Escherichia coli sister cells dynamically organize developmental rosettes

Rosettes are self-organizing, circular multicellular communities that initiate developmental processes, like organogenesis and embryogenesis, in complex organisms. Their formation results from the active repositioning of adhered sister cells and is thought to distinguish multicellular organisms form unicellular ones. Though common in eukaryotes, this multicellular behavior has not been reported in bacteria. In this study, we discovered that Escherichia coli forms rosettes by active sister cell repositioning. After division, sister cells "fold" to actively align at the 2- and 4-cell stages of clonal division, thereby producing rosettes with characteristic quatrefoil configuration. Analysis revealed folding follows an angular random walk, comprised of [~]1-{micro}m strokes and directional randomization. We further showed that this motion was produced by the flagellum, the extracellular tail whose rotation generates swimming motility. Rosette formation was found to require de novo flagella synthesis suggesting it must balance the opposing forces of Ag43 adhesion and flagellar propulsion. We went on to show that proper rosette formation was developmentally required for subsequent morphogenesis of multicellular chains, rpoS expression, and formation of hydrostatic clonal-chain biofilms. Moreover, we discovered self-folding rosette-like communities in the standard motility assay, indicating this behavior may be general to hydrostatic environments. This study establishes that self-organization of developmental rosettes is a cross-kingdom multicellular behavior. Our findings indicate the potential of targeting bacterial rosettes to interrupt biofilms or reduce their antibiotic tolerance.