Phenotype MicroArrays, nutrients. Growth on sole carbon and nitrogen sources was determined with Phenotype MicroArrays (Biolog, Hayward, CA) for wild-type 8081c cells and their isogenic flhD and fliA mutants. Bacterial solutions in IF-0 were pipetted onto PM1 (carbon sources, Panels A and C) and PM3 (nitrogen sources, Panels B and D) plates. Plates were incubated at 25°C (Panels A and B) or 4°C (Panels C and D). Growth on all plates was determined as OD630. The background OD630 (obtained from well A1) was subtracted from the OD630 for each nutrient on each plate. Growth ratios are expressed as OD630 of the wild-type cells divided by OD630 of each of the mutant strains (darker bars, flhD mutant; lighter bars, fliA mutant) for each nutrient. Nutrients that provided better growth conditions for the wild-type cells are printed in green, nutrients that provided better growth conditions for the mutants are printed in red. Dipeptides are printed in blue. The experiment was performed three to four times and the mean of the population is presented. Error bars indicate one standard deviation (1 s).