Abstract
Mutant AS2-1, derived from Clostridium saccharoperbutylacetonicum N1-4 ATCC 13564, did not produce acetone, butanol, and acetic acid, but had enhanced ethanol production and newly produced isovaleric acid at the molar ratio of 1:1. The mutant was defective in thiolase (acetyl-CoA acetyltransferase) activity, while the parent N1-4 showed high thiolase activity (103.5 units/g protein). Addition of allyl alcohol into the mutant culture significantly decreased the production of both ethanol and isovaleric acid. AS2-1 mutant, therefore, had NAD+ - and NAD(P)+-dependent aldehyde dehydrogenase on the pathway to ethanol and isovaleric acid, respectively. It was suggested that an excess of electrons accumulated as the result of the deficiency in thiolase was consumed for the reductive formation of isovalerate from pyruvate. The equation of the novel ethanol-isovaleric acid fermentation was concluded as 1.5mol glucose = 1mol ethanol +1 mol isovaleric acid+ 2 mol CO2 + 2 mol H2O +1 mol H2.
