Prof Ramin Golestanian

Abstract:

Motivated by the implications of the complex and dynamic modular geometry of an enzyme on its motion, we investigate the effect of combining long-range internal and external hydrodynamic interactions due to thermal fluctuations with short-range surface interactions. An asymmetric dumbbell consisting of two unequal subunits, in a nonuniform suspension of a solute with which it interacts via hydrodynamic interactions as well as non-contact surface interactions, is shown to have two alignment mechanisms due to the two types of interactions. In addition to alignment, the chemical gradient results in a drift velocity that is modified by hydrodynamic interactions between the constituents of the enzyme.

Abstract:

Despite possessing the machinery to sense, adhere to, and proliferate on surfaces, it is commonly observed that bacteria initially have a difficult time attaching to a surface. Before forming a bacterial biofilm, planktonic bacteria exhibit a random period of transient surface attachment known as “reversible attachment” which is poorly understood. Using community tracking methods at single-cell resolution, we examine how reversible attachment progresses during initial stages of surface sensing. Pseudomonas aeruginosa strains PAO1 and PA14, which exhibit similar exponential trends of surface cell population increase, show unanticipated differences when the behavior of each cell was considered at the full lineage level and interpreted using the unifying quantitative framework of an exactly solvable stochastic model. Reversible attachment comprises two regimes of behavior, processive and nonprocessive, corresponding to whether cells of the lineage stay on the surface long enough to divide, or not, before detaching. Stark differences between PAO1 and PA14 in the processive regime of reversible attachment suggest the existence of two complementary surface colonization strategies, which are roughly analogous to “immediate-” vs “deferred-gratification” in a prototypical cognitive-affective processing system. PAO1 lineages commit relatively quickly to a surface compared to PA14 lineages. PA14 lineages allow detaching cells to retain memory of the surface so that they are primed for improved subsequent surface attachment. In fact, it is possible to identify motility suppression events in PA14 lineages in the process of surface commitment. We hypothesize that these contrasting strategies are rooted in downstream differences between Wsp-based and Pil-Chp-based surface sensing systems.