Clostridium difficile, a proteolytic Gram-positive anaerobe, has emerged as a significant nosocomial pathogen. Stickland fermentation reactions are thought to be important for growth of C. difficile. In Stickland reactions, pairs of amino acids donate and accept electrons, generating ATP and reducing power in the process. Reduction of the electron acceptors proline and glycine requires the D-proline reductase (PR) and the glycine reductase (GR) enzyme complexes, respectively. PrdR, a sigma54-dependent regulator, activates transcription of the PR-encoding genes in the presence of proline and negatively regulates the GR-encoding genes, suggesting that PrdR is a central metabolism regulator that controls preferential utilization of proline and glycine to produce energy via the Stickland reactions. Here, transcriptional profiling of C. difficile comparing growth in TY medium supplemented with 30 mM L-proline to growth in TY medium alone is performed. Overall design: Two-condition experiment: TY with excess of proline vs. TY alone. 2 biological replicates for each condition, including a dye-swap.