Fig. 1: C. septicum germinates robustly in the presence of bile salts.

a Germination measured by optical density (OD) is shown. OD values were normalized to the starting OD. Purified wild-type spores were incubated with 25 mM of each bile salt. Germination, as indicated by decreasing OD values. was observed with CDCA, DCA and GCA. b Representative phase contrast images of the spores at the end of the OD assay in a are shown. Spores treated with CDCA, DCA and GCA were phase dark, while spores treated with CA, GDCA, TCA and TDCA remained phase bright. Scale bar, 2 μm. c Germination response curves were plotted for the three bile salt germinants. Germination was measured at 900 min post-exposure to increasing bile salt concentrations. CDCA was the most potent germinant, followed by DCA and GCA. d Maximal germination velocity curves were plotted for the three bile salt germinants. For (a, c, d) graphed data represent the average at least 3 biologically independent experiments using at least two different spore preparations. For all bile salts, n = 3 except for GCA, where n = 5. Error envelopes (dashed lines) represent the standard error of the mean. For (a), statistical significance relative to water was determined by one-way ANOVA and Dunnett’s test. For (c, d), statistical significance relative to CDCA was determined by unpaired t test between groups at each time point. ****p < 0.0001, ***p < 0.001, **p < 0.01 *p < 0.05.