Thioalkalispira microaerophila gen. nov., sp nov., a novel lithoautotrophic, sulfur-oxidizing bacterium from a soda lake

An anaerobic enrichment medium (pH 10) with thiosulfate as electron donor and nitrate as electron acceptor was inoculated with sediment from soda lake Fazda (Wadi Natrun, Egypt); a novel strain, ALEN 1(T), was isolated from the subsequent enrichment culture. Cells of strain ALEN 1(T) had a spiral morphology (0.3-0.45 x 1-4 pm), were motile and had a single polar flagellum. Sphaeroplasts were formed by the cells and were rapidly lysed during prolonged aerobic incubation of cultures. Cells of strain ALEN 1(T) contained a membrane-associated yellow pigment. The metabolism of this novel organism was obligately chemolithoautotrophic, and thiosulfate or sulfide were utilized as electron donors. Washed cells of strain ALEN 1(T) oxidized thiosulfate, sulfide, polysulfide and elemental sulfur to sulfate. Best growth was observed when the strain was grown under micro-oxic conditions (1-2% O-2 in gas phase), whereas growth was inhibited under fully oxic conditions. Nitrate was reduced to nitrite without growth of the novel organism, but other nitrogen oxides were not utilized as electron acceptors. Strain ALEN 1(T) was alkaliphilic and moderately halophilic. it grew between pH 8 and 10.4 (optimum around pH 10) with a salt concentration of between 0.3 and 1.5 M Na+ (optimum 0.5 M). The maximum growth rate (0.08 h(-1)) of the organism was achieved in a thiosulfate-limited micro-oxic continuous culture (pH 10). Phylogenetic analyses of the 16S rDNA sequences of strain ALEN 1(T) and its closest relatives demonstrated that this strain formed a deep branch within the gamma-Proteobacteria, with no obvious association to any described cluster of species/genera. On the basis of its unique physiological properties and distinct phylogenetic position, it is proposed that strain ALEN 1(T) (= DSM 14786(T) = UNICEM 212(T)) represents a novel genus within the gamma-Proteobacteria, for which the name Thioalkalispira is proposed. It is also proposed that the type species of this novel genus be named Thioalkalispira microaerophila.