A chemolithotrophic sulfur-oxidizing bacterium, strain aks1(T), was isolated from sediment of a brackish lake in Japan. The cells were curved rod-shaped and Gram-stain-negative. The G+C content of the genomic DNA was 53 mol%. The major components in the cellular fatty acid profile were C-16:0 and summed feature 3 (C-16 (: 1)omega 7c and/or C-16 (: 1)omega 6c). As electron donor for chemolithoautotrophic growth, strain aks1(T) oxidized thiosulfate, sulfide, and elemental sulfur. The strain could utilize oxygen and nitrate as an electron acceptor for thiosulfate oxidation. Growth was observed at a temperature range of 5-34 degrees C, with optimum growth at 30-32 degrees C. Growth of the strain was observed at a pH range of 6.4-8.7. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain is related to members of the family Granulosicoccaceae within the order Chromatiales, with sequence similarities around 92%. On the basis of phylogenetic and phenotypic properties, strain aks1(T) represents a novel species of a new genus, for which the name Sulfuriflexus mobilis gen. nov., sp. nov. is proposed. The type strain of the type species is aks1(T) (=DSM 102939(T) =NBRC 111889(T)).