Abstract
Intraspecific and interspecific protoplast fusions in/between C. thermocellum and C. thermohydrosulfuricum were studied. Protoplast fusions were well induced in 30-40% PEG solution, however, their fusion frequencies were low level of 1.2*10$^{-7}$ for intraspecific fusion of C. thermocellum, $6.7*10^{-7}$ for C. thermohydrosulfuricum, and 4.2*10$^{-7}$ for interspecific fusion between above two Clostridia, respectively. Most fusants were unstable and segregated after 3 subcultures. Relatively stable intraspecific C. thermocellum fusant FTT17, intraspecific C. thermohydrosulfurecum fusant FSS22 and interspecific fusant FTS3, which were stable after several subcultures, were selected and properties of fusants were further investigated, Phenotypes of the fusants were similar with wild types mostly in cellular morphology, carbon source assimilation and enzyme activities. However they were differed in assimilation of pyruvic acid and sorbitol as carbon source. The DNA contents of fusants were slightly increased compared with wild types. Ethanol production by intraspecific and/or interspecific fusants was not increased, however, acetic acid production as byproduct was decreased or not detected, which indicates that industrial thermophilic anaerobes can be improved by means of protoplast fusion of two strains.