Cytochrome P450 (CYP) genes refer to such genes that encode a superfamily of iron-containing hemoproteins with a maximum absorption spectrum near 450 nm, often characterized by conserved Cys residue in hydrophobic pocket(s) . Most of the ORFs of CYP have three distinct characteristics used often for their identification and analysis, i.e., the I-helix of putative CYPs (a highly conserved threonine involved in oxygen activation), the conserved EXXR motif located in the K-helix and the cytochrome P450 cysteine heme-iron ligand signature motif (GXXXCXG, there are exceptions) . According to a widely-accepted taxonomy, CYPs within a family share more than 40% amino acid identity and members of subfamilies share more than 55% amino acid identity . Occasionally, the decision to accept a sequence in a known family depends greatly on how it clusters on a tree, not so much on the absolute amino acid identity .
CYPs have been confirmed existing in all eukaryotic (human, animals, plants, fungi, etc.) and prokaryotic organisms (bacteria, archaea, and even in viruse) [5–8]. They often are monooxygenases involved in oxidation of a range of endogenous compounds, such as cholesterol, lipids and steroidal hormones, as well as xenobiotics such as drugs and toxic chemicals in environment [9–11]. CYPs catalyse diverse reactions, including C-H hydroxylation, epoxidation, hetero-atom oxidation, aromatic ring oxidation and dealkylation [11–13]. In the catalytic reaction process of P450 monooxygenase, one atom of O2 is inserted into substrate while the other is reduced to H2O. CYP genes responsible for secondary metabolism are often laid in antibiotic biosynthetic gene clusters to catalyze stereo- and region- specific reaction of substrates to related derivatives.
The biotransforming capabilities of bacterial CYPs have been widely elucidated. P450soy (CYP105D1) from Streptomyces griseus was involved in the degradation of a diverse array of complex agrochemicals and environmental pollutants . CYP105C1 from Actinomycete spp. had the ability to transform benanomicin A into two derivatives, 10-hydroxybenanomicin A and 11-O-demethylbenanomicin . The functions of related CYP107 family members have been reported. CYP107E from Micromonospora griseorubida was found to govern the hydroxylation and epoxidization in mycinamicin biosynthesis , P450 Terf (107 L) from Streptomyces platensis to catalyze hydroxylation of terfenadine  and hydroxylase PikC (107 L1) of Streptomyces venezuelae to convert narbomycin to picromycin . CYP124 of Mycobacterium tuberculosis demonstrated omega-hydroxylase activity of relevant methyl-branched lipids . YbdT (CYP152A) of Bacillus subtilis was involved in fatty acid beta-hydroxylation . CYP154 of Nocardia farcinica IFM10152 had the functions of the O-dealkylation and ortho-hydroxylation of formononetin  and 154H1 from Clostridium acetobutylicum performed biocatalytic reactions with different aliphatic and aromatic substrates .
Genome sequencing is an effective way to predict and annotate all the possible CYPs genes in an organism. Streptomyces coelicolor A3 (2), a typical strain which is often used for the study of physiological function and antibiotic production, is the first Streptomyces species sequenced in 2001. Its linear chromosome is 8.7 Mb  which contains 7825 open reading frames (ORFs) with 18 putative CYPs . S. avermitilis, known for producing the antiparasitic agent avermectin, contains 7600 ORFs with 33 putative CYPs in the 9 Mb chromosomes [25, 26]. The genome of Streptomyces peucetius ATCC27592 with the size of 8.7 Mb contains 19 putative CYPs .
S. virginiae IBL14, isolated from activated sludge for treatment of waste from a steroidal drug factory, is an effective degradative strain of various steroidal compounds, including progesterone, isotestosterone, dihydrotestosterone, hydrocortisone, cholesterol and ostrone . To comprehensively understand the function of CYPs of S. virginiae IBL14 in degradation and biotransformation of diosgenin, the whole genome sequencing of S. virginiae IBL14 isolated by our lab was carried out for the first time. Using in silico technology, we predict and annotate all of the putative CYPs of S. virginiae IBL14 and analyze these CYPs evolutionarily and functionally via comparison with those of other Streptomyces species. Furthermore, functions and characteristics of CYP genes svh01 and CYP svu022 in this strain are experimentally identified and analyzed.