Deletion of OmpF is Not Sufficient to Confer Sensitivity to Ethylenediaminetetraacetic Acid in Escherichia coli Strain K-12

The MlaA pathway maintains lipid asymmetry in the outer membrane of Gram negative bacteria. OmpF and OmpC proteins both interact directly with MlaA. Previous studies have demonstrated that ompC mutants of Escherichia coli are more susceptible to ethylenediaminetetraacetic acid, a membrane disrupting agent, than wildtype cells due to disruption of the MlaA pathway. However, double ompF/ompC mutants exhibit resistance to membrane disrupting agents, comparable to that of wildtype cells. To gain more insight into this apparent reversion in phenotype, we tested the sensitivity of ompF mutants to ethylenediaminetetraacetic acid using a broth dilution minimal inhibitory concentration assay adapted from Hartstein et al.. This allowed for the effect of knocking out each gene in the ompF/ompC double knockout mutants to be individually tested. Since OmpC and OmpF share similar topology, we expected ompF mutants to behave similarly to ompC mutants. The results of our adapted minimum inhibitory assay quantitatively demonstrated resistant wildtype and ompC/ompF phenotypes, and a sensitive ompC phenotype, both of which are in accordance with previous work. However, we found ompF cells to exhibit increased resistance as compared to the ompC strain, which was unexpected. Our results may suggest the presence of redundant mechanisms replacing OmpF and OmpC’s functions, and that OmpF might disrupt the function of the MlaA lipoprotein in the absence of OmpC.