Abstract
An extracellular polymeric substance was produced by Clostridium acetobutylicum during the growth and acid production phase, and also when butanol was produced simultaneously from glucose and reassimilated butyric acid. When butanol and butyric acid were produced at the same time, reutilization of previously produced polymer occurred. These phenomena were revealed by investigating material balances during different phases of batch cultures. The same scheme of polymer production and uptake could also be identified in batch cultures published in the literature. Resting cells produced a polymer, likely a polysaccharide, with a significantly high degree of acetylation when butanol was formed from glucose and reassimilated butyric acid. It is suggested that the acetylated polymer is produced when the organism requires extensive amounts of reducing power and the conditions for production of non-reduced end products are not favourable. The polymer (of unknown composition) produced during the growth phase has no obvious relation to the energy metabolism, but it is suggested that previously produced polymer can be used as a reserve carbon source when sugar is needed at high rate. In batch culture, where the pH was controlled at 6.0 the simultaneous production of acids and butanol was also observed.
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