Emergent robustness of bacterial quorum sensing in fluid flow

Bacteria use intercellular signaling, or quorum sensing (QS), to
share information and respond collectively to aspects of their
surroundings. The autoinducers that carry this information are
exposed to the external environment; consequently, they are
affected by factors such as removal through fluid flow, a ubiquitous feature of bacterial habitats ranging from the gut and
lungs to lakes and oceans. To understand how QS genetic architectures in cells promote appropriate population-level phenotypes
throughout the bacterial life cycle requires knowledge of how
these architectures determine the QS response in realistic spatiotemporally varying flow conditions. Here we develop and
apply a general theory that identifies and quantifies the conditions required for QS activation in fluid flow by systematically
linking cell- and population-level genetic and physical processes.
We predict that when a subset of the population meets these conditions, cell-level positive feedback promotes a robust collective
response by overcoming flow-induced autoinducer concentration
gradients. By accounting for a dynamic flow in our theory, we
predict that positive feedback in cells acts as a low-pass filter at
the population level in oscillatory flow, allowing a population to
respond only to changes in flow that occur over slow enough
timescales. Our theory is readily extendable and provides a framework for assessing the functional roles of diverse QS network
architectures in realistic flow conditions.