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A mobilizable suicide vector, pSUP5011, was used to introduce Tn5-mob in a new facultative sulfur lithotrophic bacterium, KCT001, to generate mutants defective in sulfur oxidation (Sox

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A Gram-negative, rod-shaped, urea-dissolving and non-spore-forming bacterium, designated strain NiVa 51 T , was isolated from water of the River Torsa in Hasimara, Jalpaiguri district, West Bengal, India. On the basis of 16S rRNA gene sequence similarity, strain NiVa 51T was shown to belong to the c-Proteobacteria and to be related to Serratia marcescens subsp.

Twelve chemolithotrophic strains were isolated from temperate orchard soil on reduced sulfur compounds as energy and electron sources and characterized on the basis of their physiological properties and ability to oxidize various reduced sulfur compounds. The new isolates could oxidize tetrathionate as well as thiosulfate, and oxidation of the latter involved conversion of thiosulfate to tetrathionate followed by its accumulation and eventual oxidation to sulfate, manifested in the production of acid. The mesophilic, neutrophilic, Gram-negative and coccoid bacteria had a respiratory metabolism. Physiologically and biochemically, all the strains were more or less similar, differing only in their growth rates and ability to utilize a few carbon compounds as single heterotrophic substrates. 16S rRNA gene sequence analysis was performed with five representative strains, which revealed a high degree of similarity (⩾99 %) among them and placed the cluster in the ‘Betaproteobacteria’. The strains showed low levels (93·5–95·3 %) of 16S rRNA gene sequence similarity to Pigmentiphaga kullae, Achromobacter xylosoxidans, Pelistega europaea and species belonging to the genera Alcaligenes, Taylorella and Bordetella. The taxonomic coherence of the new isolates was confirmed by DNA–DNA hybridization. On the basis of their uniformly low 16S rRNA gene sequence similarities to species of all the closest genera, unique fatty acid profile, distinct G+C content (54–55·2 mol%) and phenotypic characteristics that include efficient chemolithotrophic utilization of tetrathionate, the organisms were classified in a new genus, Tetrathiobacter gen. nov. In the absence of any significant discriminatory phenotypic or genotypic characteristics, all the new isolates are considered to constitute a single species, for which the name Tetrathiobacter kashmirensis sp. nov. (type strain WT001T=LMG 22695T=MTCC 7002T) is proposed.

The bacterial strain SJT T , along with 15 other mesophilic, neutrophilic and facultatively sulfur-oxidizing chemolithotrophic isolates, was isolated by enrichment on reduced sulfur compounds as the sole energy and electron source from soils immediately adjacent to the roots of Clitoria ternatea, a slender leguminous herb of the Lower Gangetic plains of India. Strain SJT T was able to oxidize thiosulfate and elemental sulfur for chemolithoautotrophic growth. 16S rRNA and recA gene sequence-based phylogenetic analyses showed that the Gram-negative rod-shaped bacterium belonged to the genus Mesorhizobium and was most closely related to Mesorhizobium loti, Mesorhizobium plurifarium, Mesorhizobium amorphae and Mesorhizobium chacoense. Unequivocally low 16S rRNA (<97 %) and recA (¡88 %) gene sequence similarities to all existing species of the most closely related genera, a unique fatty acid profile, a distinct G+C content (59?6 mol%) and phenotypic characteristics all suggested that strain SJT T represents a novel species. DNA-DNA hybridization and SDS-PAGE analysis of whole-cell proteins also confirmed the taxonomic uniqueness of SJT T . It is therefore proposed that isolate SJT T (=LMG 22697 T =MTCC 7001 T ) be classified as the type strain of a novel species, Mesorhizobium thiogangeticum sp. nov.