Laboratoire Matière et Systèmes Complexes

Slowdown of diffusive dynamics of cyanobacterium Synechocystis sp. PCC 6803: adaptation to solid surface

Thomas Vourc’h (Laboratoire APC, Paris 7).

Figure

Cyanobacteria are photosynthetic micro-organisms that colonize aquatic and terrestrial surfaces by developing biofilms. This process proceeds by (i) transport of micro-organism towards the surface, (ii) interaction with the surface and (iii) interaction between the micro-organisms. We investigate the initial stages of colonization of the cyanobacterium Synechocystis sp. PCC 6803 as a model micro-organism, by studying the surface dynamics that result from a coupling between sedimentation and surface diffusion. Time-lapse video microscopy is used to measure both transport towards the surface via the sedimentation rate, and the surface interaction via the mean-squared displacement (MSD) and the distribution function of displacement probabilities.

We have found that the motility of Synechocystis sp. PCC 6803 is an intermittent phenomenon: high-motility “run” periods are separated by low-motility “tumble” periods corresponding to trapped states. However, this intermittent motility leads to a Fickian diffusive behavior, as shown by the time evolution of the MSD. The diffusion coefficient decreases with time due to a modification of the run time. Numerical simulations as well as dimensional analysis support this scenario. Finally, we find that this slow-down of the diffusion dynamics depends on the surface on which diffusion occurs; this gives a hint on the mechanisms (based on a microscopic argument) by which cyanobacteria colonize a given environment.

Jeudi 27 avril à 17h45 en salle 646A.