An Escherichia coli sbmA tolC double mutant displays a thermosensitive colony formation phenotype

Abstract

The Escherichia coli sbmA gene has been identified in screens for mutantsresistant to the peptide antibiotics microcin B17 and microcin J25, the glycopeptide antibiotic bleomycin and eukariotic peptide antibiotics. Homologs of sbmA have been found in a wide variety of bacteria; however, the natural function of SbmA remains unknown. We demonstrate here that the combined loss of the inner membrane protein SbmA and the outer membrane protein TolC results in a heat sensitive colony formation phenotype. The sbmA and tolC mutations alone do not exhibit such phenotype. We propose that TolC and SbmA have an overlapping functionality in some cellular process, and that they backup for one another, particularly for cell growth on solid medium at high temperature. This work establishes for the first time a physiologicalphenotype for sbmA mutants and opens an avenue for an analysis of the role of this inner membrane protein in bacterial cell physiology.