Abstract
In Chromobacteium violaceum, the purple pigment violacein is under positive regulation by the N-acylhomoserine lactone CviI/R quorum sensing system and negative regulation by an uncharacterized putative repressor. In this study we report that the biosynthesis of violacein is negatively controlled by a novel repressor protein, VioS. The violacein operon is regulated negatively by VioS and positively by the CviI/R system in both C. violaceum and in a heterologous Escherichia coli genetic background. VioS does not regulate the CviI/R system and apart from violacein, VioS, and quorum sensing regulate other phenotypes antagonistically. Quorum sensing regulated phenotypes in C. violaceum are therefore further regulated providing an additional level of control.
Highlights
Many Gram-negative bacteria regulate cell density dependent behavior by producing and sensing N-acylhomoserine lactone (AHL) signal molecules by a process called quorum sensing (QS; Fuqua et al, 1994)
In this study we have examined the regulation of violacein production in C. violaceum ATCC31532 and characterized its QS system as well as a repressor mutant of this strain with respect to violacein production
The unequivocal chemical identification of C6-HSL from culture supernatants of C. violaceum ATCC 31532 and the selection of a Tn5 transposon mutant with an insertion in a putative luxI orthologue demonstrated the presence of an AHL QS system in this organism (McClean et al, 1997)
Summary
Many Gram-negative bacteria regulate cell density dependent behavior by producing and sensing N-acylhomoserine lactone (AHL) signal molecules by a process called quorum sensing (QS; Fuqua et al, 1994). CviR binds to C10-HSL with highest affinity (Morohoshi et al, 2008; Swem et al, 2009) and the cviI AHL synthase is under positive feedback regulation by. Using a combination of mutagenesisbased analysis in C. violaceum ATCC31532 and experiments in a heterologous Escherichia coli host, the vioA promoter of vioABCDE operon has been shown to be under the direct positive regulation of CviR (McClean et al, 1997; Swem et al, 2009). We propose that VioS is a novel protein that functions to fine-tune the QS regulated phenotype of violacein biosynthesis by regulating vioA promoter expression rather than modulating the regulation of cviI/cviR gene expression
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