Fig. 2

Utilization of lactate by E. coli in vitro. Mucin broth was inoculated with a 1:1 mixture of the E. coli MP1 wild-type and an isogenic strain lacking the indicated lactate dehydrogenase. Cultures were grown either aerobically (+ oxygen) or anaerobically (− oxygen). D-lactate, L-lactate, and nitrate were added as indicated. The competitive index represents the ratio of WT/mutant recovered after 16 h compared to the ratio of the inoculum. A–C L-lactate utilization by E. coli via the LldD enzyme (A), the Dld enzyme (B), and the YkgEFG enzyme (C). D–F Utilization of D-lactate by E. coli via the LldD enzyme (D), the Dld enzyme (E), and the YkgEFG enzyme (F). Columns represent geometric mean and error bars represent geometric standard deviation. Each dot represents one biological replicate. Statistical significance was assessed using a one-way ANOVA followed by Dunett’s multiple comparisons test on log-transformed data. **, p<0.01; ***, p<0.001