Q-187. Genomic Analysis of Polycyclic Aromatic Hydrocarbon Degradation in Mycobacterium vanbaalenii PYR-1

S-J. Kim, O-G. Kweon, R. C. Jones, R. D. Edmondson, C. E. Cerniglia;
US FDA Natl. Ctr. for Toxicological Res., Jefferson, AR.

Background: Mycobacterium vanbaalenii PYR-1 is well known for its ability to degrade a wide range of high-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs). Although this bacterium has been extensively studied with respect to PAH degradation pathways, the molecular basis and regulatory mechanisms involved in PAH degradation remain unknown. Methods: We analyzed the PYR-1 complete genome sequence to understand the molecular background for PAH metabolism. We have particularly focused on the aromatic catabolic genes and TCA cycle genes that are responsible for the complete degradation of PAHs. In addition, PYR-1 proteome profiles were examined to see whether the genome analysis is supported at the protein level. Results: The 6.5 Mb genome of PYR-1 contains 194 chromosomally encoded genes likely associated with degradation of aromatic compounds. The most distinctive feature of the genome is the presence of a 150 kb major catabolic region at positions 494~643 kb (region A), which is predicted to encode most enzymes for the degradation of PAHs. Region A has an atypical mosaic structure made of several gene clusters in which the genes for PAH degradation are complexly arranged and scattered around the clusters. Significant differences in the gene structure and organization as compared to other well-known aromatic hydrocarbon degraders, including Pseudomonas sp., were revealed. Many identified genes were enriched with multiple paralogs showing a remarkable range of diversity, which could contribute to the wide variety of PAHs degraded by M. vanbaalenii PYR-1. A 31 kb catabolic region involved in biphenyl/monocyclic aromatic degradation was found separately at positions 4711~4741 kb (region B). The PYR-1 genome also revealed the presence of 28 genes involved in the tricarboxylic acid (TCA) cycle. We identified 67 and 23 genes involved in PAH degradation and TCA cycle pathways, respectively, to be expressed as proteins. Conclusions: Based on the results, we proposed a pathway in which HMW PAHs are degraded into the β-ketoadipate pathway through protocatechuate and then mineralized to carbon dioxide via the TCA cycle.