Rhodospirillum sulfurexigens sp. nov., a phototrophic alphaproteobacterium requiring a reduced sulfur source for growth.

A Gram-negative, spiral-shaped, phototrophic, purple non-sulfur bacterial strain, JA143(T), was isolated from a freshwater habitat. Strain JA143(T) was motile by means of bipolar tufts of flagella. Intracellular photosynthetic membranes are of the lamellar stacked type. Bacteriochlorophyll a and carotenoids of the spirilloxanthin series with rhodovibrin are present as photosynthetic pigments. Thiamine and a reduced sulfur source are required for growth. Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain JA143(T) clusters with species of the genus Rhodospirillum, belonging to the class Alphaproteobacteria. The highest sequence similarities of strain JA143(T) were found with the type strains of Rhodospirillum rubrum (95.6 %) and Rhodospirillum photometricum (95.7 %). Based on 16S rRNA gene sequence analysis and morphological and physiological characteristics, strain JA143(T) was significantly different from the other two recognized species of the genus Rhodospirillum and represents a novel species, for which the name Rhodospirillum sulfurexigens sp. nov. is proposed. The type strain is JA143(T) (=DSM 19785(T) =NBRC 104433(T)).