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Abstract
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 ΔompC 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 ΔompF/ΔompC 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 ΔompF 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 ΔompF/ΔompC double knockout mutants to be individually tested. Since OmpC and OmpF share similar topology, we expected ΔompF mutants to behave similarly to ΔompC mutants. The results of our adapted minimum inhibitory assay quantitatively demonstrated resistant wildtype and ΔompC/ΔompF phenotypes, and a sensitive ΔompC phenotype, both of which are in accordance with previous work. However, we found ΔompF cells to exhibit increased resistance as compared to the ΔompC 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.