Zinc-induced envelope stress diminishes type III secretion in enteropathogenic Escherichia coli.

Background: Dietary supplementation with zinc has been shown to reduce the duration and severity of diarrhoeal disease caused by Enteropathogenic Escherichia coli, common in infants in developing countries. Initially this therapeutic benefit was attributed to the correction of zinc deficiency in malnourished individuals, but recently evidence has emerged that zinc significantly impacts the pathogens themselves: zinc concentrations achievable by oral supplementation can reduce the expression of key virulence-related genes in EPEC and related organisms.

Results: Here, we investigate three possible mechanisms for such zinc-induced changes in expression of EPEC virulence: direct interaction of zinc with regulators of LEE operons; genetic interaction of LEE operons with known regulators of zinc homeostasis; and finally, downregulation of LEE transcription associated with activation of the σ(E) envelope stress response by zinc.

A stable mercury-containing complex of the organomercurial lyase MerB: catalysis, product release, and direct transfer to MerA.

Bacteria isolated from organic mercury-contaminated sites have developed a system of two enzymes that allows them to efficiently convert both ionic and organic mercury compounds to the less toxic elemental mercury. Both enzymes are encoded on the mer operon and require sulfhydryl-bound substrates. The first enzyme is an organomercurial lyase (MerB), and the second enzyme is a mercuric ion reductase (MerA).

NMR structural studies reveal a novel protein fold for MerB, the organomercurial lyase involved in the bacterial mercury resistance system.

Mercury resistant bacteria have developed a system of two enzymes (MerA and MerB), which allows them to efficiently detoxify both ionic and organomercurial compounds. The organomercurial lyase (MerB) catalyzes the protonolysis of the carbon-mercury bond resulting in the formation of ionic mercury and a reduced hydrocarbon. The ionic mercury [Hg(II)] is subsequently reduced to the less reactive elemental mercury [Hg(0)] by a specific mercuric reductase (MerA).