Clostridium schirmacherense sp. nov., an obligately anaerobic, proteolytic, psychrophilic bacterium isolated from lake sediment of Schirmacher Oasis, Antarctica

Abstract

A novel obligately anaerobic, proteolytic bacterium, designated AP15^T, was isolated from lake sediments of Schirmacher Oasis, Antarctica. The bacterium produced maximum cell mass between 5 and 10°C in an anaerobic basal medium containing 0.5% tryptone and peptone. The strain grew optimally at a pH around 8·0 and tolerated NaCl up to a concentration of 7·5%. It contained diphosphatidylglycerol as the major phospholipid and C_15:0, C_16:0 and C_17:0 as the major cellular fatty acids. Several amino acids, including arginine, leucine, isoleucine, cysteine, glutamate and serine, supported growth. Glutamate was degraded to acetate, propionate, CO₂ and H₂. In addition, the strain degraded carbohydrates including glucose, raffinose, adonitol, ribose and rhamnose. The main fermentation products during growth on glucose were H₂, CO₂, formate, acetate, propionate and isovalerate. The DNA G+C content of the bacterium was 24 mol%. On the basis of a phylogenetic analysis, strain AP15^T is identified as a close relative of Clostridium subterminale ATCC 25774^T, with which it shares 99·5% similarity at the 16S rRNA gene sequence level; however, it exhibits a low DNA-DNA binding value (55%) to this strain at the whole-genome level. In addition to showing other major differences with respect to C. subterminale and other members of the genus Clostridium, AP15^T also exhibits phenotypic differences. On the basis of these differences, strain AP15^T is identified as representing a novel species of the genus Clostridium, for which the name Clostridium schirmacherense sp. nov. is proposed. The type strain is AP15^T (=DSM 17394^T=JCM 13289T).