Comparative genomic analysis of pyrene-degrading Mycobacterium species: Genomic islands and ring-hydroxylating dioxygenases involved in pyrene degradation.

The genome sequences of two pyrene-degrading bacterial strains of Mycobacterium spp. PYR10 and PYR15, isolated from the estuarine wetland of the Han river, South Korea, were determined using the PacBio RS II sequencing platform. The complete genome of strain PYR15 was 6,037,017 bp in length with a GC content of 66.5%, and contained 5,933 protein-coding genes. The genome of strain PYR10 was 5,999,427 bp in length with a GC content of 67.7%, and contained 5,767 protein-coding genes. Based on the average nucleotide identity values, these strains were designated as M. gilvum PYR10 and M. pallens PYR15. A genomic comparison of these pyrene-degrading Mycobacterium strains with pyrene-non-degrading strains revealed that the genomes of pyrene-degrading strains possessed similar repertoires of ringhydroxylating dioxygenases (RHDs), including the pyrenehydroxylating dioxygenases encoded by nidA and nidA3, which could be readily distinguished from those of pyrenenon-degraders. Furthermore, genomic islands, containing catabolic gene clusters, were shared only among the pyrenedegrading Mycobacterium strains and these gene clusters contained RHD genes, including nidAB and nidA3B3. Our genome data should facilitate further studies on the evolution of the polycyclic aromatic hydrocarbon-degradation pathways in the genus Mycobacterium.