Sporotalea propionica gen. nov. sp. nov., a hydrogen-oxidizing, oxygen-reducing, propionigenic firmicute from the intestinal tract of a soil-feeding termite

Abstract

An unusual propionigenic bacterium was isolated from the intestinal tract of the soil-feeding termite Thoracotermes macrothorax. Strain TmPN3 is a motile, long rod that stains gram-positive, but reacts gram-negative in the KOH test. It forms terminal endospores and ferments lactate, glucose, lactose, fructose, and pyruvate to propionate and acetate via the methyl-malonyl-CoA pathway. Propionate and acetate are formed at a ratio of 2:1, typical of most propionigenic bacteria. Under a H(2)/CO(2) atmosphere, the fermentation product pattern of glucose, fructose, and pyruvate shifts towards propionate formation at the expense of acetate. Cell suspensions reduce oxygen with lactate, glucose, glycerol, or hydrogen as electron donor. In the presence of oxygen, the product pattern of lactate fermentation shifts from propionate to acetate production. 16S rRNA gene sequence analysis showed that strain TmPN3 is a firmicute that clusters among the Acidaminococcaceae, a subgroup of the Clostridiales comprising obligately anaerobic, often endospore-forming bacteria that possess an outer membrane. Based on phenotypic differences and less than 92% sequence similarity to the 16S rRNA gene sequence of its closest relative, the termite hindgut isolate Acetonema longum, strain TmPN3(T) is proposed as the type species of a new genus, Sporotalea propionica gen. nov. sp. nov. (DSM 13327(T), ATCC BAA-626(T)).