Characterization of Culturable PAH and BTEX Degrading Bacteria from Heavy Oil of the Rancho La Brea Tarpits

Novel petroleum degrading bacteria have been identified in heavy oil from natural asphalt seeps using DNA-based methods, but there is little knowledge of the extent to which these bacteria can be cultured by selective enrichments on different aromatic hydrocarbons. Here we report the species composition of bacterial communities from a 40,000 yr-old asphalt deposit that could be grown on selected petroleum compounds. Species compositions of the degrader communities determined by PCR-DGGE and 16S rDNA sequencing showed that selective enrichment using (PAHs) and BTEX (benzene, toluene, ethyl benzene, and xylene) as growth substrates produced relatively simple degrader communities, and included a predominant species, Pseudomonas stutzeri, which grew on multiple compounds. PCR-based techniques further identified genes encoding naphthalene dioxygenase and catechol 2,3-dioxygenase from P. stutzeri in the enrichment cultures. The results suggest that only a small portion of the asphalt-inhabiting community can be cultured under aerobic conditions on individual substrates. Within these communities were several new species that merit further characterization as consortia, as well as new isolates of the cosmopolitan degrader, P. stutzeri.