Expression of Clostridium difficileToxins A and B and Their Sigma Factor TcdD Is Controlled by Temperature

ABSTRACTGrowth temperature was found to control the expression of toxins A and B in Clostridium difficileVPI 10463,with a maximum at 37°C and low levels at 22 and 42°C in both peptone yeast (PY) and defined media. The up-regulation of toxin A and B mRNA and protein levels upon temperature upshift from 22 to 37°C followed the same kinetics, showing that temperature control occurred at the level of transcription. Experiments with Clostridium perfringensusing gusAas a reporter gene demonstrated that both toxin gene promoters were temperature controlled and that their high activity at 37°C was dependent on the alternative sigma factor TcdD. Furthermore, tcdDwas found to be autoinduced at 37°C. Glucose down-regulated all these responses in the C. perfringensconstructs, similar to its impact on toxin production in C. difficilePY broth cultures. C. difficileproteins induced at 37°C and thus coregulated with the toxins by temperature were demonstrated by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified as enzymes involved in butyric acid production and as electron carriers in oxidation-reduction reactions. The regulation of toxin production in C. difficileby temperature is a novel finding apparently reflecting an adaptation of the expression of its virulence to mammalian hosts.