Effects of pH and added metabolites on bioconversions by immobilized non-growingClostridium acetobutylicum

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Abstract
The bioconversion activity of calcium alginate‐immobilized Clostridium acetobutylicum ATCC 824 was investigated in a continuous reactor system utilizing a defined feed medium which did not support cell growth. The changes in biocatalytic activity with time were studied at different pH values as well as when different metabolites (butyric, acetic, and acetoacetic acids) were present in the feed stream. Although the nongrowing cells were metabolically active, the product distribution was shifted from solvent production to acidogenesis. Overall activity losses occurred due to cell lysis, sporulation, and the effects of nitrogen level on macromolecular turnover. These effects were minimized under some operating conditions (e.g., pH 6), resulting in significantly longer productivity lifetimes.