Though abrB is absent from C. difficile, this does not exclude the possibility of indirect transcriptional regulation through Spo0Adependent effects on other regulators. Alternatively, Spo0A may exert a direct effect. In Clostridium acetobutylicum and C. beijerinckii, Spo0A is a direct regulator of solvent formation, as well as sporulation [22, 23] . It seems therefore conceivable that Spo0A in C. difficile also affects aspects of metabolism. In this respect, it is important to note that also in C. difficile Spo0A is detectable from early exponential growth phase on ( Figure 1B) .