A fundamental problem of cell biology is to understand how cells make measurements and then make behavioral decisions in response to these measurements. The full answer to this question is not known but there are some underlying principles that are coming to light. The short answer is that the rate of molecular diffusion contains quantifiable information that can be transduced by biochemical feedback to give control over physical structures.
In this talk, this principle will be illustrated by two specific examples of how rates of molecular diffusion contain information that is used to make a measurement and a behavioral decision.
Example 1: Bacterial populations of P. aeruginosa are known to make a decision to secrete polymer gel on the basis of the size of the colony in whch they live. This process is called quorum sensing and only recently has the mechanism for this been sorted out. It is now known that P. aeruginosa produces a chemical whose rate of diffusion out of the cell provides information about the size of the colony which when coupled with positive feedback gives rise to a hysteretic biochemical switch.
Example 2: Salmonella employ a mechanism that combines molecular
diffusion with a negative feedback chemical network to "know" how long
its flagella are. As a result, if a flagellum is cut off, it will
be regrown at the same rate at which it grew initially.
Microorganisms such as bacteria and spermatozoa move in a world where viscous forces completely dominate inertial forces, and the time evolution of their motion may be thought of as a sequence of steady state snapshots. In this world, what motility strategies give rise to efficient locomotion? The study of the fluid dynamics of microorganism motility began with the classic work of G.I. Taylor in 1951, and has been an active area of research in the last decades. Current modelling challenges include the collective dynamics of microorganisms and their interactions with surrounding physical and chemical environments, coupling of their internal force-generating mechanisms with external fluid dynamics, as well as their motion through viscoelastic fluids. We will present recent work that sheds light on these complex systems.
Understanding swimming at low Reynolds numbers: successes and challenges
Lisa Fauci - Tulane University