The copper-inducible ComR (YcfQ) repressor regulates expression of ComC (YcfR), which affects copper permeability of the outer membrane of Escherichia coli

Abstract

The pathway of copper entry into Escherichia coli is still unknown. In an attempt to shed light on this process, a lux-based biosensor was utilized to monitor intracellular copper levels in situ. From a transposon-mutagenized library, strains were selected in which copper entry into cells was reduced, apparent as clones with reduced luminescence when grown in the presence of copper (low-glowers). One low-glower had a transposon insertion in the comR gene, which encodes a TetR-like transcriptional regulator. The mutant strain could be complemented by the comR gene on a plasmid, restoring luminescence to wild-type levels. ComR did not regulate its own expression, but was required for copper-induction of the neighboring, divergently transcribed comC gene, as shown by real-time quantitative PCR and with a promoter-lux fusion. The purified ComR regulator bound to the promoter region of the comC gene in vitro and was released by copper. By membrane fractionation, ComC was shown to be localized in the outer membrane. When grown in the presence of copper, ∆comC cells had higher periplasmic and cytoplasmic copper levels, compared to the wild-type, as assessed by the activation of the periplasmic CusRS sensor and the cytoplasmic CueR sensor, respectively. Thus, ComC is an outer membrane protein which lowers the permeability of the outer membrane to copper. The expression of ComC is controlled by ComR, a novel, TetR-like copper-responsive repressor.

Survival of Escherichia coli Cells on Solid Copper Surfaces Is Increased by Glutathione

“…In Gram-negative bacteria, copper ions need to be imported into the periplasm first. OmpC and ComC (YcfR) play a role here (57,59). Although a strain deficient in the gene for the NADH: ubiquinone oxidoreductase II (Ndh) suffered a faster inactivation than its parent strain in the presence of copper and tert-butyl hydroperoxide (60), Ndh was not involved in copper tolerance in the absence of this substance (data not shown).…”

Identification of Salmonella enterica Serovar Typhimurium Genes Regulated during Biofilm Formation on Cholesterol Gallstone Surfaces

“…YcfR has been shown to have a negative role in E. coli biofilm formation only in LB with glucose, likely by decreasing bacterial aggregation and cell surface adhesion as a result of decreased hydrophobicity and increased intracellular indole concentrations (66). Others have reported that YcfR lowers the permeability of the outer membrane to copper (85). The ycfR nucleotide sequence is 81% identical between Salmonella and E. coli.…”

Copper-responsive gene regulation in bacteria

“…It remains to be elucidated whether ComC limits copper acquisition by affecting porin activity or by another mechanism. Under In contrast to many other copper-responsive regulators, ComR does not regulate its own expression (Mermod et al, 2012). It remains unknown to date whether ComR regulates target genes other than comC.…”

“…1). The outermembrane protein ComC reduces the permeability of the outer membrane to copper (Mermod et al, 2012). It remains to be elucidated whether ComC limits copper acquisition by affecting porin activity or by another mechanism.…”