True cellulase activity has been demonstrated in cell-free preparations from the thermophilic anaerobe Clostridium thermocellum . Such activity depends upon the presence of Ca 2+ and a thiol-reducing agent of which dithiothreitol is the most promising. Under these conditions, native (cotton) and derived forms of cellulose (Avicel and filter paper) were all extensively solubilized at rates comparable with cellulase from Trichoderma reesei . Maximum activity of the Clostridium cellulase was displayed at 70°C and at pH 5.7 and 6.1 on Avicel and carboxymethylcellulose, respectively. In the absence of substrate at temperatures up to 70°C, carboxymethylcellulase was much more unstable than the Avicel-hydrolyzing activity.

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A minimal chemically defined medium has been developed for Clostridium thermocellum . The growth factors required are biotin, pyridoxamine, vitamin B 12 , and p -aminobenzoic acid.

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