Responses of wastewater biofilms to chronic CeO2 nanoparticles exposure: Structural, physicochemical and microbial properties and potential mechanism

Nonlinear responses of biofilm bacteria to alkyl-chain length of parabens by DFT calculation

Parabens can particularly raise significant concerns regarding the disruption of microbial ecology due to their antimicrobial properties. However, the responses of biofilm bacteria to diverse parabens with different alkyl-chain length remains unclear. Here, theoretical calculations and bioinformatic analysis were performed to decipher the influence of parabens varying alkyl-chain lengths on the biofilm bacteria. Our results showed that the disturbances in bacterial community did not linearly response to the alkyl-chain length of parabens, and propylparaben (PrP), with median chain length, had more severe impact on bacterial community. Despite the fact that paraben lethality linearly increased with chain length, the PrP had a higher chemical reactions potential than parabens with shorter or longer alkyl-chain. The chemical reactions potential was critical in the nonlinear responses of bacterial community to alkyl-chain length of parabens. PrP could impose selective pressure to disturb the bacterial community, because it had a more profound contribution to deterministic assembly process. Furthermore, N-acyl-homoserine lactones was also significantly promoted under PrP exposure, confirming that PrP could affect the bacterial community by influencing the quorum-sensing system. Overall, our study reveals the nonlinear responses of bacterial communities to the alkyl-chain lengths of parabens and provides insightful perspectives for the better regulation of parabens. ENVIRONMENTAL IMPLICATION: Parabens are recognized as emerging organic pollutants, which specially raise great concerns due to their antimicrobial properties disturbing microbial ecology. However, few study have addressed the relationship between bacterial community responses and the molecular structural features of parabens with different alkyl-chain length. This investigation revealed nonlinear responses of the bacterial community to the alkyl-chain length of parabens through DFT calculation and bioinformatic analysis and identified the critical roles of chemical reactions potential in nonlinear responses of bacterial community. Our results benefit the precise evaluation of ecological hazards posed by parabens and provide useful insights for better regulation of parabens.

Driving Role of Zinc Oxide Nanoparticles with Different Sizes and Hydrophobicity in Metabolic Response and Eco-Corona Formation in Sprouts (Vigna radiata)

Zinc oxide nanoparticles (ZnO NPs) cause biotoxicity and pose a potential ecological threat; however, their effects on plant metabolism and eco-corona evolution between NPs and organisms remain unclear. This study clarified the molecular mechanisms underlying physiological and metabolic responses induced by three different ZnO NPs with different sizes and hydrophobicity in sprouts (Vigna radiata) and explored the critical regulation of eco-corona formation in root-nano systems. Results indicated that smaller-sized ZnO inhibited root elongation by up to 37.14% and triggered oxidative burst and apoptosis. Metabolomics confirmed that physiological maintenance after n-ZnO exposure was mainly attributed to the effective stabilization of nitrogen fixation and defense systems by biotransformation of the flavonoid pathway. Larger-sized or hydrophobic group-modified ZnO exhibited low toxicity in sprouts, with 0.89-fold upregulation of citrate in central carbon metabolism. This contributed to providing energy for resistance to NP stress through amino acid and carbon/nitrogen metabolism, accompanied by changes in membrane properties. Notably, smaller-sized and hydrophobic NPs intensely stimulated the release of root metabolites, forming corona complexes with exudates. The hydrogen-bonded wrapping mechanism in protein secondary structure and hydrophobic interactions of heterogeneous functional groups drove eco-corona formation, along with the corona evolution intensity of n-ZnO > s-ZnO > b-ZnO based on higher (α-helix + 3-turn helix)/β-sheet ratios. This study provides crucial insight into metabolic and eco-corona evolution in bionano fates.

Impact of changes in biofilm composition response following chlorine and chloramine disinfection on nitrogenous disinfection byproduct formation and toxicity risk in drinking water distribution systems

In practical drinking water treatment, chlorine and chloramine disinfection exhibit different mechanisms that affect biofilm growth. This study focused on the influence of biofilm composition changes, especially extracellular polymeric substance (EPS) fractions, on the potential formation and toxicity of nitrogenous disinfection by-products (N-DBP). Significant differences in microbial diversity and community structure were observed between the chlorine and chloramine treatments. Notably, the biofilms from the chloramine-treated group had higher microbial dominance and greater accumulation of organic precursors, as evidenced by the semi-quantitative confocal laser-scanning microscopy assay of more concentrated microbial aggregates and polysaccharide proteins in the samples. Additionally, the chloramine-treated group compared with chlorine had a higher EPS matrix content, with a 13.5 % increase in protein. Furthermore, the protein distribution within the biofilm differed; in the chlorine group, proteins were concentrated in the central region, whereas in the chloramine group, proteins were primarily located at the water-biofilm interface. Notably, functional prediction analyses of protein fractions in biofilms revealed specific functional regulation patterns and increased metabolism-related abundance of proteins in the chlorine-treated group. This increase was particularly pronounced for proteins such as dehydrogenases, reductases, transcription factors, and acyl-CoA dehydrogenases. By combining the Fukui function and density functional calculations to further analyse the effect of biofilm component changes on N-DBP production under chlorine/chloramine and by assessing the toxicity risk potential of N-DBP, it was determined that chloramine disinfection is detrimental to biofilm control and the accumulation of protein precursors has a higher formation potential of N-DBPs and toxicity risk, increasing the health risk of drinking water.

Phasor-FLIM analysis of cellulose paper ageing mechanism with carbotrace 680 dye

Ageing of paper is a complex process of great relevance for application purposes because of its widespread use as support for information storage in books and documents, and as common low-cost and green packaging material, to name a few. A key factor in paper ageing is the oxidation of cellulose, a macromolecule of natural origin that constitutes the main chemical component of paper. Such a complex process results in changes in the cellulose polymeric chains in chemical and structural properties. The scope of this work is to explore the effects of oxidation of cellulose as one of the principal mechanisms of ageing of paper using a fluorescence-based approach. To this aim, fluorescence-lifetime imaging microscopy (FLIM) measurements on pure cellulose samples stained using Carbotrace 680 dye were performed, and data were analyzed by phasor approach. The comparison with results from conventional techniques allowed to map paper microstructure as a function of the sample oxidation degree correlating the fluorescence-lifetime changes to cellulose oxidation. A two-step oxidation kinetics that produced specific modification in paper organization was highlighted indicating that FLIM measurements using Carbotrace 680 dye may provide a simple tool to obtain information on the oxidation process also adding spatial information at sub-micrometric scale.

Response mechanisms of pipe wall biofilms in water supply networks under different disinfection strategy pressures and the effect of mediating halogenated acetonitrile formation

Residual chlorine and biofilm coexistence is inevitable in drinking water transmission and distribution networks. Understanding the microbial response and its mediated effects on disinfection byproducts under different categories of residual chlorine stress is essential to ensure water safety. The aim of our study was to determine the response of pipe wall biofilms to residual chlorine pressure in chlorine and chloramine systems and to understand the microbially mediated effects on the formation and migration of haloacetonitriles (HANs), typical nitrogenous disinfection byproducts. According to the experimental results, the biofilm response changes under pressure, with significant differences noted in morphological characteristics, the extracellular polymeric substances (EPS) spatial structure, bacterial diversity, and functional abundance potential. Upon incubation with residual chlorine (1.0 ± 0.2 mg/L), the biofilm biomass per unit area, EPS, community abundance, and diversity increased in the chloramine group, and the percentage of viable bacteria increased, potentially indicating that the chloramine group provides a richer variety of organic matter precursors. Compared with the chloramine group, the chlorination group exhibited increased haloacetonitrile formation potential (HANFP), with Rhodococcus (43.2%) dominating the system, whereas the prediction abundance of metabolic functions was advantageous, especially with regard to amino acid metabolism, carbohydrate metabolism, and the biodegradation and metabolism of foreign chemicals. Under chlorine stress, pipe wall biofilms play a stronger role in mediating HAN production. It is inferred that chlorine may stimulates microbial interactions, and more metabolites (e.g., EPS) consume chlorine to protect microbial survival. EPS dominates in biofilms, in which proteins exhibit greater HANFP than polysaccharides.

Dissolved oxygen benefits N-decanoyl-homoserine lactone regulated biological nitrogen removal system to resist acute ZnO nanoparticle exposure

The beneficial effects of N-decanoyl-homoserine lactone (C₁₀-HSL), one of the typical N-acyl-homoserine lactones on biological nitrogen removal (BNR) system to resist the acute exposure of zinc oxide nanoparticles (ZnO NPs) has attracted extensive attentions. Nevertheless, the potential impact of dissolved oxygen (DO) concentration on the regulatory capacity of C₁₀-HSL in the BNR system has yet to be investigated. This study conducted a systematic investigation of the impact of DO concentration on the C₁₀-HSL-regulated BNR system against short-term ZnO NP exposure. Based on the findings, sufficient DO played a crucial role to improve the BNR system's resistance capacity to ZnO NPs. Under the micro-aerobic condition (0.5 mg/L DO), the BNR system was more sensitive to ZnO NPs. The ZnO NPs induced increased intracellular reactive oxygen species (ROS) accumulation, reduced antioxidant enzyme activities, and decreased specific ammonia oxidation rates in the BNR system. Furthermore, the exogenous C₁₀-HSL had a positive effect on the BNR system's resistance to ZnO NP-induced stress, primarily by decreasing ZnO NPs-induced ROS generation and improving ammonia monooxygenase activities, especially under low DO concentrations. The findings contributed to the theoretical foundation for regulation strategy development of wastewater treatment plants under NP shock threat.

Performance of constructed wetlands with different water level for treating graphene oxide wastewater: Characteristics of plants and microorganisms

Constructed wetlands (CWs) have been expected advantages in emerging pollutant removal, but with less known on their characteristic when treating wastewater containing graphene oxide (GO). In present study, we investigated characteristics of Iris pseudacorus, microorganisms, and pollutant removal in CWs with 60 cm and 37 cm water level (termed HCW and LCW). Plants in LCW had higher chlorophyll content and lower activities of antioxidant enzyme (superoxide dismutase, catalase, peroxidase) as well as malondialdehyde content. Substrate enzyme activities were affected by time and CW type. LCW increased only dehydrogenase activities, while HCW increased catalase, urease, neutral phosphatase, and arylsulfatase activities. Sequencing analysis revealed that microbial community showed higher richness and diversity in LCW, but this dissimilarity could be eased by time-effect. Proteobacteria (25.62-60.36%) and Actinobacteria (13.86-56.20%) were stable dominant phyla in CWs. Ratio of Proteobacteria/Acidobacteria indicated that trophic status of plant rhizosphere zone was lower in LCW. Nitrospirae were enriched to 0.16-0.68% and 0.75-1.42% in HCW and LCW. The enrichment of phyla Proteobacteria and Firmicutes in HCW was attributed to class Gammaproteobacteria and genus Enterococcus. GO transformation showed some reductions in CWs, which could be affected by water depth and substrate depth. Overall, HCW achieved nitrogen and phosphorus removal for 48.78-62.99% and 95.01%, which decreased by 8.41% and 7.31% in LCW. COD removal was less affected reaching 93%. This study could provide some new evidence for CWs to treat wastewater containing GO.

Performance Enhancement of Biogenetic Sulfidated Zero-Valent Iron for Trichloroethylene Degradation: Role of Extracellular Polymeric Substances

Chemical sulfidation has been considered as an effective strategy to improve the reactivity of zero-valent iron (S-ZVI). However, sulfidation is a widespread biogeochemical process in nature, which inspired us to explore the biogenetic sulfidation of ZVI (BS-ZVI) with sulfate-reducing bacteria (SRB). BS-ZVI could degrade 96.3% of trichloroethylene (TCE) to acetylene, ethene, ethane, and dichloroethene, comparable to S-ZVI (97.0%) with the same S/Fe ratio (i.e., 0.1). However, S-ZVI (0.21 d^-1) exhibited a faster degradation rate than BS-ZVI (0.17 d^-1) based on pseudo-first-order kinetic fitting due to extracellular polymeric substances (EPSs) excreted from SRB. Organic components of EPSs, including polysaccharides, humic acid-like substances, and proteins in BS-ZVI, were detected with 3D-EEM spectroscopy and FT-IR analysis. The hemiacetal groups and redox-activated protein in EPS did not affect TCE degradation, while the acetylation degree of EPS increased with the concentration of ZVI and S/Fe, thus inhibiting the TCE degradation. A low concentration of HA-like substances attached to BS-ZVI materials promoted electron transport. However, EPS formed a protective layer on the surface of BS-ZVI materials, reducing its TCE reaction rate. Overall, this study showed a comparable performance enhancement of ZVI toward TCE degradation through biogenetic sulfidation and provided a new alternative method for the sulfidation of ZVI.

Self-cleaning and regenerable nano zero-valent iron modified PCN-224 heterojunction for photo-enhanced radioactive waste reduction

The expansion of large-scale nuclear power causes a substantial volume of radioactive wastewater containing uranium to be released into the environment. Because of uranium's toxicity and bioaccumulation, it is critical to develop the efficient and sustainable materials for selective removal of uranium (VI). Herein, a regenerable anti-biofouling nano zero-valent iron doped porphyrinic zirconium metal-organic framework (NZVI@PCN-224) heterojunction system was successfully fabricated. Due to the Schottky-junction effect at the NZVI/MOF interface, the NZVI nanomaterial immobilized on PCN-224 could improve interfacial electron transfer and separation efficiency, and enhance entire reduction of highly soluble U(VI) to less soluble U(IV), involving photocatalytic reduction and chemical reduction. Meanwhile, the photocatalytic effect also prompts the NZVI@PCN-224 to produce more biotoxic reactive oxygen species (ROS), resulting in high anti-microbial and anti-algae activities. Under dark conditions, NZVI@PCN-224 with a large specific surface area could provide sufficient oxo atoms as the uranium binding sites and show the highest uranium-adsorbing capability of 57.94 mg/g at pH 4.0. After eight adsorption-desorption cycles, NZVI@PCN-224 still retained a high uranium adsorption capacity of 47.98 mg/g and elimination efficiency (91.72%). This sorption/reduction/anti-biofouling synergistic strategy of combining chelation, chemical reduction and photocatalytic performance inspires new insights for highly efficient treatment of liquid radioactive waste.

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.

Evaluating the role of algae in algal-bacterial granular sludge: Nutrient removal, microbial community and granular characteristics

Algal-bacterial granular sludge (ABGS) and bacterial granular sludge (BGS, control group) were operated over 240 days to investigate the role of algae in treating synthetic municipal wastewater. The results showed that algae significantly improved the removal efficiency of total nitrogen (TN). The nitrogen removal load of ABGS was 2.6 mg-N/g-VSS/day (22.8 %, light) and 1.1 mg-N/g-VSS/day (9.6 %, dark) higher than that of BGS, respectively, which was attributed to algae enhanced NH₃-N removal capacity in the anaerobic stage and increased the utilization efficiency of organics in denitrification. Algae increased the relative abundance of denitrifying bacteria, and ABGS (28.83 %) was higher than BGS (14.28 %). Moreover, the dominant phylum of algae was Chlorophyta (98.39 %), the chlorophyll-a was sustained at 1.28 ± 0.26 mg/g-VSS. Algae significantly increased the content of extracellular polymeric substances (EPS), and the increased polysaccharide came from the tightly bound EPS. This study expands the understanding of the role of algae in ABGS.

Ecological restoration performance enhanced by nano zero valent iron treatment in constructed wetlands under perfluorooctanoic acid stress

Perfluorooctanoic acid (PFOA) of widespread use can enter constructed wetlands (CWs) via migration, and inevitably causes negative impacts on removal efficiencies of conventional pollutants due to its ecotoxicity. However, little attention has been paid to strengthen performance of CWs under PFOA stress. In this study, influences of nano zero valent iron (nZVI), which has been demonstrated to improve nutrients removal, were explored after exemplifying threats of PFOA to operation performance in CWs. The results revealed that 1 mg/L PFOA suppressed the nitrification capacity and phosphorus removal, and nZVI distinctly improved the removal efficiency of ammonia and total phosphorus in CWs compared to PFOA exposure group without nZVI, with the maximum increases of 3.65 % and 16.76 %. Furthermore, nZVI significantly stimulated dehydrogenase (390.64 % and 884.54 %) and urease (118.15 % and 246.92 %) activities during 0-30 d and 30-60 d in comparison to PFOA group. On the other hand, nitrifying enzymes were also promoted, in which ammonia monooxygenase increased by 30.90 % during 0-30 d, and nitrite oxidoreductase was raised by 117.91 % and 232.10 % in two stages. Besides, the content of extracellular polymeric substances (EPS) under nZVI treatment was 72.98 % higher than PFOA group. Analyses of Illumina Miseq sequencing further certified that nZVI effectively improved the community richness and caused the enrichment of microorganisms related to nitrogen and phosphorus removal and EPS secreting. These results could provide valuable information for ecological restoration and decontamination performance enhancement of CWs exposed to PFOA.

Effects of changes in UV-B radiation levels on biofilm-forming organisms commonly found in cultural heritage surfaces

Accurate measuring and monitoring methods available since the 1980s have shown that the amount of Ultraviolet B (UV-B) radiation reaching the Earth's surface has increased as a result of degradation of the ozone layer. Since the adoption of the Montreal Protocol in 1987, ozone levels have been recovering successfully. However, in the context of the current climate change, other factors such as changes in cloud patterns and an increased incidence of natural disasters (e.g. fires) may be disrupting this recovery. The present study aimed to investigate the effects of different UV-B radiation levels on biofilms colonising heritage monuments. For this purpose, the effects of current UV-B levels on a biofilm composed of Synechocystis sp. (a cyanobacterium), Bracteacoccus minor (a green alga) and Fusarium sp. (a fungus) were compared at three points along a South-North transect: Portugal, Galicia (NW Spain) and Ireland (from highest to lowest UV-B radiation, respectively). Increased levels of UV-B radiation caused changes in the growth, physiological state and composition of subaerial biofilms, with cyanobacteria being more resistant than green algae to high levels of UV-B. A reduction of fungal growth and extracellular polymer substances (EPS) production was also observed, related to the reduction of biofilm aggregation at high UV-B levels.

Removal of tetracycline by biochar-supported biogenetic sulfidated zero valent iron: Kinetics, pathways and mechanism

The application of zero-valent iron (ZVI) is limited due to passivation and agglomeration. Therefore, biochar loading (MB) and biogenetic sulfidation via sulfate-reducing bacteria (SRB) were used to improve the reactivity of ZVI (BS-ZVI@MB) towards tetracycline (TC) degradation. Biochar provided more attachment sites for ZVI and SRB, thus alleviating the agglomeration. Additionally, quinone groups on biochar enhanced the electrons transfer through the measurement of electron donating/accepting capacities, and biogenetic sulfidation could inhibit the surface passivation of ZVI. Fe(Ⅱ/Ⅲ) produced after the addition of BS-ZVI@MB could complex with the A ring in TC to form Fe(Ⅱ/Ⅲ)-TC, which brought the oxidation of TC by complexed Fe(Ⅲ). Reactive oxygen species (ROS)(primarily •OH) were generated during the oxidation of Fe(Ⅱ), so as to promote the TC degradation. Extracellular polymeric substances (EPS) secreted from SRB had a slight quenching effect on ROS. Meanwhile, EPS formed a protective layer with Fe(Ⅱ/Ⅲ) on BS-ZVI@MB, reducing its reactivity with TC. Overall, this study showed an efficient modification technology of ZVI by biogenetic sulfidation and biochar loading for TC degradation.

Pluripotency of endogenous AHL-mediated quorum sensing in adaptation and recovery of biological nitrogen removal system under ZnO nanoparticle long-term exposure

The impacts of quorum sensing (QS) on nanoparticle (NP)-stressed biological nitrogen removal (BNR) system have seldom been addressed yet. In this study, the contributions of endogenous N-acyl-homoserine lactone (AHL)-based QS regulation to the BNR system's adaptation to the zinc oxide (ZnO) NP stress and its recovery potential were systematically investigated. Although 1 mg/L ZnO NPs exerted little impact on the BNR system, chronic exposure to 10 mg/L ones depressed the system's BNR performance which irreversibly impaired the nitrification process even when the system entered the recovery period with no NP added anymore. Meanwhile, ZnO NPs exhibited hormesis effects on the production of AHLs and extracellular polymeric substance (EPS), and activities of superoxide dismutase and catalase. During the ZnO NP exposure period, C₄-HSL, C₆-HSL, and C₁₀-HSL were discovered to be positively associated with nitrogen removal efficiency, tightly-bound EPS production, and antioxidase activities. Besides, the shifts of Nitrospira, Dechloromonas, Aeromonas, Acinetobacter, Delftia, and Bosea were expected to determine the AHL's dynamic distribution. During the system's recovery stage, Dechloromonas replaced Candidatus_Competibacter as the dominant denitrification-related genus. Dechloromonas abundance elevated with the increased contents of C₄-HSL in the aqueous and EPS phases and C₁₀-HSL in EPS and sludge phases, and were expected to promote the activities of BNR-related and antioxidant enzymes, and the EPS production to assist in the recovery of the impaired system's BNR performance. The QS-related BNR genera exhibited higher resilience to ZnO NPs than quorum quenching-related ones, indicating their critical role in nitrogen removal in the restored system. This work provided an insight into the potential pluripotency of AHL-based QS regulation on the ZnO NP-stressed BNR system's adaptation and recovery.

How multi-walled carbon nanotubes in wastewater influence the fate of coexisting antibiotic resistant genes in the subsequent disinfection process

Wastewater treatment plants (WWTPs) are important hubs for the spread of antibiotic resistance genes (ARGs). Engineered nanoparticles, which was inevitably released to WWTPs, could change environmentally sensitive of antibiotic resistant bacteria (ARB). This would influence the fate of ARGs in subsequent disinfection process and consequent health risk. In this study, the ARGs fate of the effluent in conventional sodium hypochlorite (NaClO) disinfection process was investigated as multi-walled carbon nanotubes (MWCNTs) existed in sequencing batch reactor (SBR). The results showed the existence of MWCNTs in SBR could enhance the removal efficiency of intracellular 16S rRNA gene and intI1, extracellular intI1, sul2 and tetX in the effluent by NaClO. This is mainly due to the variation of bacterial physiological status, bacterial population structure and the activation of NaClO under the role of MWCNTs. MWCNTs in SBR could increase in membrane permeability of bacterial cells, which would be conducive to the penetration of chlorination to cytoplasm. MWCNTs in SBR also could change the bacterial population structure and induce the chlorine-sensitive bacteria; thus the potential hosts of ARGs in the effluent would be more easily inactivated by NaClO. Moreover, the residual MWCNTs in the effluent could activate NaClO to generate various free radical, which would enhance the oxidizing capacity of chlorination.

Can the carbon metabolic activity of biofilm be regulated by the hydrodynamic conditions in urban rivers?

Hydrodynamic regulation is widely used to improve the water quality of urban rivers. However, it is yet to explore substantially whether hydrodynamics could regulate the metabolic activity of biofilm in such aquatic systems. Herein, the pilot experiment of hydrodynamics in the rotation tanks was designed, including two experiment phases, namely constant flow and adjusting flow for 21 days and 14 days, respectively. In constant flow phase, biofilms grew in five shear stress gradients (R1-R5, 0.0044- 0.12 Pa). The carbon metabolic rate (k) of mature biofilms evaluated by BIOLOG ECO microplates showed a hump-shaped relationship with increasing shear stress, with R3 (0.049 Pa) the highest, while R5 (0.12 Pa) the lowest. To verify whether the metabolic activity of biofilm cultured at constant flow phase can be regulated by shear stress, we initiated the adjusting flow phase, and shear stress in reactors was reset uniformly at 0.049 Pa (with the highest k). Results showed the carbon metabolic activity of biofilm in reactor R4 and R5 increased rapidly by day 3, and there was no significant difference between the carbon metabolic rates among the five treatments by day 14. Meanwhile, the utilization levels of polymers and carbohydrates by biofilms were significantly different among the five treatments after hydrodynamic regulations. These results suggested that the total carbon metabolic activity of biofilm can be regulated by hydrodynamics, while the divergent changes of the specific carbon source category might affect the biofilm-mediated carbon biogeochemical processes, which should be considered for the application of hydrodynamic regulation in river ecological restoration projects.

Pyrogenic carbon facilitated microbial extracellular electron transfer in electrogenic granular sludge via geobattery mechanism

Electroactive pyrogenic carbon (PC) is an intriguing candidate for realizing the ambitious goals of large-scale applications of microbial electrochemical technologies (METs). In this study, PC was employed to promote the extracellular electron transfer (EET) within the electrogenic granular sludge (EGS) by acting as an electron conduit. The pecan shell-derived PC prepared at three temperatures (600, 800, and 1000 ˚C) contained rich oxygenated-functional moieties (mainly quinone) on the surface, endowing a good electron transfer capacity (EEC). The maximum current density (J_max) of EGS with PC amendment outperformed the control EGS without PC amendment, i.e., 100-132 times higher than J_amx of EGS in the absence of PC. Among various pyrolysis temperatures, the PC derived from 600 ˚C produced the highest J_max (0.40 A/ m²), 0.67-times, and 0.33-times higher than that of PC derived from 800 and 1000 ˚C, respectively. Furthermore, more polysaccharides were secreted in extracellular polymeric substance with PC amendments. The microbial community analysis demonstrated that the PC favored the growth of electroactive bacteria over methanogens. The metabolic pathway revealed that PC induced more functional enzymes in the quinone biosynthesis and cytochrome c and heme synthesis, resulting in an enhanced EET. The EEC of PC was responsible for the EET enhancement effect via PC acting as a geobattery to wire up the EGS and electrodes. Overall, this study pinpoints the finding of PC role in a mixed electroactive biofilm and provides a wide scenario of the PC applications in MET at large scales.

Effect of CeO2 nanoparticles on plant growth and soil microcosm in a soil-plant interactive system

The impact of CeO₂ nanoparticles (NPs) on plant physiology and soil microcosm and the underlying mechanism remains unclear to date. This study investigates the effect of CeO₂ NPs on plant growth and soil microbial communities in both the rhizosphere of cucumber seedlings and the surrounding bulk soil, with CeCl₃ as a comparison to identify the contribution of the particulate and ionic form to the phytotoxicity of CeO₂ NPs. The results show that Ce was significantly accumulated in the cucumber tissue after CeO₂ NPs exposure. In the roots, 5.3% of the accumulated Ce has transformed to Ce³⁺. This transformation might take place prior to uptake by the roots since 2.5% of CeO₂ NPs was found transformed in the rhizosphere soil. However, the transformation of CeO₂ NPs in the bulk soil was negligible, indicating the critical role of rhizosphere chemistry in the transformation. CeO₂ NPs treatment induced oxidative stress in the roots, but the biomass of the roots was significantly increased, although the Vitamin C (Vc) content and soluble sugar content were decreased and mineral nutrient contents were altered. The soil enzymatic activity and the microbial community in both rhizosphere and bulk soil samples were altered, with rhizosphere soil showing more prominent changes. CeCl₃ treatment induced similar effects although less than CeO₂ NPs, suggesting that Ce³⁺ released from CeO₂ NPs contributed to the CeO₂ NPs induced impacts on soil health and plant physiology.

Effects of pipe materials on the characteristic recognition, disinfection byproduct formation, and toxicity risk of pipe wall biofilms during chlorination in water supply pipelines

There are growing concerns over the contributions of biofilms to disinfection byproduct (DBP) formation in engineered water systems (EWSs). Three kinds of water supply pipes, ductile iron (DI), cement-lined stainless steel (SS) and polyethylene (PE) pipes, were selected for the experiment conducted in this study. Based on test results, the three pipe biofilms showed relatively obvious differences in growth, morphological characteristics, organic components and bacterial diversity. Secreted extracellular polymeric substance (EPS) accounted for more than 90% of the biofilm and had greater disinfection byproduct formation potential (DBPFP) than the cell phases. DI pipe wall biofilms had the highest DBPFP, which to a certain extent means that denser and richer organic matter can be produced as the precursor of different types of DBPs. UHPLC-Q Exactive was used to identify the types of DBPs generated from the chlorination of histidine (His), alanine (Ala) and tryptophan (Trp) shared by the three pipe materials and their formation pathways. Compared to carbonaceous disinfection by-products (C-DBPs), nitrogenous disinfection by-products (N-DBPs) had a significant advantage in toxicity generation potentials in the biofilms, especially dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM). DCAN and haloacetic acids (HAAs) were the key to cytotoxicity in biofilms, while TCNM was dominant in biofilm genotoxicity.

Effect of long-term low concentrations of TiO2 nanoparticles on dewaterability of activated sludge and the relevant mechanism: the role of nanoparticle aging

Nanoparticles can undergo aging phenomena in sewage treatment systems, which alter their physical and chemical properties. However, the effect of aged nanoparticles on the dewatering performance of activated sludge under long-term low concentrations is yet to be reported in sewage treatment systems. Here, we compared the chronic effects of pristine and aged TiO₂ nanoparticles on the sludge dewatering index, which includes specific resistance to filtration (SRF) and bound water (BW) in a sequencing batch reactor (SBR) at μg/L concentration levels, and analyzed the relevant mechanisms. The results indicated that aging in the sludge supernatant altered the photosensitivity and water stability of nanoparticles, which was mainly due to the changes in the zeta potential and energy band of the particle and was ultimately attributed to the combined effect of particle surface inclusions such as organic matter and inorganic salt. At 10 μg/L, nanoparticles reduced the sludge dewaterability, which observed an improvement at 100 μg/L. This is because 10 μg/L promoted the secretion of extracellular polymeric substances (EPS), which regulated the structure of sludge flora and increased the abundance of secreted quorum sensing-acyl-homoserine lactones (QS-AHL) and EPS genera, while the corresponding exposure results for 100 μg/L were the opposite, owing to the damage and necrosis effects caused by exposure under long-term light, which reduced EPS production and increased sludge density. Interestingly, aging could alleviate the effects of two exposure concentrations on sludge dewatering, mainly because of the decrease in the photoactivity of the nanoparticles. The results of this study show that environmental aging could delay, but not reverse the results of exposure to specific concentrations of nanoparticles. However, the significantly different ecological effects of photosensitive nanoparticles with two environmentally relevant concentration should be refined and confirmed again in freshwater environments to provide a basis for subsequent scientific management and control of photosensitive nanoparticles.

Impact of pipe material and chlorination on the biofilm structure and microbial communities

Pipe material and residual chlorine are key factors for the drinking water distribution system, and understanding the biofilm ecosystem is vital for water quality safeguard. The aim of our study was to determine the influence of pipe materials (ductile iron, steel, polyethylene) and chlorination on the biofilm structure and microbial community, as shown by the physicochemical properties, extracellular polymeric substances (EPS) structural characteristics, bacterial community composition, and functional traits. EPS spatial properties were studied based on a semi-quantitative confocal laser scanning microscope (CLSM) description. Regarding the impact of chlorination, residule chlorine (1.0 ± 0.3 mg L^-1 free chlorine) could inhibit the bacteria colonization, and initiate a potential response to external disinfectants revealed by the EPS spatial distribution changes and communities variation compared to unchlorinated system. Regarding the impact of pipe material, polyethylene (PE) biofilms displayed lower biomass, loose zoogloea structure, lower proteins and polysaccharides content, and poor microbial diversity in contrast to ductile iron and steel biofilms. Pipe material was the more possible driving factor of the biofilm community composition compared to the chlorination based on principal coordinates analysis (PCoA) and permutational multivariate analysis of variance (PERMANOVA). Actinobacteria was dominant in the PE biofilms (45.57%-83.32%), while Alphaproteobacteria (34.30%-73.22%) and Gammaproteobacteria (6.46%-36.82%) were the major classes in the steel and ductile iron biofilms. The genus Rhodococcus was predominant in the PE biofilms. Rhodococcus, Pseudomonas, and Sphingomonas seemed to have a better growth advantage in the chlorinated system and display a stronger disinfectant resistance. Functional sketch prediction indicated the potential impact of pipe material and chlorination on functional pathway abundnce, possible functional pathways associated with infectious disease included. This study provides insights into the impact of pipe material and chlorination on biofilm structure and microbial community and might help to develop monitoring or maintenance strategies to protect the biosafety of the drinking water.

Heterogeneous Structure Regulated by Selection Pressure on Bacterial Adhesion Optimized the Viability Stratification Structure of Electroactive Biofilms

As the core of microbial fuel cells (MFCs), the components and structure of electroactive biofilms (EABs) are essential for MFC performance. Bacterial adhesion plays a vital role in shaping the structure of EABs, but the effect of bacterial adhesion under selection pressure on EABs has not been systematically studied. Here, the response of the composition, structure, and electrochemical performance of EABs to the selective adhesion pressure due to the selective coordination of Fe(III) and Co(II) with thiol and the different affinities for bacteria on hybrid electrodes (Fe₁Co, Fe₄Co, and Fe₁₀Co) were comprehensively investigated. Compared with carbon cloth (CC), the appropriate selective adhesion pressure of Fe₄Co activated the dead inner core of EABs and optimized their viability stratification structure. Both the total viability and the viability of the inner core layer in the Fe₄Co EAB (0.67, 0.70 ± 0.01) were higher than those of the CC (0.46, 0.54 ± 0.01), Fe₁Co (0.50, 0.48 ± 0.03), and Fe₁₀Co (0.51, 0.51 ± 0.03). Moreover, a higher proportion of proteins was detected in the Fe₄Co EAB, enhancing the redox activity of extracellular polymeric substances. Fe₄Co enriched Geobacter and stimulated microbial metabolism. Electrochemical analysis revealed that the Fe₄Co EAB was the most electroactive EAB, with a maximum power density of 2032.4 mW m^-2, which was 1.7, 1.3, and 1.1 times that of the CC (1202.6 mW m^-2), Fe₁Co (1610.3 mW m^-2), and Fe₁₀Co (1824.4 mW m^-2) EABs, respectively. Our findings confirmed that highly active EABs could be formed by imposing selection pressure on bacterial adhesion.

Insight into the role of extracellular polymeric substances in denitrifying biofilms under nitrobenzene exposure

Denitrifying biofilm promises to be very useful for remediation of nitro-aromatic compounds (NACs) and nitrates in wastewater. Little is known about the role of extracellular polymeric substances (EPS) in nitrobenzene (NB, a typical NAC) remediation, despite the indispensability of EPS for biofilm formation. Herein, the significance of the mechanistic role of EPS in the response of denitrifying biofilms to various levels of NB was investigated. The removal of NB was predominantly controlled via absorption, with little biodegradation during the short-term exposure. Specifically, NB was adsorbed by EPS, as shown by a total adsorption of 40.06% at the initial step, which declined to around 10.52% in the equilibrium stage, while sorption via cells gradually increased from 59.93% to 89.47% over the same period. The results suggested that EPS might act as an important reservoir for NB, which endows inner cells with increased adsorption ability. The presence of EPS might also alleviate the negative impacts of NB toxicity on inner cells, thus protecting microorganisms. This was indicated by the difference in denitrification performance and cell integrity between intact and EPS-free biofilms. High-throughput sequencing data demonstrated that EPS could maintain the stability of microbial communities under NB stress. The fluorescence quenching analysis further indicated that EPS formed stable complexes with NB mainly through hydrophobic interactions with protein-like fractions (tryptophan and tyrosine). Moreover, Fourier transform infrared spectroscopy identified that the hydroxyl, amino, carboxyl, and phosphate groups of EPS were the candidate functional groups binding with NB. Protein secondary structures were also significantly affected, resulting in a loose structure and enhanced hydrophobic performance for EPS. These results provide insights into the role of EPS in alleviating NB-caused cellular stress and the underlying binding mechanisms between NB and EPS.

Deciphering the effects of CeO2 nanoparticles on Escherichia coli in the presence of ferrous and sulfide ions: Physicochemical transformation-induced toxicity and detoxification mechanisms

The physicochemical transformations as well as the redox reaction-induced toxicity changes of ceria nanoparticles (CeO₂ NPs) in reducing conditions is extremely lacking. Herein, the behaviors, chemical modifications and toxicity of CeO₂ NPs in the presence of reduction-active ions (namely Fe²⁺ and S^2-) were investigated, with a particular emphasis on the cytotoxicity mechanism associated with their physicochemical transformations. The presence of Fe²⁺ and S^2- differently altered the surface properties and toxicity of CeO₂ NPs. Redox reactions with Fe²⁺ led to form small aggregates, boosted the reduction of Ce^IVO₂ and enhanced dissolved Ce³⁺ concentration. Moreover, CeO₂ NPs possessed a high affinity for Escherichia coli (E. coli) and induced the generation of •OH abiotically after reaction with Fe²⁺, provoking serious disruption of cell membranes and causing high toxicity to E. coli. In contrast, the amending of S^2- protected E. coli from direct contact with CeO₂ NPs by creating new Ce₂S₃ precipitated on the surface, accelerating the aggregation of NPs and reducing the concentration of dissolved Ce³⁺. This study suggested that the chemical interactions between the reactive surfaces of CeO₂ and reduction-active ions highly determined the stability and cytotoxicity of CeO₂ NPs, which provides fundamental insights into the environmental risks of CeO₂ NPs.

Excessive extracellular polymeric substances induced by organic shocks accelerate electron transfer of oxygen reducing biocathode

Electrotrophic bacteria on cathodes are promising substitutes to precious metals as oxygen reduction reaction catalysts in bioelectrochemical systems (BESs). Leading the anodic effluent to the biocathode has additional benefits of neutralizing pH and removing residual pollutants. However, the overflow of excessive organic pollutants inhibits the activity of autotrophic biocathodes. Adding glucose as an organic shock, we confirm that the startup time of biocathodes is initially prolonged by 1.2 times with a decrease in current. However, the currents inversely surpass the control in glucose-added BESs when the biofilm is mature, and the maximum current density increase by 5.5 times with a relatively stable performance. This increase is mainly attributed to the production of agglomerates dominated by polysaccharides and proteins as extracellular polymeric substances. These agglomerates wrap additional redox shuttles that accelerated the electron transfer between electrotrophic bacteria and the cathode. This study demonstrates for the first time that organic shocks enhance the electroactivity of autotrophic biocathodes and provides insights into the feedback mechanisms of electrotrophic microbial community to environmental changes.

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.

Distinct microbial metabolic activities of biofilms colonizing microplastics in three freshwater ecosystems

Concerns are growing about the increasing amounts of microplastics (MPs) and their ecological impacts, especially the influences of "plastisphere" in the freshwater ecosystems. Although the microbial structure and composition of biofilms are investigated, knowledge of their microbial functions remains limited. Herein, we investigated the functional diversity of carbon metabolism in biofilms colonizing one inert (glass) and two MPs as polyvinyl chloride (PVC) and polyethylene terephthalate (PET) substrates incubated for 44 days in situ in the Niushoushan River, the Qinhuai River, and Donghu Lake. 2D confocal laser scanning microscopy images visualized distinct micro-structures and biofilm compositions on three substrates. BIOLOG ECO microplates indicated variation on carbon utilization capacities of biofilms of inert and MPs in three freshwater ecosystems. Biofilms on PET showed lower capacities and carbon metabolism rates than those on glass and PVC, indicating the presence of substrate-specific functional diversity. The Shannon-Wiener diversity, Simpson diversity and Shannon evenness indices for the Niushoushan River and Donghu Lake were ordered as glass > PVC > PET. Besides to MPs-specific factors, environmental factors including nutrient (i.e., TN and TP) and turbidity largely shaped biofilm carbon metabolism. Overall findings demonstrated that as specific niches, MPs influenced microbial-mediated carbon cycling in the freshwater ecosystems and MPs-promoted microbial communities posed ecological significance.

Effects of Escherichia coli pollution on decomposition of aquatic plants: Variation due to microbial community composition and the release and cycling of nutrients

Determination of the effects of Escherichia coli (E. coli) pollution on agricultural pond ecosystems with vegetation at different life stages is essential for the protection of ecological functions. However, no comprehensive study has yet shown the responses of epiphytic microbial communities to E. coli invasion during plant decay. Thus, this study was conducted to clarify variation in the decay of the following aquatic plants-Myriophyllum aquaticum, Nymphaea tetragona and Phragmites australis after E. coli pollution. Exogenous E. coli especially shifted the epiphytic microbial composition and distribution of P. australis. Stronger effects of E. coli on the archaeal community (edges/nodes = 0.818 < 1, modularity = 0.654; lower clustered structure, 0.389) were found than on the bacterial community (edges/nodes = 1.538 > 1, modularity = 1.291 > 0.654; higher clustered, 0.593). During plant decomposition, E. coli weakened methanogenesis by regulating the network of core genera Methanobacterium and Methanospirillum (spearman, P <  0.05), stimulated the accumulation of organic matters in water (P <  0.05). Similarly, nitrification and denitrification increased and decreased through network regulation in relative biomass of genera Devosia and Desulfovibrio (P <  0.05), respectively. The results provided theoretical supports for eutrophication management in pond ecosystems threatened by E. coli pollution.

Surface Properties and Environmental Transformations Controlling the Bioaccumulation and Toxicity of Cerium Oxide Nanoparticles: A Critical Review

Increasing production and utilization of cerium oxide nanoparticles (CNPs) in recent years have raised wide concerns about their toxicity. Numerous studies have been conducted to reveal the toxicity of CNPs, but the results are sometimes contradictory. In this review, the most important factors in mediating CNPs toxicity are discussed, including (1) the roles of physicochemical properties (size, morphology, agglomeration condition, surface charge, coating and surface valence state) on CNPs toxicity; (2) the phase transfer and transformation process of CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S^2-, and ferrous ions. The physicochemical properties play key roles in the interactions of CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused by reactions with (in)organic ligands in both environmental and biological systems would further alter their fate, transport, and toxicity potential. Thus, the toxicity mechanisms are proposed based on the physical damage of direct adsorption of CNPs onto the cell membrane and chemical inhibition (including oxidative stress and interaction of CNPs with biomacromolecules). Finally, the current knowledge gaps and further research needs in identifying the toxicological risk factors of CNPs under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide new insights into cost-effectiveness of control options and management practices to prevent environmental risks from CNPs exposure.

Effects of heavy metals and metal (oxide) nanoparticles on enhanced biological phosphorus removal

With the rapid growth of economics and nanotechnology, a significant portion of the anthropogenic emissions of heavy metals and nanoparticles (NPs) enters wastewater streams and discharges to wastewater treatment plants, thereby potentially posing a risk to the bacteria that facilitate the successful operation of the enhanced biological phosphorus (P) removal (EBPR) process. Although some efforts have been made to obtain detailed insights into the effects of heavy metals and metal (oxide) nanoparticles [Me(O)NPs], many unanswered questions remain. One question is whether the toxicity of Me(O)NPs originates from the released metal ions. This review aims to holistically evaluate the effects of heavy metals and Me(O)NPs. The interactions among extracellular polymeric substances, P, and heavy metals [Me(O)NPs] are presented and discussed for the first time. The potential mechanisms of the toxicity of heavy metals [Me(O)NPs] are summarized. Additionally, mathematical models of the toxicity and removal of P, heavy metals, and Me(O)NPs are overviewed. Finally, knowledge gaps and opportunities for further study are discussed to pave the way for fully understanding the inhibition of heavy metals [Me(O)NPs] and for reducing their inhibitory effect to maximize the reliability of the EBPR process.

Insight into formation and biological characteristics of Aspergillus tubingensis-based aerobic granular sludge (AT-AGS) in wastewater treatment

The long start-up time and facile biomass loss of aerobic granular sludge (AGS) impede its application for actual wastewater treatment. The present study investigates a novel assist-aggregation strategy based on Aspergillus tubingensis (AT) mycelium pellets to accelerate sludge granulation, and engineered Fe₃O₄ nanoparticles (NPs) were used to further enhance flocculent sludge (FS) aggregation. The AT mycelium pellets, modified by 0.5 g/L Fe₃O₄@SiO₂-QC NPs (AT-V), had a more compact internal structure than the unmodified group (AT-I). The content of extracellular polymeric substances (EPS) and the zeta potential values were observed to increase from 39.86 mg/gVSS and -9.19 mv for AT-I to 69.64 mg/gVSS and 2.35 mv for AT-V, respectively. In optimized cultivation conditions, the aggregated sludge biomass of AT-V reached 1.54 g/g. An original AT-based AGS (AT-AGS) with a high biological activity (64.45 mgO₂/gVSS·h as specific oxygen uptake rate) and enhanced velocity (58.22 m/h) was developed in only 9 days. The removal efficiencies of total nitrogen (TN) and total phosphorus (TP) of the AT-AGS were 12.24% and 16.29% higher than those of the inoculated FS under high feeding load. Additionally, the analysis of cyclic diguanylate (c-di-GMP) and con-focal microscope images implied that polysaccharide (PS) of EPS played an important role in maintaining the stability of the AT-AGS. Finally, the dominant functional species contributing to sludge aggregation and pollutants removal of the AT-AGS showed a larger richness and diversity than those of the inoculated FS. This study might provide a novel high-efficiency strategy for the fast formation of AGS.

Pilot-scale study on the effects of cyanobacterial blooms on Vallisneria natans and biofilms at different phosphorus concentrations

Cyanobacterial blooms cause potential risk to submerged macrophytes and biofilms in eutrophic environments. This pilot-scale study investigated the growth, oxidative responses, and detoxification activity of aquatic plants in response to cyanobacterial blooms under different phosphorus concentrations. Variations of extracellular polymeric substances (EPSs) and microbial community composition were also assessed. Results showed that the biomass of Vallisneria natans increased with exposure to cyanobacterial blooms at higher phosphorous concentrations (P > 0.2 mg L^-1). The amount of microcystin compounds (MC-LR) released into the water and the accumulation of MC-LR into both plant tissue and biofilms changed according to the phosphorus concentration. Furthermore, a certain degree of oxidative stress was induced in the plants, as evidenced by increased activity of superoxide dismutase, catalase, and peroxidase, as well as increased malondialdehyde concentrations; significant differences were also seen in acid phosphatase and glutathione S-transferase activities, as well as in glutathione concentrations. Together, these responses indicate potential mechanisms of MC-LR detoxification. Broader α-D-glucopyranose polysaccharides (PS) increased with increasing phosphorous and aggregated into clusters in biofilm EPS in response to the cyanobacterial blooms. In addition, alterations were seen in the abundance and structure of the microbial communities present in exposed biofilms. These results demonstrate that cyanobacterial blooms under different concentrations of phosphorus can induce differential responses, which can have a significant impact on aquatic ecosystems.

Microbial carbon metabolic functions of biofilms on plastic debris influenced by the substrate types and environmental factors

As an artificial type of microbial carrier, plastic debris has been widely detected in freshwater habitats, and the potential impacts of the plastisphere (biofilms colonized on plastics) in aquatic ecosystems have drawn increasing attention. Distinct community compositions and structures of biofilms in plastic and natural substrates have been recorded in freshwater environments. However, the microbial metabolic functioning of the plastisphere was underestimated, especially in freshwater environments. In this study, the effects of substrate types on the carbon metabolic functions of biofilms were studied by in situ cultivation of biofilms on plastics (polyvinyl chloride, PVC and polyethylene, PE) and natural substrate (cobblestone) for 44 days in two rivers (the Niushoushan River and the Qinhuai River) and two lakes (Donghu Lake and Xuanwu Lake). Biofilms on plastics showed higher biomasses than those on natural substrates in all ecosystems. Variations in the micro-structure and compactness of biofilms developed under different substrates were observed from scanning electron microscope and confocal laser scanning microscope image analyses. The carbon metabolic activities of the biofilms evaluated by BIOLOG EcoPlate were different between plastics (PVC and PE) and natural substrate (cobblestone) in the four freshwater ecosystems. In the Niushoushan River, PE-associated biofilms had different capacity in using carbon sources from cobblestone-associated biofilms as illustrated by the Shannon-Wiener diversity index and Shannon evenness index. Additionally, the metabolic functional diversity profiles of biofilms on PVC were significantly different from those on cobblestone in the other three aquatic ecosystems. Moreover, results from variation partitioning analysis suggested that the impact of environmental factors (contribution: 21%) on microbial carbon metabolic functions was much greater than that of substrate types (contribution: 6%). These findings illustrated distinct microbial functions of biofilms inhabited on plastics, and environmental factors play a decisive role in the differentiation and specificity of carbon metabolism of the plastisphere. This study offers new insights that plastics serving as artificial microbial niches have the ability to affect the microbial-mediated carbon cycling process in aquatic ecosystems.

Responses of freshwater biofilm formation processes (from colonization to maturity) to anatase and rutile TiO2 nanoparticles: Effects of nanoparticles aging and transformation

Most of the current studies on the toxicology of pristine nanoparticles (NPs) are environmentally irrelevant, because their ''aging'' process accompanied by the physicochemical transformation is inevitable in the environment. Considering aging phenomenon will gain a better understanding of the toxicity and fate of NPs in the environment. Here, we focused on the physicochemical transformation of anatase-NPs (TiO₂-A) and rutile-NPs (TiO₂-R) after 90 days of aging and investigated the responses of freshwater biofilm formation to the stress changes of naturally aged TiO₂-NPs (aTiO₂-NPs). We found that after aging, the TiO₂-NPs underwent sophisticated physicochemical transformations in the original morphology and microstructure owing to organic and crystal salts inclusions, such as energy band changes and the formation of Ti³⁺ on the NPs surfaces. These comprehensive transformations increased the stability of NPs in the exposed suspension. However, the physicochemical transformations were crystal-forms-dependent, and aging did not change the crystal structure and crystallinity. Interestingly, compared to pristine NPs, aTiO₂-NPs showed much lower cytotoxicity and had the weaker ability to promote or inhibit the biofilm formation (p < 0.05) owing to the passivation of photoactivity caused by the comprehensive effect of the inclusions, especially for aTiO₂-A. Regardless of aging or not of crystal forms, responses of biofilm formation were exposure-concentration-dependent, namely low concentration promotion (0.1 mg/L) and high concentration inhibition (10 mg/L), e.g., role transition of the pioneers (algae or bacteria) in initial colonization, extracellular polymeric substances (EPS) secretion and compositions of development stages with polysaccharide (PS)-rich and protein (PRO)-rich stages, and biomass and cell activity at different depths of mature biofilms. The reactive oxygen species (ROS) induced by TiO₂-NPs showed typical hormesis. The changing trends of the autoinducers (c-di-GMP and quorum sensing signals including AHL and AI-2) were highly consistent with the growth stages of biofilms and were stimulated or suppressed by TiO₂-NPs. The NPs crystal-dependently changed the microorganism community structures, while the UPGMA clustering of bacteria was based on the growth stages of the biofilms. The toxic mechanisms revealed that photoactivity and nanoscale retention of particles are the main reasons for the differences in the ecological stress capacity of four kinds of TiO₂-NPs. Aging reduced characteristic differences of two pristine NPs and even reversed their relative stresses levels (p > 0.05). However, the toxicity of high-concentration aTiO₂-NPs (10 mg/L) remained serious in a water environment. This study provides a better understanding for the water environmental risks evaluation and policy control of nanoparticles, that is, the effect of time aging has to be considered.

Insights into spatial effects of ceria nanoparticles on oxygen mass transfer in wastewater biofilms: Interfacial microstructure, in-situ microbial activity and metabolism regulation mechanism

Growing international exploitation of ceria nanoparticles (CeO₂ NPs) for varied applications has increased their release into wastewater treatment plants. Mass transfer of oxygen (MTO) in wastewater biofilm is of considerable importance to influence the activity and purification ability of biofilm. Herein, we investigated the spatial distribution of oxygen in gas-liquid-biofilm phases, the microstructure of interfaces and the in-situ microbial activity to reveal the impacts of CeO₂ NPs on MTO in wastewater biofilm and the related mechanisms. After exposure to 1 and 10 mg/L CeO₂ NPs, the oxygen transfer coefficient (K_La) from gas to wastewater increased by 28.1% and 75.3% with a reduction of thickness in gas-liquid boundary layer, indicating the enhanced MTO in gas-liquid interface. In contrast, the MTO in liquid-biofilm interface was negatively affected and the thickness of liquid-biofilms boundary layer significantly increased, which was mainly attributed to the smoother surface and the decreased surface area difference of biofilm. Within biofilm, the microbial activity was inhibited by 10 mg/L CeO₂ NPs, whereas the production of extracellular polymeric substance (EPS) was significantly improved, leading to a decline of 35.0% in the internal effective diffusivity (D_B) and a 300-μm reduction of oxygen penetration depth. Moreover, the relative activities of key enzymes involved in glycometabolism indicated the transition of Embden-Meyerhof pathway to pentose phosphate pathway, which probably contributed to the enhanced EPS production and consequently increased mass transfer resistance in liquid-biofilm interface and inner biofilm. These results could potentially expand the knowledge on mass transfer of nutrients or pollutants in wastewater biofilm in response to NPs exposure.

Bacteria-nanoparticle interactions in the context of nanofouling

The attachment of microbial communities to surfaces is a well-known problem recognized to be involved in a variety of critical issues in the sectors of food processing, chronic wounds, infection from implants, clogging of membranes and corrosion of equipment. Considering the importance of the detrimental impact of biofouling, it has received much attention in the scientific community and from concerned stakeholders. With the development of nanotechnology and the nowadays widespread use of engineered nanoparticles (ENPs), concerns have been raised regarding their fate in terrestrial and aquatic environments. Safety aspects and public health issues are critical in the management of handling nanomaterials and their nanowastes. The interactions of various types of nanoparticles (NPs) with planktonic bacteria have also received attention due to their antimicrobial properties. However, their behavior in regard to biofilms is not well understood although, in the environment, most of the bacteria prefer living in sessile communities. The question appears relevant considering the need to build knowledge on the fate of nanoparticles and the fact that no one can exclude the risk of accumulation of nanoparticles in biofilms and on surfaces leading to a form of nanofouling involving both engineered nanoparticles (ENPs) and nanoplastics. The present analysis of recent research accounts allows in identifying that (1) research activities related to water remediation systems have been mostly oriented on the impact of NPs on pre-existing biofilms, (2) experimental designs are restricted to few scenarios of exposure, usually limited to relative short-time periods although nanofouling could favour the development of multi-resistant bacterial species through sub-lethal exposures over prolong periods of time (3) nanofouling in other systems in which biofilms develop remains to be addressed, and (4) new research directions are required for investigating the mechanisms involved and the subsequent impact of nanofouling on bacterial consortium responses encountered in a variety of environments such as those prevailing in food production/processing settings. Finally, this review aims at providing recent information and insights on nanoparticle-bacterial interactions in the context of biofilms in order to supply an updated outlook of research perspectives that could help establish the framework for production, use and fate of nanomaterials as well as future research directions.

Responses of nitrogen transformation processes and N2O emissions in biological nitrogen removal system to short-term ZnO nanoparticle stress

Although the adverse effects of ZnO nanoparticles (ZnO NPs) on biological nitrogen removal (BNR) processes have widely been reported, the impacts of ZnO NPs on the whole nitrogen transformation processes, especially the production of nitrous oxide (N₂O), a typical greenhouse gas in a BNR system have rarely been systematically studied yet. In this study, the performances of both the nitrification and denitrification processes were investigated and the N₂O emission was simultaneously monitored in a sequencing batch reactor (SBR) when exposed to 1, 25 or 50 mg/L ZnO NPs for one cycle. The dose-dependent ZnO NP depression effects were generally observed on denitrification processes, total nitrogen (TN) removal efficiency and N₂O emissions but not nitrification process. Meanwhile, the N₂O emission was positively correlated with NO₂^--N accumulation in the oxic stage. Further investigation showed that the expressions of nitrate (NO₃^-) reduction associated narG gene were down-regulated with the increase of NP stress, and the transcript ratios of NO₂^-/NO reduction gene to N₂O reduction one (nirK/nosZ and norB/nosZ) decreased. The released Zn²⁺ from ZnO NPs took an important role in the inhibition of denitrification processes. ZnO NPs addition also induced the dose-dependent variations in the superoxide dismutase (SOD) and catalase (CAT) activities, which probably contributed to the suppression of the excess reactive oxygen species (ROS) generations to mitigate nanotoxicity. The excessive secretion of protein (PN) in tightly bound EPS (TB-EPS) when ZnO NPs were no <25 mg/L further supported the system's potential self-regulation mechanism for nanotoxicity resistance. CAPSULE: The effects of ZnO NPs on the whole nitrogen transformation processes in a biological nitrogen removal sequencing batch reactor, including the N₂O emissions were investigated. The system's potential self-regulation mechanism for nanotoxicity resistance was addressed.

Differential responses of encoding-amoA nitrifiers and nir denitrifiers in activated sludge to anatase and rutile TiO2 nanoparticles: What is active functional guild in rate limiting step of nitrogen cycle?

The long-terms effects of different crystal-composition TiO₂ nanoparticles (NPs) on nitrogen-cycle-related functional guilds in activated sludge remain unclear, especially under natural light irradiation. Accordingly, activated sludge was exposed to anatase TiO₂-NPs (TiO₂-A) and rutile TiO₂-NPs (TiO₂-R) for up to 45 days. With markedly (p < 0.05) reducing nitrification-/denitrification-enzymatic-activities and abundances of ammonia-oxidizing-microorganisms (AOMs) and nitrite-reducing-bacteria (NRB), TiO₂-NPs triggered bacteria and archaea UPGMA clustering and a deep modification of N-cycling functional diversity guided by crystal structure. in situ¹³C-DNA-SIP confirmed ammonia-oxidizing-bacteria (AOB) (Nitrosomonas and Nitrosospira) in original sludge as main active AOMs with 75.4 times more abundance than ammonia-oxidizing-archaea (AOA), while AOA within Nitrosopumilus and Nitrososphaera genera were the main active AOMs and tended to aggregate inside sludge after 10-mg/L TiO₂-NPs exposure. Encoding-nirK NRB were more sensitive, while encoding-nirS Zoogloea with a total share of 4.97% to 14.93%, etc. were the main active NRB. AOB was more sensitive to TiO₂-A, while TiO₂-R showed the stronger toxicity to AOA and NRB resulting from differences in water environmental behaviors and crystal characteristics of two TiO₂-NPs. This work expands understanding of the ecological risks of titanium-dioxide-crystal-NPs in aquatic environment and may help devise better methods to alleviate environmental stress caused by NPs at wastewater treatment plants.

Response of submerged macrophytes and leaf biofilms to the decline phase of Microcystis aeruginosa: Antioxidant response, ultrastructure, microbial properties, and potential mechanism

Decaying cyanobacterial blooms carry a potential risk for submerged macrophyte and periphyton biofilms in aquatic environments. This study comprehensively studied the responses in growth, oxidative response, detoxification pathway, and ultrastructure characteristics of aquatic plants to Microcystis aeruginosa (M. aeruginosa) exudates and extracts released during the decline phase. Particular emphasis was placed on the variation of extracellular polymeric substances (EPS) and quorum-sensing signaling molecules. The results showed that superoxide dismutase, peroxidase, and glutathione S-transferase were significantly induced as antioxidant response, and the malondialdehyde content increased. Increased content of MC-LR (1.129 μg L^-1) and NH₄⁺-N (1.35 mg L^-1) were found in the decline phase of M. aeruginosa, which played a vital role in the damage to submerged plants. In addition, a change in the amount of osmiophilic granules and a variation of organelles and membranes was observed. A broad distribution of α-d-glucopyranose polysaccharides was dominant and aggregated into clusters in biofilm EPS in response to exposure to decaying M. aeruginosa. Furthermore, exposure to exudates and extracts changed the abundance and structure of the microbial biofilm community. Increased contents of N-acylated-L-homoserine lactone signal molecule might result in a variation of biofilm EPS production in response to decaying M. aeruginosa. These results expand the understanding of how submerged macrophyte and periphyton biofilms respond to environmental stress caused by exudates and extracts of decaying M. aeruginosa.

Microstructure, bacterial community and metabolic prediction of multi-species biofilms following exposure to di-(2-ethylhexyl) phthalate (DEHP)

The occurrence and transportation of phthalate esters in biofilms from natural and engineered sources have attracted considerable research interest. However, little information is available highlighting the responses of multi-species biofilms in terms of their physicochemical structure and bacterial community induced by phthalate esters. Di-(2-ethylhexyl) phthalate (DEHP), a model phthalate eater, was selected to treat multi-species biofilm aggregates, including an attached biofilm from a moving bed bioreactor (MBBR), a periphytic biofilm from a natural source and activated sludge in short-term exposure experiments (120 h). The production of extracellular polymeric substances (EPS) from the three biofilms initially decreased and then slightly increased after exposure to DEHP, consistent with the variation of the most dominant fluorescent compounds consisting of humic-acid-like organic substances. The MBBR and periphytic biofilms secreted more fluorescence compounds than the activated sludge during the exposure period. The organic matter in the EPS was converted into smaller molecules, while limited variation was observed in the functional groups and secondary protein structures. Acinetobacter and Bacillus demonstrated significant increases and were likely the key genera responsible for DEHP degradation. The combined use of spectral, chromatographic and sequencing analyses indicated that the periphytic biofilm was more resistant to DEHP, possibly owing to the presence of more mature assemblages, including cells with higher metabolic activity and a higher diversity within the bacterial community. This study provides insights into the microstructural and bacterial responses of multi-species biofilms following exposure to phthalate esters, and provides important guidance for bioremediation of phthalate esters using periphytic biofilms.

Insight into mature biofilm quorum sensing in full-scale wastewater treatment plants

Quorum sensing (QS) has been thoroughly investigated during initial biofilm formation stages, while the role of QS in mature biofilms has received little research attention. This study assessed QS in 22 biofilm samples from full-scale wastewater treatment plants in China. Results showed that the concentration of acyl-homoserine lactones (AHLs) in various biofilm bound forms, ranged from 15.63 to 609.76 ng/g. The highest concentration of AHLs was found in the tightly bound biofilm fraction, while the lowest concentrations were observed in the surface biofilm fraction. Environmental variables, C/N ratio and temperature, were found to be significant factors influencing biofilm AHL distribution (p < 0.01). Higher C/N ratios (ranging from 3 to 12) and low temperatures contributed to the higher concentration of AHLs in biofilms. Dominant AHLs (C10-HSL and C12-HSL) were significantly associated with biofilm activity (R² = 0.98/0.97, p < 0.05), with the tightly bound biofilm fraction (TB-biofilm) presenting the highest activity (ATP concentration). Biofilm aging and re-formation processes were more active in the surface biofilm layer (S-biofilm), while the stable structure of the TB-biofilm layer which is attached to the surface of bio-carriers ensures high biofilm activity. This study furthers our understanding of the roles of AHLs in the regulation of mature biofilm activities.

Physicochemical and Biological Effects on Activated Sludge Performance and Activity Recovery of Damaged Sludge by Exposure to CeO2 Nanoparticles in Sequencing Batch Reactors

Recently, the growing release of CeO₂ nanoparticles (CeO₂ NPs) into sewage systems has attracted great concern. Several studies have extensively explored CeO₂ NPs' potential adverse impacts on wastewater treatment plants; however, the impaired activated sludge recovery potentials have seldom been addressed to date. To explore the physicochemical and biological effects on the activated sludge performance and activity recovery of damaged sludge by exposure to CeO₂ NPs in sequencing batch reactors (SBRs), four reactors and multiple indicators including water quality, key enzymes, microbial metabolites, the microbial community structure and toxicity were used. Results showed that 10-week exposure to higher CeO₂ NP concentration (1, 10 mg/L) resulted in a sharp decrease in nitrogen and phosphorus removal efficiencies, which were consistent with the tendencies of key enzymes. Meanwhile, CeO₂ NPs at concentrations of 0.1, 1, and 10 mg/L decreased the secretion of tightly bound extracellular polymeric substances to 0.13%, 3.14%, and 28.60%, respectively, compared to the control. In addition, two-week recovery period assays revealed that the functional bacteria Proteobacteria, Nitrospirae and Planctomycetes recovered slightly at the phyla level, as analyzed through high-throughput sequencing, which was consistent with the small amount of improvement of the effluent performance of the system. This reflected the small possibility of the activity recovery of damaged sludge.

Effect of Increased Influent COD on Relieving the Toxicity of CeO2 NPs on Aerobic Granular Sludge

Due to the increased use of cerium oxide nanoparticles (CeO₂ NPs), their potential environmental risks have caused concern. However, their effects on the aerobic granular sludge (AGS) process and the later recovery of AGS are still unclear. In this study, we comprehensively determined the changes in pollutant removal and the levels of extracellular polymeric substances (EPS) in AGS that were exposed to CeO₂ NP treatments (0 (the control, R0), 1 (R1), and 5 (R5) mg/L), following an increase in the influent chemical oxygen demand (COD). An increase in the CeO₂ NP concentration enhanced their inhibitory effect on the removal of total nitrogen (TN) and total phosphorus (TP), and promoted the production of polysaccharides (PS) and proteins (PN) in loosely bound EPS (LB-EPS) or tightly bound EPS (TB-EPS), as well as the dissolved organic carbon (DOC) components in EPS, but had no long-term effects on the removal of organic matter. When the addition of CeO₂ NPs was stopped and the concentration of influent COD increased, the TN and TP removal efficiencies in R1 and R5 slowly increased and recovered. In R1, they were only 4.55 ± 0.55% and 2.71 ± 0.58% lower than in R0, respectively, while the corresponding values for R5 were 5.06 ± 0.46% and 6.20 ± 0.63%. Despite the LB-EPS and TB-EPS concentrations in the R1 and R5 treatments recovering and being similar to the levels in the control when no CeO₂ NPs were added, they were still slightly higher than in the R0, which indicating that the negative effects of CeO₂ NPs could not be completely eliminated due to the residual CeO₂ NP levels in AGS.

Impacts of Continuous Inflow of Low Concentrations of Silver Nanoparticles on Biological Performance and Microbial Communities of Aerobic Heterotrophic Wastewater Biofilm

Attached-growth wastewater processes are currently used in water resource recovery facilities (WRRFs) for required upgrades due to an increase in influent loading or to reach more stringent discharge criteria. Yet, the distribution and long-term inhibitory effects of silver nanoparticles (AgNPs) in attached-growth biological wastewater processes and their impact on involved microbial communities are poorly understood at relevant, low concentrations. Retention, distribution, and long-term inhibitory effect of polyvinylpyrrolidone (PVP)-coated AgNPs were evaluated in bench-scale moving bed biofilm reactors (MBBRs), achieving soluble organic matter removal, over a 64 day exposure to nominal concentrations of 10 and 100 μg/L. Distributions of continuously added AgNPs were characterized in the influent, bioreactor, and effluent of MBBRs using single particle inductively coupled plasma mass spectroscopy (spICP-MS). Aerobic heterotrophic biofilms in MBBRs demonstrated limited retention capacity for AgNPs over long-term exposure, with release of AgNPs, and Ag-rich biofilm sloughed from the carriers. Continuous exposure to both influent AgNP concentrations significantly decreased soluble chemical oxygen demand (S_COD) removal efficiency (11% to 31%) and reduced biofilm viability (8% to 30%). Specific activities of both intracellular dehydrogenase (DHA) and extracellular α-glucosidase (α-Glu) and protease (PRO) enzymes were significantly inhibited (8% to 39%) with an observed NP dose-dependent intracellular reactive oxygen species (ROS) production and shift in biofilm microbial community composition by day 64. Our results indicated that long-term exposure to AgNPs in biofilm processes at environmentally relevant concentrations can impact the treatment process stability and the quality of the discharged effluent.

Toxicity of Three Crystalline TiO2 Nanoparticles in Activated Sludge: Bacterial Cell Death Modes Differentially Weaken Sludge Dewaterability

The eco-toxicities of different crystalline phases of TiO₂-NPs are controversial, and the effects and mechanisms on activated sludge are unclear. Therefore, we assessed the acute-toxicities (8-h exposure) of P25, anatase, and rutile TiO₂-NPs in activated sludge using flow cytometry under simulated sunlight (hereafter-sun) and evaluated the relationship between sludge dewatering and bacterial cell death modes using Pearson's correlation coefficients ( r). Additionally, the response of the microbial community structure was examined by high throughput sequencing. Bacterial survival and death were observed by confocal laser scanning microscopy. Toxicity indicators (e.g., lactate dehydrogenase (LDH) and reactive oxygen species (ROS)) were determined. Overall, TiO₂-NPs toxicity was concentration-dependent and crystalline-phase-dependent. The responses of bacterial communities to crystalline phases were more obvious than that of dosage. P25-sun and anatase-sun caused necrosis-like cell death via strong photo-oxidation confirmed by 131%/123% (1 mg/L) and 301%/254% (50 mg/L) LDH released by the control, while rutile-sun induced apoptosis-like death via intracellular ROS production increased to 165% (1 mg/L) and 420% (50 mg/L) of the control. P25 and anatase NPs had higher protein and polysaccharide affinities, while rutile NPs exhibited stronger attachment onto phospholipids. TiO₂-NPs-sun reduced activated sludge dewaterability. Specific resistance to filtration (SRF) showed the strongest positive correlation with tightly bound extracellular polymeric substances (EPS) and total soluble microbial byproducts ( r = 0.974, p < 0.01) and was closely related to EPS content and composition, especially the increased bound water (BW) content and sludge protein concentrations. High Pearson correlation coefficients were observed between early apoptotic cells and BW content ( r = 0.952, p < 0.01) resulting from massive polysaccharides and between necrotic (including late apoptotic) cells and SRF ( r = 0.959, p < 0.01) resulting from high protein and EPS concentrations. Thus, in response to TiO₂-NPs, bacterial cell death modes differentially weakened sludge dewatering.

Responses of flocculated activated sludge to bimetallic Ag-Fe nanoparticles toxicity: Performance, activity enzymatic, and bacterial community shift

Ever-increasing production and use of nanoparticles (NPs) have aroused overarching concerns for their toxic effects on the environment and human. In the present study, the toxic effects of Silver (Ag) and Iron (Fe) NPs on the performance of activated sludge were investigated under continuous aerobic/anoxic/anaerobic conditions in laboratory-scale sequencing batch reactors (SBRs).Activated sludge was exposed to various concentrations (5-100 mg/L) of Ag-Fe NPs for 60 days and its response was assessed through the enzymatic activity, COD, nitrogen (TN) and phosphorus (TP) removal, toxicity tests, as well as variations in bacterial community. Compared with the pristine control sample, the exposure to NPs suppressed TN and TP removal efficiencies. Indeed, the respiration rate and biomass concentration were significantly affected by the NPs. Although the simultaneous exposure to Ag-Fe NPs did affect the integrity of cell membrane (LDH) and key enzymes activities, the higher concentration induced an increased generation of reactive oxygen species (ROS). The metagenome analysis revealed a marked shift in the microbial community structure suggesting that both heterotrophic and autotrophic communities were affected by the presence of Ag-Fe NPs. Our results provide some evidence for compounded effects of NPs in their simultaneous presence, and generate new leads for future research efforts.

Effects of cerium oxide nanoparticles on bacterial growth and behaviors: induction of biofilm formation and stress response

In this paper, the effects of cerium oxide nanoparticles (CeO₂ NPs) on the group bacterial behaviors were elaborated. After 36-h cultivation, the biofilm biomass was enhanced by the sub-lethal concentrations of 0.5 and 2 mg/L CeO₂ NP exposure. Meanwhile, the promoted production of total amino acids in microbes further resulted in the increased surface hydrophobicity and percentage aggregation. To resist the CeO₂ NPs stress, the biofilm exhibited a double-layer microstructure, with the protein (PRO) and living cells occupying the bottom, the polysaccharide (PS), and dead cells dominating the top. The bacterial diversity was highly suppressed and Citrobacter and Pseudomonas from the phylum of γ-Proteobacteria strongly dominated the biofilm, indicating the selective and enriched effects of CeO₂ NPs on resistant bacteria. The stimulated inherent resistance of biofilm was reflected by the reduced adenosine triphosphate (ATP) content after 4 h exposure. The increased levels of reactive oxygen species (ROS) in the treatments of 8 h CeO₂ NP exposure led to the upregulated quorum sensing signals of acylated homoserine lactone (AHL) and autoinducer 2 (AI-2), beneficial to mitigating the environmental disturbance of CeO₂ NPs. These results provide evidences for the accelerating effects of CeO₂ NPs on biofilm formation through oxidative stress, which expand the understanding of the ecological effects of CeO₂ NPs.