Chemoorganoautotrophic lifestyle of the anaerobic enrichment culture N47 growing on naphthalene.

In almost all respiratory organisms, organic substrates are degraded via catabolic processes to the central metabolite acetyl-CoA which is then oxidized to CO2 for energy metabolism or used as a building block for anabolism. Most microorganisms have either the closed tricarboxylic acid cycle or the complete Wood-Ljungdahl-pathway for acetyl-CoA oxidation, but the sulfate-reducing, naphthalene-degrading culture N47 possesses both completely. Combining 13C- labeled substrates and mass-specific GC-MS analysis of amino acids and fatty acids with enzyme activity assays suggests that N47 has a chemoorganoautotrophic metabolism degrading complex organic substrates such as naphthalene. Surprisingly, however, the biomass is mainly produced from acetyl-CoA generated de novo via CO2-fixation. This metabolism probably requires both a complete Wood-Ljungdahl pathway for acetyl-CoA oxidation and a reverse tricarboxylic acid cycle for CO2 fixation. Based on genome analysis, this chemoorganoautotrophic metabolism seems to also occur in other sulfate-reducers and anaerobic ammonium-oxidizers.