Social Behavior Optimizes Bacterial Swarming

When: Tuesday, June 11, 2013 at 4:00 pm
Where: DA 114
Speaker: Mark Alber
Organization: University of Notre Dame, Interdisciplinary Center for the Study of Biocomplexity, Departments of Applied and Computational Mathematics and Statistics and Physics
Sponsor: Physics Colloquium

“Treatment of a broad spectrum of human health issues, ranging from lethal infections from opportunistic pathogens such as those in cystic fibrosis patients, to catastrophic failure of prosthetic implants, could improve with a greater understanding of biofilm formation. Among the biofilm development steps for which we lack understanding is the ability of bacteria to first colonize host surfaces. Bacterial swarming motility has been shown to be crucial to biofilm formation. Many bacteria can rapidly traverse surfaces from which they are extracting nutrient for growth by generating flat, spreading colonies, called swarms because they resemble swarms of insects. M. xanthus are common soil bacteria that are among the most “social” bacteria in nature. In addition, cells undergo regular directional reversals [1]. In this talk swarming mechanism of M. xanthus will be described using combination of experimental movies obtained using a novel high-resolution, time-lapse microscopy approach and model simulations. It will be demonstrated how cell mixing and propagation of information through cell-cell contact could be affected by the physical and behavioral properties of the individual cells. The most striking finding is that the population has the maximum level of mixing when cells reverse direction every 5-7 minutes which is consistent with the reversal period observed in experiments.

In the second half of the talk, population of bacteria P. aeruginosa, main infection in hospitals, will be shown to propagate as high density waves that move symmetrically as rings within swarms towards the extending tendrils. Biologically-justified cell-based multi-scale model simulations suggest a mechanism of wave propagation as well as branched tendril formation at the edge of the population that depend upon competition between the changing viscosity of the bacterial liquid suspension and the liquid film boundary expansion caused by Marangoni forces [2]. P. aeruginosa efficiently colonizes surfaces by controlling the physical forces responsible for expansion of thin liquid films and by propagating towards the tendril tips. Therefore, P. aeruginosa can efficiently colonize surfaces by controlling the physical forces responsible for expansion of thin liquid films and by propagating towards the tendril tips. The model predictions of wave speed and swarm expansion rate as well as cell alignment in tendrils were confirmed experimentally.”

1. Wu, Y., Jiang, Y., Kaiser, D., and M. Alber [2009], Periodic reversal of direction allows Myxobacteria to swarm, Proc. Natl. Acad. Sci. USA 106 4 1222-1227 (featured in the Nature News, January 20th, 2009, doi:10.1038/news.2009.43).

2. Du, H., Xu, Z., Anyan, M., Kim, O., Leevy , W. M., Shrout, J.D., and M. Alber [2012], High density waves of the bacterium Pseudomonas aeruginosa in propagating swarms result in efficient colonization of surfaces, Biophysical Journal 103(3), 601-609.