Escherichia coli tol-pal Mutants Form Outer Membrane Vesicles

Abstract

Mutations in the tol-pal genes induce pleiotropic effects such as release of periplasmic proteins into the extracellular medium and hypersensitivity to drugs and detergents. Other outer membrane defective strains such as tolC, lpp, and rfa mutations are also altered in their outer membrane permeability. In this study, electron microscopy and Western blot analyses were used to show that strains with mutations in each of thetol-pal genes formed outer membrane vesicles after growth in standard liquid or solid media. This phenotype was not observed intolC and rfaD cells in the same conditions. AtolA deletion in three different Escherichia coli strains was shown to lead to elevated amounts of vesicles. These results, together with plasmid complementation experiments, indicated that the formation of vesicles resulted from the defect of any of the Tol-Pal proteins. The vesicles contained outer membrane trimeric porins correctly exposed at the cell surface. Pal outer membrane lipoprotein was also immunodetected in the vesicle fraction oftol strains. The results are discussed in view of the role of the Tol-Pal transenvelope proteins in maintaining outer membrane integrity by contributing to target or integrate newly synthesized components of this structure.

Changes in Escherichia coli outer membrane subproteome under environmental conditions inducing the viable but nonculturable state

“…We also identified TolC, a multifunctional outer membrane protein with a function similar to OmpA (Bernadac et al, 1998). Moreover, TolC is involved in the export of a wide variety of molecules, including those that are toxic to the bacterium (Sharff et al, 2001).…”

The Tol proteins of Escherichia coli and their involvement in the uptake of biomolecules and outer membrane stability

“…Mutations in any of the tolQRAB genes of E. coli make the bacterium hypersensitive to bile salts and other deleterious agents, and result in the release of periplasmic proteins into the medium [10]. The tol-QRAB and pal mutants form outer membrane vesicles which contain periplasmic components that are released into the medium [11]. Like rfa and pal mutants, tolQRAB mutants show a temperature-dependent mucoid phenotype, due to the induction of colanic acid synthesis which is believed to protect the cell against desiccation.…”

Profiling the Humoral Immune Response of Acute and Chronic Q Fever by Protein Microarray

“…The other two consistent switch events are antigens CBU0092 and CBU0545 (the YbgF tol-pal system protein and LemA proteins, respectively). CBU0092 (tol-pal system protein YbgF) was found in both phases of C.burnetii (23,24) and experiments using E. coli mutants with defects in tol-pal proteins led to a loss of outer membrane integrity leading to hypersensitivity to drugs and detergents, periplasmic leakage, and outer membrane vesicle formation (25)(26)(27). We have consistently identified CBU0545 (lemA protein) as a diagnostic antigen (13,14) for acute Q fever.…”