The Role of Adhesins in Bacterial Motility Modification

Bacterial biofilms are structured multicellular communities responsible for a broad range of infections. The initial stages of biofilm formation requires free-swimming bacteria to attach to surfaces and eventually become pinned or trapped, yet the mechanisms by which this occurs are unknown. To investigate the early-stage formation of biofilms, we have developed high-throughput techniques to quantify the motility of surface-associated bacteria. We translate microscopy movies of Pseudomonas aeruginosa bacteria into a searchable database of trajectories using tracking algorithms adapted from colloidal physics. By analyzing the motion of both wild-type and isogenic knockout mutants, we have characterized four fundamental motility mechanisms in P. aeruginosa. Here, we develop biometric routines to recognize signatures of adhesion and trapping. We find that newly attached bacteria move faster than previously adherent bacteria, and are more likely to be oriented out-of-plane. In addition, motility appendages influence the bacterium's ability to become trapped: wild-type bacteria exhibit two types of trapped trajectories, whereas flagella-deficient bacteria rarely become trapped. These results suggest that the flagella play a key role in P. aeruginosa adhesion.