P. Durre et al., SOLVENTOGENIC ENZYMES OF CLOSTRIDIUM-ACETOBUTYLICUM - CATALYTIC PROPERTIES, GENETIC ORGANIZATION, AND TRANSCRIPTIONAL REGULATION, FEMS microbiology reviews, 17(3), 1995, pp. 251-262
The enzymes acetoacetate decarboxylase and coenzyme A transferase cata
lyse acetone production from acetoacetyl-CoA in Clostridium acetobutyl
icum. The ade gene encoding the former enzyme is organized in a monoci
stronic operon, while the ctf genes form a common transcription unit w
ith the gene (adhE) encoding a probable polyfunctional aldehyde/alcoho
l dehydrogenase. This genetic arrangement could reflect physiological
requirements at the onset of solventogenesis. In addition to AdhE, two
butanol dehydrogenase isozymes and a thiolase are involved in butanol
synthesis. RNA analyses showed a sequential order of induction for th
e different butanol dehydrogenase genes, indicating an in vivo functio
n of BdhI in low level butanol formation. The physiological roles of A
dhE and BdhII most likely involve high level butanol formation, with A
dhE being responsible for the onset of solventogenesis and BdhII ensur
ing continued butanol production. Addition of methyl viologen results
in artificially induced butanol synthesis which seems to be mediated b
y a still unknown set of enzymes. Although the signal that triggers th
e shift to solventogenesis has not yet been elucidated, recent investi
gations suggest a possible function of DNA supercoiling as a transcrip
tional sensor of the respective environmental stimuli.