Communication between commensal bacteria and their hosts is bidirectional. Bacterial factors modulate host immunity and antibacterial barrier defenses, and commensal bacteria also sense and respond to many host factors and communicate amongst themselves. Quorum-sensing autoinducers are small molecules produced by many species of bacteria, and these molecules trigger group behaviors at high cell density. Ismail et al. engineered a strain of Vibrio harveyi that bioluminesces when exposed to the autoinducer AI-2 but does not produce AI-2 or respond to the related autoinducer AI-1. This detector strain responded when cocultured with cell lines derived from epithelial tissues or treated with conditioned medium from intestinal epithelial Caco-2 cells, but not when cocultured with hematopoietic cell lines, suggesting that epithelial cells released a molecule that mimicked AI-2. Production of the AI-2 mimic by Caco-2 cells required the presence of bacteria but did not require direct contact with bacteria. V. harveyi with a mutant form of the AI-2 receptor LuxP that cannot bind ligand did not respond to Caco-2 cells. Disruption of cell junctions with dextran sulfate sodium also induced Caco-2 cells to produce the AI-2 mimic. A bacterial mutagenesis screen identified several candidates important for the ability of bacteria to induce production of or respond to the AI-2 mimic. One of these, the secreted bacterial toxin aerolysin, was sufficient to induce Caco-2 cells to produce the AI-2 mimic. Although the chemical identity of the AI-2 mimic is not yet known, these results indicate that the intestinal epithelium exploits bacterial quorum sensing to influence commensal bacteria (see Surette).
A. S. Ismail, J. S. Valastyan, B. L. Bassler, A host-produced autoinducer-2 mimic activates bacterial quorum sensing. Cell Host Microbe 19, 470–480 (2016). [PubMed]
M. G. Surette, Look who’s talking now. Cell Host Microbe 19, 429–430 (2016). [PubMed]