Mutant analysis of luminescence and autoinduction in a marine bacterium

Abstract

The marine symbiotic bacterium Vibrio fischeri is striking for its ability both to emit light and to dramatically regulate light emission using a cell-to-cell signalling mechanism called autoinduction. The latter is mediated by a signal molecule called the "autoinducer". The mechanistic bases of both luminescence and autoinduction are well known in V. fischeri, but this knowledge is mostly derived from studies of the cloned luminescence and autoinduction genes expressed in Escherichia coli. In this study, luminescence and autoinduction mutations were systematically generated in V. fischeri to explore aspects of luminescence and autoinduction not addressable in E. coli, such as the adaptive significance of luminescence. Most dramatically, the mutants revealed the presence of multiple autoinducers and autoinducer synthases in V. fischeri. One of the autoinducers (autoinducer-2, or AI-2) was chemically purified and shown to be Noctanoyi- L-homoserine lactone. The genetic locus encoding the AI-2 synthase was cloned and designated ain (autoinducer). Manipulation of ain and AI-2 in V. jischeri demonstrated that the function of AI-2 appears to be to inhibit rather than to promote autoinduction.