The LuxS‐dependent autoinducer AI‐2 controls the expression of an ABC transporter that functions in AI‐2 uptake in Salmonella typhimurium

Abstract

In a process called quorum sensing, bacteria communicate with one another using secreted chemical signalling molecules termed autoinducers. A novel autoinducer called AI‐2, originally discovered in the quorum‐sensing bacterium Vibrio harveyi, is made by many species of Gram‐negative and Gram‐positive bacteria. In every case, production of AI‐2 is dependent on the LuxS autoinducer synthase. The genes regulated by AI‐2 in most of these luxS‐containing species of bacteria are not known. Here, we describe the identification and characterization of AI‐2‐regulated genes in Salmonella typhimurium. We find that LuxS and AI‐2 regulate the expression of a previously unidentified operon encoding an ATP binding cassette (ABC)‐type transporter. We have named this operon the lsr (luxS regulated) operon. The Lsr transporter has homology to the ribose transporter of Escherichia coli and S. typhimurium. A gene encoding a DNA‐binding protein that is located adjacent to the Lsr transporter structural operon is required to link AI‐2 detection to operon expression. This gene, which we have named lsrR, encodes a protein that represses lsr operon expression in the absence of AI‐2. Mutations in the lsr operon render S. typhimurium unable to eliminate AI‐2 from the extracellular environment, suggesting that the role of the Lsr apparatus is to transport AI‐2 into the cells. It is intriguing that an operon regulated by AI‐2 encodes functions resembling the ribose transporter, given recent findings that AI‐2 is derived from the ribosyl moiety of S‐ribosylhomocysteine.