NirS-type denitrifying bacteria in aerobic water layers of two drinking water reservoirs: Insights into the abundance, community diversity and co-existence model

Enhanced nitrogen removal from low C/N ratio wastewater by coordination of ternary electron donors of Fe0, carbon source and sulfur: Focus on oxic/anoxic/oxic process

Insufficient organics was the major obstacle for total nitrogen (TN) removal in conventional pre-anoxic denitrification when treating low carbon to nitrogen (C/N) ratio wastewater. This study constructed a novel ternary-electron donors (Fe0, organics and S0) enhanced oxic/anoxic/oxic (O/A/O) process, integrating simultaneous nitrification and denitrification and autotrophic denitrification (ADN), and evaluated its feasibility to achieve efficient nutrient removal under organics-deficient condition. Long-term operation results showed that TN removal was lower (9.9 %) when Fe0 added individually, then raised to 27.3 %∼46.0 % in simultaneous presence of Fe0 and organics. And the highest TN removal (82.0 %) was obtained by coordination of ternary-electron donors, with 8.46 ± 0.43 mg/L TN in effluent. Meanwhile, the O/A/O process exhibited excellent total phosphorous (TP) removal (84.8 %∼98.4 %) derived from chemical precipitation by Fe0, of which the effluent was <0.76 ± 0.04 mg/L TP. Metabolic characteristics indicated that the coordination of multi-electron donors improved microbial metabolism and denitrifying enzymatic activities, thereby promoting ammonia assimilation and enhancing TN removal. And the secretion of EPS was also stimulated, which favored the bio-utilization of Fe0 and S0 and alleviated organics dependence. Besides, the notable increase in abundances of aerobic denitrifiers (23.95 %∼27.37 %), autotrophic denitrifiers (9.31 %) and denitrifying genes further verified the synergy effect of multi-electron donors on TN removal. This study revealed the enhancement mechanism of O/A/O process by coordination of ternary-electron donors, verified its cost-effectiveness and provided innovative insights on low C/N ratio wastewater remediation.

Spatio-temporal dynamics variation of dissolved organic matter and water quality parameters in Giheung Reservoir: A vertical perspective

Water reservoirs in densely populated areas play a crucial role in water supply, irrigation, and flood regulation. This study investigated the spatiotemporal dynamics of dissolved organic matter (DOM) and its interactions with water quality parameters in Giheung Reservoir, South Korea. Monthly water samples were collected at three depths, measuring fifteen physicochemical properties alongside DOM characterization using Excitation-Emission Matrix Parallel Factor Analysis (EEM-PARAFAC), identifying four DOM components: C1 (microbial protein-like), C2 (humic-like), C3 (terrestrial humic-like), and C4 (tyrosine/tryptophan-like). Seasonal stratification influenced DOM distribution, with humic-like DOM (C2, C3) accumulating in deeper layers during summer, while protein-like DOM (C1, C4) dominated surface waters due to enhanced biological productivity, and mixing periods homogenizing DOM across depths. The dimictic thermal regime, with moderate summer stratification and full mixing in spring and autumn, governed these patterns. 2D correlation spectroscopy (2D-COS) identified sequential DOM variation across layers, with humic-like DOM increasing at depth during stratification. Fluorescence indices-Fluorescence Index (FI), Humification Index (HIX), and Biological Index (BIX)-were integrated into structural equation modeling (SEM), showing that temperature and dissolved oxygen strongly drive protein-like DOM, while nitrogen and phosphorus compounds shape DOM reactivity. These findings enhance understanding of DOM biogeochemical processes and provide valuable insights for reservoir management to maintain water quality.

Activation of algicidal bacteria and nitrogen-phosphorus removal bacteria during controlling cyanobacteria bloom in Taihu lake by artemisinin algaecide

Cyanobacterial harmful algal blooms (CyanoHABs) in Taihu Lake pose a persistent environmental challenge. This study investigated the inhibitory effects of artemisinin algaecide (AMA) on cyanobacteria in Taihu Lake and assessed its impact on nutrients, as well as the structures of particle-attached (PA) and free-living (FL) bacterial communities and potential ecological mechanisms. The results indicated that A-3 (0.8 g artemisinin/L) effectively inhibited CyanoHABs (inhibition rate = 93 %) and significantly increased the alpha diversity of PA and FL bacterial communities during the stationary phase， thereby promoting the proliferation of algicidal bacteria (AB) (e.g., Acinetobacter, Stenotrophomonas, and Exiguobacterium) and heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria (e.g., Acinetobacter, Stenotrophomonas, and Bacillus) through the utilization of dissolved organic carbon (DOC) from the dead cyanobacteria. This proliferation enhanced nitrogen metabolism and increased the abundance of nitrogen-cycling functional genes, improving nutrient cycling and enhancing system stability. The increased abundance of AB continuously suppressed cyanobacteria, while the proliferation of HN-AD bacteria removed nitrogen and phosphorus from the water, thus limiting nutrients available for cyanobacterial growth. Our findings demonstrate that AMA effectively inhibits CyanoHABs and prevents secondary blooms, providing a scientific foundation for the widespread application in cyanobacterial management, enhancing the effectiveness and sustainability of CyanoHAB control efforts.

Effects of low temperature on the microbial community of MBBR filler biofilm

Moving bed biofilm reactors can purify urban domestic sewage through microbial biodegradation. High-throughput sequencing was used to study the response mechanism of the biofilm microbial community to temperature. The effluent quality of the reactor declined with the decrease in temperature. Proteobacteria, Bacteroidota, and Nitrospirota were the dominant bacteria, accounting for 59.2, 11.9, and 9.4%, respectively. Gammaproteobacteria (38.3%), Alphaproteobacteria (23.2%), and Bacteroidia (12.4%) were the dominant bacteria at the class level. Low temperature had an obvious directional domestication effect on microbial flora, and the composition of the bacterial community was more similar. Pseudomonas was one of the dominant bacterial groups at 5 °C. Nitrospira (p < 0.001) and Trichococcus (p < 0.05) were significantly negatively correlated with effluent ammonia nitrogen and significantly positively correlated with NO3- (p < 0.05) at low temperature. Functional bacteria related to chemoheterotrophy (25.88%) and aerobic_chemoheterotrophy (21.56%) accounted for a relatively high proportion. The bacteria related to nitrate reduction only accounted for 2.62%. Studies have shown that low temperatures can inhibit the growth of nitrogen-cycling bacteria, and few domesticated and selected nitrogen-cycling bacteria play a major role in the removal and transformation of ammonia nitrogen. The degradation of chemical oxygen demand can still be achieved through the adsorption and degradation of dominant functional bacteria.

Aerobic denitrifying bacterial community with low C/N ratio remove nitrate from micro-polluted water: Metagenomics unravels denitrification pathways

The efficient nitrogen removal from micro-polluted source water is an international challenge to be solved urgently. However, the inner denitrification mechanism of native aerobic denitrifying bacterial communities in response to carbon scarcity remains relatively unclear. Here, the bacterial community XT6, screened from an oligotrophic reservoir, exhibited aerobic denitrifying capacity under low-carbon environments. Up to 76.79-81.64 % of total organic carbon (TOC) and 51.48-67.60 % of NO3--N were removed by XT6 within 48 h at C/N ratios of 2.0-3.0. Additionally, the nitrogen balance experiments further manifested that 26.27-38.13 % of NO3--N was lost in gaseous form. As the C/N ratio decreased, XT6 tended to generate more extracellular polymeric substances (EPS), with the tightly bound EPS showing the largest increase. Pseudomonas and Variovorax were quite abundant in XT6, constituting 59.69 % and 28.65 % of the total sequences, respectively. Furthermore, metagenomics analysis evidenced that XT6 removed TOC and nitrate mainly through the tricarboxylic acid cycle and aerobic denitrification. Overall, the abovementioned results provide a deeper understanding of the nitrogen metabolic pathways of indigenous aerobic denitrifying bacterial communities with low C/N ratios and offer useful guidance for controlling nitrogen pollution in oligotrophic ecosystems.

Metagenomic Analysis of Sediment Bacterial Diversity and Composition in Natural Lakes and Artificial Waterpoints of Tabuk Region in King Salman Bin Abdulaziz Royal Natural Reserve, Saudi Arabia

The Tabuk region is located in the northern part of Saudi Arabia, and it has an area of 117,000 km2 between longitudes 26° N and 29° N and latitudes 34° E and 38° E. King Salman Bin Abdulaziz Royal Natural Reserve (KSRNR) is the largest natural reserve in Saudi Arabia and covers about 130,700 km2. It represents a new tourist attraction area in the Tabuk region. Human activities around the lake may lead to changes in water quality, with subsequent changes in microenvironment components, including microbial diversity. The current study was designed to assess possible changes in bacterial communities of the water sediment at some natural lakes and artificial waterpoints of KSRNR. Water samples were collected from ten different locations within KSRNR: W1, W2, W3 (at the border of the royal reserve); W4, W5, W6, W7 (at the middle); and W8, W9, and W10 (artificial waterpoints). The total DNA of the samples was extracted and subjected to 16S rRNA sequencing and metagenomic analysis; also, the environmental parameters (temperature and humidity) were recorded for all locations. Metagenomic sequencing yielded a total of 24,696 operational taxonomic units (OTUs), which were subsequently annotated to 193 phyla, 215 classes, 445 orders, 947 families, and 3960 genera. At the phylum level, Pseudomonadota dominated the microbial communities across all samples. At the class level, Gammaproteobacteria, Clostridia, Alphaproteobacteria, Bacilli, and Betaproteobacteria were the most prevalent. The dominant families included Enterobacteriaceae, Pseudomonadaceae, Clostridiaceae, Comamonadaceae, and Moraxellaceae. At the genus level, Pseudomonas, Clostridium, Acinetobacter, Paenibacillus, and Acidovorax exhibited the highest relative abundances. The most abundant species were Hungatella xylanolytica, Pseudescherichia vulneris, Pseudorhizobium tarimense, Paenibacillus sp. Yn15, and Enterobacter sp. Sa187. The observed species richness revealed substantial heterogeneity across samples using species richness estimators, Chao1 and ACE, indicating particularly high diversity in samples W3, W5, and W6. Current study results help in recognizing the structure of bacterial communities at the Tubaiq area in relation to their surroundings for planning for environmental protection and future restoration of affected ecosystems. The findings highlight the dominance of various bacterial phyla, classes, families, and genera, with remarkable species richness in some areas. These results underscore the influence of human activities on microbial diversity, as well as the significance of monitoring and conserving the reserve's natural ecosystems.

Coordination of elemental sulfur and organic carbon source stimulates simultaneous nitrification and denitrification toward low C/N ratio wastewater

The feasibility of inducing simultaneous nitrification and denitrification (SND) by S0 for low carbon to nitrogen (C/N) ratio wastewater remediation was investigated. Compared with S0 and/or organics absent systems (-3.4 %∼5.0 %), the higher nitrogen removal performance (18.2 %∼59.8 %) was achieved with C/N ratios and S0 dosages increasing when S0 and organics added simultaneously. The synergistic effect of S0 and organics stimulated extracellular polymeric substances secretion and weakened intermolecular binding force of S0, facilitating S0 bio-utilization and reducing the external organics requirement. It also promoted microbial metabolism (0.16 ∼ 0.24 μg O2/(g VSS·h)) and ammonia assimilation (5.9 %∼20.5 %), thereby enhancing the capture of organics and providing more electron donors for SND. Furthermore, aerobic denitrifiers (15.91 %∼27.45 %) and aerobic denitrifying (napA and nirS) and ammonia assimilating genes were accumulated by this synergistic effect. This study revealed the mechanism of SND induced by coordination of S0 and organics and provided an innovative strategy for triggering efficient and stable SND.

Algicidal activity synchronized with nitrogen removal by actinomycetes: Algicidal mechanism, stress response of algal cells, denitrification performance, and indigenous bacterial community co-occurrence

The harmful algal blooms (HABs) can damage the ecological equilibrium of aquatic ecosystems and threaten human health. The bio-degradation of algal by algicidal bacteria is an environmentally friendly and economical approach to control HABs. This study applied an aerobic denitrification synchronization algicidal strain Streptomyces sp. LJH-12-1 (L1) to control HABs. The cell-free filtrate of the strain L1 showed a great algolytic effect on bloom-forming cyanobacterium, Microcystis aeruginosa (M. aeruginosa). The optimal algicidal property of strain L1 was indirect light-dependent algicidal with an algicidal rate of 85.0%. The functional metabolism, light-trapping, light-transfer efficiency, the content of pigments, and inhibition of photosynthesis of M. aeruginosa decreased after the addition of the supernatant of the strain L1 due to oxidative stress. Moreover, 96.05% nitrate removal rate synchronized with algicidal activity was achieved with the strain L1. The relative abundance of N cycling functional genes significantly increased during the strain L1 effect on M. aeruginosa. The algicidal efficiency of the strain L1 in the raw water was 76.70% with nitrate removal efficiency of 81.4%. Overall, this study provides a novel route to apply bacterial strain with the property of denitrification coupled with algicidal activity in treating micro-polluted water bodies.

Diversity, community structure, and abundance of nirS-type denitrifying bacteria on suspended particulate matter in coastal high-altitude aquaculture pond water

Denitrifying bacteria harboring the nitrate reductase S (nirS) gene convert active nitrogen into molecular nitrogen, and alleviate eutrophication in aquaculture water. Suspended particulate matter (SPM) is an important component of aquaculture water and a carrier for denitrification. SPM with different particle sizes were collected from a coastal high-altitude aquaculture pond in Maoming City, China. Diversity, community structure, abundance of nirS-type denitrifying bacteria on SPM and environmental influencing factors were studied using high-throughput sequencing, fluorescence quantitative PCR, and statistical analysis. Pseudomonas, Halomonas, and Wenzhouxiangella were the dominant genera of nirS-type denitrifying bacteria on SPM from the ponds. Network analysis revealed Pseudomonas and Halomonas as the key genera involved in the interaction of nirS-type denitrifying bacteria on SPM in the ponds. qPCR indicated a trend toward greater nirS gene abundance in progressively larger SPM. Dissolved oxygen, pH, temperature, and SPM particle size were the main environmental factors influencing changes in the nirS-type denitrifying bacterial community on SPM in coastal high-altitude aquaculture pond water. These findings increase our understanding of the microbiology of nitrogen cycle processes in aquaculture ecosystem, and will help optimize aquatic tailwater treatment strategies.

Multivariate statistical and bioinformatic analyses for the seasonal variations of actinobacterial community structures in a drinking water reservoir

Actinobacterial community is a conspicuous part of aquatic ecosystems and displays an important role in the case of biogeochemical cycle, but little is known about the seasonal variation of actinobacterial community in reservoir ecological environment. In this study, the high-throughput techniques were used to investigate the structure of the aquatic actinobacterial community and its inducing water quality parameters in different seasons. The results showed that the highest diversity and abundance of actinobacterial community occurred in winter, with Sporichthya (45.42%) being the most abundant genus and Rhodococcus sp. (29.32%) being the most abundant species. Network analysis and correlation analysis suggested that in autumn the dynamics of actinobacterial community were influenced by more factors and Nocardioides sp. SX2R5S2 was the potential keystone species which was negatively correlated with temperature (R = -0.72, P < 0.05). Changes in environmental factors could significantly affect the changes in actinobacterial community, and the dynamics of temperature, dissolved oxygen (DO), and turbidity are potential conspicuous factors influencing seasonal actinobacterial community trends. The partial least squares path modeling further elucidated that the combined effects of DO and temperature not only in the diversity of actinobacterial community but also in other water qualities, while the physiochemical parameters (path coefficient = 1.571, P < 0.05) was strong environmental factors in natural mixture period. These results strengthen our understanding of the dynamics and structures of actinobacterial community in the drinking water reservoirs and provide scientific guidance for further water quality management and protection in water sources.

Spatial distribution characteristics of denitrification functional genes and the environmental drivers in Liaohe estuary wetland

Genes nirS, nirK, and nosZ are specific for the denitrification process, which is associated with greenhouse gas N2O emission. The abundances and diversities of community containing these three genes are usually used as a common index to reflect the denitrification process, and they would be affected by differences in environmental factors caused by changes from warm to cold conditions. The quantification of denitrification in natural wetlands is complex, and straightforward identification of spatial distribution and drivers affecting the process is still developing. In this study, the bacterial communities, gene diversities, and relative abundances involved in denitrification were investigated in Liaohe Estuary Wetland. We analyzed the relative abundances, diversities, and communities of bacteria containing the three genes at warm and cold conditions using Illumina MiSeq sequencing and detected the potential environmental factors influencing their distribution by using a random forest algorithm. There are great differences in the community composition of the bacteria containing genes nirS, nirK, and nosZ. All the abundant taxa of nirS and nirK communities belonged to phylum Proteobacteria. Compared with the community composition of bacteria containing nirS and nirK, the community of bacteria containing nosZ is more diverse, and the subdivision taxa of phylum Euryarchaeota was also abundant in the community containing nosZ. The distribution characteristics of the relative abundance of nirS and nirK showed obvious differences both at warm and cold climate conditions. The oxidation-reduction potential, nitrite nitrogen, and salinity were detected as potential variables that might explain the diversity of nirS. The total nitrogen and nitrite nitrogen were the important variables for predicting the relative abundance of nirS at warm climate condition, while oxidation-reduction potential and pH contributed to the diversity of nirS at cold condition. The bulk density of sediment was detected as a potential variable affecting the relative abundance of nirK at warm and cold conditions, and diversity of nirK at warm condition, while nitrite nitrogen was detected as an important environmental factor for predicting the diversity of nirK at cold condition. Overall, our results show that the key environmental factors, which affect the relative abundance, diversity, and community of bacteria containing the functional denitrification genes, are not exactly the same, and the diversities of nirS, nirK, and nosZ have a higher environmental sensitivity than their relative abundances.

Pollutants reduction via artificial mixing in a drinking water reservoir: Insights into bacterial metabolic activity, biodiversity, interactions and co-existence of core genera

Endogenous pollution due to long periods of hypolimnetic anoxia in stratified reservoirs has become a worldwide concern, which can threaten metabolic activity, biodiversity, water quality security, and ultimately human health. In the present study, an artificial mixing system applied in a drinking water reservoir was developed to reduce pollutants, and the biological mechanism involved was explored. After approximately 44 days of system operation, the reservoir content was completely mixed resulting in the disappearance of anoxic layers. Furthermore, the metabolic activity estimated by the Biolog-ECO microplate technique and biodiversity was enhanced. 16S rRNA gene sequencing indicated a great variability on the composition of bacterial communities. Co-occurrence network analysis showed that interactions among bacteria were significantly affected by the proposed mixing system. Bacteria exhibited a more mutualistic state and >10 keystone genera were identified. Pollutants, including nitrogen, phosphorus, organic matter, iron, and manganese decreased by 30.63-80.15 %. Redundancy discriminant analysis revealed that environmental factors, especially the temperature and dissolved oxygen, were crucial drivers of the bacterial community structure. Furthermore, Spearman's correlation analysis between predominant genera and pollutants suggested that core genus played a vital role in pollutant reduction. Overall, our findings highlight the importance and provide insights on the artificial mixing systems' microbial mechanisms of reducing pollutants in drinking water reservoirs.

Activation of indigenous denitrifying bacteria and enhanced nitrogen removal via artificial mixing in a drinking water reservoir: Insights into gene abundance, community structure, and co-existence model

Nitrogen pollution poses a severe threat to aquatic ecosystems and human health. This study investigated the use of water lifting aerators for in situ nitrogen reduction in a drinking water reservoir. The reservoir was thoroughly mixed and oxygenated after using water-lifting aerators for 42 days. The average total nitrogen concentration, nitrate nitrogen, and ammonium nitrogen-in all water layers-decreased significantly (P < 0.01), with a reduction efficiency of 35 ± 3%, 34 ± 2%, and 70 ± 6%, respectively. Other pollutants, including organic matter, phosphorus, iron, and manganese, were also effectively removed. Quantitative polymerase chain reactions indicated that bacterial nirS gene abundance was enhanced 26.34-fold. High-throughput sequencing, phylogenetic tree, and network analysis suggested that core indigenous nirS-type denitrifying bacteria, such as Dechloromonas, Simplicispira, Thauera, and Azospira, played vital roles in nitrogen and other pollutant removal processes. Furthermore, structural equation modeling revealed that nitrogen removal responded positively to WT, DO, and nirS gene abundance. Our findings provide a promising strategy for nitrogen removal in oligotrophic drinking water reservoirs with carbon deficiencies.

Unveiling the nitrogen removal performance from microbial network establishment in vertical flow constructed wetlands

The combined effects of substrate types (natural zeolite or shale ceramsite) and hydraulic retention time (HRT, 3-day or 6-day) on nutrient removal and microbial co-occurrence networks in vertical flow constructed wetlands (VFCWs) remains to be elucidated. In this study, zeolite-packed VFCWs demonstrated superior removal rates, achieving 93.65% removal of NH4+-N and 83.84% removal of COD at 6-day HRT. The activity and establishment of microbial community were influenced by combined operating conditions. The abundances of Amx, amoA, nxrA, and nosZ genes increased with longer HRTs in zeolite-packed VFCWs. Additionally, a 6-day HRT significantly increased the relative abundances of Proteobacteria and Nitrospirae. At the species level, zeolite-packed VFCWs exhibited ecological niche sharing as a coping strategy in response to environment changes, while ceramsite-packed VFCWs displayed ecological niche differentiation. Both zeolite-packed and ceramsite-packed VFCWs established functional networks of nitrogen-transforming genera that utilized ecological niche differentiation strategies.

Actinobacteria produce taste and odor in drinking water reservoir: Community composition dynamics, co-occurrence and inactivation models

Taste and odor (T&O) has become a significant concern for drinking water safety. Actinobacteria are believed to produce T&O during the non-algal bloom period; however, this has not been widely investigated. In this study, the seasonal dynamics of the actinobacterial community structure and inactivation of odor-producing actinobacteria were explored. The results indicated that the diversity and community composition of actinobacteria exhibited significant spatiotemporal distribution. Network analysis and structural equation modeling showed that the actinobacterial community occupied a similar environmental niche, and the major environmental attributes exhibited spatiotemporal dynamics, which affected the actinobacterial community. Furthermore, the two genera of odorous actinobacteria were inactivated in drinking water sources using chlorine. Amycolatopsis spp. have a stronger chlorine resistance ability than Streptomyces spp., indicating that chlorine inactivates actinobacteria by first destroying cell membranes and causing the release of intracellular compounds. Finally, we integrated the observed variability in the inactivation rate of actinobacteria into an expanded Chick-Watson model to estimate its effect on inactivation. These findings will deepen our understanding of the seasonal dynamics of actinobacterial community structure in drinking water reservoirs and provide a foundation for reservoir water quality management strategies.

Water-lifting and aeration system improves water quality of drinking water reservoirs: Biological mechanism and field application

Reservoirs have been served as the major source of drinking water for dozens of years. The water quality safety of large and medium reservoirs increasingly becomes the focus of public concern. Field test has proved that water-lifting and aeration system (WLAS) is a piece of effective equipment for in situ control and improvement of water quality. However, its intrinsic bioremediation mechanism, especially for nitrogen removal, still lacks in-depth investigation. Hence, the dynamic changes in water quality parameters, carbon source metabolism, species compositions and co-occurrence patterns of microbial communities were systematically studied in Jinpen Reservoir within a whole WLAS running cycle. The WLAS operation could efficiently reduce organic carbon (19.77%), nitrogen (21.55%) and phosphorus (65.60%), respectively. Biolog analysis revealed that the microbial metabolic capacities were enhanced via WLAS operation, especially in bottom water. High-throughput sequencing demonstrated that WLAS operation altered the diversity and distributions of microbial communities in the source water. The most dominant genus accountable for aerobic denitrification was identified as Dechloromonas. Furthermore, network analysis revealed that microorganisms interacted more closely through WLAS operation. Oxidation-reduction potential (ORP) and total nitrogen (TN) were regarded as the two main physicochemical parameters influencing microbial community structures, as confirmed by redundancy analysis (RDA) and Mantel test. Overall, the results will provide a scientific basis and an effective way for strengthening the in-situ bioremediation of micro-polluted source water.

Nitrogen removal by algal-bacterial consortium during mainstream wastewater treatment: Transformation mechanisms and potential N2O mitigation

This work investigated nitrogen transformation pathways of the algal-bacterial consortium as well as its potential in reducing nitrous oxide (N₂O) emission in enclosed, open and aerated reactors. The results confirmed the superior ammonium removal performance of the algal-bacterial consortium relative to the single algae (Chlorella vulgaris) or the activated sludge, achieving the highest efficiency at 100% and the highest rate of 7.34 mg N g MLSS^-1 h^-1 in the open reactor with glucose. Enhanced total nitrogen (TN) removal (to 74.6%) by the algal-bacterial consortium was achieved via mixotrophic algal assimilation and bacterial denitrification under oxygen-limited and glucose-sufficient conditions. Nitrogen distribution indicated that ammonia oxidation (∼41.8%) and algal assimilation (∼43.5%) were the main pathways to remove ammonium by the algal-bacterial consortium. TN removal by the algal-bacterial consortium was primarily achieved by algal assimilation (28.1-40.8%), followed by bacterial denitrification (2.9-26.5%). Furthermore, the algal-bacterial consortium contributed to N₂O mitigation compared with the activated sludge, reducing N₂O production by 35.5-55.0% via autotrophic pathways and by 81.0-93.6% via mixotrophic pathways. Nitrogen assimilation by algae was boosted with the addition of glucose and thus largely restrained N₂O production from nitrification and denitrification. The synergism between algae and bacteria was also conducive to an enhanced N₂O reduction by denitrification and reduced direct/indirect carbon emissions.

Novel insights into aerobic denitrifying bacterial communities augmented denitrification capacity and mechanisms in lake waters

Scanty attention has been paid to augmenting the denitrification performance of polluted lake water by adding mix-cultured aerobic denitrifying bacterial communities (Mix-CADBCs). In this study, to solve the serious problem of nitrogen pollution in lake water bodies, aerobic denitrifying bacteria were added to lake water to enhance the nitrogen and carbon removal ability. Three Mix-CADBCs were isolated from lake water and they could remove >94 % of total nitrogen and dissolved organic carbon, respectively. The balance of nitrogen analysis shown that >70 % of the initial nitrogen was converted to gaseous nitrogen, and <11 % of the initial nitrogen was converted into microbial biomass. The batch experiments indicated that three Mix-CADBCs could perform denitrification under various conditions. According to the results of nirS-type sequencing, the Hydrogenophaga sp., Prosthecomicrobium sp., and Pseudomonas sp. were dominated genera of three Mix-CADBCs. The analysis of network indicated Pseudomonas I.Bh25.14 and Vogsella LIG4 were correlated with the removal of total nitrogen (TN) and dissolved organic carbon in the Mix-CADBCs. Compared with lake raw water, the addition of three Mix-CADBCs could promote the denitrification capacity (the removal efficiencies of TN > 78.72 %), microbial growth (optical density increased by 0.015-0.138 and the total cell count increased by 2 times), and organic degradation ability (the removal efficiency chemical oxygen demand >38 %) of lake water. In general, the findings of this study demonstrated that Mix-CADBCs could provide a new perspective for biological treatment lake water body.

Nitrogen reduction by aerobic denitrifying fungi isolated from reservoirs using biodegradation materials for electron donor: Capability and adaptability in the lower C/N raw water treatment

Biological denitrification was considered an efficient and environmentally friendly way to remove the nitrogen in the water body. However, biological denitrification showed poor nitrogen removal performance due to the lack of electron donors in the low C/N water. In this study, three novel aerobic denitrifying fungi (Trichoderma sp., Penicillium sp., and Fusarium sp.) were isolated and enhanced the performance of aerobic denitrification of fungi in low C/N water bodies combined with polylactic acid/polybutylene adipate-co-terephthalate (PLA/PBAT). In this work, the aerobic denitrifying fungi seed were added to denitrifying liquid medium and mixed with PLA/PBAT. The result showed that Trichoderma sp., Penicillium sp., and Fusarium sp. could reduce 89.93 %, 89.20 %, and 87.76 % nitrate. Meanwhile, the nitrate removal efficiency adding PLA/PBAT exceeded 1.40, 1.68, and 1.46 times that of none. The results of material characterization suggested that aerobic denitrifying fungi have different abilities to secrete proteases or lipases to catalyze ester bonds in PLA/PBAT and utilize it as nutrients in denitrification, especially in Penicillium brasiliensis D6. Besides, the electron transport system activity and the intracellular ATP concentration were increased significantly after adding PLA/PBAT, especially in Penicillium brasiliensis D6. Finally, the highest removal efficiency of total nitrogen in landscape water by fungi combined with PLA/PBAT was >80 %. The findings of this work provide new insight into the possibility of nitrogen removal by fungi in low C/N and the recycling of degradable resources.

Effects of copper sulfate algaecide on the cell growth, physiological characteristics, the metabolic activity of Microcystis aeruginosa and raw water application

Harmful cyanobacteria blooms (HCBs) occurred frequently and become a serious scientific challenge. Copper sulfate (CuSO₄) is a broad-spectrum chemical algaecide to control algae blooms. Herein, the Microcystis aeruginosa was exposed to different CuSO₄ (0.0, 0.2 and 0.5 mg/L) to assess the variations in algal physiological process and metabolic profiles. The results indicated that exposure to CuSO₄ of 0.5 mg/L at 72 h could significantly inhibit the cell growth and photosynthetic capacity of M. aeruginosa, including chl-a content and chlorophyll fluorescence parameters. Plasma membrane damage causing cell lysis of M. aeruginosa increased the K⁺ release. The increase of SOD and CAT suggested that CuSO₄ treatment caused oxidative stress in algal cells. Different doses of CuSO₄ modified the carbon metabolic potential, algal cells had their unique metabolic mode thereby. Moreover, the research further verified that CuSO₄ would also inhibit algal growth and change algal community structure in site-collected water application. Overall, laboratory results of M. aeruginosa to CuSO₄ and site-collected water application of algal responses to CuSO₄ might be conducive to uncovering the controlling mechanism of algae and the potential effect of carbon cycling in an ecological environment.

Re-circulation of Fe/persulfate regulated sludge fermentation products for sewage treatment: Focus on pollutant removal efficiency, microbial community and metabolic activity

Persulfate (PS)-based technologies have been demonstrated as efficient methods for enhancing the performance of waste activated sludge (WAS) anaerobic fermentation. Except for volatile fatty acids (VFAs), however, some exogenous substances would be also released during this process, which might affect its application as a carbon source for sewage treatment. To fill this knowledge gap, the feasibility of sludge fermentation liquid regulated by Fe/persulfate (PS) (PS-FL) as a carbon source for sewage treatment was investigated in this study. Results indicated that PS-FL exhibits distinct effects on the pollutants removal compared with commercial sodium acetate. It facilitates PO₄^3--P removal but slightly inhibited COD removal & denitrification, and sludge settleability was also decreased. The mechanistic analysis demonstrated that PS-FL could stimulate the enrichment of phosphorus-accumulating bacteria (i.e. Candidatus Accumulibacter) and the enhancement of their metabolic activities (i.e. PKK), thereby enhancing the biological PO₄^3--P removal. Moreover, Fe ions in PS-FL could combine with PO₄^3--P to form a precipitate and thus further contributed to PO₄^3--P removal. Conversely, the sulfate reduction process induced by SO₄^2- in PS-FL inhibits denitrification by reducing the abundance of denitrifying bacteria (i.e. Dechloromonas) and metabolic activities (i.e. narG). Additionally, PS-FL also decreased the abundance of flocculation bacteria (i.e. Flavobacterium) and down-regulated the expression of functional genes responsible for COD removal, by which it exhibited certain negative effects on COD removal and sludge settleability. Overall, this work demonstrated that PS-FL can re-circulation as a carbon source for sewage treatment, which provides a new approach to recovering valuable carbon sources from WAS.

Microplastics drive nitrification by enriching functional microorganisms in aquaculture pond waters

The plastisphere refers to biofilm formation on the microplastic (MP) surface, but its subsequent functions, especially driving the nitrogen biogeochemical cycle, are rarely studied. Here, MPs were incubated in the pelagic water and benthic water-sediment interface of an aquaculture pond, and the two corresponding microcosms amended with incubated plastisphere were simulated. The results showed decreased ammonia concentrations and increased nitrification rates in microcosms with either pelagic or benthic plastispheres. To uncover the possible mechanisms, the community structure and function of the plastisphere were investigated. As clarified by 16S rRNA, the community diversity of the pelagic plastisphere was significantly higher than that of the corresponding hydrosphere. Plastisphere communities, especially those incubated in pelagic water, were separated from the hydrosphere. Moreover, the abundance of Proteobacteria increased while the abundance of Cyanobacteria decreased in both plastispheres. Metagenome further revealed that the abundance of amoA and annotated Nitrososphaeraceae_archaeon and hao and affiliated Nitrosomonas_europaea, which contributed to ammonia oxidation to nitrite, was higher in the benthic plastisphere. Comparing the pelagic plastisphere with the corresponding hydrosphere, however, the abundance of nxrA and annotated Nitrobacter hamburgensis and nxrB and the affiliated Nitrospira moscoviensis, which are involved in nitrite oxidation, was more abundant in the plastisphere. These findings suggest that the plastisphere might selectively enrich functional microorganisms and genes in a habitat-dependent manner to promote nitrification in aquaculture ponds.

Sediment nitrogen contents controlled by microbial community in a eutrophic tributary in Three Gorges Reservoir, China

Nitrogen pollution caused serious environmental problems in reservoir ecosystems. Reducing nitrogen pollution by enhancing nitrogen removal in river sediments deserved intensive research. Distributions of nitrogen contents in sediment-water interface were characterized along the Xiangxi bay (XXB), a eutrophic tributary in Three Gorges Reservoir, China. More than 47% of total Kjeldahl nitrogen (TKN) and 67% of total organic nitrogen (TON) were degraded during burial. Higher TN, TON and NH₄⁺ consuming at downstream sites indicated stronger nitrogen mineralization and release due to higher turbulence of the overlying density currents. Nitrifying bacteria, denitrifying bacteria, anaerobic ammonium oxidizing (anammox) bacteria and nitrite/nitrate-dependent anaerobic methane oxidation (N-DAMO) bacteria were detected in nitrate-ammonium transition zone. Nitrogen contents transitions were responded to microbial stakeholders indicated microbially mediated nitrogen cycling in sediments. The dissolved oxygen and nitrate availabilities were the key limits of denitrification and associated reactions. These results suggested microbial mediated nitrogen cycling processes in sediments were critical for nitrogen removal in aquatic ecosystems, and replenishing dissolved oxygen and nitrate was expected to enhance sediment denitrification and strengthen potential environmental self-purification.

The scale-dependence of spatial distribution of reservoir plankton communities in subtropical and tropical China

Distance-decay relationships (DDRs) represent a very useful approach to describing the spatial distribution of biological communities. However, plankton DDR patterns and community assembly mechanisms are still poorly understood at different spatial scales in reservoir ecosystems. We collected phytoplankton, zooplankton and water samples in 24 reservoirs from subtropical and tropical China from July to August 2018. We examined DDR patterns across three distinct spatial scales, i.e., within-reservoir, within-drainage (but between reservoirs) and between drainages. We tested whether the rate of change (i.e., slope) of DDRs is consistent across different spatial scales. We assessed the relative importance of spatial and environmental variables in shaping the community distribution of plankton and quantitatively distinguished the community assembly mechanisms. We observed significant DDR curves in phytoplankton and zooplankton communities, in which slopes of the DDRs were steepest at the smallest spatial scale. Both spatial and environmental factors had significant impacts on DDR and dispersal assembly was a slightly stronger process in reservoir phytoplankton and zooplankton community assembly than niche-based process. We conclude that DDRs of reservoir phytoplankton and zooplankton vary with spatial scale. Our data shed light on how spatial and environmental variables contribute to plankton community assembly together. However, we revealed that dispersal process contributes to the biogeography of reservoir plankton slightly more strongly than environmental filtering. Collectively, this study enhances the understanding of plankton biogeography and distribution at multiple spatial scales.

Stagnation trigger changes to tap water quality in winter season: Novel insights into bacterial community activity and composition

The drinking water distribution system is important for water supply and it affects the quality of the drinking water. Indoor pipeline water quality is regulated by physical, hydraulic and biological elements, such as indoor temperature and stagnation. In this work, the effects of indoor heating and overnight stagnation on the variation in bacterial community structure and the total cell count were assessed by full-length 16S rRNA gene sequencing and flow cytometry, respectively. The results exhibited that the average intact cell count was 6.99 × 10⁴ cells/mL and the low nucleic acid (LNA) bacteria was 4.48 × 10⁴ cells/mL after stagnation. The average concentration of total and intracellular adenosine triphosphate (ATP) was 3.64 × 10^-12 gATP/mL and 3.13 × 10^-17 gATP/cell in stagnant water, respectively. The growth of LNA cells played a crucial role in increasing ATP. The dominant phylum observed was Proteobacteria (87.21 %), followed by Actinobacteria (8.25 %). Opportunistic pathogens increased the risk of disease in stagnant water (up to 1.2-fold for Pseudomonas sp. and 5.8-fold for Mycobacterium sp.). Meanwhile, structural equation model (SEM) and redundancy analysis (RDA) also illustrated that water temperature, residual chlorine and Fe significantly affected the abundance and composition of bacterial community. Taking together, these results show response of tap water quality to overnight stagnation and indoor heating, and provide scientific basis for drinking water security management in winter season.

Bacterial community structure and metabolic activity of drinking water pipelines in buildings: A new perspective on dual effects of hydrodynamic stagnation and algal organic matter invasion

Eutrophication and algal blooms have become global issues. The drinking water treatment process suffers from pollution by algal organic matter (AOM) through cell lysis during the algal blooms. Nevertheless, it remains unclear how AOM invasion affects water quality and microbial communities in drinking water, particularly in the stagnant settings. In this study, the addition of AOM caused the residual chlorine to rapidly degrade and below the limit of 0.05 mg/L, while the NO₂^--N concentration ranged from 0.11 to 3.71 mg/L. Additionally, total bacterial counts increased and subsequently decreased. The results of Biolog demonstrated that the AOM significantly improved the utilization capacity of carbon sources and changed the preference for carbon sources. Full-length 16S rRNA gene sequencing and network modeling revealed a considerable reduction in the abundance of Proteobacteria, whereas that of Bacteroidetes increased significantly under the influence of AOM. Furthermore, the species abundance distributions of the Microcystis group and Scenedesmus group was most consistent with the Mandelbrot model. According to redundancy analysis and structural equation modeling, the bacterial community structure of the control group was most positively regulated by the free residual chlorine concentrations, whereas the Microcystis group and Scenedesmus group were positively correlated with the total organic carbon (TOC) concentration. Overall, these findings provide a scientific foundation for the evolution of drinking water quality under algae bloom pollution.

Patterns of internal nitrogen and phosphorus loadings in a cascade reservoir with a large water level gradient: Effects of reservoir operation and water depth

Internal nutrient loadings pose a high risk of being an additional N and P source, exacerbating eutrophication and deteriorating water quality. In this study, we selected the Daheiting Reservoir (DHTR) in North China, with a pronounced water level gradient, to investigate internal N and P loadings, estimate N and P fluxes across the sediment‒water interface based on the pore water profiles, and reveal the potential effects of water discharge from an upstream reservoir and high-intensity cage aquaculture on the risks of internal N and P release. The results indicated that DHTR presented with severe internal nutrient loadings, and the N and P fluxes showed significant spatiotemporal variations. NH₄⁺-N and soluble reactive phosphorus (SRP) fluxes were higher in deep areas (averages of 26.14 and 9.9 mgm^-2d^-1, respectively) than in shallow areas near inflows (averages of 5.0 and 1.24 mgm^-2d^-1, respectively). Unexpectedly, the estimated NH₄⁺-N and SRP fluxes were the lowest in summer (averages of 3.94 and 0.33 mgm^-2d^-1, respectively), which may have been influenced by seasonal thermal stratification and copious discharge from the hypolimnion of the upstream reservoir (Panjiakou Reservoir). Comparison of annual internal and external N and P loadings revealed that water discharge from the upstream Panjiakou Reservoir was the dominant source of N and P to the reservoir, contributing up to 83.6% of N input and 55.4% of P input. The internal P loading also contributed to water eutrophication to a great extent, accounting for 34.7% of the total P input. Our results highlight the impact of upstream reservoir discharge operation on downstream reservoir water quality and the importance of controlling the internal nutrient loading in cascade reservoirs, and further provide theoretical and practical foundations for the development of policies and strategies to conserve reservoir ecosystems.

Autochthonous sources and drought conditions drive anomalous oxygen-consuming pollution increase in a sluice-controlled reservoir in eastern China

Freshwater reservoirs are an important type of inland waterbody. However, they can suffer from oxygen-consuming pollution, which can seriously threaten drinking water safety and negatively impact the health of aquatic ecosystems. Oxygen-consuming pollutants originate from both allochthonous and autochthonous sources, and have temporally and spatially heterogeneous drivers. Datanggang Reservoir, China, is located in a small agricultural watershed; it is controlled by multiple sluice gates. Anomalously high oxygen consumption indicators were observed in this reservoir in March 2021. Here, it was hypothesized that autochthonous sources were the primary drivers of oxygen-consuming pollution in the reservoir under drought conditions. Datasets of water quality, precipitation, primary productivity, and sediment were used to analyze water quality trends in the reservoir and inflow rivers, demonstrating the effects of allochthonous inputs and autochthonous pollution. No correlation was found between reservoir oxygen consumption indicators and allochthonous inputs; reservoir oxygen consumption indicators and chlorophyll-a concentration were significantly positively correlated (p < 0.05). Substantially lower precipitation and higher water temperature and pH (compared to historical levels) were also observed before the pollution event. Therefore, during this period the hydrological conditions, water temperature, pH, and other variables caused by short-term drought conditions may have facilitated phytoplankton growth in the reservoir. This contributed to a large increase in autochthonous oxygen-consuming pollutants, as reflected by the abnormally high indicators. Sediments contaminated with organic matter may also have been an important contributor. As the effects of environmental management and pollution control continue to emerge, exogenous pollutants imported from the land to reservoirs are currently effectively controlled. However, endogenous pollutants driven by a variety of factors, such as meteorology and hydrology, will likely become the main drivers of short-term changes in oxygen-consuming pollution in freshwater reservoirs in the foreseeable future.

Cyanobacterial bloom intensities determine planktonic eukaryote community structure and stability

The intensity of cyanobacterial blooms that predominate in the world's lakes and reservoirs is variable, which may lead to differing effects on the freshwater ecosystem. Planktonic eukaryotes play key roles in the structure and function of freshwater ecosystems; however, little is known about the influence of cyanobacterial blooms on eukaryotic plankton communities and their function. Herein, the dynamics of eukaryotic plankton communities in Hongze Lake, which is the fourth largest freshwater lake in China, with a range of bloom levels occurred, from low to high, were studied to reveal the effect of cyanobacterial blooms' spatial heterogeneity on planktonic eukaryotes. Results showed that the diversity, richness, and evenness of eukaryotic plankton community were not affected by low level of bloom; however, they were decreased obviously by high level of bloom. Metazoa, Ochrophyta, Chloroplastida, Cryptomonadales, and Ciliophora were the main planktonic eukaryotes in this lake. Metazoa relative abundance declined 25.1% and relative abundance of eukaryotic phytoplankton (mainly Ochrophyta, Chloroplastida, and Cryptomonadales) and Ciliophora increased 17.4% and 2.0%, respectively, during the period with low level of bloom; conversely, the site with the high bloom level manifested the opposite changes. The linkage density of planktonic eukaryotic network was 0.188 and 0.138 with low and high level of bloom, respectively, indicating the stability of planktonic eukaryotes was lower when a high level of bloom occurred compared to that of a low bloom level. Our findings indicate that cyanobacterial blooms should be controlled at low level to avoid their obvious negative impact on microeukaryotes in lakes or reservoirs.

Cooperation triggers nitrogen removal and algal inhibition by actinomycetes during landscape water treatment: Performance and metabolic activity

The actinomycetes strain Streptomyces sp. XD-11-9-3 and Streptomyces sp. 5 were isolated and presented poor denitrification performance. Co-culture of actinomycetes triggers nitrogen removal capacity under aerobic conditions (reduced 96% of total nitrogen). Nitrogen balance analysis presented that 71% of initial nitrogen converted as gaseous nitrogen. Moreover, co-culture increased the concentrations of adenosine triphosphate (>2.1 folds) and electron-transmission system activity (>1.5 folds) significantly. The co-culture presented excellent carbon source metabolism activity (especially amines and carboxylic acids) compared with monoculture. The removal efficiency of total nitrogen in the micro-polluted landscape water water reached 61% in the co-culture system, and the algal survival could be inhibited significantly. However, the dominant niche of the co-culture system restrained the diversity of the indigenous nirS-type denitrifying bacterial community. This study provided a novel pathway to the research of co-culture inefficiency aerobic denitrifier and further application in the restoration of polluted water.

Spatial Variation and Environmental Parameters Affecting the Abundant and Rare Communities of Bacteria and Archaea in the Sediments of Tropical Urban Reservoirs

Microbial communities in freshwater sediments play an important role in organic matter remineralization, contributing to biogeochemical cycles, nutrient release, and greenhouse gases emissions. Bacterial and archaeal communities might show spatial or seasonal patterns and were shown to be influenced by distinct environmental parameters and anthropogenic activities, including pollution and damming. Here, we determined the spatial variation and the environmental variables influencing the abundant and rare bacterial and archaeal communities in the sediments of eutrophic-hypereutrophic reservoirs from a tropical urban area in Brazil. The most abundant microbes included mainly Anaerolineae and Deltaproteobacteria genera from the Bacteria domain, and Methanomicrobia genera from the Archaea domain. Microbial communities differed spatially in each reservoir, reflecting the establishment of specific environmental conditions. Locations with better or worst water quality, or close to a dam, showed more distinct microbial communities. Besides the water column depth, microbial communities were affected by some pollution indicators, including total phosphorus, orthophosphate, electrical conductivity, and biochemical oxygen demand. Distinct proportions of variation were explained by spatial and environmental parameters for each microbial community. Furthermore, spatial variations in environmental parameters affecting these communities, especially the most distinct ones, contributed to microbial variations mediated by spatial and environmental properties together. Finally, our study showed that different pressures in each reservoir affected the sediment microbiota, promoting different responses and possible adaptations of abundant and rare bacterial and archaeal communities.