Production of a low-molecular-weight, alkaline-active, thermostable protease by a novel, spiral-shaped bacterium, Kurthia spiroforme, sp. nov

A Gram-positive bacterium exhibiting a spiral morphology at near neutral pH was isolated from a thermal spring. Growth occurs over a temperature range of 4° to 47°C and a pH range of 7.0 to 11.5. Growth optimum is at 30°C and pH 10.5. Gas chromatographic analysis of the cellular fatty acids identified the organism as a Kurthia sp. Morphological and physiological traits differ significantly from other Kurthia sp.; therefore we have named the organism Kurthia spiroforme, sp. nov. The organism produces a unique extracellular, alkaline-active, thermostable protease with an extremely low molecular weight of 8 kilodaltons. Optimum activity of the protease is observed at pH 11.0 and 60°C. At 50°C (pH 9.0) the protease has a half-life of 41 h.