Anaerobic Biodegradation of Long-Chain n-Alkanes under Sulfate-Reducing Conditions

The ability of anaerobic microorganisms to degrade a wide variety of crude oil components was investigated using chronically hydrocarbon-contaminated marine sediments as the source of inoculum. When sulfate reduction was the predominant electron-accepting process, gas chromatographic analysis revealed almost complete n -alkane removal (C 15 −C 34 ) from a weathered oil within 201 d of incubation. No alteration of the oil was detected in sterile control incubations or when nitrate served as an alternate electron acceptor. The amount of sulfate reduced in the oil-amended nonsterile incubations was more than enough to account for the complete mineralization of the n -alkane fraction of the oil; no loss of this anion was observed in sterile control incubations. The mineralization of the alkanes was confirmed using 14 C-14,15-octacosane (C 28 H 58 ), with 97% of the radioactivity recovered as 14 CO 2 . These findings extend the range of hydrocarbons known to be amenable to anaerobic biodegradation. Moreover, the rapid and extensive alteration in the n -alkanes can no longer be considered a defining characteristic of aerobic oil biodegradation processes alone.