Swarming Bacteria

Proteus mirabilis bacteria exhibit locust-like phase transitions at microscopic scale. At low density, cells swim independently through liquid. When surface colonization creates crowding, cells transform: they elongate dramatically, sprout hundreds of additional flagella, and begin coordinated surface swarming. The behavioral and morphological changes parallel locust gregarization—same genes, different expression triggered by density.

The swarming phase enables rapid surface colonization. Coordinated rafts of elongated cells move together across surfaces faster than individual swimming could achieve. The collective movement allows colonization of territories—including human tissues during infection—that swimming cells cannot reach. The density-triggered transformation is a competitive strategy: when enough cells gather, switch to the mode that exploits local dominance.

Quorum sensing mediates the transition. Bacteria release signaling molecules; when concentrations exceed thresholds indicating sufficient density, transformation triggers. This chemical voting system enables collective decisions without central coordination—each cell responds to aggregate signals, and synchronized transformation emerges from individual responses. The business parallel reveals that phase transition dynamics operate across scales. The same logic—density-triggered transformation, quorum sensing, threshold-dependent behavioral switching—appears in bacteria, insects, and potentially organizations. Companies may undergo cultural phase transitions when workforce density, communication intensity, or competitive pressure crosses thresholds, shifting collective behavior without any individual deciding to change.