Inhibition of quorum signalling and biofilm formation in Chromobacterium violaceum in the presence of cadmium, cobalt and nickel divalent cations
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Bacteria are single celled organisms capable of acting as a single unit by sensing and responding to population density via a phenomenon called quorum signaling. Quorum signaling regulates a variety of phenotypes including biofilm formation and virulence factor production. In the soil bacterium Chromobacterium violaceum the virulence factor violacein results in a deep purple pigmentation and is one such regulated phenotype. Previously, a number of biological and organic molecules have been described as quorum signaling inhibitors, but to date no metal-based inhibitors have been identified. In this study, we show that quorum sensing is inhibited in C. violaceum when in the presence of sub-lethal concentrations of cadmium based salts. Cobalt and nickel salts have also been indicated as inhibitors in other gram negative species. Inhibitory effects of cadmium divalent cations on C. violaceum were shown in biofilm formation, pigmentation and virulence factor production, as well as transcript levels for genes involved in these processes. This study represents the first description of heavy metal based quorum sensing inhibition in C. violaceum.