title: Loss of FlhE in the flagellar Type III secretion system allows proton influx into Salmonella and Escherichia coli.
abstract: flhE belongs to the flhBAE flagellar operon in Enterobacteria, whose first two members function in Type III secretion (T3S). In Salmonella enterica, absence of FlhE affects swarming, but not swimming, motility. Based on a chance observation of a 'green' colony phenotype of flhE mutants on pH indicator plates containing glucose, we have established that this phenotype is associated with lysis of flagellated cells in an acidic environment created by glucose metabolism. The flhE mutant phenotype of Escherichia coli is similar overall to that of S. enterica but is seen in the absence of glucose and, unlike in S. enterica, causes a substantial growth defect. flhE mutants have a lowered cytoplasmic pH in both bacteria, indicative of a proton leak. GFP reporter assays indicate that the leak is dependent on the flagellar system, is present before the T3S system switches to secretion of late substrates, and gets worse after the switch and upon filament assembly, leading to cell lysis. We show that FlhE is a periplasmic protein that co-purifies with flagellar basal bodies. FlhE may act as a plug or a chaperone to regulate proton flow through the flagellar T3S system.
authors.affiliation: Section of Molecular Genetics and Microbiology & Institute of Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Jaemin
authors.initials: J
authors.lastname: Lee
authors.forename: Rasika M
authors.initials: RM
authors.lastname: Harshey
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D001692:Biological Transport; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005407:Flagella / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D011522:Protons; D012486:Salmonella typhimurium / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D011522:Protons