Advantages of run-reverse motility pattern of bacteria for tracking light and small food sources in dynamic fluid environments.

Marine bacteria are fundamental to the processes and cycles that sustain ocean ecosystems. Their activity at small scales, where they search for food sources in a highly heterogeneous and dynamic environment, for example controls the decomposition of organic matter. To be effective, these microorganisms have evolved sophisticated behaviours, which include extremely rapid swimming speeds, a precise chemosensing ability and particular swimming patterns. One of these peculiar motility patterns often recorded in the ocean is run-reverse (Mitchell et al 1996 Clustering of marine bacteria in seawater enrichments. Appl. Environ. Microbiol. 62, 3716-3721. (doi:10.1128/aem.62.10.3716-3721.1996), Stocker R. 2011 Reverse and flick: hybrid locomotion in bacteria. Proc. Natl Acad. Sci. USA 108, 2635-2636. (doi:10.1073/pnas.1019199108), where bacteria alternate between forward (pushing) and backwards (pulling) swimming modes. In this study, we investigate whether this swimming pattern offers advantages to microorganisms that actively track small and light food sources carried by a dynamic flow. For that we develop an individual-based model, where elongated self-propelled particles (microswimmers) track passive food particles (tracers) in a random kinematic flow field, also known as synthetic turbulent flow. We compare the widely studied motility pattern of run-and-tumble with the run-reverse mode used by marine bacteria. Our results reveal a significant hydrodynamic advantage of the run-reverse motility pattern of bacteria combined with their elongated shapes for efficiently tracking light food sources in dynamic fluid environments.