Isolation and characterization of an obligately anaerobic, polysaccharolytic, extremely thermophilic member of the genus Spirochaeta

An obligately anaerobic, extremely thermophilic Spirochaeta species was isolated from a thermal spring on the edge of Green Lake on Raoul Island of the Kermadec archipelago. The strain, RI 19.B1 (= DSM 6192) was typical of Spirochaeta species: regularly coiled long thin cells consisting of a crenulated outer sheath surrounding a central coiled protoplasmic cylinder. Between the outer sheath and the protoplasmic cylinder were two longitudinal periplasmic fibrils in a 1-2-1 arrangement, each anchored by an insertion disc near one pole, whereas the other end was not anchored. The strain displayed a strictly anaerobic, chemoorganotrophic, fermentative metabolism and was able to grow on a variety of mono-, di- and polysaccharides, including cellulose. Sugar alcohols, organic and amino acids were not utilized. Growth supplements were not required, but CO sub(2) was required to produce consistent growth. Strain RI 19.B1 had temperature, pH and salinity optima of 64-66 degree C, pH 6.95 and 0.4% NaCl respectively. The maximum growth temperature and salinity were 73 degree C and 2.5% respectively. Glucose was fermented to lactate acetate, carbon dioxide, and hydrogen. Succinate, ethanol and formate were not detected. The strain displayed the resistance to rifampicin typical of Spirochaeta) species.