Microinterface-dependent defense of algae against nanoparticles: two-layered barriers involving exopolymers and cell...

Silver nanoparticles (AgNPs) are widely used as antimicrobial agents and detected in wastewater streams. Residual AgNPs may pose a potential threat to primary producers such as microalgae. In this study, we demonstrated that algae Chlamydomonas reinhardtii employed a two-layer microinterface barrier composed of extracellular polymeric substances (EPS) and the cell wall, which cooperatively governed nanoparticle adsorption, dissolution, and intracellular transport. In particular, EPS functioned as the primary defense by reducing the intracellular Ag accumulation by 39.1%, likely via surface adsorption and extracellular immobilization. The cell wall then served as a secondary physical barrier, reducing the total Ag uptake flux to approximately 26.7% of that observed in the wild-type cells. Mechanistic studies further indicated that EPS deficiency predominantly promoted enhanced influx by facilitating contact with AgNPs, whereas cell wall deficiency facilitated Ag ion entry by competitive interaction with copper transport pathways. Importantly, the double-deficient exhibited the highest Ag influx rate (3.0 × 10^-8 amol cm^-2 h^-1), representing a twofold increase relative to the wild type, alongside pronounced oxidative stress and significant suppression of photosynthetic activity. These mechanistic insights enabled the design of biofilm-based materials that efficiently immobilize and detoxify nanoparticles.