A Sensory Pathway that Controls Bacterial Zorbing

Abstract

How cells transition between distinct modes of collective organization is a fundamental question in biology. We uncover the regulatory landscape governing the choice between bacterial swarming and zorbing. In Flavobacterium johnsoniae, zorbs are spherical, biofilm-like microcolonies that migrate collectively, whereas swarms are multilayered and ordered populations that expand planarly. We identify RgzAB, an unorthodox sensor kinase-response regulator pair governing this transition; suppressor and knockout mutants establish the importance of RgzA phosphorelay and RgzB as a downstream component. Transcriptomic and perturbation analyses link this switch to iron availability, connecting environmental sensing to collective behavior. Remarkably, RgzA activity also governs spatial organization within mixed populations: activated cells encapsulate wildtype neighbors into segregated co-zorbs, within which wildtype cells assemble into networks undergoing an abundance-dependent, percolation-like transition. Together, these findings reveal that one sensory circuit governs bacterial collectives at nested scales, from motility choice to the internal architecture of the collective.