Syntrophic acetate oxidation in haloalkaline environments

Acetate is one of the key intermediates in anaerobic organic matter degradation. Acetate oxidation is thermodynamically unfavorable and can only proceed in syntrophy when the end product formed by a syntrophic acetate oxidizing bacterium (SAOB) is consumed by a hydrogenotrophic partner, typically a methanogen or a sulfate reducer. SAO is a dominant pathway for methanogenesis in anaerobic digesters, e.g. for biogas production, with high ammonia concentrations. However, not much is known of the importance of SAO in the environment and under which conditions it occurs. We investigated the metabolism and occurrence of SAO at haloalkaline conditions with methanogenic (M-SAO) and sulfate-reducing SAO (S-SAO) enrichment cultures from Siberian hypersaline soda lakes obtained previously. We sequenced the metagenome of the M-SAO culture and reconstructed the first draft genome of 'Candidatus Syntrophonatronum acetioxidans', a haloalkalphilic SAOB from the family Syntrophomonadaceae (phylum Firmicutes).