Isolation from soil and properties of the extreme thermophile Clostridium thermohydrosulfuricum

Abstract

Thirteen strains of a strict anaerobic, extreme thermophilic bacterium were isolated from soil samples of moderate temperature, from a sewage plant in Georgia, and from hot springs in Utah and Wyoming [USA]. They were identified as strains of C. thermohydrosulfuricum. The guanosine + cytosine content (moles percent) was 37.6 (determined by buoyant density) and 34.1 (determined by melting temperature). All strains required a factor present in yeast extract or tryptone for growth. Growth characteristics were as follows: a pH range of 5-9 with the optimum between 6.9-7.5, in a temperature range of 40-78.degree. C, with the optimum at 68.degree. C. The doubling time, when grown on glucose at temperature and pH optima, was 1.2 h. The main products of glucose fermentation were ethanol, lactate, acetate, CO2 and H2. The fermentation was inhibited by H2. Formation of spores occurred easily on glucose-agar medium or when cultures growing at temperatures above 65.degree. C were allowed to cool to temperatures below 55.degree. C. C. thermohydrosulfuricum occurs widely distributed in the natural environment.