Growth phenotype of the mutant strains. (A) Cultures of C. crescentus strains NA1000 (wild type), ΔczrA, ΔnczA, and the double mutant ΔczrAΔnczA at an initial OD of 0.05 were inoculated into PYE medium with or without the indicated concentrations of metal salts. The cultures were incubated at 30°C for 24 h, and then growth was assessed by determination of OD at 600 nm. The results shown are the average of two experiments. Error bars indicate standard deviations. Asterisks indicate results significantly different than those of of the same time points without metal (p ≤ 0.05). (B) Equal amounts of cells from cultures of C. crescentus strains NA1000, ΔczrA, ΔnczA, and the two complemented strains ΔczrA + and ΔnczA + were streaked on solid PYE medium. The plates were incubated at 30°C for 72 h before the pictures were taken.