Bacterial rheotaxis

Abstract

The motility of organisms is often directed in response to environmental stimuli. Rheotaxis is the directed movement resulting from fluid velocity gradients, long studied in fish, aquatic invertebrates, and spermatozoa. Using carefully controlled microfluidic flows, we show that rheotaxis also occurs in bacteria. Excellent quantitative agreement between experiments with Bacillus subtilis and a mathematical model reveals that bacterial rheotaxis is a purely physical phenomenon, in contrast to fish rheotaxis but in the same way as sperm rheotaxis. This previously unrecognized bacterial taxis results from a subtle interplay between velocity gradients and the helical shape of flagella, which together generate a torque that alters a bacterium's swimming direction. Because this torque is independent of the presence of a nearby surface, bacterial rheotaxis is not limited to the immediate neighborhood of liquid-solid interfaces, but also takes place in the bulk fluid. We predict that rheotaxis occurs in a wide range of bacterial habitats, from the natural environment to the human body, and can interfere with chemotaxis, suggesting that the fitness benefit conferred by bacterial motility may be sharply reduced in some hydrodynamic conditions. low Reynolds number | directional motion | chirality T he effectiveness and benefit of motility are largely determined by the dependence of movement behavior on environmental stimuli. For example, chemical stimuli may affect the spreading of tumor cells (1) and allow bacteria to increase uptake by swimming toward larger nutrient concentrations (2, 3), whereas hydrodynamic stimuli can stifle phytoplankton migration (4), allow protists to evade predators (5), and change sperm-egg encounter rates for external fertilizers (6). Microorganisms exhibit a broad range of directed movement responses, called "taxes". Whereas some of these responses, such as chemotaxis (7) and thermotaxis (8), are active and require the ability to sense and respond to the stimulus, others, such as magnetotaxis (9) and gyrotaxis (4), are passive and do not imply sensing, instead resulting purely from external forces.Chemotaxis is the best studied among these directional motions: Bacteria measure chemical concentrations and migrate along gradients (Fig. 1A). For instance, chemotaxis guides Escherichia coli to epithelial cells in the human gastrointestinal tract, favoring infection (10); Rhizobium bacteria to legume root hairs in soil, favoring nitrogen fixation (2); and marine bacteria to organic matter, favoring remineralization (3). Equally as pervasive as chemical gradients in microbial habitats are gradients in ambient fluid velocity or "shear" (Fig. 1B). Although nearly every fluid environment experiences velocity gradientsfrom laminar shear in bodily conduits and soil to turbulent shear in streams and oceans-the effect of velocity gradients on bacterial motility has received negligible attention compared with chemical gradients, partly due to the difficulty of studying motility under controlled flow conditi...

Propensity of undulatory swimmers, such as worms, to go against the flow

“…Rheotaxis has been observed in organisms as simple as single motile cells such as bacteria (7,(29)(30)(31)(32) and sperm (6,33,34), where hydrodynamics is implicated as the cause of rheotactic behavior (29)(30)(31)(32)(33)(34). In contrast, in the case of zebrafish, a vertebrate, an active response of the animal that involves its sensory nervous system is believed to influence the rheotactic behavior (8).…”

Batchelor Prize Lecture Fluid dynamics at the scale of the cell

“…Results of this type can be used to design microfluidic devices that can rectify swimmers' motion in interesting ways I close this section by noting that the strong interaction of swimming microorganisms with surfaces is thought to underlie the process of rheotaxis, in which they swim upstream against a bulk flow. Of particular interest recently has been bacterial rheotaxis (Marcos et al 2012), where the chirality of the helical flagella plays an important role in reorientation of cells along the walls bounding the flow. Analogous phenomena have been seen in sperm rheotaxis .…”

Modelling the dispersal of riverine fish larvae: from a raster-based analysis of movement patterns within a racetrack flume to a rheoreaction-based correlated random walk (RCRW) model approach

“…Models of larval fish dispersal patterns within riverine ecosystems are rare (e.g., Wolter and Sukhodolov 2008;Korman et al 2004;Cowan et al 1993). However, models that include rheoreaction have been developed for several organisms and their larval developmental stages (Marcos et al 2012;Mork et al 2012;Booker et al 2008). Kingsford et al (2002) recommended obtaining high-resolution spatial information on navigation, at scales of less than 1 m, before implementation into models of larval fish dispersal (from metres to kilometres).…”