Global Analysis of the Sporulation Pathway of Clostridium difficile
Figure 8
Comparison of sporulation regulatory network architecture in the Firmicutes.
The temporal progression of sporulation is shown from top to bottom as determined in B. subtilis, C. difficile, C. perfringens, and C. acetobutylicum. Transcription factors and sigma factors are shown in bold, and proteins enclosed in boxes directly participate in trans-septum signaling. Dashed boxes indicate that the function of the proteins in trans-septum signaling has not been tested yet. Text color denotes whether the factor has been detected at both the transcript and protein level (black), at either the transcript or protein level (purple), or has not been tested yet at the transcript or protein level (blue), indicating the need for further experimentation. SpoIIQ* denotes the predicted clostridial homolog to B. subtilis SpoIIQ based on bioinformatics analyses [13]. Pro-σE in C. acetobutylicum is shown in parentheses to indicate that the pro-form has not been detected by Western blot [31]. Black arrows indicate transcriptional control of gene expression, red arrows indicate signaling pathways, dashed arrows indicate that the regulatory relationship between the factors has not been tested, and thick arrows demarcate notable points of divergence from the pathway defined in B. subtilis. AND gates are indicated. Unique features of the sporulation pathway in C. difficile include the post-translational activation of σG by σF and the absence of proteolytic activation of σK; the σE-dependent SpoIIIA-H feeding tube appears to be dispensable for σG activation.