Defend or divert: Reactive oxygen species signaling drives opposite EPS strategies in marine bacteria under nanoplastic stress.

Nanoplastic pollution represents a pervasive threat to marine ecosystems, yet the molecular mechanisms governing microbial adaptation remain elusive. This study reveals how reactive oxygen species (ROS) signaling drives opposite extracellular polymeric substance (EPS) strategies in marine bacteria under NP stress. Pseudomonas aeruginosa enacts a proactive defend strategy, increasing EPS secretion by 6.66%-53.17%. Driven by a ROS surge, it allocates resources to EPS precursors and maintains transcriptional homeostasis through global fine-tuning to secure protein homeostasis and energy stability. Conversely, Bacillus subtilis undergoes a rapid metabolic divert response, causing a persistent EPS inhibition of 18.49%-27.31%. By systematically redirecting carbon and nitrogen fluxes away from EPS production through the downregulation of precursor-supplying pathways, this strain diverts energy and metabolic precursors toward emergency survival pathways such as membrane homeostasis maintenance, cellular stress protection, and sporulation. Our defend or divert framework provides a mechanistic paradigm for assessing how emerging contaminants dictate cellular resource allocation and reshape the ecological trajectory of marine microbial communities.