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

Abstract

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.

Redox-Responsive Repressor Rex Modulates Alcohol Production and Oxidative Stress Tolerance in Clostridium acetobutylicum

“…Determination of fermentation product formation revealed different product spectra between the wild type and rexinactivated mutant in the absence of MV (Fig. 8), which is in accordance with a recent report (10). Mutation of rex resulted in a significantly increased ethanol and a slightly elevated butanol production, while acetone synthesis was reduced; thus, the alcohol (butanol plus ethanol)-to-acetone ratio was improved from 2.7 to 4.8 (Fig.…”

“…Several genes associated with fermentation pathways have been identified as Rex targets in C. acetobutylicum (10). However, whether Rex also regulates transcription of other genes is not known.…”

“…Recently, the redox-sensing transcriptional repressor Rex has been found to play a role in the solventogenic shift of C. acetobutylicum (10). Rex was first discovered in Streptomyces coelicolor and is widely distributed among Gram-positive bacteria.…”

Coenzyme A-transferase-independent butyrate re-assimilation in Clostridium acetobutylicum—evidence from a mathematical model

“…However, the underlying regulatory mechanisms are poorly understood. It is speculated that the intracellular ATP and NADH pools play a crucial role in the clostridial adaptation to changing environmental condition including the pH level (Girbal and Soucaille 1994;Wietzke and Bahl 2012), nutritional composition (Bahl et al 1986;Girbal and Soucaille 1994), and further limitations (e.g. iron (Junelles et al 1988;Vasileva et al 2012)).…”

Small acid-soluble spore proteins of Clostridium acetobutylicum are able to protect DNA in vitro and are specifically cleaved by germination protease GPR and spore protease YyaC

“…C. acetobutylicum ATCC 824 was grown under anaerobic conditions at 37 uC in complex CGM medium or chemically defined minimal medium MS-MES (Voigt et al, 2014). C. acetobutylicum was stored as a spore suspension at 220 uC and the non-sporulating C. acetobutylicum spo0A mutant was maintained in glycerine-CGM stocks at 270 uC (Wietzke & Bahl, 2012). When necessary, the growth medium contained the following antibiotics: chloramphenicol (25 mg ml 21 ), ampicillin (100 mg ml 21 ) or erythromycin (20 mg ml 21 ).…”