Chemical conversations in the gut microbiota.

The gut microbiota is a complex, densely populated community, home to many different species that collectively provide huge benefits for host health. Disruptions to this community, as can result from recurrent antibiotic exposure, alter the existing network of interactions between bacteria and can render this community susceptible to invading pathogens. Recent findings show that direct antagonistic and metabolic interactions play a critical role in shaping the microbiota. However, the part played by quorum sensing, a means of regulating bacterial behavior through secreted chemical signals, remains largely unknown. We have recently shown that the interspecies signal, autoinducer-2 (AI-2), can modulate the structure of the gut microbiota by using Escherichia coli to manipulate signal levels. Here, we discuss how AI-2 could influence bacterial behaviors to restore the balance between the 2 major bacteria phyla, the Bacteroidetes and Firmicutes, following antibiotic treatment. We explore how this may impact on host physiology, community susceptibility or resistance to pathogens, and the broader potential of AI-2 as a means to redress the imbalances in microbiota composition that feature in many infectious and non-infectious diseases.