Tn916-induced mutants of Clostridium acetobutylicum defective in regulation of solvent formation

Sixteen Tn916-induced mutants of Clostridium acetobutylicum were selected that were defective in the production of acetone and butanol. Formation of ethanol, however, was only partially affected. The strains differed with respect to the degree of solvent formation ability and could be assigned to three different groups. Type I mutants (2 strains) were completely defective in acetone and butanol production and contained one or three copies of Tn916 in the chromosome. Analysis of the mutants for enzymes responsible for solvent production revealed the presence of a formerly unknown, specific acetaldehyde dehydrogenase. The data obtained also strongly indicate that the NADP⁺-dependent alcohol dehydrogenase is in vivo reponsible for ethanol formation, whereas the NAD⁺-dependent alcohol dehydrogenase is probably involved in butanol production. No activity of this enzyme together with all other enzymes in the acetone and butanol pathway could be found in type I strains. All tetracycline-resistant mutants obtained did no longer sporulate.Non-standard abbreviations AADC acetoacetate decarboxylase - AcaDH acetaldehyde dehydrogenase - BuaDH butyraldehyde dehydrogenase - CoA-TF acetoacetyl coenzyme A: acetate/butyrate: coenzyme A transferase - NAD-ADH, NAD⁺ dependent alcohol dehydrogenase - NADP-ADH, NADP⁺ dependent alcohol dehydrogenase