[en] Highlights: • Periphyton had sustainable pollutant removal capacity despite toxic effects of TiO₂-NPs. • Community and metabolism changes are critical in maintaining functional sustainability. • EPS especially protein was overproduced to bind or aggregate NPs to reduce nanotoxicity. • Exposure duration is important for evaluating nanotoxicity on microbial community. -- Abstract: Responses of microbial communities to nanotoxicity in aquatic ecosystems are largely unknown, particularly with respect to relationship between community dynamics and functions. Here, periphytic biofilms were selected as a model of species-rich microbial communities to elucidate their responses when exposed to titanium dioxide nanoparticles (TiO₂-NPs). Especially, the relationships between the functions (e.g. organic matter and Cu²⁺ removal) and community dynamics after long-term exposure to TiO₂-NPs were assessed systematically. After 5 days exposure to TiO₂-NPs (5 mg L⁻¹), periphytic biofilms showed sustainable functions in pollutant removal and strong plasticity in defensing the toxic disturbance of TiO₂-NPs, including photosynthesis and carbon metabolic diversity. The sustainable pollutant removal functions of periphytic biofilms were attributed to their functional redundancy. Specifically, periphytic biofilms altered their composition with cyanobacteria, Sphingobacteriia and Spirochaetes being the newly dominant taxa, and changed the carbon substrate utilization pattern to maintain high photosynthesis and metabolic rates. Moreover, extracellular polymeric substances (EPS) especially proteins were overproduced to bind the NPs and thereby reduce the nanotoxicity. The information obtained in this study may greatly help to understand the interactions between microbial community dynamics and function under NPs exposure conditions and functional redundancy is an important mechanism of periphytic biofilms to maintain sustainable functions.

[en] Highlights: • DOM enrichment increased biomass, N and P accumulation in periphytic biofilms • Growth and decay of periphytic biofilms release humic and protein-like substances • Biomass decay of periphytic biofilms reduced WSP but released AAP to the soil Dissolved organic matter (DOM) plays vital roles in carbon and other nutrient transformation at soil-water interfaces (SWI) in paddy fields. It is associated with the growth and withering of periphytic biofilms. However, the interactions between DOM and periphytic biofilms remain largely unknown. In this study, a microcosm experiment with different initial DOM contents elucidated that the biomass, and biomass nitrogen and phosphorus contents were greatly influenced by humic-like substances (C2 and C3), while the growth of periphytic biofilms increased the contents of humic-like (C1 and C2) and tryptophan-like substances (C5) in soil. Moreover, the decomposition of periphytic biofilms significantly increased soil pH, DOM, C2, C3 and C5 contents, but caused decrease in Eh, with consequent reduce in water soluble phosphorus (WSP) and release of algal available phosphorus (AAP). Results from this study revealed how DOM interacts with periphytic biofilms and the consequent effects on changes of bioactive phosphorus fractions, and provide practical information for designing periphytic biofilm based biofertilizer from the perspective of soil DOM.

[en] Highlights: • Ag⁺ released from AgNPs has heavier impact on photosynthesis than intact AgNPs. • Ag⁺ blocks electron transport and damages phycobilisome of algae in periphyton. • Energy absorption is increased to maintain electron transfer in photosynthesis. • PSII and PSI work in complement to cope with stress by intact AgNPs and Ag⁺. Silver nanoparticles (AgNPs) including a mix of intact nanoparticle-Ag and ‘free’ Ag⁺ pose high risks to benthic photoautotrophs, but the photosynthetic responses of benthic microbial aggregates to AgNPs still remain largely unknown. Here, periphyton and Nostoc were used to elucidate the photosynthetic responses of benthic algae community to intact nanoparticle-Ag and Ag⁺. During exposure, both intact nanoparticle-Ag and Ag⁺ imposed negative effects on photosynthesis of benthic algae, but via different pathways. Specifically, Ag⁺ had stronger effects on damaging the oxygen-evolving complex (OEC) and thylakoid membrane than intact nanoparticle-Ag. Ag⁺ also suppressed electron transfer from Q_A to Q_B, and impaired phycobilisome. Intact nanoparticle-Ag inhibited the expression of PsbD and PsbL in PSII, but prompted the ROS scavenging capacity. In response to the stress of AgNPs, the benthic algae increased light energy absorption to maintain the electron transport efficiency, and up-regulated PSI reaction center protein (PsaA) to compensate the degraded PSII. These results reveal how intact nanoparticle-Ag and Ag⁺ influence electron transport, energy conversion and protein expression in the photosynthesis of periphyton, and provide deep insights into the responses of benthic photoautotrophs to different components of AgNPs.