Transcriptional analysis of catabolite repression in Clostridium acetobutylicum growing on mixtures of d-glucose and d-xylose

Clostridium acetobutylicum is a strict anaerobic organism that is used for biotechnological butanol fermentation. It ferments various hexoses and pentoses to solvents but prefers glucose presumably using a catabolite repression mechanism. Accordingly during growth on a mixture of d-glucose and d-xylose a typical diauxic growth pattern was observed. We used DNA microarrays and real-time RT-PCR to study gene expression during growth on d-glucose, d-xylose mixtures on a defined minimal medium together with monitoring substrate consumption and product formation. We identified two putative operons involved in d-xylose degradation. The first operon (CAC1344–CAC1349) includes a transporter, a xylulose-kinase, a transaldolase, a transketolase, an aldose-1-epimerase and a putative xylose isomerase that has been annotated as an arabinose isomerase. This operon is induced by d-xylose but was catabolite repressed by d-glucose. A second operon (CAC2610–CAC2612) consists of a xylulose-kinase, a hypothetical protein and a gene that has been annotated as a l-fucose isomerase that might in fact code for a xylose isomerase. This operon was induced by d-xylose but was not subject to catabolite repression. In accordance with these results we identified a CRE site in the catabolite repressed operon but not in the operon that was not subject to catabolite repression.