Effects of cobalt on Chromobacterium violaceum quorum signaling in the absence and presence of oxygen
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Bacteria exist as colonial organisms, that utilize signaling system for communication. Quorum signaling is a cell-density dependent cell-to-cell bacterial communication which regulates several phenotypes such as biofilm formation, pigmentation, and virulence. Chromobacterium violaceum is a gram-negative, facultative anaerobic bacterium dwelling in the soil and water of tropical environments. Quorum signaling is responsible for the C. violaceum biofilm formation and deep purple pigment (violacein) production. Several organic and biological molecules have been identified as quorum signaling inhibitors. As well, recent studies showed that sub-lethal concentrations of heavy metals such as cadmium and nickel also inhibited C. violaceum quorum signaling resulting in reduced violacein production, virulence, biofilm formation, and quorum-regulated gene expression. In the current study, I showed that cobalt inhibited suspended cell aggregation (floc biofilm formation) in both aerobic and anaerobic conditions but did not affect surface-attached biofilm. Also, cobalt inhibited expression of several genes involved in quorum signaling. This study is the first report of the effects of heavy metal on quorum signaling inhibition of C. violaceum in anaerobic condition.