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Abstract
A novel group of moderately halophilic, obligately chemolithoautotrophic, sulfur-oxidizing Gammaproteobacteria was found in sediments of various inland hypersaline lakes and a solar saltern. These bacteria were enriched and isolated with thiosulfate as electron donor and nitrate as electron acceptor at 2 M NaCl. Ten isolates (HLD strains) were long non-motile rods. They grew anaerobically as complete denitrifiers, and aerobically under micro-oxic conditions. Sulfate was the final product of thiosulfate and sulfide oxidation, and nitrite and N2O were intermediates of nitrate reduction to N2. The HLD strains grew optimally at pH 7.3–7.8, and at NaCl concentrations of 1.5–2.0 M. On the basis of phenotypic and genetic analysis, the moderately halophilic, thiodenitrifying isolates are proposed to be assigned to a new genus and species, Thiohalomonas denitrificans gen. nov., sp. nov. The type strain is HLD 2T (=DSM 15841T=UNIQEM U222T ). A single strain, HRhD 3spT, with vibrio-shaped cells, was obtained from a co-culture capable of complete denitrification of nitrate in the presence of either thiocyanate or thiosulfate as electron donor. It grew anaerobically with thiosulfate, reducing nitrate to nitrite, or under micro-oxic conditions at 1.0–2.5 M NaCl with an optimum at 1.0 M. Strain HRhD 3spT was genetically related to the HLD strains at the level of a separate species and is described as Thiohalomonas nitratireducens sp. nov. The type strain is HRhD 3spT (=DSM 16925T=UNIQEM U248T).
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