Demonstration of a missing outer membrane protein in tolG mutants of Escherichia cell

A class of Escherichia coli mutants called tolG are specifically tolerant to bacteriocin JF246. Cell envelopes were prepared from three independent spontaneous E. coli. tolG mutants and the parental strain (tolG⁺). Electrophoresis of these preparations in polyacrylamide gels containing sodium dodecyl sulfate showed that the tolG strains lacked a cell envelope protein found in the tolG⁺ strain. It was estimated that this protein accounted for 10% of the total cell envelope proteins by densitometer tracings of gels stained with Fast Green. Membrane fractionation by isopycnic centrifugation in a sucrose density gradient showed that this protein was located in the outer membrane of tolG⁺ cells. Genetic studies using conjugation, transduction and reversion showed that, in the limited number of recombinants or revertants studied, strains exhibiting the tolerant phenotype lacked the outer membrane protein, whereas the protein was present in bacteriocin-sensitive strains.