a) Measurement of the proton motive force (PMF) in WT and narG::tet cells growing on SK with and without lactate or malate, and with or without CCCP. The PMF was measured before and 40 min after addition of 40 mM nitrate. CCCP was added to confirm that the observed changes were associated with the proton gradient (n=3 biological replicates). b) Lactate (n=3 biological replicates) and aspartate (n=2 biological replicates) consumption were measured in resting WT cells resuspended in resting cell (RC) buffer with or without nitrate. c) Lactate consumption (n=4 biological replicates) was measured in growing atp::tet cells with or without nitrate. Both metabolites were measured in the supernatant using colorimetric techniques. d) Growth experiments with WT Veillonella and a strain lacking LldP (lldP::chl) in SK, SKL, SKN, and SKLN media (n=4 biological replicates). Cells lacking the LldP transporter are nearly unable to grow with lactate as the carbon source. Growth rates (μmax) were calculated for each growth curve. Data (a-d) represent mean ± SEM, analyzed by two-sided t-test (a, b, and c), or one-way ANOVA and Tukey’s HSD test (growth rates in d). NS, not significant.