Fig. 6: Loss of cytochrome bd impairs efflux by diminishing respiratory flux.

a, b Efflux of ethidium bromide was measured in planktonic cells (a) and cells extracted from homogenized colony biofilms (b). Data were fit to a one phase decay model, and statistical comparisons were made between the curve of best fit for each strain. Data are presented as mean ± 95 percent confidence interval. c RT-qPCR was performed to measure acrB transcript abundance normalized to gyrB abundance in UTI89 and ∆cydAB planktonic and biofilm cells. Mean values were statistically compared with a two-tailed unpaired t-test. Data are presented as mean ± SEM, and each dot represents a biological replicate. d, e Respiratory flux was quantified in wild-type, ∆ubiI (ubiquinone synthase mutant), and quinol oxidase mutants by measuring triphenyl tetrazolium chloride (TTC) reduction. d Quantification of TTC reduction per unit area in spot colonies. Data were analyzed by a one-way ANOVA with Dunnett’s multiple comparisons test. Data are presented as mean ± SEM, and each dot represents a biological replicate. e Representative images of TTC reduction assays. Red color indicates respiratory activity. Data in a–c are representative of three biological replicates, and data in d, e are representative of at least eight biological replicates. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.