FIG 8.

Abbreviated model of influence of nutrition on sporulation. Under nutrient-rich conditions, CodY and CcpA act as repressors of the opp oligopeptide transporter operon, the putative sinRI regulatory genes, and numerous genes involved in nutrient acquisition. As nutrient levels decrease, CodY and CcpA transcriptional repression is alleviated. The oligopeptide transporters Opp and App import peptides, and the branched-chain amino acids (BCAAs) derived from imported peptides bind to CodY, increasing its DNA-binding capacity. SinR is hypothesized to act as a transcriptional repressor of the sporulation master regulator Spo0A. The putative SinI of C. difficile is thought to act as a repressor of SinR. Gray hatched arrows show hypothesized regulatory effects.