Sulfate-dependent acetate oxidation under extremely natron-alkaline conditions by syntrophic associations from hypersaline soda lakes

So far, anaerobic sulfate-dependent acetate oxidation at high pH has only been demonstrated for a low-salt-tolerant syntrophic association of a clostridium ‘Candidatus Contubernalis alkalaceticum’ and its hydrogenotrophic sulfate-reducing partner Desulfonatronum cooperativum. Anaerobic enrichments at pH 10 inoculated with sediments from hypersaline soda lakes of the Kulunda Steppe (Altai, Russia) demonstrated the possibility of sulfate-dependent acetate oxidation at much higher salt concentrations (up to 3.5 M total Na+). The most salt-tolerant purified cultures contained two major components apparently working in syntrophy. The primary acetate-fermenting component was identified as a member of the order Clostridiales forming, together with ‘Ca. Contubernalis alkalaceticum’, an independent branch within the family Syntrophomonadaceae. A provisional name, ‘Ca. Syntrophonatronum acetioxidans’, is suggested for the novel haloalkaliphilic clostridium. Two phylotypes of extremely haloalkaliphilic sulfate-reducing bacteria of the genus Desulfonatronospira were identified as sulfate-reducing partners in the acetate-oxidizing cultures under extreme salinity. The dominant phylotype differed from the two species of Desulfonatronospira described so far, whilst a minor component belonged to Desulfonatronum thiodismutans. The results proved that, contrary to previous beliefs, sulfate-dependent acetate oxidation is possible, albeit very slowly, in nearly saturated soda brines

Analysis of community composition of sulfur-oxidizing bacteria in hypersaline and soda lakes using soxB as a functional molecular marker

The diversity of soxB gene encoding a key enzyme of the Sox pathway sulfate thiohydrolase has been investigated in pure cultures of various halophilic and haloalkaliphilic sulfur-oxidizing bacteria (SOB) and in salt and soda lakes in southwestern Siberia and Egypt. The gene was detected in the majority of strains belonging to eleven SOB genera excluding members of genera Thiohalospira and Thioalkalimicrobium. The uncultured diversity of soxB in salt and soda lakes was low with a majority of detected sequences belonging to autotrophic SOB from the Gammaproteobacteria. In addition, the soxB analysis allowed detection of putative heterotrophic Gamma- and Alphaproteobacterial SOB yet unknown in culture. All clone libraries obtained from soda lakes contained soxB belonging to the genus Thioalkalivibrio in agreement with the cultivation results. Besides, representatives of the genera Halothiobacillus, Marinobacter, and Halochromatium and of the family Rhodobacteraceae have been detected in both type of saline lakes