Utilization of methylacetoin by the strict anaerobePelobacter carbinolicusand consequences for the catabolism of acetoin

Pelobacter carbinolicus strain GraBd1 fermented methylacetoin, which is a good carbon source for growth ( μ = 0.16 h −1 ) of this strict anaerobic bacterium, to acetone, acetate and ethanol (main products), acetoin, 2,3-butanediol and methylbutanediol (minor products). During growth on 2,3-butanediol, acetoin and methyl-acetoin the formation of a protein exhibiting acetoin: DCPIP oxidoreductase activity is induced. This enzyme amounts to a substantial portion of the soluble proteins. In vitro, it cleaves acetoin into acetate and acetaldehyde but reacts also with diacetyl or methylacetoin. We discussed four different models for the degradation of acetoin in the cells and came to the conclusion that in vivo the oxidative-thiolytic acetoin cleavage model is most probably realized in P. carbinolicus .