title: Chemotaxis when bacteria remember: drift versus diffusion.
abstract: Escherichia coli (E. coli) bacteria govern their trajectories by switching between running and tumbling modes as a function of the nutrient concentration they experienced in the past. At short time one observes a drift of the bacterial population, while at long time one observes accumulation in high-nutrient regions. Recent work has viewed chemotaxis as a compromise between drift toward favorable regions and accumulation in favorable regions. A number of earlier studies assume that a bacterium resets its memory at tumbles - a fact not borne out by experiment - and make use of approximate coarse-grained descriptions. Here, we revisit the problem of chemotaxis without resorting to any memory resets. We find that when bacteria respond to the environment in a non-adaptive manner, chemotaxis is generally dominated by diffusion, whereas when bacteria respond in an adaptive manner, chemotaxis is dominated by a bias in the motion. In the adaptive case, favorable drift occurs together with favorable accumulation. We derive our results from detailed simulations and a variety of analytical arguments. In particular, we introduce a new coarse-grained description of chemotaxis as biased diffusion, and we discuss the way it departs from older coarse-grained descriptions.
authors.affiliation: Department of Physics, Technion, Haifa, Israel. sakuntala@physics.technion.ac.il
authors.forename: Sakuntala
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Rava Azeredo
authors.initials: RA
authors.lastname: da Silveira
authors.forename: Yariv
authors.initials: Y
authors.lastname: Kafri
mesh_terms: D000465:Algorithms; D018407:Bacterial Physiological Phenomena; D002633:Chemotaxis / Q000502:physiology*; D019295:Computational Biology; D003198:Computer Simulation; D004058:Diffusion; D004926:Escherichia coli / Q000502:physiology*; D008954:Models, Biological