ABSTRACTThe formation of biofilm at the air-liquid interface of a still flask is related to the emergence of exopolysaccharides (EPS) overproducers. These mutants have the ability to remain near the surface, where oxygen is abundant. Yet, it is still unclear what role oxygen plays in cellular metabolism under this condition. A. Besse, M.-C. Groleau and E. Déziel (mSphere e00057-23, 2023;https://doi.org/10.1128/msphere.00057-23) explains that the redox state of cells is key in understanding the emergence of EPS overproducers. They found that the spatial distribution of oxidizing agent (not oxygen specifically) controls the advantage of remaining near the air-liquid interface, and hence the advantage that EPS-overproduction confers. All together this research paves the way for a deeper comprehension of the relationship between the environment's spatial structure and population dynamics.