Adaptive significance of quorum sensing-dependent regulation of public goods by integration of growth rate: a trade-off between survival and efficiency

Quorum sensing (QS) is a mechanism of communication used by bacteria to monitor cell density and coordinate cooperative behaviors. An emerging framework is that the adaptive significance of QS in regulation of production of costly extracellular metabolites (public goods) is to maintain the homeostasis of cooperation. We investigated the functionality of QS-dependent regulation of rhamnolipids, extracellular surface-active glycolipids promoting the social swarming motility behavior, in Burkholderia glumae and found that QS is superfluous under rich nutritional conditions. In contrast, decreasing nutrient concentrations to reduce the growth rate amplifies rhamnolipid biosynthesis gene expression, revealing a system where QS-dependent regulation is triggered by the growth rate of the population rather than by its cell density. Our results provide evidence that the adaptive significance of QS in regulation of public goods is to maintain an optimized demand-driven supply of target cooperative behavior, wherein efficiency can be traded off against survival.