Mechanical determinants of bacterial collective behavior: from active turbulence to early biofilm organization

During early colonization, motile bacteria can shift from independent swimming to coordinated collective states shaped by environmental mechanics, with consequences for subsequent biofilm development and tolerance. This critical review integrates active matter physics with biofilm microbiology to evaluate a working model in which viscoelasticity, mechanotransduction, and geometric confinement form a synergistic triad of mechanical determinants that may bias communities toward tolerant states before matrix immobilization dominates. Community mechanics remains underexplored because established non-genetic mechanisms explain only part of the striking gap between planktonic killing and biofilm tolerance. Within this model, viscoelasticity of host fluids and nascent matrix, captured by an effective Deborah number, may extend hydrodynamic coupling between cells. Surface mechanotransduction can convert flagellar or pilus load into rapid cyclic di-GMP signaling, while geometric confinement in tissues and device lumens can restrict collective states available to bacteria. Together, these factors motivate testable links among viscoelasticity, bacterial density, and velocity correlation length. Current evidence derives mainly from simplified in vitro systems, and validation in three-dimensional polymicrobial clinical materials remains limited. The review highlights priorities and translational hypotheses, including motion phenotyping, rheology-modifying adjuvants, and geometry-based disruption as complements to antimicrobial therapy.