The mRNA expression levels of two components of the macA2B2 locus in the WT and ΔtonB123 mutant. RNA was isolated from the log-phase bacteria that had been cultured in LB broth. The recA gene was chosen as the internal control. The results are expressed as n-fold increase with respect to the control. Data represent the means ± SEM from three independent experiments. “ns” signifies not statistically significant.