Phylogenetically diverse new sulfur chemolithotrophs of α-proteobacteria isolated from Indian soils

Five facultative sulfur chemolithotrophs were isolated from soils to study the diversity of sulfur lithotrophy. Phenotypic characteristics, including sulfur lithotrophic properties and chemotaxonomic features of the isolates, were similar to those of the members of the colorless sulfur bacteria. 16S rDNA sequence analyses rendered placing the isolates to three distinct phylogenetic clusters of alpha-proteobacteria. Three isolates, AS001, AS002, and KCT002, were identified as members of the genus Paracoccus. The strains AS001 and AS002, having identical 16S-rDNA sequence, showed significant 16S rDNA sequence similarity (99.1%) to Paracoccus versutus. The strain KCT002 showed highest (98%) 16S rDNA sequence similarity to P. alcaliphilus and 96% similarity to the pair AS001 and AS002. Isolate KCT001 appeared to be closely related to Pseudaminobacter salicylatoxidans, although sulfur lithotrophy of P. salicylotoxidans is not known. The other isolate, TCK, showed almost identical 16S rDNA (99.9%) sequence with two recently described unclassified chemolithoautotrophic arsenite oxidizing strains. Physiological and chemotaxonomic characteristics and phylogenetic analyses of the five new strains emphasize the need of polyphasic bacterial taxonomy of sulfur lithotrophs.