Acetoclastic methanogenesis is likely the dominant biochemical pathway of palmitate degradation in the presence of sulfate.

Abstract

Long chain fatty acids (LCFAs) are important intermediates in the anaerobic degradation of n-alkanes. In order to find out the biochemical processes involved in the degradation of LCFAs, palmitate (a typical LCFA) was used as a substrate, and low-temperature oilfield production fluids were used as a source of microorganisms to establish two anaerobic systems, one with addition of sulfate as exogenous electron acceptor (SP), another without exogenous electron acceptor (MP) and both incubated at room temperature. After more than 2 years of incubation, about 48 and 57.4% of the palmitate were degraded in samples of MP and SP, respectively. Methane production reached 1408 and 1064 μmol for MP and SP, respectively. Clone libraries of archaeal 16S rRNA genes showed that the predominant archaea in the sulfate-amended cultures (SP) was Methanosaeta whereas Methanocalculus dominated the culture without addition of exogenous sulfate (MP). This observation shows that palmitate could be biodegraded into methane through β-oxidation and acetoclastic methanogenesis in the presence of with or without sulfate. The high occurrence of Methanosaeta in the sulfate-amended system indicates that acetoclastic methanogenesis was not inhibited/little affected by the addition of sulfate. Acetoclastic methanogenesis might be the predominant biochemchimcal pathway of methane generation in enrichment cultures amended with sulfate. These results shed light on alternative methanogenic pathways in the presence of sulfate.