Quorum sensing in Escherichia coli, Salmonella typhimurium, and Vibrio harveyi: A new family of genes responsible for autoinducer production

In bacteria, the regulation of gene expression in response to changes in ce ll density is called quorum sensing, Quorum-sensing bacteria produce, relea se, and respond to hormone-like molecules (autoinducers) that accumulate in the external environment as the cell population grows. In the marine bacte rium Vibrio harveyi two parallel quorum-sensing systems exist, and each is composed of a sensor-autoinducer pair. V. harveyi reporter strains capable of detecting only autoinducer I (AI-1) or autoinducer 2 (AI-2) have been co nstructed and used to show that many species of bacteria, including Escheri chia coli MG1655, E. coli O157:H7, Salmonella typhimurium 14028, and S. typ himurium LT2 produce autoinducers similar or identical to the V. harveyi sy stem 2 autoinducer AI-2, However, the domesticated laboratory strain E. col i DH5 alpha does not produce this signal molecule. Here we report the ident ification and analysis of the gene responsible for AI-2 production in V. ha rveyi, S. typhimurium, and E. coli, The genes, which we have named luxS(V.h .),, luxS(S.t.), and luxS(E.c.), respectively, are highly homologous to one another but not to any other identified gene. E, coli DH5 alpha can be com plemented to AI-2 production by the introduction of the luxS gene from V. h arveyi or E. coli O157:H7, Analysis of the E. coli DH5 alpha luxS(E.c.) gen e shows that it contains a frameshift mutation resulting in premature trunc ation of the LuxS(E.c.) protein. Our results indicate that the luxS genes d efine a new family of autoinducer-production genes.