Quantifying Bacterial Crowd Surfing in Pseudomonas aeruginosa
Type IV pili (T4P) are adhesive protein filaments that can be extended and retracted by certain classes of Gram-negative bacteria. The motion of bacteria on surfaces by T4P is referred to as twitching motility, and it has been shown that this leads to complex, collective motion of large numbers of cells. We have observed that twitching cells of P. aeruginosa PAO1 could transport inert micrometre-sized objects (“crowd surfing”). Crowd surfing also extends to non-motile bacterial cells, and can lead to the transport of pathogenic bacterial cells, with direct implications for the spread of bacterial infections. We have designed and constructed a custom-built environmental chamber to quantify this phenomenon under precisely controlled environmental conditions. We found that the twitching bacterial cells drive the motion of the microspheres with a well-defined average speed, and that the directionality of their motion remains highly correlated for the largest time scales observed in the experiments.