Hydrodynamic flow in the gut hinders the fixation of beneficial mutants but accelerates their invasion

Hydrodynamic flow in the gut reduces the fixation probability of beneficial mutants arising randomly upon division compared with a well-mixed case, with suppression set by spatial heterogeneity of mutant fate.

• Why it matters: Gut bacteria live in a spatially structured, flowing environment, yet how hydrodynamics reshapes both fixation and invasion of beneficial mutants is unclear.
• What they did: Using a branching-process framework, the authors compared mutant outcomes in a gut-like spatial setting versus a matched well-mixed model, varying advective flow strength.
• The result: Hydrodynamic flow suppresses fixation and simultaneously accelerates invasion of mutant lineages that avoid early stochastic extinction; stronger advective flow further decreases fixation probabilities while increasing invasion.

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