Responses of Periphyton to Fe2O3 Nanoparticles: A Physiological and Ecological Basis for Defending Nanotoxicity

Diet dependent trophic transfer of nanoparticles (ZnO and TiO2) along the "photic biofilm-snail" food chain

Multispecies biofilm exhibited high resistance to nanotoxicity by secreting extracellular polymeric substances (EPS) and undergoing alterations in the community composition. Scarce information was available to assess how these changes could further influence the transfer of nanoparticles (NPs) through the biofilm-based food chain. Photic biofilm was exposed to two distinct NPs (ZnO and TiO2) and subsequently grazed by snails. Exposure to different NPs led to variations in biomass, chlorophyll content, EPS productivity, alpha diversity, and community composition of the photic biofilm. The presence of ZnO NPs facilitated the growth of phylum Cyanobacteria while TiO2 promoted EPS productivity of photic biofilm. EPS were capable of embedding NPs (TiO2 and ZnO) within its matrix, thereby mitigating their aggregation within the biofilm matrix. These alterations were subsequently confirmed to have an impact on the trophic transfer factors (TTF) of NPs through the constructed biofilm-snail food chain. The TTF of ZnO was lower than that of TiO2 in feeding scenario 1 (only fed on TiO2 or ZnO biofilm) but higher than that of TiO2 in feeding scenario 2 (fed on TiO2 and ZnO biofilm simultaneously), which was attributed to the shifts in the algae composition and a smaller size of ZnO NPs in EPS. This study demonstrated that the response of photic biofilm to NPs further affected the TTFs of NPs through the food chain.

Negative effects of polyvinyl chloride microplastics and the plasticizer DnOP on earthworms: Co-exposure enhances oxidative stress and immune system damage in earthworms

Polyvinyl chloride microplastics (PVC-MPs) are the most used plastics in agriculture. Di-n-octyl phthalate (DnOP), a commonly used plasticizer in PVC-MPs, may be released from plastic and coexist with PVC-MPs. The effects of DnOP alone and coexisting with PVC-MPs are not known. We evaluated the effects of DnOP or/and PVC-MPs on earthworms, and used integrated biomarker response (IBR) to assess the combined toxicity. Molecular docking and transcriptomics were employed for further interpretation of possible toxicity mechanisms. The results showed that exposure to DnOP or/and PVC-MPs caused oxidative damage and interfered with reproduction, adversely affecting the growth and reproduction of earthworms. IBR results showed that toxicity of DnOP+PVC-MPs exposure was greater than that of DnOP and PVC-MPs exposure alone. DnOP has the ability to directly bind to proteins that are associated with antioxidant enzymes and alter their structure. The transcriptomics results indicated that DnOP and PVC-MPs exposure alone mainly affected growth and development-related pathways, while co-exposure affected apoptosis and immune system-related pathways more. To the best of our knowledge, this is the first comprehensive investigation of the combined toxicity of DnOP or/and PVC-MPs to earthworms from different perspectives, which gives scientifically sound evidence for the rational use of plasticizers DnOP and PVC-MPs.

Development and challenges of emerging biological technologies for algal-bacterial symbiosis systems: A review

The algal-bacterial symbiosis system (ABSS) is considered as a sustainable wastewater treatment process. This review provides a comprehensive overview of the mechanisms of ABSS for the removal of common pollutant, heavy metals, and especially for emerging pollutants. For the macroscopical level, this review not only describes in detail the reactor types, influencing factors, and the development of the algal-bacterial process, but also innovatively proposes an emerging process that combines an ABSS with other processes, which enhances the efficiency of removing difficult-to-biodegrade pollutants. Further for the microscopic level, interactions between algae and bacteria, including nutrient exchange, signaling transmission and gene transfer, have been deeply discussed the symbiotic relationship with nutrient removal and biomass production. Finally, recommendations are given for the future development of the ABSS. This review comprehensively examines ABSS principles, development, algal-bacterial interactions, and application in wastewater treatment, aiming to deepen theoretical and practical understanding and advance ABSS technology.

Antifouling characteristics and mechanisms in visible-light photocatalytic membrane bioreactor based on g-C3N4 modified membrane

A novel visible-light photocatalytic membrane bioreactor (R3) was constructed for membrane fouling control and effluent quality improvement. Specially, g-C3N4 modified membrane was evaluated for the performance of synergistic separation and photocatalysis. Another two parallel reactors, MBRs with ceramic membrane (R1) and g-C3N4 membrane in dark condition (R2), were operated synchronously for comparison. A satisfactory effluent quality was obtained in R3 with COD and NH4+-N around 22.0 mg/L and 1.02 mg/L during 60-day operation, which was superior to R1 (27.8, 1.42 mg/L) and R2 (29.9, 2.26 mg/L). The thickness of cake layer on membranes in R3 (2.46 μm) was thinner than R1 (3.52 μm) and R2 (4.97 μm) after operation, indicating the introduction of visible light could effectively mitigate membranes fouling. Moreover, microorganism community analysis revealed that visible light increased the relative abundance of Bacteroidetes and Chryseolinea, which not only enhanced the activity of microorganisms in metabolizing organic nutrients, but also improved the transfer and utilization of photogenerated electrons on the semiconductor-microorganism interface. The active aromatic protein metabolism and the upregulated related enzymes further demonstrated the synergistic effect of photocatalysis and microbial communities on the membrane fouling mitigation. This work provides a novel application of photocatalysis into antibiofouling effect in MBRs, and opens a strategy for bacteria inactivation and foulants removal with eco-friendly solar energy.

Nano-sized polystyrene and magnetite collectively promote biofilm stability and resistance due to enhanced oxidative stress response

Despite the growing prevalence of nanoplastics in drinking water distribution systems, the collective influence of nanoplastics and background nanoparticles on biofilm formation and microbial risks remains largely unexplored. Here, we demonstrate that nano-sized polystyrene modified with carboxyl groups (nPS) and background magnetite (nFe3O4) nanoparticles at environmentally relevant concentrations can collectively stimulate biofilm formation and prompt antibiotic resistance. Combined exposure of nPS and nFe3O4 by P. aeruginosa biofilm cells stimulated intracellular reactive oxidative species (ROS) production more significantly compared with individual exposure. The resultant upregulation of quorum sensing (QS) and c-di-GMP signaling pathways enhanced the biosynthesis of polysaccharides by 50 %- 66 % and increased biofilm biomass by 36 %- 40 % relative to unexposed control. Consistently, biofilm mechanical stability (measured as Young's modulus) increased by 7.2-9.1 folds, and chemical stress resistance (measured with chlorine disinfection) increased by 1.4-2.0 folds. For P. aeruginosa, the minimal inhibitory concentration of different antibiotics also increased by 1.1-2.5 folds after combined exposure. Moreover, at a microbial community-wide level, metagenomic analysis revealed that the combined exposure enhanced the multi-species biofilm's resistance to chlorine, enriched the opportunistic pathogenic bacteria, and promoted their virulence and antibiotic resistance. Overall, the enhanced formation of biofilms (that may harbor opportunistic pathogens) by nanoplastics and background nanoparticles is an overlooked phenomenon, which may jeopardize the microbial safety of drinking water distribution systems.

The interplay of hematite and photic biofilm triggers the acceleration of biotic nitrate removal

The soil-water interface is replete with photic biofilm and iron minerals; however, the potential of how iron minerals promote biotic nitrate removal is still unknown. This study investigates the physiological and ecological responses of photic biofilm to hematite (Fe2O3), in order to explore a practically feasible approach for in-situ nitrate removal. The nitrate removal by photic biofilm was significantly higher in the presence of Fe2O3 (92.5%) compared to the control (82.8%). Results show that the presence of Fe2O3 changed the microbial community composition of the photic biofilm, facilitates the thriving of Magnetospirillum and Pseudomonas, and promotes the growth of photic biofilm represented by the extracellular polymeric substance (EPS) and the content of chlorophyll. The presence of Fe2O3 also induces oxidative stress (•O2-) in the photic biofilm, which was demonstrated by electron spin resonance spectrometry. However, the photic biofilm could improve the EPS productivity to prevent the entrance of Fe2O3 to cells in the biofilm matrix and mitigate oxidative stress. The Fe2O3 then promoted the relative abundance of Magnetospirillum and Pseudomonas and the activity of nitrate reductase, which accelerates nitrate reduction by the photic biofilm. This study provides an insight into the interaction between iron minerals and photic biofilm and demonstrates the possibility of combining biotic and abiotic methods to improve the in-situ nitrate removal rate.

Exposure and recovery: The effect of different dilution factors of treated and untreated metal mining effluent on freshwater biofilm function and structure

Abandoned mines generate effluents rich in heavy metals, and these contaminants are released uncontrolled into the nearby aquatic ecosystems, causing severe pollution. However, no real solution exists, leaving a legacy of global pollution. In this study, the efficiency of the treatment technologies in reducing the ecological impacts of mining effluents to freshwater ecosystems with different dilution capacities was tested using biofilm communities as biological indicators. The functional and structural recovery capacity of biofilm communities after 21 days of exposure was assessed. With this aim, we sampled aquatic biofilms from a pristine stream and exposed them to treated (T) and untreated (U) metal mining effluent from Frongoch abandoned mine (Mid Wales, UK). Additionally, we simulated two different flow conditions for the receiving stream: high dilution (HD) and low dilution (LD). After exposure, the artificial streams were filled with artificial water for 14 days to assess the biofilm recovery. Unexposed biofilm served as control for biofilm responses (functional and structural) measured throughout time. During the exposure, short term effects on biofilm functioning (photosynthetic efficiency, nutrient uptake) were observed in T-LD, U-HD, and U-LD, whereas long term effects (community composition, chl-a, and diatom metrics) were observed on the structure of all biofilms exposed to the treated and untreated mining effluent. On the other hand, metal accumulation occurred in biofilms exposed to the mining effluents. However, a functional recovery was observed for all treatments, except in the U-LD in which biofilm structure did not present a significant recovery after the exposure period. The results presented here highlight the need to consider the dilution capacity of the receiving stream to assess the real efficiency of treatment technologies applied to mining effluents to mitigate the ecological impact on freshwater ecosystems.

Differential toxicity of various mineral nanoparticles to Synechocystis sp.: With and without ciprofloxacin

Mineral nanoparticles (M-NPs) are ubiquitous in aquatic environments, but their potential harms to primary producers and impacts on the toxicity of coexisting pollutants are largely unknown. Herein, the toxicity mechanisms of various M-NPs (i.e., SiO2, Fe2O3, Al2O3, and TiO2 NPs) to Synechocystis sp. in absence and presence of ciprofloxacin (CIP) were comprehensively investigated. The heteroaggregation of cells and M-NPs can hinder substrate transfer or light acquisition. The attraction between Synechocystis sp. and M-NPs increased in the order of SiO2 < Fe2O3 < Al2O3 ≈ TiO2 NPs. Therefore, SiO2 and Fe2O3 NPs exerted slight effects on physiology and proteome of Synechocystis sp.. Al2O3 NPs with the rod-like shape caused physical damage to cells. Differently, TiO2 NPs with photocatalytic activities provided photogenerated electrons for Synechocystis sp., promoting photosynthesis and the Calvin cycle for CO2 fixation. SiO2, Fe2O3, and Al2O3 NPs alleviated the toxicity of CIP in an adsorption-depended manner. Conversely, the combination of CIP and TiO2 NPs exerted more pronounced toxic effects compared to their individuals, and CIP disturbed the extracellular electron transfer from TiO2 NPs to cells. The findings highlight the different effects of TiO2 NPs from other M-NPs on cyanobacteria, either alone or in combination with CIP, and improve the understanding of toxic mechanisms of M-NPs.

Impact of biological activated carbon filtration and backwashing on the behaviour of PFASs in drinking water treatment plants

PFASs are present in surface water, tap water and even commercial drinking water and pose a risk to human health. In this study, the treatment efficiency of 14 PFASs was studied in a large drinking water treatment plant (DWTP) using Taihu Lake as the source, and it was found that the ozone/biological activated carbon (O₃-BAC) process was the most effective process for the removal of PFASs in DWTPs. For the O₃-BAC process, there were differences in the removal of PFASs by BACs (1,4,7,13 years) of different ages. The sterilization experiments revealed that for GAC, its physical adsorption capacity reached saturation after one year, while for BAC with mature biofilms, biosorption was the main mechanism for the removal of PFASs. The abundance of Alphaproteobacteria and Gammaproteobacteria in biofilms was positively correlated with the age of the BAC. The microbial community with higher abundance is beneficial to the biodegradation of organic matter and thus provides more active sites for the adsorption of PFASs. PFASs can leak in the early stage of filtration after backwashing, so it is necessary to pay close attention to the influent and effluent concentrations of PFASs during biofilm maturation after backwashing.

Synergy between microalgae and microbiome in polluted waters

Microalga-microbiome interactions are central to both health and disease of aquatic environments. Despite impressive advances in deciphering how microorganisms participate in and impact aquatic ecosystems, the evolution and ecological involvement of microalgae and the microbiome in polluted waters are typically studied independently. Here, the phycosphere (i.e., the consortia of microalgae and the related microbiome) is regarded as an independent and integrated life form, and we summarize the survival strategies exhibited by this symbiont when exposed to anthropogenic pollution. We highlight the cellular strategies and discuss the modulation at the transcriptional and population levels, which reciprocally alters community structure or genome composition for medium-term acclimation or long-term adaptation. We propose a 'PollutantBiome' concept to help the understanding of microalga-microbiome interactions and development of beneficial microbial synthetic communities for pollutant remediation.

Effect of humic acid on bioreduction of facet-dependent hematite by Shewanella putrefaciens CN-32

Interfacial reactions between iron (Fe) (hydr)oxide surfaces and the activity of bacteria during dissimilatory Fe reduction affect extracellular electron transfer. The presence of organic matter (OM) and exposed facets of Fe (hydr)oxides influence this process. However, the underlying interfacial mechanism of facet-dependent hematite and its toxicity toward microbes during bioreduction in the presence of OM remains unknown. Herein, humic acid (HA), as typical OM, was selected to investigate its effect on the bioreduction of hematite {100} and {001}. When HA concentration was increased from 0 to 500 mg L^-1, the bioreduction rates increased from 0.02 h^-1 to 0.04 h^-1 for hematite {100} and from 0.026 h^-1 to 0.05 h^-1 for hematite {001}. Since hematite {001} owned lower resistance than hematite {100} irrespective of the HA concentration, and hematite {100} was less favorable for reduction. Microscopy-based analysis showed that more hematite {001} nanoparticles adhered to the cell surface and were bound more closely to the bacteria. Moreover, less cell damage was observed in the HA-hematite {001} treatments. As the reaction progressed, some bacterial cells died or were inactivated; confocal laser scanning microscopy showed that bacterial survival was higher in the HA-hematite {001} treatments than in the HA-hematite {100} treatments after bioreduction. Spectroscopic analysis revealed that facet-dependent binding was primarily realized by surface complexation of carboxyl functional groups with structural Fe atoms, and that the binding order of HA functional groups and hematite was affected by the exposed facets. The exposed facets of hematite could influence the electrochemical properties and activity of bacteria, as well as the binding of bacteria and Fe oxides in the presence of OM, thereby governing the extracellular electron transfer and concomitant bioreduction of Fe (hydr)oxides. These results provide new insights into the interfacial reactions between OM and facet-dependent Fe oxides in anoxic, OM-rich soil and sediment environments.

The response of bacterial community to UVB was significantly different between immature periphyton and mature periphyton, but not for physiological indicators

Periphyton has important ecological functions. It can even exist in environments with strong ultraviolet radiation. However, knowledge of periphyton under ultraviolet is limited, which limits the understanding and application of periphyton in environments with high ultraviolet radiation. In this study, immature periphyton (IMP) and mature periphyton (MP) under ultraviolet B (UVB) irradiation were investigated and compared in terms of physiological characteristics and bacterial community. Analysis of the physiological characteristics showed that the response patterns of IMP and MP to UVB were similar. IMP and MP could adapt to UVB of 1 W/m² well. However, high-intensity UVB (2 and 3 W/m²) reduced the periphyton biomass, inhibited photosynthesis and antioxidant enzyme activity and caused severe lipid peroxidation in both IMP and MP. Integrated Biological Response (IBR) analysis and toxicological model fitting showed that the ED₅₀ values of UVB for IMP and MP were 1.25 and 1.50 W/m², respectively. 16 S rRNA gene analysis showed that in both IMP and MP, bacterial community composition, assembly and function were affected by UVB. In addition, the response of the bacterial community in IMP to UVB was stronger than that in MP. The diversity of the IMP community was inhibited by UVB, but that of the MP community was not. Proteobacteria and Deinococcus-Thermus are key microorganisms responsible for tolerance to UVB stress. Neutral community model fitting showed that both UVB and the development process caused the determinism of bacterial succession. However, UVB may weaken the deterministic process caused by development. Functional prediction showed that many metabolic functions of periphyton were inhibited by UVB in IMP and MP. However, UVB caused different changes (enhancement or inhibition) of some ecological functions in them. This study provides valuable information for understanding periphyton in environments with UVB radiation, which may be used to improve the application of periphyton in these environments.

Periphytic biofilms-mediated microbial interactions and their impact on the nitrogen cycle in rice paddies

Rice paddies are unique waterlogged wetlands artificially constructed for agricultural production. Periphytic biofilms (PBs) at the soil-water interface play an important role in rice paddies characterized by high nutrient input but low utilization efficiency. PBs are composed of microbial aggregates, including a wide variety of microorganisms (algae, bacteria, fungi, protozoa, and metazoa), extracellular polymeric substances and minerals (iron, aluminum, and calcium), which form an integrated food web and energy flux within a relatively stable micro-ecosystem. PBs are crucial to regulate and streamline the nitrogen cycle by neutralizing nitrogen losses and improving rice production since PBs can serve as both a sink by capturing surplus nitrogen and a source by slowly re-releasing this nitrogen for reutilization. Here the ecological advantages of PBs in regulating the nitrogen cycle in rice paddies are illustrated. We summarize the key functional importance of PBs, including the intricate and delicate community structure, microbial interactions among individual phylotypes, a wide diversity of self-produced organics, the active adaptation of PBs to constantly changing environments, and the intricate mechanisms by which PBs regulate the nitrogen cycle. We also identify the future challenges of microbial interspecific cooperation in PBs and their quantitative contributions to agricultural sustainability, optimizing nitrogen utilization and crop yields in rice paddies.

Distinct Responses of Biofilm Carbon Metabolism to Nanoplastics with Different Surface Modifications

Recently, there is an increasing concern regarding the toxicity of nanoplastics (NPs) on freshwater organisms. However, knowledge about the potential impacts of NPs with different surface modification on freshwater biofilms is still very limited. In this research, biofilms were cultured in lab and exposed to nano polystyrene (PS) beads: non-functionalized PS NPs, PS-COOH NPs, and the carbon source utilization of biofilms were measured by BIOLOG ECO microplates. The results showed that both two types of PS NPs significantly reduced the total carbon metabolic activity of biofilms, compared with the controls, whereas the carbon metabolic rate increased notably, especially for the PS-COOH NPs treatments at day 14. Moreover, results from six categories of carbon sources analysis suggested that PS NPs with different surface chemical properties exhibit distinct effects on the carbon utilization of biofilms, and the divergent changes of the specific carbon source category were observed at day 21 from the two PS NPs treatments. In addition, the metabolic functional diversity of biofilms were not altered by the PS NPs treatments. These findings highlighted that chemical properties of NPs play an important role in the toxic effects on the carbon metabolism activities of the biofilms. This study offers new insights that nanoplastics of different chemical characteristics have the ability to affect the microbial-mediated carbon cycling process in aquatic ecosystems.

Natural biofilm as a potential integrative sample for evaluating the contamination and impacts of PFAS on aquatic ecosystems

Natural biofilm can be a suitable medium for the monitoring of pollutants. Limited information is currently available regarding the occurrence of per- and polyfluoroalkyl substances (PFAS) in periphytic biofilm and low-trophic level organisms of freshwater ecosystems. In this study, surface water, biofilm, phytoplankton, and freshwater snails were collected from Taihu Lake, China, and characterized for 16 PFAS, including legacy compounds (PFSAs/PFCAs) and PFAS of emerging concern (fluorotelomer sulfonates and F-53B). The colonized biofilms effectively bioaccumulated PFAS from water, with the total concentration (∑PFAS) in the range of 1.96-20.1 ng/g wet weight, and the bioaccumulation factor increased with the PFAS log K_ow values. As compared with phytoplankton, the ∑PFAS in biofilms displayed a stronger correlation with those in water. PFAS distinctly biomagnified from the biofilm to freshwater snail, with the biomagnification factor in the range of 3.09 ± 2.03 - 17.8 ± 10.2, implying the important role of biofilm in PFAS transfer in aquatic environment. Extracellular proteins production in biofilm increased with the water PFAS concentrations. The total extracellular polymeric substances (EPS) content increased with the water PFAS concentration firstly and then declined to a steady level, while the algal chlorophyll level exhibited a similar relationship with the PFAS in biofilm. High PFAS levels were also associated with depressed alpha diversity of fungal community in biofilms. Biofilm appears as a relevant indicator to characterize the occurrence of PFAS in aquatic ecosystems.

Contribution, Composition, and Structure of EPS by In Vivo Exposure to Elucidate the Mechanisms of Nanoparticle-Enhanced Bioremediation to Metals

Bacterial extracellular polymeric substances (EPS) have been recently found to contribute most for metal removal in nanoenhanced bioremediation. However, the mechanism by which NPs affect EPS-metal interactions is not fully known. Here, Halomonas sp. was employed to explore the role of EPS after in vivo exposure to Cd/Pb and polyvinylpyrrolidone (PVP) coated iron oxide nanoparticles (IONPs, 20 mg L^-1) for 72 h. Cd-IONPs produced the highest concentrations of EPS proteins (136.3 mg L^-1), while Cd induced the most production of polysaccharides (241.0 mg L^-1). IONPs increased protein/polysaccharides ratio from 0.2 (Cd) to 1.2 (Cd-IONPs). The increased protein favors the formation of protein coronas on IONPs surface, which would promote Cd adsorption during NP-metal-EPS interaction. FTIR analysis indicated that the coexistence of Cd and IONPs interacted with proteins more strongly than with polysaccharides. Glycosyl monomer analyses suggested mannose and glucose as target sugars for EPS complexation with metals, and IONPs reduced metal-induced changes in monosaccharide profiles. Protein secondary structures changed in all treatments, but we could not distinguish stresses induced by metals from those by IONPs. These findings provide greater understanding of the role of EPS in NP-metal-EPS interaction, providing a better underpinning knowledge for the application of NP-enhanced bioremediation.

Remarkable characteristics and distinct community of biofilms on the photoaged polyethylene films in riverine microcosms

Recalcitrant plastics in the environment are gradually fragmented into weathered debris distinguished from their original state by the integrative action of influencing factors, such as UV light, heating and physical abrasion. As new artificial carbon-source substrates in aquatic ecosystems, plastic products can be colonized by biofilms and even utilized by microorganisms. To investigate the influences of weathering of plastics on the colonized biofilms, freshwater samples from the Yangtze River (Nanjing, China) were collected for biofilm incubation. Based on the characterization of plastics and biofilms, the effects of plastic surface properties on biofilm characteristics were revealed by the analysis of partial least squares regression (PLSR). Roughness was the principal influencing factor, while rigidity had the opposite effect to it. 16S rRNA gene high-throughput sequencing results indicated the high relative abundance of Cyanobacteria and rising proportion of harmful components (e.g., Flavobacterium) on photoaged polyethylene plastics. The microbial functional profiles (KEGG) predicted by Tax4Fun showed that the functions (e.g., membrane transport, energy metabolism, etc.) of biofilm on photoaged plastics were dissimilar with those on original ones. These findings suggested that the distinct microbial community and the adverse functional changes in biofilms on photoaged plastics potentially enhanced their environmental risks. On the other hand, 28-day cultured biofilms on original low-density polyethylene (LDPE) films were dominated by Exiguobacterium. The previously ignored potentials of this microorganism in rapidly accommodating to a hydrophobic substrate and its plastic degrading ability were both worthy of attention. Therefore, it is necessary to consider the weathering process of plastics in exploring the "plastisphere", and to give further insights into the double-edged nature of the "plastisphere".

Propelling the practical application of the intimate coupling of photocatalysis and biodegradation system: System amelioration, environmental influences and analytical strategies

The intimate coupling of photocatalysis and biodegradation (ICPB) possesses an enhanced ability of recalcitrant contaminant removal and energy generation, owing to the compact communication between biotic components and photocatalysts during the system operation. The photocatalysts in the ICPB system could dispose of noxious contaminants to relieve the external pressure on microorganisms which could realize the mineralization of the photocatalytic degradation products. However, due to the complex components in the composite system, the mechanism of the ICPB system has not been completely understood. Moreover, the variable environmental conditions would play a significant role in the ICPB system performance. The further development of the ICPB scheme requires clarification on how to reach an accurate understanding of the system condition during the practical application. This review starts by offering detailed information on the system construction and recent progress in the system components' amelioration. We then describe the potential influences of relevant environmental factors on the system performance, and the analytical strategies applicable for comprehending the critical processes during the system operation are further summarized. Finally, we put forward the research gaps in the current system and envision the system's prospective application. This review provides a valuable reference for future researches that are devoted to assessing the environmental disturbance and exploring the reaction mechanisms during the practical application of the ICPB system.

Feedback mechanisms of periphytic biofilms to ZnO nanoparticles toxicity at different phosphorus levels

The increasing use of nanoparticles (NPs) has raised concerns about their potential environmental risks. Many researches on NPs focused on the toxicity mechanism to microorganisms, but neglect the toxicity effects in relation to nutritional conditions. Here, we evaluated the interactive effects of zinc oxide (ZnO) NPs and phosphorus (P) levels on the bacterial community and functioning of periphytic biofilms. Results showed that long-term exposure to ZnO NPs significantly reduced alkaline phosphatase activity (APA) of periphytic biofilms just in P-limited conditions. Co-occurrence network analysis indicated that ZnO NPs exposure reduced network complexity between bacterial taxa in P-limited conditions, while the opposite trend was observed in P-replete conditions. Correlation analysis and random forest modeling suggested that excessive Zn²⁺ released and high reactive oxygen species (ROS) production might be mainly responsible for the inhibition of APA induced by ZnO NPs under P-limited conditions, while adjustment of bacterial diversity and improvement of keystone taxa cooperation were the main mechanisms in maintaining APA when subjected to weak toxicity of ZnO NPs in P-replete conditions. Taken together, our results provide insights into the biological feedback mechanism involved in ZnO NPs exposure on the ecological function of periphytic biofilms in different P nutritional conditions.

Pollutants affect algae-bacteria interactions: A critical review

With increasing concerns on the ecological risks of pollutants, many efforts have been devoted to revealing the toxic effects of pollutants on algae or bacteria in their monocultures. However, how pollutants affect algae and bacteria in their cocultures is still elusive but crucial due to its more environmental relevance. The present review outlines the interactions between algae and bacteria, reveals the influential mechanisms of pollutants (including pesticides, metals, engineered nanomaterials, pharmaceutical and personal care products, and aromatic pollutants) to algae and bacteria in their coexisted systems, and puts forward prospects for further advancing toxic studies in algal-bacterial systems. Pollutants affect the physiological and ecological functions of bacteria and algae by interfering with their relationships. Cell-to-cell adhesion, substrate exchange and biodegradation of organic pollutants, enhancement of signal transduction, and horizontal transfer of tolerance genes are important defense strategies in algal-bacterial systems to cope with pollution stress. Developing suitable algal-bacterial models, identifying cross-kingdom signaling molecules, and deciphering the horizontal transfer of pollutant resistant genes between algae and bacteria under pollution stress are the way forward to fully exploit the risks of pollutants in natural aquatic environments.

Integration of subcellular partitioning and chemical forms to understand silver nanoparticles toxicity to lettuce (Lactuca sativa L.) under different exposure pathways

The current understanding of the biological impacts of silver nanoparticles (AgNPs) is restricted to the direct interactions of the particles with biota. Very little is known about their intracellular fate and subsequent toxic consequences. In this research we investigated the uptake, internal fate (i,e., Ag subcellular partitioning and chemical forms), and phytotoxicity of AgNPs in lettuce following foliar versus root exposure. At the same AgNP exposure concentrations, root exposure led to more deleterious effects than foliar exposure as evidenced by a larger extent of reduced plant biomass, elevated oxidative damage, as well as a higher amount of ultrastructural injuries, despite foliar exposure leading to 2.6-7.6 times more Ag bioaccumulation. Both Ag subcellular partitioning and chemical forms present within the plant appeared to elucidate this difference in toxicity. Following foliar exposure, high Ag in biologically detoxified metals pool (29.2-53.0% by foliar exposure vs. 12.8-45.4% by root exposure) and low Ag proportion in inorganic form (6.1-11.9% vs. 14.1-19.8%) potentially associated with AgNPs tolerance. Silver-containing NPs (24.8-38.6 nm, 1.5-2.3 times larger than the initial size) were detected in lettuce plants exposed to NPs and to dissolved Ag+, suggesting possible transformation and/or aggregation of AgNPs in the plants. Our observations show that the exposure pathway significantly affects the uptake and internal fate of AgNPs, and thus the associated phytotoxicity. The results are an important contribution to improve risk assessment of NPs, and will be critical to ensure food security.

Phosphorus recovery by core-shell γ-Al2O3/Fe3O4 biochar composite from aqueous phosphate solutions

Biochar can act as an adsorbent for phosphate removal from water sources, which can be highly beneficial in limiting eutrophication and recycling elemental phosphorus (P). However, it is difficult to use a single biochar material to overcome problems such as low adsorption efficiency, difficulty in reuse, and secondary pollution. This study addresses these challenges using a novel core-shell structure γ-Al₂O₃/Fe₃O₄ biochar adsorbent (AFBC) with significant P uptake capabilities in terms of its high adsorption capacity (205.7 mg g^-1), magnetic properties (saturation magnetization 24.70 emu g^-1), and high reuse stability (91.0% removal efficiency after five adsorption-desorption cycles). The highest partition coefficient 1.04 mg g^-1 μM^-1, was obtained at a concentration of 322.89 μM. Furthermore, AFBC exhibited strong regeneration ability in multiple cycle trials, making it extremely viable for sustainable resource management. P removal mechanisms, i.e., electrostatic attraction and inner-sphere complexation, were explained using Fourier transform infrared (FT-IR) spectra and X-ray photoelectron spectroscopy (XPS) measurements. A surface complexation model was established by considering the formation of monodentate mononuclear and bidentate binuclear surface complexes of P to illustrate the adsorption process. Owing to its high adsorption efficiency, easy separation from water, and environmental friendliness, AFBC is a potential adsorbent for P recovery from polluted waters.

Insights into the effect of cerium oxide nanoparticle on microalgal degradation of sulfonamides

Nanoparticles have been commercially used worldwide; however, there is a lack of information of their environmental impacts and ecotoxicity. In this study, the effect of cerium oxide nanoparticle (CeO₂NP) on a green microalga Scenedesmus obliquus, and microalgal biodegradation of four sulfonamides (sulfamethazine, sulfamethoxazole, sulfadiazine, and sulfamethoxazole) was investigated. There is insignificant inhibition of microalgal growth induced by CeO₂NP; however, it substantially influenced the expression of genes involved in key cellular metabolic activities of S. obliquus. For example, genes involved in photosynthetic activity (psbA) and energy production (ATPF0C) were downregulated with exposure to CeO₂NP. The low concentrations of CeO₂NP improved microalgal degradation of sulfonamides. This may be because of the upregulated genes encoding hydrogenase and oxidoreductase. The exploration of this study has provided a new understanding of the environmental impacts of CeO₂NP on microalgae-based biotechnologies for treatment of wastewater containing emerging organic contaminants.

Effects of Ag NPs on denitrification in suspended sediments via inhibiting microbial electron behaviors

The wide use of silver nanoparticles (Ag NPs) inevitably leads to their increasing emission into aquatic environments. However, before their final deposition into sediments, the ecological effects of Ag NPs in suspended sediment (SPS) systems have not received much attention. Herein, we investigated the influences of Ag NPs on denitrification in SPS systems, and explored the potential toxicity mechanism through microbial metabolism (electron behaviors) and isotope tracing (added ¹⁵NO₃^-). After exposure to 10 mg/L Ag NPs, electron generation, transport and consumption during denitrification were clearly inhibited, which led to a decrease in the SPS denitrification rate. Specifically, the generation of NADH (electron donor) was significantly decreased to 59.92-86.47% with the Ag NPs treatments by affecting the degradation of glucose, one of the major reasons for the decreased denitrification. It also indicated that Ag NPs could affect nitrogen metabolism by influencing carbon metabolism. In addition, ETSA was clearly inhibited by the affected electron transfer and reception during denitrification; that was the most direct way in the microbial electron transport chain to affect the SPS denitrification rate. Furthermore, the particle size and concentration of SPS affected the toxicity of Ag NPs. The denitrification process in SPS systems with a smaller particle size and lower particle concentration was easily affected by Ag NPs, suggesting that SPS systems dominated by clay (particle size < 3.9 μm) or that less turbulence (having low SPS concentration) might be at greater risk factor when exposed to NPs. Thus, it is important to understand the risks of pollutants, such as Ag NPs, to biogeochemical cycles and ecosystem function in SPS systems.

Cultivation substrata differentiate the properties of river biofilm EPS and their binding of heavy metals: A spectroscopic insight

River biofilms inevitably serve as recipients of heavy metals including copper (Cu) and cadmium (Cd) following their introduction in fluvial systems. Nevertheless, the effects of cultivation substrata on the characteristics of river biofilm extracellular polymeric substances (EPS) and the binding behaviors of heavy metals on biofilms remain unclear. Integrating spectroscopic methods with chemometric analyses, we explored the binding behaviors of Cu(II) and Cd(II) onto biofilm EPS cultivated from two representative substrata at the molecular level. Chemical analysis revealed that biofilm cultivated on polyethylene (PE) pieces contained more non-fluorescent protein fractions, whereas EPS from periphyton grown on mineral, i.e., cobblestones was richer in aromatic fractions and polysaccharides. Excitation-emmision matrix combined with parallel factor analysis suggested a stronger interaction between fluorophores in periphytic EPS with Cu(II) compared to fluorophores in plastic biofilm EPS. Integrated use of infrared spectroscopy and two-dimensional correlation analyses revealed that, during the heavy metal binding processes, the amines and phenolics in plastic biofilm EPS gave the fastest responses to metal binding. While the amides and the aliphatic fractions in periphytic EPS showed a preferential binding to heavy metals. This study differentiates the effects of cultivation substrata on structuring the biofilm EPS characteristics and offers new insights into the environmental behaviors of heavy metal discharge into fluvial systems in river biofilm matrix.

Nano-TiO2 enhances the adsorption of Cd(II) on biological soil crusts under mildly acidic conditions

Biological soil crusts (BSCs), which are ubiquitous in paddy fields, are known to remove pollutants from paddy fields systems. The Nano-TiO₂ enhanced the removal of Cd(II) by BSC under acidic irrigation water was found, and its mechanism was investigated. After the addition of nano-TiO₂, the Cd(II) removal efficiency of BSC_S increased by 26.70% than that of pure BSCs, and the Nano-TiO₂ induced faster removal velocity as well. Zeta potential and potentiometric titration results revealed that BSCs generated more negative charges and sites concentration after addition of Nano-TiO₂ at acidic environment. The carboxyl and amino/hydroxyl groups were the main functional groups on BSC and the BSC + TiO₂. The higher concentration of amino/hydroxyl groups in BSC + TiO₂ (0.33 ± 0.08 mmol/g) was present than that of pristine BSCs (0.62 ± 0.02 mmol/g), and they were with similar concentration of phosphate groups and carboxyl groups. This result was attributed to the Nano-TiO₂ stimulated the BSCs to produce more extracellular polysaccharides and proteins. Our findings would provide novel strategy for the removal of cadmium from acidic irrigation water.

Acute effects of nanoplastics and microplastics on periphytic biofilms depending on particle size, concentration and surface modification

Microplastics (MPs) can disintegrate into smaller sized microplastics and even nanoplastics (NPs). The toxicity of nanoplastics and microplastics on freshwater organisms have been well explored recently, however, very little is known about the potential impacts of NPs on freshwater biofilms, which are essential for primary production and nutrient cycling in aquatic ecosystems. In this study, we studied the acute effects (3 h of exposure) of polystyrene beads (PS, with diameter range from 100 nm to 9 μm) on five biological endpoints targeting community and ecosystem-level processes in biofilms: chlorophyll a, photosynthetic yield, and three extracellular enzyme activities. The results showed that the large size PS beads (500 nm, 1 μm, and 9 μm) exhibited negligible effects on the determined biological endpoints in biofilms within the range of concentrations (5-100 mg/L) in this study. However, high concentration of PS beads (100 nm, 100 mg/L) significantly decreased the content of chlorophyll a, and the functional enzyme activities of β-glucosidase and leucine aminopeptidase, suggesting negative effects on the carbon and nitrogen cycling of freshwater biofilms. Moreover, the influences of PS NPs (100 nm) on biofilms strongly depended on the surface modification of PS particles, with the positively charged PS NPs (amide-modified) exhibiting the highest toxicity to biofilms. The excess generation of reactive oxygen species (ROS) in this study indicated oxidative stress induced by PS NPs, which might lead to the observed nano-toxic effects on biofilms. In response, the antioxidant activity of biofilm was enhanced as indicated by the increased total antioxidant capacity (T-AOC). Overall, our findings highlight nanoplastics have potential to disrupt the basic ecological functions of biofilms in aquatic environments.

Effects of Nanoplastics on Freshwater Biofilm Microbial Metabolic Functions as Determined by BIOLOG ECO Microplates

Nanoplastic (NP) contamination is becoming a pervasive issue as NPs, originating from microplastic particles, pose potentially harmful environmental impacts on aquatic ecosystems. The environmental hazards of NPs on microorganisms have been well documented in recent studies; however, little is known about their ecotoxicity effects on freshwater biofilms, which serve as important primary producers and decomposers and are highly connected with other ecosystem components. We investigated the effects of NPs on the microbial metabolic functions of freshwater biofilms in terms of carbon source utilization ability. Biofilm samples were collected, cultivated in a hydrodynamic flume for six weeks, and then exposed in polystyrene (PS) beads (100 nm in size) with different NP concentrations (1, 5, and 10 mg/L). BIOLOG ECO microplates were used to quantify carbon source utilization characteristics. The data were analyzed using average well-color development (AWCD), functional diversity indices, and principle component analysis (PCA). Results showed that the total carbon metabolic functions (represented by AWCD) remained constant (p > 0.05) with elevated NP concentrations, but some specific carbon sources (e.g., esters) changed in their utilization ability (p < 0.05). The microbial functional diversity (Shannon-Wiener diversity index, Simpson diversity index, and Shannon evenness index) was significantly reduced under 10 mg/L NPs (p < 0.05), indicating an inhibiting effect of NPs on biofilm metabolic diversity. This study examined NP ecotoxicity effects on microbial metabolic activities at the community level, but further studies are required to fully understand the mechanisms driving this change.

Impact of adding metal nanoparticles on anaerobic digestion performance - A review

Anaerobic digestion is the most widely adopted biological waste treatment processes with renewable energy production. The effects of adding metal nanoparticles (NPs) on improving digestion performance are well noted. This paper reviewed the traditional view on the cytotoxicity of NPs to living organisms and the contemporary view of mechanisms for enhancement in anaerobic digestion performance in the presence of metal NPs. The complicated interactions acquire further studies for comprehending the physical and chemical interactions of metal NPs to the constituent compounds and to the living cells, and the involvement of mechanisms such as direct interspecies electron transfer for better design and control of the "NP strategy" for anaerobic digestion performance enhancement.

Influence of FeONPs amendment on nitrogen conservation and microbial community succession during composting of agricultural waste: Relative contributions of ammonia-oxidizing bacteria and archaea to nitrogen conservation

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe₂O₃ and Fe₃O₄ NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe₂O₃ NPs, reduced total nitrogen (TN) loss, and reserved more NH₄⁺-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH₄⁺-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Size-Dependent Bacterial Toxicity of Hematite Particles

Submicron-sized iron oxide particles can influence the activity of bacteria, but the exact mechanisms of oxide toxicity toward bacteria remain elusive. By using atomic force microscopy (AFM), soft X-ray tomography (Nano-CT), and Fourier transform infrared (FTIR) spectrometry, we show how the size-dependent interfacial interactions between hematite particles and bacteria in the absence of any ligands contribute to the antimicrobial properties against Gram-positive and Gram-negative bacterial strains. We found that surface adhesion between hematite particles and bacterial cells is initially dominated by Lifshitz van der Waals and electrostatic forces. Subsequently, the rapid formation of P-O-Fe bonds occurs, followed by changes in the structures of membrane proteins in 2 h, resulting in the loss of the structural integrity of the membrane within 10 h. Thus, particles can migrate into the cells. After contact with bacterial cells, reactive oxygen species are generated on the surface of hematite particles, leading to cell permeabilization. G^- bacteria appear to be more susceptible to this process than G⁺ bacteria because the latter exhibit weaker adhesion forces toward hematite and benefit from the protective effects of the peptidoglycan layers. Our work revealed that hematite nanoparticles are more toxic to bacteria than microscaled particles due to their strong interfacial physicochemical interactions with the cells.

Advances in the technologies for studying consortia of bacteria and cyanobacteria/microalgae in wastewaters

The excessive generation and discharge of wastewaters have been serious concerns worldwide in the recent past. From an environmental friendly perspective, bacteria, cyanobacteria and microalgae, and the consortia have been largely considered for biological treatment of wastewaters. For efficient use of bacteria‒cyanobacteria/microalgae consortia in wastewater treatment, detailed knowledge on their structure, behavior and interaction is essential. In this direction, specific analytical tools and techniques play a significant role in studying these consortia. This review presents a critical perspective on physical, biochemical and molecular techniques such as microscopy, flow cytometry with cell sorting, nanoSIMS and omics approaches used for systematic investigations of the structure and function, particularly nutrient removal potential of bacteria‒cyanobacteria/microalgae consortia. In particular, the use of specific molecular techniques of genomics, transcriptomics, proteomics metabolomics and genetic engineering to develop more stable consortia of bacteria and cyanobacteria/microalgae with their improved biotechnological capabilities in wastewater treatment has been highlighted.

Low concentrations of copper oxide nanoparticles alter microbial community structure and function of sediment biofilms

In this study, we investigated the effects of copper oxide (CuO) NPs on freshwater sediment biofilms in terms of the functional properties and microbial community structure. Biofilms were incubated in microcosms and CuO NPs (1 mg/L uncoated and humic-acid-coated) were exposed with Cu²⁺ (Cu(NO₃)₂) as the positive control. As determined from DO (dissolved oxygen) microelectrodes measurements, a high-DO region emerged inside the biofilms after 5-day exposure to CuO NPs compared with those before NP additions, which suggested CuO NPs inhibit the oxygen respiration activity. These results were consistent with the decreased heterotrophic respiration. CuO NPs significantly altered the bacterial community composition and decreased the abundances of Anaerolineaceae, Acidobacteria, Aminicenantes, and Anaerolinea. Functional analysis from PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States)-predicted metagenomes indicated that bacterial genera depleted by CuO NP treatments were related to carbohydrate and glycan biosynthesis and metabolism, and biosynthesis of other secondary metabolites. These functional profiles combined with the decreased activities of extracellular enzymes, β-glucosidase (GLU) and l-leucine aminopeptidase (LAP), suggested that the introduction of CuO NPs exhibit negative effects on the biogeochemical processes and the cycling of carbon and nitrogen in biofilm systems. Whereas these toxic effects of CuO NPs could be mitigated when the aquatic environment is enriched with natural organic matters such as humic acid.

Protection Mechanisms of Periphytic Biofilm to Photocatalytic Nanoparticle Exposure

Researchers are devoting great effort to combine photocatalytic nanoparticles (PNPs) with biological processes to create efficient environmental purification technologies (i.e., intimately coupled photobiocatalysis). However, little information is available to illuminate the responses of multispecies microbial aggregates against PNP exposure. Periphytic biofilm, as a model multispecies microbial aggregate, was exposed to three different PNPs (CdS, TiO₂, and Fe₂O₃) under xenon lamp irradiation. There were no obvious toxic effects of PNP exposure on periphytic biofilm as biomass, chlorophyll content, and ATPase activity were not negatively impacted. Enhanced production of extracellular polymetric substances (EPS) is the most important protection mechanism of periphytic biofilm against PNPs exposure. Although PNP exposure produced extracellular superoxide radicals and caused intracellular reactive oxygen species (ROS) accumulation in periphytic biofilm, the interaction between EPS and PNPs could mitigate production of ROS while superoxide dismutase could alleviate biotic ROS accumulation in periphytic biofilm. The periphytic biofilms changed their community composition in the presence of PNPs by increasing the relative abundance of phototrophic and high nutrient metabolic microorganisms (families Chlamydomonadaceae, Cyanobacteriacea, Sphingobacteriales, and Xanthomonadaceae). This study provides insight into the protection mechanisms of microbial aggregates against simultaneous photogenerated and nanoparticle toxicity from PNPs.

Metal toxicity and recovery response of riverine periphytic algae

In the present study, in situ assessment of metal (Cu and Zn) toxicity followed by their recovery response was examined in periphyton dominated by diatoms. For doing so, metal diffusing substrates (MDS) were constructed and deployed in the river water for 6 weeks (3 weeks stress and 3 weeks recovery after replacing metal solution from the MDS). The use of MDS ensured that colonised periphyton on metal diffusing and control substrates were exposed to similar environmental conditions. The metal toxicity and recovery response of the community was examined in terms of traditional algal community parameters (biovolume, species richness, Shannon index, relative abundance) as well as with the newer non-taxonomical parameters (deformities and lipid bodies in diatoms). Both traditional and non-taxonomical parameters indicated complete recovery (from metal toxicity) of periphytic communities after 3 weeks following the withdrawal of Cu and Zn solution from the diffusing substrates. Newer non-taxonomical parameters, such as, deformities and lipid bodies, provide a new insight to understand metal toxicity and recovery response of diatom assemblages (the dominant autotrophs in the periphyton community) because these features are directly visible in live frustules, need no expertise in identification of diatoms and can be globally assessed with simple protocol. The experimental loss of metal pollutants and the constant immigration of algae (not previously exposed to high levels of metals) in fluvial systems aided periphyton recovery. Lastly, it is found that periphytic biofilms (dominated by diatoms) proved to be good bioindicators of metal toxicity and recovery in fluvial ecosystem.

A New Concept of Promoting Nitrate Reduction in Surface Waters: Simultaneous Supplement of Denitrifiers, Electron Donor Pool, and Electron Mediators

The efficiency of biological nitrate reduction depends on the community composition of microorganisms, the electron donor pool, and the electron mediators participating in the biological reduction process. This study aims at creating an in situ system comprising of denitrifiers, electron donors, and electron mediators to reduce nitrate in surface waters. The ubiquitous periphytic biofilm in waters was employed to promote in situ nitrate reduction in the presence of titanium dioxide (TiO₂) nanoparticles (NPs). The nitrate removal rate in the periphytic biofilm and TiO₂ NPs system was significantly higher than the control (only periphytic biofilm or TiO₂ NPs). TiO₂ NPs optimized the community composition of periphytic biofilm for nitrate reduction by increasing the relative abundance of four dominant denitrifying bacteria. Periphytic biofilm showed a substantial increase in extracellular polymeric substance, especially the humic acid and protein content, due to the presence of TiO₂ NPs. The synergistic action of humic acid, protein, denitrifying bacteria of the periphytic biofilm, and TiO₂ NPs contributed to 80% of the nitrate reduction. The protein and humic acid, acting as electron mediators, facilitated the transfer of exogenous electrons from photoexcited TiO₂ NPs to periphytic biofilm containing denitrifiers, which enhanced nitrate reduction in surface waters.

Effect of TiO2 and CeO2 nanoparticles on the metabolic activity of surficial sediment microbial communities based on oxygen microelectrodes and high-throughput sequencing

Environmental concerns regarding the potential ecological risks of metallic oxide nanoparticles (MNPs) in aquatic ecosystems are increasing; sediment is considered a sink for these MNPs. Although several studies have studied the potential impact of MNPs on microbial communities in freshwater and estuarine sediments, limited information is available regarding the influence of MNPs on the metabolic activity of surficial sediment microbial communities and related biogeochemical conditions. To address these issues, a microcosm approach was established to study the metabolic response of surficial sediment microbial communities to a single addition of TiO₂ or CeO₂ NPs (5 mg/L) using oxygen microelectrodes, enzyme activity measurements, and high-throughput sequencing. Rapid sedimentation of MNPs (regardless of NP type) was observed in freshwater samples, and most (up to 85%) accumulated in surface sediments (<5 mm). Microelectrode profile measurements in pre-incubated sediments treated with MNPs showed that the oxygen concentration decreased at a slower rate with increasing sediment depth compared to that in untreated controls. Biological oxygen consumption in the uppermost sediment layer (0-1500 μm) was significantly inhibited by MNPs, as calculated from steady-state microprofiles, with CeO₂ NPs resulting in enhanced acute toxicity than TiO₂ NPs. High-throughput sequencing showed that MNP exposure increased the bacterial diversity and altered the bacterial community structure, regardless of NP type. The abundance of three dominant bacterial genera, Methylotenera, Cytophagceae_uncultured (classified as an aerobic bacterium), and Cyanobacteria_norank (a facultative bacterium), was markedly reduced by MNPs, which was primarily responsible for inhibiting microbial-mediated oxygen consumption in surficial sediments. In summary, short-term exposure to MNPs negatively affected the metabolic activity of benthic microbial communities, which could influence the biogeochemical functions along the sediment-water interface.

Enhanced effects of maghemite nanoparticles on the flocculent sludge wasted from a high-rate anammox reactor: Performance, microbial community and sludge characteristics

Magnetic nanoparticles (NPs) have been widely applied in environmental remediation, biomass immobilization and wastewater treatment, but their potential impact on anaerobic ammonium oxidation (anammox) biomass remains unknown. In this study, the short-term and long-term impacts of maghemite NPs (MHNPs) on the flocculent sludge wasted from a high-rate anammox reactor were investigated. Batch assays showed that the presence of MHNPs up to 200 mg L^-1 did not affect anammox activity, reactive oxygen species production, or cell membrane integrity. Moreover, long-term addition of 1-200 mg L^-1 MHNPs had no adverse effects on reactor performance. Notably, the specific anammox activity, the abundance of hydrazine synthase structural genes and the content of extracellular polymeric substance were increased with elevated MHNP concentrations. Meanwhile, the community structure was shifted to higher abundance of Candidatus Kuenenia indicated by high-throughput sequencing. Therefore, MHNPs could be applied to enhance anammox flocculent sludge due to their favorable biocompatibility.