Applied Microbiology and Biotechnology

, Volume 96, Issue 3, pp 749–761 | Cite as

The redox-sensing protein Rex, a transcriptional regulator of solventogenesis in Clostridium acetobutylicum

  • Mandy Wietzke
  • Hubert BahlEmail author
Applied genetics and molecular biotechnology


Solventogenic clostridia are characterised by their biphasic fermentative metabolism, and the main final product n-butanol is of particular industrial interest because it can be used as a superior biofuel. During exponential growth, Clostridium acetobutylicum synthesises acetic and butyric acids which are accompanied by the formation of molecular hydrogen and carbon dioxide. During the stationary phase, the solvents acetone, butanol and ethanol are produced. However, the molecular mechanisms of this metabolic switch are largely unknown so far. In this study, in silico, in vitro and in vivo analyses were performed to elucidate the function of the CAC2713-encoded redox-sensing transcriptional repressor Rex and its role in the solventogenic shift of C. acetobutylicum ATCC 824. Electrophoretic mobility shift assays showed that Rex controls the expression of butanol biosynthetic genes as a response to the cellular NADH/NAD+ ratio. Interestingly, the Rex-negative mutant C. acetobutylicum rex::int(95) produced high amounts of ethanol and butanol, while hydrogen and acetone production were significantly reduced. Both ethanol and butanol (but not acetone) formation started clearly earlier than in the wild type. In addition, the rex mutant showed a de-repression of the bifunctional aldehyde/alcohol dehydrogenase 2 encoded by the adhE2 gene (CAP0035) as demonstrated by increased adhE2 expression as well as high NADH-dependent alcohol dehydrogenase activities. The results presented here clearly indicated that Rex is involved in the redox-dependent solventogenic shift of C. acetobutylicum.


Biofuel Butanol ABE fermentation Redox regulation ClosTron 



The authors thank Tina Lütke-Eversloh, Department of Microbiology, University Rostock for many fruitful discussions and useful comments on the manuscript. We are also grateful to Nigel P. Minton and John T. Heap, University of Nottingham for kindly providing the ClosTron plasmids and to Philippe Soucaille, INSA, Toulouse for kindly providing pCons::upp.

Supplementary material

253_2012_4112_MOESM1_ESM.pdf (1.1 mb)
ESM 1 (PDF 1140 kb)


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© Springer-Verlag 2012

Authors and Affiliations

  1. 1.Abteilung Mikrobiologie, Institut für BiowissenschaftenUniversität RostockRostockGermany

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