They swim, they swarm, they twitch and glide…they even ride on comet tails, and now it seems that bacteria can ‘walk’ as Maxsim Gibiansky and colleagues demonstrate in their short but sweet research published in Science.
Gibiansky et al. studied the behaviour of Pseudomonas aeruginosa, a bacteria that is ordinarily found in soil and water, but has increasingly been associated with opportunistic infections in humans (and is a particular problem in those with cystic fibrosis). A key feature of P. aeruginosa is that these bacteria form multicellular, surface-bound communities called biofilms and are able to move within these communities by twitching motility owing to their type IV pili (hair-like structures on bacteria that can extend, tether to a surface and then retract to move bacteria along). The researchers studied microscopy movies of the P. aeruginosa biofilms and used computer software to track how the bacteria transitioned from planktonic state (that is, freely suspended in liquid) to the surface-bound biofilm.
Two different surface motility mechanisms were observed just after P. aeruginosa bacteria attached to a surface, but before a microcolony of bacteria were formed. The scientists studied mutant bacteria lacking flagella (a tail-like bacterial appendage that can also enable bacteria to move) that can only move using their type IV pili. These bacteria tended to ‘crawl’ in one direction when positioned horizontal to the surface and ‘walked’ in all directions when attached vertically to the surface by one end of the bacteria. Each movement mechanism was useful for surface exploration; crawling enabled directional movement across larger areas (6 μm distance) than walking, which enabled rapid exploration in local areas (up to 2 μm distance). Furthermore, these same movements were observed in wild-type bacteria. Moreover, the orientation of bacteria influenced biofilm morphology. Surface detachment was facilitated by type IV pili by tilting bacteria from horizontal to vertical positions and after bacterial division newborn bacteria detach and then ‘walk’ away. Finally, bacteria lacking type IV pili could neither ‘crawl’ or ‘walk’.
Scientific observations like this brevia report add to the understanding of bacterial behaviour in biofilms and could eventually lead to useful, new treatments against biofilm-forming pathogens.
Gibiansky, M., Conrad, J., Jin, F., Gordon, V., Motto, D., Mathewson, M., Stopka, W., Zelasko, D., Shrout, J., & Wong, G. (2010). Bacteria Use Type IV Pili to Walk Upright and Detach from Surfaces Science, 330 (6001), 197-197 DOI: 10.1126/science.1194238