CNLD Seminar with Yasa Baig (Stanford University)

Abstract: In Nature there are significant relationships known between

microorganisms from two kingdoms of life, as in the supply of vitamin B-

12 by bacteria to algae. Such interactions motivate general

investigations into the spatio-temporal dynamics of metabolite

exchanges. In this talk, I will discuss a recent study combining

experiment and theory of a model system: a coculture of the

bacterium B. subtilis an obligate aerobe that is chemotactic to oxygen,

and a nonmotile mutant of the alga C. reinhardtii which

photosynthetically produces oxygen when illuminated. Strikingly, when a

shaft of light illuminates a thin, initially uniform suspension of the two, the

chemotactic influx of bacteria to the photosynthetically active region

leads to expulsion of the algae from that area. We propose that this

effect arises from advection by the inhomogeneous bacterial

concentration. The resulting generalization of Fick's law has been

proposed in the context of chemotaxis, and is mathematically

related to the turbulent pumping in magnetohydrodynamics. Biologically,

our work highlights the rich dynamics which underly symbiosis in a simple model system on O(hour) time scales.

Physically, we highlight a striking un