Methylibium petroleiphilum PM1

Methylibium petroleiphilum strain PM1 (ATCC BAA-1232) is a motile phototrophic methylotrophic Gram-negative bacterium phylogenetically associated with the beta subdivision of the Proteobacteria and representing a new species within the Rubrivivax group (Comamonadaceae family). It is found in many gasoline-contaminated aquifers (freshwater, sewage, and activated sludge) and can grow in the dark under aerobic conditions or photosynthetically under anaerobic conditions. PM1 can also grow on carbon dioxide or on hydrogen. It was isolated by Dr. Scow in 1998 from a sewage treatment plant biofilter that was used for treating discharge from oil refineries in Los Angeles, California. Methylibium petroleiphilum is a model organism for the study of photosynthetic processes due to its genetic tractability. Strain PM1 is capable of degrading the gasoline additive methyl tert-butyl ether (MTBE) and its daughter product tert-butyl alcohol (TBA). Strain PM1 also degrades aromatic hydrocarbons (benzene, toluene, and xylene) and n-alkanes (C5 to C12) present in petroleum products. It is capable of aerobic growth on methanol, formate and succinate, but not on methylamine. Whole-genome analysis of PM1 revealed a 4-Mb circular chromosome and a 600-kb megaplasmid. Hydrocarbon (aromatic and alkane) degradation, metal resistance (arsenic, chromate, copper, cobalt, nickel, molybdenum, iron), and methylotrophy are encoded on the chromosome. The megaplasmid contains an unusual t-RNA island, numerous insertion sequences, and large repeated elements (including tandem repeat encoding phosphonate transport and cobalamin biosynthesis). It was suggested that the plasmid was recently acquired and apparently carries the genetic information responsible for PM1 ability to degrade MTBE and alkanes. The genetic basis for MTBE and TBA conversion is not known, although different classes of monooxygenases have been proposed to play a role in metabolism or cometabolism of these compounds including P-450 monooxygenase and alkane monooxygenase (hydroxylase) systems. It is noteworthy that MTBE degrading strains (PM1, MG4 and 312), from diverse locations possess nearly identical megaplasmids. PM1 can serve as a model for other MTBE-degrading methylotrophs such that the knowledge gained from analysis of its genome, transcriptome, and proteome can be applied to PM1-like bacteria. An understanding of the MTBE degradation pathway and its regulation will allow for optimization of MTBE bioremediation and the ability to monitor this unique process in situ using molecular tools. (EBI Integr8)