A novel facultatively anaerobic, sulfur-oxidizing bacterium, strain skB26(T), was isolated from anoxic water of a freshwater lake in Japan. The cells were rod-shaped, motile and Gram-negative. Strain skB26(T) oxidized elemental sulfur and thiosulfate to sulfate as sole energy sources. Strain skB26(T) was microaerobic and could also utilize nitrate as an electron acceptor, reducing it to nitrogen. Growth was observed at temperatures below 28 °C; optimum growth was observed at 22°C. The pH range for growth was 6.0-9.0, and the optimum pH was 7.5-8.0. Optimum growth of the isolate was observed in medium without NaCl, and no growth was observed in medium containing more than 220 mM NaCl. The G+C content of genomic DNA was around 59 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the strain was a member of the class Betaproteobacteria, and the closest cultivated relative was 'Thiobacillus plumbophilus' DSM 6690, with 93 % sequence similarity. Phylogenetic analyses were also performed using sequences of genes involved in sulfur oxidation, inorganic carbon fixation and nitrate respiration. On the basis of its phylogenetic and phenotypic properties, strain skB26(T) (=NBRC 105220(T) =DSM 22764(T)) is proposed as the type strain of a novel species of a new genus, Sulfuricella denitrificans gen. nov., sp. nov.