Impact of different types of anthropogenic pollution on bacterial community and metabolic genes in urban river sediments

Efficient anaerobic biodegradation of trimethoprim driven by electrogenic respiration: Optimizing bioelectro-characterization, elucidating biodegradation mechanism and fate of antibiotic resistance genes systematically

In this study, a bioelectrochemical system, with trimethoprim (TMP) as the sole carbon source, was constructed to evaluate the bioelectrogenic respiration on the acceleration of TMP degradation. The bioelectro-characterization was comprehensively optimized. The results showed that the optimal removal efficiency of TMP was achieved (99.38 %) when the external resistance, pH, and concentration of phosphate buffer solution were 1000 Ω, 7, and 25 mM, respectively. The potential TMP degradation pathways were speculated based on Liquid Chromatography-Mass Spectrometry and density functional theory calculations, including demethylation, demethoxy, hydroxylation and methylene bridge cracking. The overall biotoxicity of TMP biodegradation products after electrogenic respiration treatment was generally reduced. Electroactive bacteria (3.85 %) and potential degraders (27.18 %) were markedly increased in bioelectrogenic anaerobic treatment system, where bioelectrogenic respiration played a crucial role in promoting TMP biodegradation. However, it was observed that under long-term toxic stress of TMP, there was an enrichment of antibiotic resistance genes (ARGs) among the TMP-degrading bacteria. Furthermore, the comprehensive interaction between microbial communities and environmental variables was extensively investigated, revealing that electroactive bacteria and potential degraders were strongly positively correlated with TMP removal and biomineralization efficiency. This study provides guidance and promising strategy for the effective treatment of antibiotic-containing wastewater in practical applications.

Comprehensive profiling and risk assessment of antibiotic resistomes in surface water and plastisphere by integrated shotgun metagenomics

The ever-increasing microplastics (MPs) and antibiotic-resistance genes (ARGs) in aquatic ecosystems has become a serious global challenging issue. However, the impact of different pollution sources on microbiome and antibiotic resistome in surface water (SW) and plastisphere (PS) remains largely elusive. Here, shotgun metagenomics was used to analyze microbiome structure and antibiotic resistome in SW and PS under the influence of different pollution sources. Pseudomonas were the most abundant genus, followed by Flavobacterium, Acinetobacter, Acidovorax, and Limnohabitans. However, their relative abundance varied significantly both across the sampling sites and habitats i.e. SW and PS (p < 0.05). Additionally, various ARGs were detected in SW and PS, with PS (372) having significantly more potential ARGs than SW (293). The results further showed significant variations in the relative abundance of potential pathogenic bacteria across the sampling sites and habitats (p < 0.05). Further moreover, significant differences were observed in antibiotic resistome risk scores, ARGs and MGEs across different habitats. Over all, this study suggests that pollution source and water quality parameters had a significant impact on microbiome composition and antibiotic resistome in SW and PS.

Identifying human activities causing water pollution based on microbial community sequencing and source classifier machine learning

Identifying and differentiating human activities is crucial for effectively preventing the threats posed by environmental pollution to aquatic ecosystems and human health. Machine learning (ML) is a powerful analytical tool for tracking human impacts on river ecosystems based on high-through datasets. This study employed an ML framework and 16S rRNA sequencing data to reveal microbial dynamics and trace human activities across China. The results revealed that the microbial assembly was mainly dominated by deterministic factors (environmental factors and interactions between species), and the metacommunity partition was significantly associated with human activities in both water and sediment (Chi-square testwP = 1.93 × 10-22; Chi-square testsP = 6.00 × 10-6). Human activities increased the vulnerability of interspecific occurrence networks and the influence of environmental factors on the OTUs similarity and phylogenetic distance. Combined of microbiological indices (MBIs), microbial relative abundance (MRA), and environmental and geographical indices (EGIs), the source classifier machine learning (SCML) algorithm was used to categorize five human activities (i.e., low human-impact, agricultural inputs, domestic inputs, industrial inputs, and dam construction). The SCML optimal configuration is (MBIs + MRA + EGIs) exhibited strong performance with TestW R2 of 0.882 and TestS R2 of 0.924. This study provides valuable insights for improving ecosystem management, supporting sustainable water resource management and advancing pollution mitigation efforts.

Evaluating the role of recalcitrant dissolved organic matter in bacterial community dynamics in urbanized freshwater ecosystems

Dissolved organic matter (DOM) and recalcitrant dissolved organic matter (RDOM) play distinct roles in shaping microbial communities. However, characterizing these roles is difficult, especially in ecosystems subjected to varying degrees of anthropogenic influence. This study investigated the molecular compositions and ecological impacts of DOM and RDOM in the Fen River, Shanxi Taiyuan, comparing pristine upstream regions with highly urbanized downstream areas. Using 16S rRNA gene sequencing and LC-MS-based metabolomics, we observed significant shifts in microbial community composition, diversity, and metabolic functions. Upstream communities, characterized by higher diversity, were dominated by Bacteroidota, Proteobacteria, and Cyanobacteria, while downstream communities, influenced by pollution, exhibited increased expression of genes related to amino acid metabolism. Fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that upstream DOM contained higher proportions of complex, high molecular weight compounds, including significant proportions of carboxyl-rich alicyclic molecules (CRAM) and island of stability (IOS) compounds, which play key roles in long-term carbon storage and microbial carbon sequestration. In contrast, downstream DOM was characterized as having lower aromaticity and more saturated compounds, with reduced proportions of CRAM and IOS, reflecting the impact of anthropogenic activities. These findings underscored the critical roles of CRAM and IOS in regulating DOM stability and microbial communities, further highlighting the need for targeted pollution control strategies to preserve ecosystem function in urbanized water bodies.

Riverine bacterial communities are more shaped by species sorting in intensive urban and agricultural watersheds

Bacterial communities play a crucial role in maintaining the stability of river ecosystems and driving biogeochemical cycling, exhibiting high sensitivity to environmental change. However, understanding the spatial scale effects and assembly mechanisms of riverine bacterial communities under distinct anthropogenic disturbances remains a challenge. Here, we investigated bacterial communities across three distinct watersheds [i.e., intensive urban (UW), intensive agricultural (AW), and natural (NW)] in both dry and wet seasons. We explored biogeographic patterns of bacterial communities and the influence of landscape patterns at multi-spatial scales and water chemistry on bacterial communities. Results showed that α diversity was significantly lower in UW and AW compared to NW, particularly in the dry season. A gradient of β diversity with NW > UW > AW was observed across both seasons (p < 0.05). Pseudomonadota, Bacteroidota, and Actinobacteriota were the most abundant phyla across all watersheds, with specific taxa enriched in each watershed (i.e., the class Actinobacteria was significant enrichment in UW and AW, and Clostridia in NW). The influence of landscape patterns on bacterial communities was significantly lower in human-disturbed watersheds, particularly in UW, where this influence also varied slightly from near riparian buffers to sub-watershed. Homogeneous selection and drift jointly dominated the bacterial community assembly across all watersheds, with homogeneous selection exhibiting a greater influence in UW and AW. Landscape patterns explained less variance in bacterial communities in UW and AW than in NW, and more variance was explained by water chemistry (particularly in UW). These suggest that the stronger influence of species sorting in UW and AW was driven by more allochthonous inputs of water chemistry (greater environmental stress). These findings provide a theoretical foundation for a deeper understanding of riverine bacterial community structure, spatial scale effects, and ecological management under different anthropogenic activities.

Evaluating the role of high N2O affinity complete denitrifiers and non-denitrifying N2O reducing bacteria in reducing N2O emissions in river

Freshwater rivers are hotspots of N2O greenhouse gas emissions. Dissolved organic carbon (DOC) is the dominant electron donor for microbial N2O reduction, which can reduce N2O emission through enriching high N2O affinity denitrifiers or enriching non-denitrifying N2O-reducing bacteria (N2ORB), but the primary regulatory pathway remains unclear. Here, field study indicated that high DOC concentration in rivers enhanced denitrification rate but reduced N2O flux by improving nosZ gene abundance. Then, four N2O-fed membrane aeration biofilm reactors inoculated with river sediments from river channel, estuary, adjacent lake, and a mixture were continuously performed for 360 days, including low, high, and mixed DOC stages. During enrichment stages, the (nirS+nirK)/nosZ ratio showed no significant difference, but the community structure of denitrifiers and N2ORB changed significantly (p < 0.05). In addition, N2ORB strains isolated from different enrichment stages positioned in different branches of the phylogenetic tree. N2ORB strains isolated during high DOC stage showed significant higher maximum N2O-reducing capability (Vmax: 0.6 ± 0.4 ×10-4 pmol h-1 cell-1) and N2O affinity (a0: 7.8 ± 7.7 ×10-12 L cell-1 h-1) than strains isolated during low (Vmax: 0.1 ± 0.1 ×10-4 pmol h-1 cell-1, a0: 0.7 ± 0.4 ×10-12 L cell-1 h-1) and mixed DOC stages (Vmax: 0.1 ± 0.1 ×10-4 pmol h-1 cell-1, a0: 0.9 ± 0.9 ×10-12 L cell-1 h-1) (p < 0.05). Hence, under high DOC concentration conditions, the primary factor in reducing N2O emissions in rivers is the enrichment of complete denitrifiers with high N2O affinity, rather than non-denitrifying N2ORB.

Deciphering the roles of nitrogen source in sharping synchronous metabolic pathways of linear alkylbenzene sulfonate and nitrogen in a membrane biofilm for treating greywater

Nitrogen (N) source is an important factor affecting biological wastewater treatment. Although the oxygen-based membrane biofilm showed excellent greywater treatment performance, how N source impacts the synchronous removal of organics and N is still unclear. In this work, how N species (urea, nitrate and ammonia) affect synchronous metabolic pathways of organics and N were evaluated during greywater treatment in the membrane biofilm. Urea and ammonia achieved efficient chemical oxygen demand (>97.5%) and linear alkylbenzene sulfonate (LAS, >98.5%) removal, but nitrate enabled the maximum total N removal (80.8 ± 2.6%). The nitrate-added system had poor LAS removal ratio and high residual LAS, promoting the accumulation of effluent protein-like organics and fulvic acid matter. N source significantly induced bacterial community succession, and the increasing of corresponded functional flora can promote the transformation and utilization of microbial-mediated N. The nitrate system was more conducive to the accumulation of denitrification related microorganisms and enzymes, enabling the efficient N removal. Combining with high amount of ammonia monooxygenase that contributing to LAS and N co-metabolism, LAS mineralization related microbes and functional enzymes were generously accumulated in the urea and ammonia systems, which achieved the high efficiency of organics and LAS removal.

Distribution Characteristics of Nitrogen-Cycling Microorganisms in Deep-Sea Surface Sediments of Western South China Sea

Nitrogen-cycling processes in the deep sea remain understudied. This study investigates the distribution of nitrogen-cycling microbial communities in the deep-sea surface sediments of the western South China Sea, using metagenomic sequencing and real-time fluorescent quantitative PCR techniques to analyze their composition and abundance, and the effects of 11 environmental parameters, including NH4+-N, NO3--N, NO2--N, PO43--P, total nitrogen (TN), total organic carbon (TOC), C/N ratio, pH, electrical conductivity (EC), SO42-, and Cl-. The phylum- and species-level microbial community compositions show that five sites can be grouped as a major cluster, with sites S1 and S9 forming a sub-cluster, and sites S13, S19, and S26 forming the other; whereas sites S3 and S5 constitute a separate cluster. This is also evident for nitrogen-cycling functional genes, where their abundance is influenced by distinct environmental conditions, including water depths (shallower at sites S1 and S9 against deeper at sites S13, S19, and S26) and unique geological features (sites S3 and S5), whereas the vertical distribution of nitrogen-cycling gene abundance generally shows a decreasing trend against sediment depth. Redundancy analysis (RDA) exploring the correlation between the 11 environmental parameters and microbial communities revealed that the NO2--N, C/N ratio, and TN significantly affect microbial community composition (p < 0.05). This study assesses the survival strategies of microorganisms within deep-sea surface sediments and their role in the marine nitrogen cycle.

Comparing Sediment Bacterial Communities of Volcanic Lakes and Surrounding Rivers in Inner Mongolia Autonomous Region, Northeastern China

Volcanic lakes originate from a volcanic crater or caldera, and were a crucial component of aquatic ecosystems. Sediment bacteria play an important role in the nutrient cycling of aquatic ecosystems; however, their patterns distribution in volcanic lakes and the surrounding river habitats are unknown. In this study, we compare the sediment bacterial communities and their co-occurrence networks between these two habitats in the Inner Mongolia Autonomous Region, Northeastern China (the Arxan UNESCO Global Geopark), using 16S rRNA gene amplicon sequencing. The results revealed that there were significant variations in the physicochemical parameters of the sediment between these two habitats. The bacterial α-diversity, β-diversity, and community composition of the sediment also significantly differed between these two habitats. Network analysis showed that the co-occurrence patterns and keystone taxa in the sediment differed between these two habitats. The sediment bacterial communities in the river habitats were more stable than those in the lake habitats in the face of environmental change. Canonical correspondence analysis demonstrated that both physical (pH and MC) and nutrition-related factors (TN, TP, LOI, and TOC) were the most important environmental factors shaping the variations of bacterial community composition (BCC) in the sediment between these two habitats. This work could greatly improve our understanding of the sediment BCC of the sediment from aquatic ecosystems in the UNESCO Global Geopark.

Exogenous compound bacteria enhance the nutrient removal efficiency of integrated bioremediation systems: Functional genes and microorganisms play key roles

With the continuous development of intensive mariculture, the application of the integrated bioremediation system of aquaculture wastewater (IBSAW) is increasingly promoted. However, the process and nutrients removal performance of the IBSAW need to be further optimized due to its immature technologies. In this study, exogenous compound bacteria (ECB) were added to IBSAW to investigate its pollutants removal efficiency and the relevant mechanisms. High-throughput sequencing and Geochip gene array were used to analyze the correlation between nutrients and bacteria, and the abundance of N and P cycling genes were quantified. Multivariable statistics, dimensionality reduction analysis, and network analysis were applied to explore the mechanisms of IBSAW operation. The results showed that the nutrients decreased significantly after adding ECB, with the brush treatment group significantly outperforming the ceramsite in removing NO3- and PO43-. Ceramsite has an advantage in removing NO2--N. The addition of ECB and different substrates significantly affected the composition of bacterial communities. The contents of nosZ and nirKS related to denitrification in the treatment groups were significantly higher than those in the control group, and the contents in the brush treatment group were significantly higher than that of ceramsite. The biomarkers Psychroserpens and Ruegeria on the biofilm of the brush treatment group were positively correlated with nirKS, while Mycobacterium, Erythrobacter and Paracoccus, Pseudohaliea in the ceramsite group were positively correlated with nirS and nirK, respectively. Therefore, it is speculated that the ECB significantly promoted the increase of denitrification bacteria by affecting the composition of bacterial communities, and the ECB combined with functional genera improved the efficiency of nutrients removal in the system. This study provided a reference for understanding the process and mechanism of nutrients removal, optimizing the wastewater purification technology of the IBSAW and improving the performance of the system.

Microbial community structure and diversity attached to the periphyton in different urban aquatic habitats

Periphyton is a complex community composed of diverse prokaryotes and eukaryotes; understanding the characteristics of microbial communities within periphyton becomes crucial for biogeochemical cycles and energy dynamics of aquatic ecosystems. To further elucidate the community characteristics of periphyton across varied aquatic habitats, including unpolluted ecologically restored lakes, aquaculture ponds, and areas adjacent to domestic and industrial wastewater treatment plant outfalls, we explored the composition and diversity of prokaryotic and eukaryotic communities in periphyton by employing Illumina MiSeq sequencing. Our findings indicated that the prokaryotic communities were predominantly composed of Proteobacteria (40.92%), Bacteroidota (21.01%), and Cyanobacteria (10.12%), whereas the eukaryotic communities were primarily characterized by the dominance of Bacillariophyta (24.09%), Chlorophyta (20.83%), and Annelida (15.31%). Notably, Flavobacterium emerged as a widely distributed genus among the prokaryotic community. Unclassified_Tobrilidae exhibited higher abundance in unpolluted ecologically restored lakes. Chaetogaster and Nais were enriched in aquaculture ponds and domestic wastewater treatment plant outfall area, respectively, while Surirella and Gomphonema dominated industrial sewage treatment plant outfall area. The alpha diversity of eukaryotes was higher in unpolluted ecologically restored lakes. pH and nitrogen content (NO 2 - - N ,NO 3 - - N , and TN) significantly explained the variations for prokaryotic and eukaryotic community structures, respectively. Eukaryotic communities exhibited a more pronounced response to habitat variations compared to prokaryotic communities. Moreover, the association networks revealed an intensive positive correlation between dominant Bacillariophyta and Bacteroidota. This study provided useful data for identifying keystone species and understanding their ecological functions.

Microcystin influence on soil-plant microbiota: Unraveling microbiota modulations and assembly processes in the rhizosphere of Vicia faba

Microcystins (MCs) are frequently detected in cyanobacterial bloom-impacted waterbodies and introduced into agroecosystems via irrigation water. They are widely known as phytotoxic cyanotoxins, which impair the growth and physiological functions of crop plants. However, their impact on the plant-associated microbiota is scarcely tackled and poorly understood. Therefore, we aimed to investigate the effect of MCs on microbiota-inhabiting bulk soil (BS), root adhering soil (RAS), and root tissue (RT) of Vicia faba when exposed to 100 μg L-1 MCs in a greenhouse pot experiment. Under MC exposure, the structure, co-occurrence network, and assembly processes of the bacterial microbiota were modulated with the greatest impact on RT-inhabiting bacteria, followed by BS and, to a lesser extent, RAS. The analyses revealed a significant decrease in the abundances of several Actinobacteriota-related taxa within the RT microbiota, including the most abundant and known genus of Streptomyces. Furthermore, MCs significantly increased the abundance of methylotrophic bacteria (Methylobacillus, Methylotenera) and other Proteobacteria-affiliated genera (e.g., Paucibacter), which are supposed to degrade MCs. The co-occurrence network of the bacterial community in the presence of MCs was less complex than the control network. In MC-exposed RT, the turnover in community composition was more strongly driven by deterministic processes, as proven by the beta-nearest taxon index. Whereas in MC-treated BS and RAS, both deterministic and stochastic processes can influence community assembly to some extent, with a relative dominance of deterministic processes. Altogether, these results suggest that MCs may reshape the structure of the microbiota in the soil-plant system by reducing bacterial taxa with potential phytobeneficial traits and increasing other taxa with the potential capacity to degrade MCs.

Effects of flow rate and wastewater concentration on the transformation of nitrogen in sediment-water system of sewage pipelines

In this work, the transformation law of nitrogen in sediment-water system under different flow rates and wastewater concentrations were investigated in a simulated sewage pipeline system. Results showed that the different flow rates and wastewater concentrations in the pipeline caused differences in microbial community in sediments and nitrogen transformation. When the flow rate increased from 0.05 to 0.2 m/s, the scouring effect was enhanced, resulting in higher concentrations of NH4 + -N and NO3 - -N in the overlying water. At 0.2 m/s, the relative abundance of Clostridium_sensu_stricto_1 in sediments was higher, resulting in a greater conversion of amino acid nitrogen (AAN) to NH4 + -N. Meanwhile, many denitrifying bacteria (Trichococcus, Dechloromonas, norank_f__norank_o__Gaiellales, Thiobacillus) had high relative abundance in the sediments, and the denitrification process was common. When the wastewater concentration was high, the nitrification reaction was great in overlying and interstitial water. Moreover, the ammoniation process was great in the sediments, and the variation flux of AAN was large (remarkably reduced). PRACTITIONER POINTS: AAN transformed to NH4 + -N in sediment under different flow rate and concentration. Scouring was enhanced at 0.2 m/s, increasing nitrogen contents in overlying water. Difference in microbial community led to more AAN conversion to NH4 + -N at 0.2 m/s. The ammoniation process was greater in sediment at a high concentration of sewage. NH4 + -N migrated from overlying water to sediment at a high concentration of sewage.

Linking ecological niches to bacterial community structure and assembly in polluted urban aquatic ecosystems

Introduction

Bacterial communities play crucial roles in the functioning and resilience of aquatic ecosystems, and their responses to water pollution may be assessed from ecological niches. However, our understanding of such response patterns and the underlying ecological mechanisms remains limited.

Methods

In this study, we comprehensively investigated the effects of water pollution on the bacterial structure and assembly within different ecological niches, including water, sediment, submerged plant leaf surfaces, and leaf surfaces, using a 16S high-throughput sequencing approach.

Results

Ecological niches had a greater impact on bacterial community diversity than pollution, with a distinct enrichment of unique dominant phyla in different niches. This disparity in diversity extends to the bacterial responses to water pollution, with a general reduction in α-diversity observed in the niches, excluding leaf surfaces. Additionally, the distinct changes in bacterial composition in response to pollution should be correlated with their predicted functions, given the enrichment of functions related to biogeochemical cycling in plant surface niches. Moreover, our study revealed diverse interaction patterns among bacterial communities in different niches, characterized by relatively simply associations in sediments and intricate or interconnected networks in water and plant surfaces. Furthermore, stochastic processes dominated bacterial community assembly in the water column, whereas selective screening of roots and pollution events increased the impact of deterministic processes.

Discussion

Overall, our study emphasizes the importance of ecological niches in shaping bacterial responses to water pollution. These findings improve our understanding of the complicated microbial response patterns to water pollution and have ecological implications for aquatic ecosystem health.

Cd contamination determined assembly processes and network stability of AM fungal communities in an urban green space ecosystem

The effects of cadmium (Cd) contamination on the assembly mechanism and co-occurrence patterns of arbuscular mycorrhizal (AM) fungal communities remain unclear, especially in urban green spaces. This study sequenced AM fungal communities in greenbelt soils in Zhengzhou (China). The effects of Cd contamination on the AM fungal diversity, community assembly processes, and co-occurrence patterns were explored. We found that (1) an increase in Cd contamination changed the community composition, which resulted in a significant improvement in the diversity of specialists of AM fungi and a significant decrease in the diversity of generalists. (2) Deterministic processes dominated the community assembly of specialists and stochastic processes dominated the community assembly of generalists. (3) Specialists played a more important role than generalists in maintaining the stability of AM fungal networks under Cd contamination. Overall, Cd contamination affected the ecological processes of AM fungi in urban green space ecosystems. However, the effects on the assembly processes and network stability of different AM fungi taxa (specialists and generalists) differed significantly. The present study provides deeper insight into the effect of Cd contamination on the ecological processes of AMF and is helpful in further exploring the ecological risk of Cd contamination in urban green spaces.

Transformation trend of nitrogen and phosphorus in the sediment of the sewage pipeline and their distribution along the pipeline

Microorganisms transform nitrogen and phosphorus in the sediment of sewage pipelines. When the sediment was scoured by water flow, these elements migrate. This work studied the changes in biofilm morphology and microbial community structure, and focused on the differences in the transformation of nitrogen and phosphorus along the pipeline. The results showed that the nitrogen and phosphorus concentrations varied systematically with time and space (the front, middle, and posterior segments of the pipe). With time, amino acid nitrogen (AAN) concentration in the sediment gradually decreased, NH₄⁺-N concentration slowly increased, NO₃^--N concentration began to increase after 25 days, and TP concentration continued to increase after 9 days. The AAN, NH₄⁺-N, and TP concentrations were highest in the posterior segment of the pipe and lowest in the front segment. However, NO₃^--N showed two stages: its concentration was highest in the front segment and lowest in the posterior segment during the first 17 days, after which the opposite was observed. Changes in the nitrogen and phosphorus concentrations were related to the microbial communities in the sediments. The abundances of Rhodobacter (0.001 <p ≤ 0.01), Trichococcus (p ≤ 0.001), Nakamurella (0.01 <p ≤ 0.05), and norank_f__norank_o__PeM15 (0.001 <p ≤ 0.01) in the terminal sediments were significantly higher than those in the initial sediments. Meanwhile, the abundances of Clostridium_sensu_stricto_1, Rhodobacter, norank_f__norank_o__PeM15, and Brevundimonas were different in the front, middle, and posterior segments. Furthermore, nitrogen and phosphorus were easily adsorbed on the small particles and were scoured and re-deposited on the posterior segment of the pipe, resulting in enrichment. The temporal variation in nitrogen and phosphorus and its spatial distribution along the pipeline were due to the combination of biotransformation and migration.

Microbiologically induced calcite precipitation for in situ stabilization of heavy metals contributes to land application of sewage sludge

Microbiologically induced calcite precipitation (MICP) has shed new light on solving the problem of in situ stabilization of heavy metals (HMs) in sewage sludge before land disposal. In this study, we examined whether MICP treatment can be integrated into a sewage sludge anaerobic digestion-land application process. Our results showed that MICP treatment not only prevented the transfer of ionic-state Cd from the sludge to the supernatant (98.46 % immobilization efficiency) but also reduced the soluble exchangeable Pb and Cd fractions by up to 100 % and 48.54 % and increased the residual fractions by 22.54 % and 81.77 %, respectively. In addition, the analysis of the stability of HMs in MICP-treated sludge revealed maximum reductions of 100 % and 89.56 % for TCLP-extractable Pb and Cd, respectively. Three-dimensional fluorescence, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy analyses confirmed the excellent performance of the ureolytic bacteria Sporosarcina ureilytica ML-2 in the sludge system. High-throughput sequencing showed that the relative abundance of Sporosarcina sp. reached 53.18 % in MICP-treated sludge, and the urease metabolism functional genes unit increased by a maximum of 239.3 %. The MICP technology may be a feasible method for permanently stabilizing HMs in sewage sludge before land disposal.

Water quality status response to multiple anthropogenic activities in urban river

Water quality evaluation and degrading factors identification are crucial for predicting water quality evolution trends in an urban river. However, under the coupling of multiple factors, these targets face great challenges. The water quality status response to multiple anthropogenic activities in an urban river was evaluated and predicted based on comprehensive assessment methods and random forest (RF) model. We found that the distribution of each physicochemical parameter exhibits an obvious spatial clustering. The mean pollution level and trophic status of the urban river are medium pollution (water quality index = 59.79; Nemerow's pollution index = 2.00) and light eutrophication (trophic level index = 57.30). The water quality status is sensitive to anthropogenic activities, showing the following order of TLI and NPI values: residential district > industrial district > agricultural district and downtown > suburbs > countryside. According to the redundancy analysis, constructed land (F = 15.90, p < 0.01) and domestic sewage (F = 14.20, p < 0.01) evinced as the crucial factors that aggravated the water quality pollution level. Based on the simulation results of the RF model (variation explained = 94.91%; R² = 0.978), improving domestic sewage treatment standards is the most effective measure to improve the water quality (increased by 40.3-49.3%) in residential and industrial districts. While in a suburban district, improving the domestic sewage collection rate has more effectively (23%) than those in the residential and industrial districts. Conclusively, reducing exogenous pollution input and improving domestic sewage treatment standards are vital to urban river restoration. Clinical trial registration Not applicable.

Effects of Different Types of Human Disturbance on Total and Nitrogen-Transforming Bacteria in Haihe River

Haihe River is the largest water system in North China and is injected into the Bohai Sea in Tianjin City. In this study, different types of human disturbance (urban sewage, industrial pollution, ship disturbance) were selected from the upper reaches of Haihe river Tianjin section down to the estuary that connected with Bohai Sea for evaluation. By metagenomic sequencing, the effects of different types of disturbances on bacteria communities in Haihe sediments were studied, with a special focus on the function of nitrogen-cycling bacteria that were further analyzed through KEGG comparison. By analyzing the physical and chemical characteristics of sediments, results showed that human disturbance caused a large amount of nitrogen input into Haihe River, and different types of human disturbance led to distinct spatial heterogeneity in different sections of Haihe River. The bacteria community was dominated by Proteobacteria, followed by Chloroflexi, Bacteroidetes, Actinobacteria and Acidobacteria. The relative abundance of each phylum varied at different sites as a response to different types of human disturbances. In nitrogen cycling, microorganisms including nitrogen fixation and removal were detected at each site, which indicated the active potential for nitrogen transformation in Haihe River. In addition, a large number of metabolic pathways relating to human diseases were also revealed in urban and pollution sites by function potential, which provided an important basis for the indicative role of urban river ecosystem for public health security. In summary, by evaluating both the ecological role and function potential of bacteria in Haihe River under different types of human disturbance, the knowledge of microorganisms for healthy and disturbed river ecosystems has been broadened, which is also informative for further river management and bioremediation.

Water Quality and Microbial Community in the Context of Ecological Restoration: A Case Study of the Yongding River, Beijing, China

Ecological water replenishment via interbasin water diversion projects provides opportunities for ecological river restoration. Untangling water quality changes, microbiota dynamics, and community functions is necessary for sustainable ecological management. Using the Yongding River as a case study, we monitored the water quality and applied genomic sequencing to investigate microbial communities of the river in different stages after ecological water replenishment. Our results showed that river water quality represented by chemical oxygen demand (COD), total nitrogen (TN), and chlorophyll-a (Chl-a) did not change significantly during months after water replenishment. The bacterial community composition varied in different months and river subsections. The Cyanobium_PCC-6307, CL500-29 marine group, and Pseudomonas were dominant in the later stages after water replenishment. Water temperature, pH, and nutrient levels significantly affected the microbial community composition, and ecological restoration may have the potential to influence nitrogen cycling in the river. Our results can provide ecological insights into sustainable water quality maintenance and river management following ecological restoration enabled by ecological water replenishment.

Effect of microbial community structures and metabolite profile on greenhouse gas emissions in rice varieties

Rice paddy fields are major sources of atmospheric methane (CH₄) and nitrous oxide (N₂O). Rice variety is an important factor affecting CH₄ and N₂O emissions. However, the interactive effects of rice metabolites and microorganisms on CH₄ and N₂O emissions in paddy fields are not clearly understood. In this study, a high greenhouse gas-emitting cultivar (YL 6) and a low greenhouse gas-emitting cultivar (YY 1540) were used as experimental materials. Metabolomics was used to examine the roots, root exudates, and bulk soil metabolites. High-throughput sequencing was used to determine the microbial community composition. YY 1540 had more secondary metabolites (flavonoids and isoflavonoids) in root exudates than YL 6. It was enriched with the uncultured members of the families Gemmatimonadanceae and Rhizobiales_Incertae_Sedis in bulk soil, and genera Burkholderia-Caballeronia-Paraburkholderia, Magnetospirillum, Aeromonas, and Anaeromyxobacter in roots, contributing to increased expression of pmoA and nosZ genes and reducing CH₄ and N₂O emissions. YL 6 roots and root exudates contained higher contents of carbohydrates [e.g., 6-O- acetylarbutin and 2-(3- hydroxyphenyl) ethanol 1'-glucoside] than those of YY 1540. They were enriched with genera RBG-16-58-14 in bulk soil and Exiguobacterium, and uncultured member of the Kineosporiaceae family in roots, which contributed to increased expression of mcrA, ammonia-oxidizing archaea, ammonia-oxidizing bacteria, nirS, and nirK genes and greenhouse gas emissions. In general, these results established a link between metabolites, microorganisms, microbial functional genes, and greenhouse gas emissions. The metabolites of root exudates and roots regulated CH₄ and N₂O emissions by influencing the microbial community composition in bulk soil and roots.