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Induction of toxins in Clostridium difficile is associated with dramatic changes of its metabolism

¹ Swedish Institute for Infectious Disease Control, Department of Bacteriology, S-171 82 Solna, Sweden
² Karolinska Institute, Microbiology and Tumor Biology Center, S-171 77 Stockholm, Sweden

Correspondence
Thomas Åkerlund
Thomas.Akerlund{at}smi.se

Certain amino acids, and cysteine in particular, promptly blocked toxin expression in Clostridium difficile strain VPI 10463 when added to late-exponential-phase peptone-yeast cultures, i.e. prior to normal induction of toxins A and B. Glucose reduced toxin yields by 80-fold, but only when supplemented at inoculation. Forty upregulated C. difficile proteins were identified during maximum toxin expression, and most of these were enzymes involved in energy exchange, e.g. succinate, CO/folate and butyrate metabolism. Transcription of tcdA (toxin operon) and folD (CO/folate operon) was induced by 20- and 10-fold, respectively, and with strikingly similar kinetics between OD 0.8 and 1.2. The sigma factors tcdR and sigH were upregulated simultaneously with tcdA and folD (3.5-fold increase of mRNA level), whereas transcription of tcdC, codY, sigB and sigL showed little or no correlation with that of tcdA and folD. The results suggest a connection between toxin expression, alternative energy metabolism and initial sporulation events in C. difficile.

Two supplementary tables showing primers used for quantitative real-time PCR and identified proteins in C. difficile VPI 10463, and a supplementary figure showing a proteome map of C. difficile VPI 10463, are available with the online version of this paper.