Turbulent mixing controls fixation of growing antagonisticpopulations

Unlike coffee and cream that homogenize when stirred, growing micro-organisms(e.g., bacteria, baker's yeast) can actively kill each other and avoid mixing. How dosuch antagonistic interactions impact the growth and survival of competing strains,while being spatially advected by turbulent flows? By using numerical simulations of acontinuum model, we study the dynamics of two antagonistic strains that are dispersedby incompressible turbulent flows in two spatial dimensions. A key parameter is theratio of the fluid transport time to that of biological reproduction, which determinesthe winning organism that ultimately takes over the whole population from an initialheterogeneous state, a process known as fixation. By quantifying the probability andmean time for fixation along with the spatial structure of concentration fluctuations,we demonstrate how turbulence raises the threshold for biological nucleation andantagonism suppresses flow-induced mixing by depleting the population at interfaces.Our work highlights the unusual biological consequences of the interplay of turbulentfluid flows with antagonistic population dynamics, with potential implications formarine microbial ecology and origins of biological chirality.