We determined the expression of C. difficile Spo0A throughout growth. We found that the protein is present in lysates from exponential to stationary growth phase cells. We performed immunoblotting using polyclonal antibodies against C. difficile Spo0A on total lysates of wild type and spo0A mutant cells grown in a trypton-yeast based medium (TTY). We found a clear signal of the size expected for full length Spo0A (,31 kDa) as early as 3 hours post inoculation (exponential growth phase), through transition phase (8 h) as well as 24 and 48 hours post inoculation (stationary growth phase) ( Figure 1B; 630Derm) . The signals were specific for C. difficile Spo0A as they were absent from lysates from the C. difficile spo0A mutant (Fig. 1B , CT::spo0A). We obtained similar results in other media, such as the commonly used supplemented brain heart infusion broth (BHIS; data not shown).