From active matter to sustainable agriculture: how do beneficial bacteria use collective motility to colonise plant roots?

Beneficial bacteria play a major role in agriculture by recycling essential nutrients and safeguarding plants from disease. These positive interactions between plants and bacteria can be enhanced when motile bacteria actively navigate towards plant roots by sensing the compounds they secrete. This project will study bacteria from the genus Flavobacterium which are key regulators of plant health and inhibit plant pathogens. Strikingly, Flavobacterium have a unique mode of movement, propelling themselves along surfaces using gliding motility. At high cell densities, these soil bacteria actively self-organise to generate spectacular patterns of collective motility that allows them to spread much quicker than non-motile cells. We have observed Flavobacterium spontaneously form swirling, ring-shaped structures that each contain thousands of cells, generating what is known as "chiral active matter". However, we do not understand how individual Flavobacterium cells interact with one another in these collectives and existing theories of bacterial motility cannot explain this spectacular form of collective movement.
This project will develop new tools to shed light on the fundamental non-equilibrium physics that underlie this unique pattern formation and how the resultant collective motility facilitates the colonisation of plant roots. To accomplish this, this project will combine microfluidic devices, high-performance microscopy, automated cell tracking, and bacterial genetics to quantify how Flavobacterium modulates its movement in response to plant secretions. These experiments will expose cells to short pulses of compounds isolated from plant roots, allowing us to use machine learning to systematically explore how the behaviour of individual bacteria control the emergent dynamics of the collective. Deciphering the physical mechanisms bacteria use to colonise plant roots is fundamental to the development of bioinoculants and microbial interventions that...