Phylogenetically Diverse New Sulfur Chemolithotrophs of -Proteobacteria Isolated from Indian Soils Chirajyoti Deb, 1 Erko Stackebrandt, 2 Silke Pradella, 2 Anupama Saha, 1 Pradosh Roy 1 1 Department of Microbiology, Bose Institute, Acharya J. C. Bose Birth Centenary Building, Kankurgachhi, P-1/12, C. I. T. Scheme VII-M, Kolkata-700 054, India 2 DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Mascheroder Weg 1B, D-38124 Braunschweig, Germany Received: 6 October 2003 / Accepted: 4 November 2003 Abstract. Five facultative sulfur chemolithotrophs were isolated from soils to study the diversity of sulfur lithotrophy. Phenotypic characteristics, including sulfur lithotrophic properties and chemotaxo- nomic 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 -pro- teobacteria. 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 oxi- dizing strains. Physiological and chemotaxonomic characteristics and phylogenetic analyses of the five new strains emphasize the need of polyphasic bacterial taxonomy of sulfur lithotrophs. In the “sulfur cycle,” the anoxic sulfate reduction process by sulfate-reducing bacteria produces hydrogen sulfide, whereas the lithotrophic sulfur oxidation results in the reverse order, in which hydrogen sulfide is oxidized to sulfate. Since sulfate is the most available form to the microbes and plants for assimilation, the dissimilatory sulfur metabolism by sulfur lithotrophs, which results in the final oxidation product sulfate, contributes most to the bioavailability of sulfur. Moreover, sulfide, polysul- fides, elemental sulfur, thiosulfate, polythionates, and sulfites are the major forms of sulfur in the environment [18], all of which can be oxidized by the sulfur-oxidizing chemolitho- or photolithotrophic bacterial or archaeal species [5, 6]. However, the knowledge of lithotrophic sulfur biology developed primarily from the studies on non-phototrophic (colorless) sulfur bacteria and espe- cially the members of the genus Thiobacillus [5, 15]. Recently, with advanced systematic analyses based on molecular phylogeny by 16S rDNA sequence similarity data, the genus Thiobacillus has been reorganized [11, 14, 16, 20]. In view of the revision of Thiobacillus, many of the newly introduced taxons such as Starkeya gen. nov. [16]. Thermithiobacillus, or Halothiobacillus gen. nov. [14] are represented by a single species only. How- ever, predominant or key phenotype(s) and chemotaxo- nomic characteristics of each of the newly introduced genera cannot be evaluated with a single species, nor can the significance and phylogenetic limits [25] be derived of those taxa. Further, a sufficient number of strains of each species are a prerequisite for a minimal and reliable phenotypic description of the intraspecies variability [30, 31]. This report describes isolation and characterizations including phylogenetic analyses of five new facultatively sulfur-oxidizing bacterial strains, which belong to three distinct clusters within -proteobacteria. Materials and Methods Isolation of facultative sulfur chemolithotrophs from soil. Faculta- tive sulfur lithotrophs were grown in mineral salts–thiosulfate–succi- Correspondence to: P. Roy; email: prodosh@bic.boseinst.ernet.in CURRENT MICROBIOLOGY Vol. 48 (2004), pp. 452– 458 DOI: 10.1007/s00284-003-4250-y Current Microbiology An International Journal © Springer-Verlag New York LLC 2004