Extraction of violacein from Chromobacterium violaceum provides a new quantitative bioassay for N-acyl homoserine lactone autoinducers

Fatty acyl homoserine lactones (AHLs) are used as extracellular quorum sens ing signals by a variety of Gram-negative bacteria. By activating proteins belonging to the LuxR family of transcriptional regulators, these signal me tabolites allow population density-dependent gene regulation within a speci es, as well as interspecies communication among different bacteria. The exp erimental detection of AHLs is important in the identification of quorum se nsing capabilities in bacteria. Chromobacterium violaceum is a Gram-negativ e bacterium that produces the purple pigment violacein in response to the p resence of the AHL N-hexanoyl homoserine lactone (C6HSL). The mini-Tn5 muta nt strain C. violaceum CV0blu is deficient in the production of this signal molecule but retains the ability to synthesize violacein in response to th e presence of C6HSL and a variety of other short-chain AHLs. We have develo ped a quantitative bioassay that measures the amount of violacein produced by this strain in response to the presence of different concentrations of v arious AHL molecules. This new assay provides a means of quantifying the am ount of a given AHL present in a bacterial culture and can be used to measu re differences in AHL production among different strains or different batch cultures of a given species. (C) 2000 Elsevier Science B.V. All rights res erved.