C. difficile Spo0A-DBD Binds to DNA Upstream of tcdB It has previously been reported that the deletion of Spo0A in C. difficile results in a significantly lower toxin production and a ,1000-fold reduction in the toxicity of culture supernatant derived from spo0A negative cells towards Vero cells [35] . Considering the absence of a homolog of the abrB repressor, direct binding of Spo0A and concomitant activation of toxin gene transcription is a likely mechanism through which this could occur. We found evidence for direct binding of Spo0A-DBD to the region upstream of tcdB, encoding one of the major clostridial toxin genes, and possibly tcdC, but this did not seem to result in lower toxin levels in our hands.