Two strains of obligate chemolithoautotrophic sulfur-oxidizing bacteria were isolated from soda-lake sediments by enrichment culture with thiocyanate and nitrate at pH 9·9. The isolates were capable of growth with thiocyanate or thiosulfate as electron donor, either aerobically or anaerobically, and with nitrate or nitrite as electron acceptor. Cyanate was identified as an intermediate of thiocyanate oxidation, while sulfate, ammonia and dinitrogen gas were the final products. The anaerobic growth on thiocyanate plus nitrate was much slower (μ_max=0·006 h⁻¹) than on thiosulfate plus nitrate (μ_max=0·02 h⁻¹), while growth yields were similar (4·8 and 5·1 g protein mol⁻¹, respectively). On the basis of their phenotypic and genetic properties, strains ARhD 1^Tand ARhD 2 are described as a novel species of the genusThialkalivibrio, with the highest similarity toThialkalivibrio denitrificans. The nameThialkalivibrio thiocyanodenitrificanssp. nov. is proposed for this novel species.