Phosphate deficiency confers transient SDS-EDTA resistance in Escherichia coli K12 ompC knockout mutant

OmpC is a general diffusion protein located in the outer membrane (OM) of gram-negative bacteria. It is known to associate with components of the Mla pathway to facilitate OM lipid asymmetry, which protects against harmful external stressors such as antibiotics and detergents. It has been demonstrated that Escherichia coli ΔompC mutants are more sensitive to sodium dodecyl sulfate-ethylenediaminetetraacetic acid (SDS-EDTA) treatment than the wild type strain. PhoE is another general diffusion protein that shares structural similarity with OmpC. While ompC is constitutively expressed, phoE is thought to be upregulated in phosphate limiting conditions. Phosphate deficiency in minimal media has been shown to restore SDS-EDTA resistance in ΔompC strains over a period of 16 hours and is thought to be attributed to the upregulation of phoE. However, it has also been found that phosphate deficiency can hamper growth, and that passaging cells in phosphate limiting media helps mitigate this issue. This study investigated changes to the resistance of E. coli ΔompC mutants to SDS-EDTA under phosphate sufficient and deficient conditions when grown until the end of stationary phase, as well as the effects of serially passaging wild type and ΔompC mutants in phosphate deficient and sufficient media. We hypothesized that SDSEDTA resistance would be observed in ΔompC mutants. We also hypothesized that adaptation of cells to the phosphate limiting minimal media would decrease the length of the lag phase. To test this, we serially passaged wild type and ΔompC strains in phosphate sufficient and phosphate deficient media, and then performed SDS-EDTA growth assays. We found that serially passaging the strains a minimum of 4 times in phosphate sufficient or deficient media resulted in a decreased lag phase, higher growth rates, and higher growth
yields for both ΔompC mutants and wild type cells compared to non-passaged cells. Additionally, we replicated the previously established findings that ΔompC mutants grow better in SDS-EDTA during exponential phase than the wild type, but this resistant phenotype was not observed in the transition to stationary phase. On the basis of our results and those of other studies, it is possible that phoE may be upregulated upon primary exposure to SDSEDTA in E. coli cells lacking ompC, after adaptation to phosphate deficient media. However, SDS-EDTA resistance appear to be transient and there may be several other components
influencing the resistant phenotype.