Hydrodynamic flow and concentration gradients in the gut enhance neutral bacterial diversity (Darka Labavic / LPT / seminar). – 23/11, 14 H.

Darka Labavic (Laboratoire Jean Perrin) – en visio

In humans, the digestive tract contains the majority if the microbiota which is essential for the health of an individual. The digestive tract itself, is a complex system from a point of view of geometry, fluid mechanics, population dynamics, and biodiversity. In this work, we propose a minimal model of evolution of bacteria in the gut. Because most bacteria in the human digestive tract are located in the bulk of the colon lumen, we focus on this compartment. Since most bacteria in the digestive tract have no self-motility, we consider that they are carried passively with the digesta. The motion of the digesta is complex, but it can be approximated as a one-dimensional flow with net velocity and effective diffusion representing mixing. Within this model of the gut that includes hydrodynamic flow and resulting gradients of food and bacterial concentrations, we ask how the fixation probability of a neutral mutant compares with that in an equivalent well-mixed chemostat. We find that the structure of the gut can increase this fixation probability, specifically in the regime where the profiles of food and bacterial concentration are strongly spatially-dependent. In this regime, fixation probability becomes independent of total population size, in stark contrast with a well-mixed population, where fixation probability is inversely proportional to total population size. We show that this behavior can be understood by introducing the notion of active population, which corresponds to the fraction of the bacterial population that is actively consuming food and dividing.