Movement of bacteria in the soil and the rhizosphere.

The soil and the rhizosphere are physicochemically heterogeneous environments that host diverse macro- and micro-organisms that together influence soil productivity. The ability of organisms to disperse in these environments allows them to exploit resources and to occupy niches that support growth and protect them from predation and stressful conditions. The dispersal of soil macroorganisms has been much better characterized than that of bacteria because of the complexity and physicochemical heterogeneity of the soil and the rhizosphere, and challenges in quantifying the dispersion of bacteria in these environments. However, even limited bacterial dispersal in soils and the rhizosphere could have the potential to alter the local microbiome composition and its function. Active bacterial movement includes swimming and swarming using flagella, twitching motility using pili, as well as emerging forms of motility that result from microbe-microbe interactions. Passive transport of bacteria throughout the soil may be mediated by passive physical factors such as rainfalls, as well as through transport mediated by protists, nematodes, or hitchhiking using other microbes' appendages. This minireview focuses on the modes of bacterial movement in the soil and the rhizosphere that do not depend on passive physical factors (e.g., rainfalls) and identifies areas of future research.