Community context redirects evolutionary trajectories under stress.

Adaptation to abiotic stress is typically studied in single-species cultures, yet bacteria inhabit and evolve in multispecies communities where neighboring organisms reshape, for example, nutrient availability, redox state, and cellular physiology. We recently demonstrated that interspecies interactions can alter the fitness effects of antibiotic resistance mutations, and we suggest that this reflects a broader principle. Stress-response networks are extensively cross-regulated and draw upon a shared, finite pool of proteomic and energetic resources. Consequently, activation of one pathway constrains others, creating physiological trade-offs. Because microbial interactions routinely perturb the physiological inputs to these networks, they can systematically redirect evolutionary trajectories under abiotic stress. We discuss the evidence, limitations, and implications of this framework for predicting evolution and understanding microbiome stability.