Characterization of long-chain fatty-acid-degrading syntrophic associations from a biodegraded oil reservoir.

Molecular methods were used to characterize stearate- and heptadecanoate-degrading methanogenic consortia enriched from a low-temperature biodegraded oil field. Stearate- and heptadecanoate-degrading cultures formed acetate. Growth on heptadecanoate was also accompanied by the production of propionate. These fermentation products were transiently accumulated at the beginning of the exponential phase and were further consumed with the concomitant production of methane. Clone libraries of bacterial and archaeal 16S rRNA genes were generated for each stable enrichment. Our 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that the predominant microorganisms in the associations were affiliated with a clone cluster close to the genus Syntrophus in the class "Deltaproteobacteria" and with the methanogenic genera Methanocalculus and Methanosaeta. Confocal scanning laser microscopy showed that the bacterial and archaeal cells formed compact aggregates around the insoluble substrates. No layered structure was observed in the aggregate organization. This study reports the presence of new fatty-acid-degrading syntrophic consortia in oil fields and our results suggest that such associations may have an important ecological role in oil fields under methanogenic conditions.