So far, anaerobic acetate oxidation with sulfate as electron acceptor at high pH has only been demonstrated for a low salt-tolerant syntrophic association of a clostridium Candidatus "Contubernalis alkalaceticum" and its hydrogenothotrophic sulfate-reducing partner Desulfonatronum cooperativum. Anaerobic enrichments at pH 10 inoculated with sediments from hypersaline soda lakes of the Kulunda Steppe (Altai, Russia) demonstrated a possibility of sulfate-dependent acetate oxidation at extremely natronophilic conditions (up to 3.5 M total Na+). Purification by serial dilution reduced the composition of 2 most salt-tolerant cultures to 2 major components apparently working in syntrophy. The primary acetate oxidizing component was identified as a member of the order Clostridiales forming, together with C. alkalaceticum, an independent branch associated with the family Syntrophomonadaceae. A provisional name Candidatus "Syntrophonatronum acetoxidans" is suggested for the novel natronophilic clostridium. Two phylotypes of extremely natronophilic sulfate-reducing bacteria (SRB) of the genus Desulfonatronospira were identified as sulfate-reducing partners in the acetate-oxidizing cultures at extreme salinity. The dominant phylotype differed from two so far described species of Desulfonatronospira, while a minor component belonged to D. thiodismutants. The results have proven that, contrary to previous beliefs, anaerobic sulfate-dependent acetate oxidation is possible, albeit very slowly, at nearly saturated salt concentration in hypersaline soda lakes.