Production of the autoinducer-2 signalling molecule in Escherichia coli -monoassociated mice

Quorum sensing is a kind of bacterial communication mediated by a chemical signalling molecule called an autoinducer. The luxS gene is responsible for the production of autoinducer-2 (AI-2). The production of AI-2 was measured in the faeces of Escherichia coli -monoassociated mice. The production of AI-2 was higher during the initial stage of E. coli growth in the intestine. However, the level of AI-2 was significantly lower in vivo than in an in vitro culture in Luria-Bertani (LB) broth. Bacterial culturing in a caecal suspension from germ-free mice decreased AI-2 levels as low as those in vivo . Supplementing the caecal suspension with 0.5% glucose generated a significant increase in AI-2 levels. The culture conditions, aerobic or anaerobic, also affected AI-2 levels in vitro . Both in the caecal suspension and LB broth, the level of AI-2 was lower under anaerobic than aerobic culture conditions. The increase in the AI-2 level produced by supplementing with glucose was less marked in the anaerobic culture than the aerobic culture. Substrate availability and environmental stress in the intestine seem to play important roles in the production of AI- 2 in vivo.