Escherichia coli strains blocked in Tat-dependent protein export exhibit pleiotropic defects in the cell envelope

The Tat system is a recently discovered protein export pathway that serves to translocate folded proteins, often containing redox cofactors, across th e bacterial cytoplasmic membrane. Here we report that tat strains are assoc iated with a mutant cell septation phenotype, where chains of up to 10 cell s are evident. Mutant strains are also hypersensitive to hydrophobic drugs and to lysis by lysozyme in the absence of EDTA, and they leak periplasmic enzymes, characteristics that are consistent with an outer membrane defect. Both phenotypes are similar to those displayed by strains carrying point m utations in the lpxC (envA) gene. The phenotype was not replicated by mutat ions affecting synthesis and/or activity of all known or predicted Tat subs trates.