The invention provides a recombinant, carboxydotrophic Clostridium bacterium that expresses one or more of pyruvate:ferredoxin oxidoreductase (EC 1.2.7.1), acetolactate synthase (EC 2.2.1.6), and acetolactate decarboxylase (EC 4.1.1.5). The invention further provides a method of producing a fermentation product by fermenting the recombinant bacterium in the presence of a gaseous substrate comprising CO to produce one or more of ethanol, butanol, isopropanol, isobutanol, higher alcohols, butanediol, 2,3-butanediol, succinate, isoprenoids, fatty acids, biopolymers, and mixtures thereof.