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Anaerobic enrichments with H₂ 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 H₂ 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 …