Cell-to-cell signaling via small chemical signals is an ancient process shared by most living organisms. Whether these signals are produced by mammals, insects, plants, or bacteria and are called hormones, pheromones, or autoinducers, they convey vital information about the status of the cell and its extracellular environment. The discovery of bacterial cell-to-cell signaling, or quorum sensing (QS), revealed that single-celled prokaryotic organisms possess sophisticated methods for coordinating their behavior by secreting chemical or peptide signals and ushered in a new field of Microbiology.

The study of quorum sensing has mainly focused on identifying the components making up quorum sensing circuits in bacteria, and significant progress has been made in elucidating the structures of the chemical signals, identifying the receptors that detect these signals and affect QS-dependent gene expression, and mapping the signal transduction pathways involved. However, we are also beginning to understand that these bacterial quorum sensing signals (QSS) are perceived, responded to, and degraded by both eukaryotes and members of the host-associated microbial communities. Thus, the question arises,“How do host cells perceive QSS and what are the consequences of this crosskingdom communication?”