Flow Is Ubiquitous In Bacterial Habitats.pdf

Microbes often live in moving fluids, and fluid flow has significant implications for microbial ecology and environmental microbiology. Despite this, the physical effects of flow on microorganisms have only recently been systematically studied using tools and frameworks from fluid physics. This research field has produced important contributions to understanding the physical interaction between microbes and flow, revealing the complexity of the resulting dynamics. Fluid flow is a ubiquitous feature of microbial habitats, and microbes in various environments, including marine, aquatic, soil, and human and animal bodies, are exposed to turbulence, laminar flow, or other types of flow. Shear, or gradients in fluid velocity, is a key mechanical feature of fluid flow that affects microorganisms, causing torques that influence their behavior, including motility, chemotaxis, and nutrient uptake. The effects of flow on individual cells in dilute suspensions, both in bulk and near surfaces, are significant, with flow-induced rotations affecting microorganisms' direction of motion and ability to disperse, seek nutrients, or reach surfaces. Elongated microorganisms, in particular, spend most of their time aligned with the flow direction, flipping orientation periodically, which can have important ecological consequences. Mathematical models and experimental studies have been used to investigate the trajectories of microorganisms in flow, including the trapping of bacteria by shear and the effects of geometrical properties, such as cell shape and flagella chirality, on their dynamics.