Phosphate deficiency restores SDS-EDTA resistance in an Escherichia coli K12 ompC knockout mutant


Christiane Boen, Faith Cheung, Milena Kovacevic, Ian Yen

Volume 5
Fall 2018 / Winter 2019

The asymmetric outer membrane (OM) of Gram-negative bacteria protects against external insults, such as antibiotics and detergents. OmpC is a general diffusion porin found in the OM that plays a role in maintaining OM asymmetry. Previous studies have shown that E. coli ompC knockout strains are sensitive to treatment with sodium dodecyl sulfate (SDS) and EDTA compared to wild type. PhoE is another general diffusion porin that is similar in structure and function to OmpC, but normally expressed only under phosphatedeficient conditions. We hypothesized that phosphate deficiency would restore SDS-EDTA resistance in △ompC mutants by inducing PhoE expression, which could compensate for the lack of OmpC. To test this, we performed growth assays of wild type and △ompC mutant strains grown in phosphate-sufficient or phosphate-deficient media with increasing SDS-EDTA concentrations. Our study found that the △ompC mutant strain is resistant to SDS-EDTA when grown in phosphate-deficient media compared to phosphate-sufficient media. SDS-PAGE was used to investigate the expression of PhoE in phosphate-deficient media. Our results suggest that phosphate deficiency results in changes in cellular protein expression and restores SDS-EDTA resistance in E. coli △ompC strains.