Barriers to bacterial motility on unsaturated surfaces

Our knowledge of the spatial organization and spatial dynamics of microbial populations in soil at a scale close to that of the microorganisms is scarce. While passive dispersal via water ow or soil biota is probably a major dispersal route, it is reasonable to consider that active dispersal also contributes to microbial spatial dynamics.

In bacteria, active dispersal is enabled by a diversity of appendages and, in the case of swarming motility, by the secretion of surface active biomolecules. It is however unclear to which degree di_erent types of motility can take place in the soil pores, a habitat characterized by complex 3D geometry and variable hydration.

To approach these questions we take advantage of the Porous Surface Model (PSM) a unique experimental platform that allows direct monitoring of microbial motion under precisely controlled matric potential. Using gfp-tagged Pseudomonas strains and their isogenic mutants unable to express various type of motility we aimed to quantify the physical limits of bacterial motility.

Our results demonstrate how hydration controls bacterial motility under unsaturated conditions. They can form the base of improved biodegradation models that include microbial dispersal processes.