A novel obligately organotrophic, facultatively microaerophilic spirillum, designated strain D-427(T), was isolated from sulfidic sludge of a municipal wastewater-treatment plant. Cells were Gram-negative, large and highly motile due to bipolar tufts of flagella covered with mucous sheaths. Coccoid cells were sometimes formed. Strain D-427(T) grew optimally at pH 7.5-7.8 and 28 degrees C in the presence of 2 % O(2) in the gas phase. The organism showed oxidase and very low catalase activity. The isolate grew chemo-organotrophically with a limited number of organic acids as substrates. The DNA G+C content was 38.0 mol% (T(m)). Phylogenetic analysis of the 16S rRNA gene sequence placed strain D-427(T) in the genus Spirillum within the class Betaproteobacteria. The 16S rRNA gene sequence similarity between strain D-427(T) and Spirillum volutans ATCC 19554(T), the type strain of the single species of the genus, was 98.6 %. The low level of DNA-DNA hybridization and different phenotypic properties indicate that strain D-427(T) is clearly distinguishable from Spirillum volutans. No strain of S. volutans is available from any established culture collection or from the authors who described this species. Therefore, on the basis of phenotypic and genotypic data and the fact that the type and single species of the genus Spirillum cannot be included in any scientific study, since the type strain has been lost, we propose to assign strain D-427(T) as a novel species of the genus Spirillum, Spirillum winogradskyi sp. nov. (type strain D-427(T) =DSM 12756(T) =VKM B-2518(T)), and we request that the Judicial Commission place the name Spirillum volutans on the list of rejected names if a suitable type strain is not found or a neotype is not proposed within 2 years following the publication of this paper. An emended description of the genus Spirillum is also provided.