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Abstract
A novel strictly anaerobic, endospore-forming, rod-shaped, Gram-positive bacterium, designated strain SGB2T, was isolated from a mixed culture from a pond sediment during screening for sulfate-reducing bacteria capable of degrading cyanophycin (CGP). In this study, the taxonomic characterization of this mesophilic, proteolytic Clostridium isolate and the role which it, and its phylogenetic relatives, may play in peptide degradation and in the sulfur cycle are reported. Strain SGB2T was a commensal strain, utilizing CGP degradation products produced by other micro-organisms. Cells were motile until sporulation, forming oval, terminal spores that swell the cells. It showed optimum growth at 34 °C, pH 6.6 and in the absence of NaCl. Strain SGB2T utilized proteinaceous compounds such as peptone, Casamino acids, gelatin and trypticase soy, in addition to several amino acids and pyruvate. Utilization of many of these compounds was enhanced in the presence of thiosulfate. The isolate was unable to use any of the carbohydrates or alcohols investigated or CGP as carbon and energy sources. Thiosulfate and elemental sulfur were used as terminal electron acceptors. Phylogenetic analysis revealed that strain SGB2T belongs to the low-G+C-containing Clostridiales group. It exhibited 99 % 16S rRNA gene sequence similarity to its closest relatives Clostridium thiosulfatireducens Lup21T and Clostridium subterminale DSM 6970T. DNA–DNA hybridization values with these two strains were 39.4 and 42.1 %, respectively. Based on phenotypic, genotypic and phylogenetic characteristics, we conclude that the isolate represents a novel species of the genus Clostridium, Clostridium sulfidigenes sp. nov. The type strain is SGB2T (=DSM 18982T =ATCC BAA-1538T).
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