Beyond quorum sensing: the complexities of prokaryotic parliamentary procedures

Bacterial quorum-sensing regulatory systems can be summarized in a simple model wherein an autoinducer molecule accumulates in cultures and stimulates regulatory changes in gene expression upon reaching a critical threshold concentration. Although quorum sensing was originally thought to be an isolated phenomenon governing the regulation of a handful of processes in only a few bacteria, it is now considered to be a widespread mechanism for coordinating bacterial gene expression. Over decades of research, investigations of autoinducer-mediated regulation have revealed that these systems are far more complicated than originally appreciated, and such discoveries have accelerated recently with the application of molecular and genomic tools. The focus of this review is to highlight recent advances describing complexities that go beyond the simple model of quorum sensing. These complexities include the regulation of autoinducer production and degradation, the presence of multiple quorum-sensing systems in individual bacteria that regulate diverse genes, often in coordination with other regulatory elements, and the influence of interorganismal interactions on quorum sensing.