The acquisition of additional feedback loops may optimize and speed up the response of quorum sensing

Abstract

Bacterial quorum sensing (QS) is a cell-to-cell communication system in which specific signals are activated to coordinate, for example, pathogenic behaviors and help bacteria collectively respond to perturbations. QS in Gram-negative bacteria is typically regulated by a N-acyl-homoserine lactone (AHL) molecules-mediated system, homologous of Vibrio fischeri LuxI-R. In many cases, bacteria possess more than one QS system, based on different types of molecules, that interact through a complex regulatory network. Presumably, these configurations have emerged over time from simpler ones through the acquisition of novel players (e.g. transcription factors) that have been successfully integrated into the native regulatory systems. However, the advantages provided by these alternative/additional configurations on QS-related phenotypes is poorly predictable only based on their underlying network structure. Here, we have adopted a modelling approach to infer the possible improvements conferred by the acquisition of additional control over bacterial regulation of QS. We use the Burkholderia genus as a case study because some of these strains, besides the LuxIR-like system (named CepIR), possess an integrated regulatory module named CciIR that interferes with the CepIR system through the implementation of several positive and negative control loops. Being associated to a genomic island (cci island), this additional module is prone to being horizontally transferred, giving rise to a potentially patchy genomic distribution and, in turn, to a complete (CepIR and CciIR systems together) vs. core (CepIR only) organization of QS regulation in this group of microorganisms. By using both deterministic and stochastic modelling we show that, upon their activation, the two regulatory schemes may lead to different phenotypes and to distinct responses to the extracellular concentration of signalling molecules. In particular, our simulations show that the presence of the additional regulatory module may confer specific improvements, including a faster response time and optimized control of QS regulation. Interestingly, some of these features may be particularly advantageous during host invasion, thus highlighting once more the importance of QS in the establishment and maintenance of bacterial infections.