ELSEVIER FEMS Microbiology Letters 125 (1995) 115-120 Differential induction of genes related to solvent formation during the shift from acidogenesis to solventogenesis in continuous culture of Clostridium acetobutylicum Uwe Sauer ‘, Peter Dike * Institut jiir Mikrobiologie, Georg-August-Uniuersitiit Gattingen, Grisebachstrape 8, D-37077 Gijttingen, Germany Received 14 October 1994; accepted 27 October 1994 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Abstract The expression of all sequenced acetone and butanol formation genes was followed using mRNA analysis during the shift from acidogenesis to solventogenesis in continuous culture of Clostridium acetobutylicum. Differential induction or derepression of the bdhA, bdhB, and adc genes as well as the sol operon was observed during the pH-induced shift. The order of induction of the three different butanol dehydrogenase genes was found to be bdhA-sol operon-bdhB, offering an explanation for the physiological role of the respective enzymes. Peak mRNA synthesis of an autolysin and a heat shock gene at the onset of solventogenesis was detected in addition to the above-mentioned genes. None of the hitherto sequenced genes of butanologenic enzymes was found to be involved in butanol production during the Methyl viologen-induced shift, indicating the presence of yet unknown genes encoding alcohol and aldehyde dehydrogenases. Keywords: Autolysin; Clostridium acetobutylicum; Induction of transcription; Methyl viologen shift; Solventogenesis; Stress response 1. Introduction The Gram-positive, strictly anaerobic bacterium Clostridium acetobutylicum is characterized by a biphasic fermentation pattern in batch culture (for reviews see [1,2]). During the exponential growth phase, acetic and butyric acid are predominantly produced, resulting in a drastic decrease of the pH value of the culture medium. Solvent formation is * Corresponding author. Tel.: (+49-551) 393 796; Fax: (+49- 551) 393 793; e-mail: pduerre@gwdg.de ’ Present address: Instimt ftir Biotechnologie, ETB Hijngger- berg, HPT, CH-8093 Ztirich, Switzerland initially observed in the post-exponential growth phase and dominates throughout stationary phase [1,2]. The cells actively take up the preformed acids and form the main products acetone and butanol, due to induction or derepression of genes encoding sol- ventogenic enzymes [3]. Sequence information about many genes, that are regulated at the onset of solventogenesis in C. aceto- butylicum, became available within the last 4 years, thus allowing investigations on the induction of their transcription. The recently described sol operon [4] comprises the genes of the acetoacetyl CoA:acetate/butyrate:CoA transferase (~$4 and cijB) and an alcohol/aldehyde dehydrogenase (a&E). The former catalyses the activation of acids 0378-1097/95/$09.50 0 1995 Federation of European Microbiological Societies. All rights reserved SSDI 0378-1097(94)00483-8