Dethiobacter alkaliphilus gen. nov sp nov., and Desulfurivibrio alkaliphilus gen. nov sp nov.:: two novel representatives of reductive sulfur cycle from soda lakes

Anaerobic enrichments with H-2 as electron donor and thiosulfate/polysulfide as electron acceptor at pH 10 and 0.6 M total Na+ yielded two non sulfate-reducing representatives of reductive sulfur cycle from soda lake sediments. Strain AHT 1 was isolated with thiosulfate as the electron acceptor from north-eastern Mongolian soda lakes and strain AHT 2-with polysulfide as the electron acceptor from Wadi al Natrun lakes in Egypt. Both isolates represented new phylogenetic lineages: AHT 1-within Clostridiales and AHT 2-within the Deltaproteobacteria. Both bacteria are obligate anaerobes with respiratory metabolism. Both grew chemolithoautotrophically with H-2 as the electron donor and can use thiosulfate, elemental sulfur and polysulfide as the electron acceptors. AHT 2 also used nitrate as acceptor, reducing it to ammonia. During thiosulfate reduction, AHT 1 excreted sulfite. dsrAB gene was not found in either strain. Both strains were moderate salt-tolerant (grow up to 2 M total Na+) true alkaliphiles (grow between pH 8.5 and 10.3). On the basis of the phenotypic and phylogenetic data, strains AHT 1 and AHT 2 are proposed as new genera and species Dethiobacter alkaliphilus and Desulfurivibrio alkaliphilus, respectively.