ABSTRACTClostridium difficilespore germination is essential for colonization and disease. The signals that initiateC. difficilespore germination are a combination of taurocholic acid (a bile acid) and glycine. Interestingly, the chenodeoxycholic acid class (CDCA) bile acids competitively inhibit taurocholic acid-mediated germination, suggesting that compounds that inhibit spore germination could be developed into drugs that prophylactically preventC. difficileinfection or reduce recurring disease. However, a recent report called into question the utility of such a strategy to prevent infection by describingC. difficilestrains that germinated in the apparent absence of bile acids or germinated in the presence of the CDCA inhibitor. Because the mechanisms ofC. difficilespore germination are beginning to be elucidated, the mechanism of germination in these particular strains could yield important information on howC. difficilespores initiate germination. Therefore, we quantified the interaction of these strains with taurocholic acid and CDCA, the rates of spore germination, the release of DPA from the spore core, and the abundance of the germinant receptor complex (CspC, CspB, and SleC). We found that strains previously observed to germinate in the absence of taurocholic acid correspond to more potent 50% effective concentrations (EC50values; the concentrations that achieve a half-maximum germination rate) of the germinant and are still inhibited by CDCA, possibly explaining the previous observations. By comparing the germination kinetics and the abundance of proteins in the germinant receptor complex, we revised our original model for CspC-mediated activation of spore germination and propose that CspC may activate spore germination and then inhibit downstream processes.IMPORTANCEClostridium difficileforms metabolically dormant spores that persist in the health care environment. In susceptible hosts,C. difficilespores germinate in response to certain bile acids and glycine. Blocking germination byC. difficilespores is an attractive strategy to prevent the initiation of disease or to block recurring infection. However, certainC. difficilestrains have been identified whose spores germinate in the absence of bile acids or are not blocked by known inhibitors ofC. difficilespore germination (calling into question the utility of such strategies). Here, we further investigate these strains and reestablish that bile acid activators and inhibitors of germination affect these strains and use these data to suggest another role for theC. difficilebile acid germinant receptor.
Study of the Gametophytic phase of Diplazium caudatum (Athyriaceae, Polypodiopsida) from Spain
