Fig. 6.

Model for the proposed role of CD2830 in regulation of adhesion versus motility in C. difficile. The C. difficile secreted protease CD2830 cleaves adhesin proteins CD2831 and CD3246, thereby releasing these cell surface anchors. Both adhesin mRNAs contain a riboswitch type II (red balls), which is turned on by elevated levels of c-di-GMP, a central mediator of motility and adhesion in bacteria (top panel). In total, four genes in the C. difficile strain 630 genome contain the type II riboswitch. The cd2830 gene contains a riboswitch type I (blue balls), which is turned on at lower levels of c-di-GMP, as was also shown for the flagellar operon. We postulate that this opposite regulation of expression of adhesins and CD2830 by c-di-GMP plays an important role in the regulation of motility and adhesion: low c-di-GMP concentrations result in the down-regulation of surface levels of adhesins both by repressing their gene expression and by the concomitant cell surface release mediated by CD2830 protease cleavage.