Collective movement by soil bacteria during the colonisation of the rhizosphere

<p>Migrations are essential for soil microorganisms to exploit scarce and heterogeneously distributed resources in the rhizosphere, but mobility in soil remains poorly studied due to experimental limitations. In this study, time-lapse images collected using live microscopy techniques captured collective and coordinated groups of <em>B. subtilis</em> cells exhibiting &#8220;crowd movement&#8221; during rhizosphere colonisation. Groups of <em>B. subtilis</em> cells moved through transparent soil toward plant roots and re-arranged dynamically around root tips in the form of elongating and retracting &#8220;flocks&#8221; resembling collective behaviour usually associated with higher organisms (e.g., bird flocks or fish schools). These <em>B. subtilis</em> flocks are likely driven by the diffusion of extracellular signalling molecules (e.g., chemotaxis and quorum sensing) and may be impacted by the physical properties of the environment. Our findings advance the understanding of bacterial migration through soil matrices and expand known behaviours for coordinated bacterial movement.</p><p>&#160;</p>