Growth and sporulation kinetics of C. difficile 630 derivatives in broth cultures. a) Growth curves of the C. difficile 630∆ erm parental strain and its spo0A isogenic mutant. Shown are the OD600 measurements on the left y-axis and ethanol-resistant spore-derived CFUs on the right y-axis. The gray vertical arrow indicates that sampling point. b) Western blot analysis demonstrating that Spo0A is expressed under exponential and stationary growth stages by the parental C. difficile 630∆ erm strain but not the isogenic spo0A mutant. Spo0A-his6 protein was purified protein as described before .