A taxonomic study was carried out on a novel aerobic bacterial strain (designated CC-LY736(T)) isolated from a fermentor in Taiwan. Cells of strain CC-LY736(T) were Gram-stain negative, spiral-shaped and motile by means of a monopolar flagellum. Strain CC-LY736(T) shared the greatest degree of 16S rRNA gene sequence similarity to Azospirillum irakense DSM 11586(T) (97.2 %), Rhodocista centenaria JCM 21060(T) (96.3 %) and Rhodocista pekingensis JCM 11669(T) (96.1 %). The major fatty acids were C16:0, C16:1 �s5c, C19:0 cyclo �s8c, C18:1 �s7c/C18:1 �s6c, C16:0 3-OH and C18:1 2-OH. The predominant polar lipids included phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidyldimethylethanolamine and two unidentified glycolipids. The common major respiratory quinone was ubiquinone Q-10 and predominant polyamines were sym-homospermidine and putrescine. The DNA G+C content of strain CC-LY736(T) was 67.6 �� 0.1 mol %. During phylogenetic analysis, strain CC-LY736(T) formed a unique phyletic lineage associated with Rhodocista species. However, the combination of genetic, chemotaxonomic and physiological data clearly indicated that strain CC-LY736(T) was a novel representative of the family Rhodospirillaceae. Based on the polyphasic comparison, the name Niveispirillum fermenti gen. nov., sp. nov. is proposed; the type strain of the type species is CC-LY736(T) (= BCRC 80504(T) = LMG 27263(T)). In addition, the reclassifications of Azospirillum irakense as Niveispirillum irakense comb. nov. (type strain KBC1(T) = ATCC 51182(T) = BCRC 15764(T) = CIP 103311(T)), and Azospirillum amazonense as Nitrospirillum amazonense gen. nov., sp. nov. (type strain Am14(T) = ATCC 35119(T) = BCRC 14279(T) = DSM 3787(T)) are proposed based on the polyphasic taxonomic data obtained in this study.