Spatio-temporal dynamics of nutrient exchanges in microbial active matter

Microorganisms inhabit highly fluctuating environments and survive in a low-nutrient resource bath. It is now well recognized that symbiotic relationships between microbes play a vital role in their survival. The existence of such interaction raises general questions about the spatio-temporal dynamics of nutrient exchanges. Here we experimentally and theoretically examine a model system of this problem – bacteria, an obligate microbe capable of chemotactic response towards oxygen, in a co-culture with green algae, which produce oxygen when illuminated. Even in their simplest arrangement in a localized illuminated domain, we find a complex dynamics involving nutrient exchanges, enhanced algal diffusivity due to the bacteria, and a stochastic version of “flux expulsion”.