Mxd expression in S. oneidensis MR-1 wild type, ∆ arcS and ∆ arcA mutants. Mxd expression in S. oneidensis MR-1 wild type, ∆arcS and ∆arcA mutant cells grown under LB medium conditions. Wild type, ∆arcS and ∆arcA mutants carrying the mxd promoter transcriptionally fused to lacZ were grown under LB medium conditions for 24 h. Cells were harvested after 2 h, 6 h or 24 h and assayed for β-galactosidase activity. Optical densities are shown for all time points. Data represent an average of three independent experiments.