Selection in chemostat culture of a mutant strain of Clostridium tyrobutyricum improved in its reduction of ketones.

Growth of Clostridium tyrobutyricum on mannitol was possible only when an ancillary oxidant was additionally supplied. Hexacyanoferrate(III) in the presence of methylviologen could fulfil this role, which is normally better accomplished by acetate (and some other organic electron acceptors including acetoin, crotonate and 3-hydroxybutyrate). Several ketones, including pentan-2-one, although slowly reducible by the organism were unable to support its batch culture growth on mannitol. However, when a chemostat culture supplied with excess mannitol but limiting acetate was supplemented with pentan-2-one, a spontaneous mutant strain was selected that was much improved in its specific rate of reduction of this and other ketones, and which was capable of batch growth on mannitol plus pentan-2-one. This procedure may more generally be employed to select strains of anaerobic bacteria improved in their bioreductive abilities.