Caging dynamics in bacterial colonies

In colonies, bacteria are often densely packed due to strong attractive forces between neighboring cells. For organisms where aggregation is mediated by type 4 pili interactions, the pilus-mediated motor activity fluidizes these but it unclear how close packaging affects bacterial motility. Here, we characterize dynamics of single cells over five orders magnitude in time. At short timescales, find pilus-driven ballistic dynamics, which depending on volume fraction cells, transitions caged or diffusive at intermediate timescales. Long-term dominated growth-induced radial motion overcoming caging high packings. Reducing interactions antibiotic treatment delays and introduces long-ranged collective motion.