ENDOSPORE FORMATION BY THERMOANAEROBIUM-BROCKII HTD4

The formation of heat-resistant endospores could be induced in Thermoanaerobium brockii HTD4 by cultivation on a minimal medium with D-xylose as the sole carbon source (MMX) using cultures pregrown on trypticase-yeast extract-glucose (TYEG) as an inoculum. Sporulation was not observed when transferring from TYEG to TYEG, or from MMX to MMX. The spores were shown to be heat-resistant, and after killing vegetative cells at 115-degrees-C for 80 mins, germinated to produce cultures with morphological and physiological characteristics identical with the original culture. This finding is interesting in the light of mixed sporogenous and asporogenous taxonomic and phylogenetic groupings reported by other workers among the thermophilic glycolytic anaerobic bacteria. It is suggested that Thermoanaerobium brockii remains a valid taxon, rather than reassigning the species to the genus Clostridium.