditions allowing the expression of said exogenous DNA sequences,   Contacting said microorganism culture with a substrate currently used in industrial processes, and   Recovering steroid hormones precursors and derivatives.       

     By “Sterol mixes currently used in industrial processes” are meant substrates, such as generol 100 and ADM90 (comprising brassicasterol+campesterol+stigmasterol+β-sitosterol at different ratios) as illustrated in examples 3-5 and in  FIG. 12 . 
     By “contacting” said microorganism culture with a substrate, is meant to make physically interacting said microorganism according to the present invention with a substrate according to the present invention. This interaction can be achieved within a culture medium or not. In a specific embodiment, said culture medium contains agents for the permeabilization of a microorganism according to the present invention and/or the solubilization of a substrate according to the present invention. Dissolution of the substrate in these agents can be prior to the addition to microorganism culture. 
     These agents can be selected from the group consisting of ethanol, Tween-80, tergitol, polyvinylpyrrolidone (PVP), saponins (such as  Quillaja saponin  which is contained within crude extracts of the soap bark tree  Quillaja saponaria  for example), cyclodextrins and derivatives thereof (e.g. 2-hydroxypropyl-β-cyclodextrin). In another specific embodiment, mixtures of these agents can be used, such as a mixture of ethanol and Tween-80, a mixture of tergitol and ethanol, a mixture of saponins (e.g.  Quillaja saponin ) and cyclodextrins as non-limiting examples. Cyclodextrins derivatives can be used such as 2-hydroxypropyl-β-cyclodextrin as a non-limiting example. In another specific embodiment, substrates are co-crystallized with polyvinylpyrrolidone (PVP). 
     In another specific embodiment, substrate is first dissolved in 2-hydroxypropyl-β-cyclodextrin prior to the addition to the microorganism culture wherein said culture contains  Quillaja saponin . In another specific embodiment, substrates are dissolved in a solution comprising a percentage of 2-hydroxypropyl-β-cyclodextrin ranging from 10 to 60%, preferentially 20 to 50%, more preferably 40 to 50% and a percentage of  Quillaja saponin  ranging from 1 to 10%, preferably 2 to 8%, more preferably, 3 to 6%. In another specific embodiment, substrates are dissolved in a solution comprising 45% of 2-hydroxypropyl-β-cyclodextrin and 4% of  Quillaja saponin  as mentioned in example 2. 
     In another embodiment, final concentration of 2-hydroxypropyl-β-cyclodextrin in the microorganism culture is between 1 and 4%, preferably between 2 and 3%, more preferably 2.25% as illustrated in example 2. In another embodiment, final concentration of  Quillaja saponin  in the microorganism culture is between 0.05 and 0.25%, preferably between 0.075 and 0.225%, more preferably between 0.1 and 0.2% as illustrated in example 2. 
     In a specific embodiment, the present invention pertains to a method for producing steroid hormones precursors and derivatives, comprising the steps of:
         Providing a microorganism as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”,   Culturing said microorganism under conditions allowing the expression of said exogenous DNA sequences,   Contacting said microorganism culture with a substrate, wherein said substrate has been previously dissolved in a solution comprising 2-hydroxypropyl-β-cyclodextrin and  Quillaja saponin , and   Recovering steroid hormones precursors and derivatives.       

     In another specific embodiment, the present invention pertains to a method for producing steroid hormones precursors and derivatives, comprising the steps of:
         Providing a microorganism as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”,   Culturing said microorganism under conditions allowing the expression of said exogenous DNA sequences,   Contacting said microorganism culture with a substrate,
           i. wherein said substrate has been previously dissolved in a solution comprising 2-hydroxypropyl-β-cyclodextrin and  Quillaja saponin,      ii. wherein final concentrations of these components in the culture medium are respectively 2.25% and 0.2%, and   
           Recovering steroid hormones precursors and derivatives.       

     3. Methods of Preparing Recombinant Strains According to the Invention 
     A third aspect of the present invention is a method of preparing recombinant strains which are improved with respect to the conversion of substrates such as cholesterol and derived-analogs into steroid hormones precursors as described above, comprising the steps of:
         Providing a microorganism according to the present invention,   Introducing by means of genetic engineering techniques into said microorganism at least one DNA sequence encoding a cytochrome P450 of eukaryotic origin according to the present invention, an exogenous DNA sequence encoding Adx, and an exogenous DNA sequence encoding AdR.       

     In a specific embodiment, said method comprises a cytochrome P450 of eukaryotic origin selected from the group consisting of CYP11A1, CYP17A1, CYP11B1, CYP21A1, CYP11B2, CYP3A4, CYP46A1, CYP27A1 and CYP21A2 (EC: 1.14.99.10). 
     In another specific embodiment, said method includes a microorganism comprising a functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”. 
     In another specific embodiment, said microorganism of the present method is  Bacillus megaterium . In another specific embodiment, said microorganism of the present method is  Bacillus megaterium  MS941 strain. 
     In another embodiment, the method of the present invention further comprises the step of modulating by means of genetic engineering techniques into said microorganism, the expression of at least one gene involved in the building of PHA-bodies as described in the above paragraph entitled “Genetically engineered microorganisms according to the invention”. 
     4. Methods of Increasing the Storage Capacity of a Microorganism According to the Invention 
     Surprisingly, the inventors have now found that it was possible to express and catalyze the bioconversion of substrates from cytochrome P450 monooxygenases of eukaryotic origin at high rates, by using a microorganism as a whole-cell catalyst and by increasing its storage capacity dependent of polyhydroxyalkanoate granules. 
     Therefore, a fourth aspect of the invention is drawn to a method for increasing the storage capacity of a microorganism for hydrophobic or hydrophilic compounds comprising the steps of:
         a. Providing a microorganism comprising a functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies as described in the above paragraphs; and   b. Modulating by means of genetic engineering techniques into said microorganism, the expression of at least one gene involved in the building of PHA-bodies, as described in the above paragraphs,
 
thereby obtaining a microorganism with increased storage capacity for hydrophobic or hydrophilic compounds.
       

     In a specific embodiment, said hydrophobic compounds are:
         (i) cholesterol, cholesterol analogs and derivatives thereof, and/or   (ii) steroid hormones precursors and derivatives thereof.       

     Therefore, this aspect of the invention is also drawn to a method for increasing the storage capacity of a microorganism for (i) cholesterol, cholesterol analogs and derivatives thereof, and/or (ii) steroid hormones precursors and derivatives thereof comprising the steps of:
         a. Providing a microorganism comprising a functional endogenous polymerase system capable of building polyhydroxyalkanoate bodies as described in the above paragraphs; and   b. Modulating by means of genetic engineering techniques into said microorganism, the expression of at least one gene involved in the building of PHA-bodies, as described in the above paragraphs,
 
thereby obtaining a microorganism with increased storage capacity for (i) cholesterol, cholesterol analogs and derivatives thereof, and/or (ii) steroid hormones precursors and derivatives thereof.
       

     The activity of said polymerase system capable of building polyhydroxyalkanoate bodies according to the present invention can be measured by staining with nile red or nile blue and fluorescence microscopy (Ostle A. G. and Holt J. G., 1982; Spierkemann P. et al. 1999; Der-Shyan S. et al. 2000) and as mentioned in example 4. 
     In a specific embodiment, said storage capacity is proportionally increased with respect to PhaC polymerase gene expression. In other terms, the introduction of an exogenous DNA sequence encoding a PhaC gene allows to increase the capacity of the microorganism according to the present invention to store Polyhydroxyalkanoates in granules and to increase the capacity of said microorganism to convert said substrate into products. As non-limiting example, by overexpressing exogenous phaC gene into  Bacillus megaterium  MS941 overexpressing CYPA11 and its redox partners, the inventors increased the capacity of said genetically engineered microorganism to convert cholesterol, cholesterol analogs and derivatives into steroid hormones precursors, hydroxylated cholesterol analogs and secosteroids, as described in examples 3 to 5. 
     In another specific embodiment, said storage capacity is proportionally increased with respect to PhaP gene expression. In other words, the overexpression of an exogenous DNA sequence encoding a PhaP gene allows increasing the capacity of the microorganism according to the present invention to store Polyhydroxyalkanoates in granules and to increase the capacity of said microorganism to convert said substrate into products. 
     In another specific embodiment, said storage capacity is proportionally increased with respect to PhaA gene expression. In other words, the overexpression of an exogenous DNA sequence encoding a PhaA gene allows to increase the capacity of the microorganism according to the present invention to store Polyhydroxyalkanoates in granules and to increase the capacity of said microorganism to convert said substrate into products. 
     In another specific embodiment, said storage capacity is proportionally increased with respect to Pha depolymerase genes (PhaZ, poly(3-hydroxyalkanoic acid) depolymerase, PhaZ1, PhaZ2 and PhaZ3) down-regulation. In other words, knock-out of the Pha depolymerase genes (PhaZ, poly(3-hydroxyalkanoic acid) depolymerase, PhaZ1, PhaZ2 and PhaZ3) and suppression or down regulation of the protein(s) encoded by said gene(s) allows to increase the capacity of the microorganism according to the present invention to store Polyhydroxyalkanoates in granules and to increase the capacity of said microorganism to convert said substrate into products. 
     In another specific embodiment, said storage capacity is proportionally increased with respect to concomitant overexpression of PhaA (3-Ketothiolase), PhaB (Acetoacetyl-CoA reductase), PhaC (pha synthase) and PhaR (pha synthase). In other words, the overexpression of exogenous DNA sequences encoding PhaA, PhaB, PhaC and PhaR genes allows to increase the capacity of the microorganism according to the present invention to store Polyhydroxyalkanoates in granules and to increase the capacity of said microorganism to convert said substrate into products. 
     In another specific embodiment, said storage capacity is proportionally increased with respect to concomitant overexpression of PhaC (pha synthase) and PhaR (pha synthase) as subunits of a same pha polymerase class IV. In other words, the overexpression of exogenous DNA sequences encoding PhaC and PhaR genes allows to increase the capacity of the microorganism according to the present invention to store Polyhydroxyalkanoates in granules and to increase the capacity of said microorganism to convert said substrate into products. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1 : Immunostainings of CYP11A1 (A) and AdR/Adx (B); Lane 1: wildtype strain of  B. megaterium  MS941; lane 2: strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 2 : HPLC chromatogram showing the conversion of cholesterol (“S” for substrate) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 3 : HPLC chromatogram showing the conversion of 7-dehydrocholesterol (“S” for substrate) to 7-dehydro pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 4 : HPLC chromatogram showing the conversion of campesterol (“S” for substrate) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 5 : HPLC chromatogram showing the conversion of ergostadienol (“S” for substrate) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 6 : HPLC chromatogram showing the conversion of desmosterol (“S” for substrate) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 7 : HPLC chromatogram showing the conversion of mixture of oxysterols (“S1”, “S2” and “S3” for the different oxysterol substrates) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 8 : HPLC chromatogram showing the conversion of ergosterol (“S” for substrate) to hydroxy-ergosterol (“P1”, “P2”, “P3” and “P4” for the different hydroxylated forms of products) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 9 : HPLC chromatogram showing the conversion of vitamin D (“S” for substrate) to hydroxyl-vitamin D (“P1” and “P2” for the different hydroxyl-vitamin D forms) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA (Solid line) compared to  B. megaterium  MS941 (Dotted line). 
         FIG. 10 : HPLC chromatogram showing the conversion of beta-sistosterol (“S” for substrate) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 11 : HPLC chromatogram showing the conversion of stigmasterol (“S” for substrate) to hydroxyl-stigmasterol (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 12 : HPLC chromatogram showing the conversion of generol 100 (“S1”, “S2” and “S3” for three of the different sterols contained in general 100) to pregnenolone (“P” for product) by strain of  B. megaterium  MS941 transformed with pSMF2.1_SCCAA. 
         FIG. 13 : Comparison of CYP11A1 in vivo activity in absence and presence of polyhydroxybutyrate-bodies (KO: PhaC knockout strain of  B. megaterium  MS941; WT: wildtype of  B. megaterium  MS941 strain) after 24 and 48 hours of reaction. 
         FIG. 14 : Restoration of substrate conversion activity in a PHB-depleted strain (MS941_deltaphaC) overexpressing CYP11A1 and its redox partners; comparison of CYP11A1 in vivo activity in absence (Structure Knockout strain(MS941_deltaphaC)+CYP11A1) and presence of polyhydroxybutyrate-bodies (Wildtype strain+CYP11A1) and in a strain wherein PHB-bodies have been reconstituted by transforming the strain with a plasmid encoding the structure operon (Structure Knockout strain(MS941_deltaphaC)+CYP11A1+reconstitution of structures(pMGBm19_RBCP). 
         FIG. 15 : Map of expression vector pSMF2.1_SCCAA. 
         FIG. 16 : Comparison of pregnenolone yields produced in different microorganisms expression different cytochrome P450. 
     
    
    
     BRIEF DESCRIPTION OF THE SEQUENCES 
     SEQ ID NO: 1: Plasmid sequence of pSMF2.1_SCCAA. 
     SEQ ID NO: 2: Amino acid sequence of CYP11A1. 
     SEQ ID NO: 3: Amino acid sequence of AdR. 
     SEQ ID NO: 4: Amino acid sequence of Adx. 
     EXAMPLES 
     Example 1: Construction of  B. megaterium  Expression Plasmid pSMF2.1 SCCAA 
     For the cloning of the respective genes, the following restriction enzymes were used:
         CYP11A1: Spel/Mlul   AdR: Kpnl/Sacl   Adx: BsRGI/Sphl       

     Plasmid pSMF2.1_SCCAA is derived from  Bacillus megaterium  shuttle vector pKMBm4 (obtained from the group of Prof. Dr. Dieter Jahn, T U Braunschweig, Stammen S. et al. (2010)). pKMBm4 was modified as as described below: 
     A) the Pacl-restriction site was deleted by mutagenesis, 
     B) a new multiple cloning site was inserted, (Bleif et al., 2012) 
     C) fragments encoding adrenodoxin, adrenodoxin reductase and CYP11A1 were inserted. 
     All three genes are under the control of the strong-inducible promoter PXyIA. Each gene contains its own ribosomal binding site. 
     In  E. coli , the beta-lactamase is expressed, conferring ampicillin resistance. 
     In  B. megaterium , the tetracycline-resistance protein is expressed, conferring tetracycline resistance. 
     Plasmid map and sequence of pSMF2.1_SCCAA are respectively provided in  FIG. 15  and SEQ ID N° 1. 
       Bacillus megaterium  strain MS941 were obtained from the group of D. Jahn/Technische Universitat Braunschweig (Wittchen K. D. und Meinhardt F., 1995) derived from DSM319/Deutsche Stammsammlung von Mikroorganismen und Zellkulturen. 
       B. megaterium  cells were transformed according to the PEG-mediated protoplast transformation by Barg H. et. al (2005). 
     Example 2: Cultivation Conditions for Recombinant  B. megaterium  and Samples Treatment 
     Either LB-(25 g/L), TB-(24 g/L yeast extract, 12 g/L tryptone, 0.4% glycerol, 10 mM potassium phosphate buffer) or EnPresso™ Tablet medium have been used for the cultivation of  B. megaterium . All reagents are listed in table 1 below. 
     Pre-Culture: 
     Inoculation of 50 mL medium containing 10 μg/mL tetracycline were performed with cells from a plate or glycerol stock. 
     Main Culture: 
     Inoculation of 50 mL medium containing 10 μg/mL tetracycline were performed with 500 μL sample of the pre-culture. 
     Induction of Protein Expression: 
     The main culture was grown until an optical density of ˜0.4 has been reached. Protein expression was induced after addition of 0.25 g xylose dissolved in 1 mL distilled water. 
     Substrate Solubilization: 
     Steroids were dissolved in a 45% 2-hydroxypropyl-β-cyclodextrin/4%  Quillaja saponin -solution. 2.5 ml of the solution were added to the culture directly after protein induction leading to a final  Quillaja saponin  concentration of 0.2% and a final concentration of 2-hydroxypropyl-β-cyclodextrin of 2.25%. 
     Sample Treatment for HPLC-Analysis: 
     Steroids without intrinsic absorption were converted into their Δ 4-3 -keto-derivatives, to allow photometric detection at 240 nm. 
     1 mL Culture samples was boiled in water for 1 min. 20 μl cholesterol oxidase-solution (5 mg cholesterol oxidase and 5 mg Na-cholate dissolved in 5 ml 50 mM HEPES buffer pH 7, containing 0.05% Tween-20) was added and the sample was incubated at 37° C. with 1000 rpm shaking for 1 hour. For HPLC analysis, the sample was extracted twice with 1 mL ethylacetate and the extract was dissolved in the appropriate solvent. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 List of reagents 
               
            
           
           
               
               
               
            
               
                   
                 Reagent 
                 Manufacturer 
               
               
                   
                   
               
               
                   
                 2-Hydroxypropyl-β-cyclodextrin 
                 Sigma-Aldrich (332607) 
               
               
                   
                 Ampicillin 
                 Roth 
               
               
                   
                 Cholesterol oxidase ( Nocardia  sp.) 
                 CALBIOCHEM 
               
               
                   
                 EnPresso tablet medium 
                 Biosilta 
               
               
                   
                 Ethylacetate 
                 Sigma-Aldrich 
               
               
                   
                 Glycerol 
                 Grüssing 
               
               
                   
                 HEPES 
                 Roth 
               
               
                   
                 K 2 HPO 4   
                 Grüssing 
               
               
                   
                 KH 2 PO 4   
                 Grüssing 
               
               
                   
                 LB 
                 BD 
               
               
                   
                 Na-cholate 
                 SERVA 
               
               
                   
                   Quillaja  saponin 
                 Sigma-Aldrich (S7900) 
               
               
                   
                 Restriction enzymes 
                 NEB 
               
               
                   
                 Tetracycline 
                 SERVA 
               
               
                   
                 Tryptone 
                 BD 
               
               
                   
                 Tween-20 
                 Roth 
               
               
                   
                 Yeast extract 
                 BD 
               
               
                   
                   
               
            
           
         
       
     
     Example 3: Conversion of Cholesterol, Cholesterol Analogs and Derivatives into Pregnenolone by Genetically Engineered  B. megaterium  MS941 Expressing Bovine CYP11A1 and its Redox Partners Adx and AdR 
       Bacillus megaterium  strain MS941 has been genetically modified to express the steroidogenic enzyme CYP11A1 and its redox partners Adx and AdR.  B. megaterium  has been transformed with the expression vector pSMF2.1_SCCAA ( FIG. 1 ) comprising genes for CYP11A1, AdR and Adx under the control of the strongly-inducible promoter PXyIA as described in example 1 and encoding respectively for proteins of SEQ ID NO: 2, SEQ ID NO: 3 and SEQ ID NO: 4. So far, the mitochondrial cytochrome P450 CYP11A1 has not been expressed in  Bacillus megaterium.    
     The expression of all three proteins has been confirmed by immunostaining ( FIG. 1 ). 
     The following substrates have been solubilized with 2-hydroxypropyl-β-cyclodextrin and  Quillaja saponin  and converted in-vivo with the aforementioned recombinant strain: Cholesterol, 7-Dehydrocholesterol, Campesterol, Ergosta-5,24-dienol, Desmosterol, mixture of oxysterols, Ergosterol, Vitamin D, Beta-Sitosterol, Stigmasterol, Generol. ( FIGS. 2-12 ). 
     As a conclusion, this system allows the whole-cell biocatalysis of the hydrophobic steroids cholesterol, its plant-derived analogs and vitamin D and has the ability to take up high concentrations of highly water-insoluble compounds and convert them at high rates. The product yield of this system is superior to other pregnenolone-producing systems ( FIG. 16 ). 
     Example 4: Role of Polyhydroxybutyrate-Bodies (PHB-Bodies) into the Conversion of Cholesterol, Cholesterol Analogs and Derivatives into Pregnenolone by Genetically Engineered  B. megaterium  MS941 Expressing Bovine CYP11A1 and its Redox Partners Adx and AdR 
     Fluorescent cholesterol analog 25-NBD cholesterol has been shown to localize to the carbon-storage serving PHB-bodies in living  B. megaterium -cells (data not shown). In order to localize CYP11A1 in  B. megaterium -cells, a fusion protein was expressed in living  B. megaterium -cells consisting of the fluorescent protein eGFP and CYP11A1. Similar to 25-NBD cholesterol, CYP11A1eGFP was localized in the PHB-bodies, whose identity was confirmed by nile red staining (data not shown). 
     The PHB-body producing polymerase PhaC has been deleted from the genome of  B. megaterium  by homologous recombination. Briefly, a deletion cassette was constructed, consisting of flanking regions of the PhaC gene. This construct was cloned on a plasmid containing a temperature-sensitive origin of replication. After two homologous recombination events, the curing of the plasmid was achieved by incubation at the non-permissive replication temperature. The deletion of the gene was verified by PCR. In order to verify the role of the PHB-bodies in CYP11A1 aggregation and substrate storage, the resulting absence of PHB-bodies in the  B. megaterium -cells has been monitored by nile red-staining (data not shown). This morphological change leaded to a drastic decrease in whole-cell conversion activity of the PhaC-knockout strain transformed with pSMF2.1_SCCAA ( FIG. 13 ). 
     Example 5: Modulation of Polyhydroxybutyrate-Bodies (PHB-Bodies) into a Genetically Engineered  B. megaterium  MS941 Strain Expressing Bovine CYP11A1 and its Redox Partners Adx and AdR 
     a-Conversion of Cholesterol, Cholesterol Analogs and Derivatives into Pregnenolone 
     Substrate conversion activity of the structure-depleted CYP11A1 expressing strain has been restored by transforming it with a plasmid encoding the structure operon encoding for PhaR, PhaB, PhaC and PhaP genes under the control of the original promoter of PhaR, PhaB and PhaC genes (pMGBm19_RBCP plasmid,  FIG. 14 ). The complemented strain exhibited an increase of product yield by more than 100% after 48 hours compared with the structure-depleted strain. The conversion activity was still significantly lower compared with the wildtype strain, since the recombinant expression of the structure operon likely leaded to a reduced expression of CYP11A1 and its redox partners (due to the co-expression of the additional proteins). 
     These data convincingly illustrates the importance of the granule structures for the whole-cell system. 
     b-Storage Capacity of  Bacillus megaterium  MS941 by Modulation of Pha System Genes. 
     The following strategies are applied: 
     1) Phasin gene (in case of  Bacillus megaterium  phaP) is overexpressed to modify the size of the granules. Phasin gene is inserted into a vector under control of a xylose inducible promoter.  Bacillus megaterium  is transformed with the resulting plasmid. Yield of substrate conversion into product in the strain overexpressing phaP is measured as described in example 2 and in  FIGS. 2-12 . 
     2) Pha depolymerase gene is knocked-out to hinder the depolymerization of the granules. Pha depolymerase genome locus is amplified via PCR by introducing a deletion of the locus leading to a nonfunctional gene. This nonfunctional DNA fragment is inserted into a “knock out” vector in order to replace the original genomic functional gene with a nonfunctional one in an gene replacement experiment. Yield of substrate conversion into product in the strain knocked out in the depolymerase gene is measured as described in example 2 and in  FIGS. 2-12 . 
     3)  Bacillus megaterium  metabolism is engineered to increase the production of Acetyl-CoA, the main precursor of the metabolism for the granule production, by inserting 3-Ketothiolase gene (phaA) into a vector under control of a xylose inducible promoter.  Bacillus megaterium  is transformed with the resulting plasmid. Yield of substrate conversion into product in the strain overexpressing phaA is measured as described in example 2 and in  FIGS. 2-12 . 
     4) Genes involved in granule synthesis (3-Ketothiolase (phaA), Acetoacetyl-CoA reductase (phaB), Phasin (phaP) and pha synthase (phaC/phaR) are overexpressed. The above-mentioned genes are inserted into a vector under control of a xylose inducible promoter.  Bacillus megaterium  is transformed with the resulting plasmid. Yield of substrate conversion into product in the strain overexpressing phaA, phaB, phaP, phaC and phaR is measured as described in example 2 and in  FIGS. 2-12 . 
     5) More active pha synthases from other organisms are introduced into  Bacillus megaterium  MS941 strain to produce more polymer. Pha genes, from  Ralstonia eutropha, Pseudomonas aeruginosa  and  Allochromatium vinosum  are used.  Exogenous pha synthases  genes are inserted into a vector under control of a xylose inducible promoter.  Bacillus megaterium  is transformed with the resulting plasmid. Yield of substrate conversion into product in the strain overexpressing pha synthase(s) from other microorganisms is measured as described in example 2 and in  FIGS. 2-12 . 
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