Jump-start and push-start: How signal crosstalk can drive the activation of quorum sensing pathways

Many bacterial species are able to coordinate population-wide phenotypic responses through the exchange of diffusible chemical signals, a behavior known as quorum sensing. A quorum sensing bacterium may employ multiple types of chemical signals and detect them using pathways that are intertwined and crosstalk with each other. While there are many hypotheses for the benefits of using multiple signals, the prevalence of crosstalk and its functional significance are much less understood. Here we explore the effect of intracellular signal crosstalk on quorum sensing using a simple model. Our model captures key aspects of typical quorum sensing pathways, including positive feedback, signal crosstalk at the receptor and promoter levels, and upstream/downstream positioning of different pathways. We find that a variety of behaviors can be tuned by modifying crosstalk and feedback strengths. These include both activation and inhibition of an output by a non-cognate signal, broadening of dynamic range of the outputs, and the ability of the upstream or downstream branches to activate each other. Our findings suggest that signal crosstalk between quorum sensing pathways is not as much a detriment to the flow of information as it is a mechanism that enhances the functional range of the entire regulatory system. The general formulation of crosstalk as synergizing with feedback is readily applicable to a variety of quorum sensing pathways that regulate important phenotypes in microbial communities.