These data suggest that the capability of n-alkane biodegradation, although present in this production facility, may not occur within sessile communities and that the degradation of the n-alkanes is carried out by planktonic organisms. In this case, it is likely that the fatty acids produced from planktonicphase hydrocarbon biodegradation would be utilized by the biofilm dwellers. Indeed, 16S rRNA sequence and metabolic analyses from this and other studies provide support for such a scenario. The major anaerobic microbial cookie DNA sequences were found to be associated with the thermophilic syntroph, Thermacetogenium, and the H2S-producing Thermodesulfobacterium commune. T. commune can incompletely oxidize fatty acids to produce acetate