Effects of silver sulfide nanoparticles on the microbial community structure and biological activity of freshwater biofilms†
Ensuring the safety of silver sulfide nanoparticles (Ag2S NPs) is essential for their application in various fields. Here, we explored changes in the microbial community composition and biological activity of freshwater biofilms treated with Ag2S NPs (0.2, 1, and 5 mg L−1) for 5 days. Our results indicated that the Ag2S NPs significantly changed the physiological properties of the biofilms to different extents, e.g., increasing the amount of extracellular polymeric substances, enhancing the activity of antioxidant systems, and decreasing algal biomass. The microbial community structure was obviously changed; the predominant bacteria Phormidium dramatically decreased while Flavobacterium became the dominant genus, exhibiting different levels of resistance and tolerance for Ag2S NPs. Moreover, changes in the functional capacities of biofilms, including photosynthesis potential and functional extracellular enzymes related to nutrient cycling, varied after Ag2S NP exposure in a concentration-dependent manner. Our findings suggested that the harmful effects of Ag2S NPs on aquatic ecosystems should be considered carefully.