Bioturbation by the razor clam (Sinonovacula constricta) on the microbial community and enzymatic activities in the sediment of an ecological aquaculture wastewater treatment system

Divergent impacts of animal bioturbation on methane and nitrous oxide emissions from mariculture ponds

Aquaculture systems are of increasing concern as an important source of atmospheric methane (CH4) and nitrous oxide (N2O). However, the role of animals in regulating CH4 and N2O emissions from aquaculture systems remains unclear. Here, we established mesocosm trials to investigate impacts of bioturbation of different aquaculture species (i.e., clam, shrimp, and crab) on CH4 and N2O fluxes in a mariculture pond. Across the initial, middle, and final culturing stages, mean CH4 flux in mesocosm without animals was 4.81 ± 0.09 µg CH4 m‒2 h‒1, while the existence of clam, shrimp, and crab significantly increased CH4 flux by 35.3 %, 80.6 %, and 138 %, respectively. Bioturbation significantly decreased dissolved oxygen (DO) concentration by 5.19‒44.8 % but increased porewater CH4 concentration by 14.1‒59.9 %, indicating that lowered DO caused by animal respiration promoted CH4 production in sediment. Moreover, bioturbation of animals significantly increased ebullitive CH4 fluxes by 41.0‒216 %, contributing 57.4‒77.2 % of the increased CH4 emission in mesocosms with animals. However, shrimp and crab significantly reduced N2O flux by 30.3 % and 42.5 %, respectively, primarily due to lowered DO conditions suppressing nitrification and limiting NO3‒ supply for denitrification. By contrast, clam significantly increased N2O emission by 181 % because its filter-feeding behavior excreted more NH4+ and NO3‒ into overlying water and thereby facilitating N2O production. The N2O concentration in overlying water was 1.72‒2.83-fold of that in porewater, and the calculated diffusive N2O flux was 1.80‒37.5 % greater than chamber-measured N2O efflux. This implied that N2O might be primarily produced in overlying water rather than sediments, and the produced N2O can either evade as water-air fluxes or diffuse downwards into sediments to be consumed. Overall, our study advocates that aquaculture-related climate mitigation strategies should place more attention on the divergent impacts of animal bioturbation on CH4 and N2O emissions.

Freshwater snails (Bellamya aeruginosa) bioturbation to enhance nitrogen removal and associated mechanism in constructed wetlands

In this study, total nitrogen (TN) removal efficiency of Pontederia cordata and Myriophyllum elatinoides in surface flow constructed wetlands (SFCWs) with Bellamya aeruginosa were 6.43% and 3.54% higher, respectively, than those in non-B. aeruginosa SFCWs. Further, bioturbation could promote N uptake by plants and release from sediment. In summer and autumn, potential nitrification rate was significantly higher in SFCWs with snails than that in SFCWs without snails. In each season, potential denitrification rate was significantly higher in SFCWs with snails than that in SFCWs without snails. Additionally, ammonia oxidizing archaea, narG, nirS, nirK and nosZ gene abundances were significantly higher in SFCWs with snails than those in SFCWs without snails. Structural equation model analysis revealed a strong positive correlation between nitrifiers and denitrifiers in SFCWs with snails, suggesting that bioturbation enhanced N removal by increasing synergistic effect of nitrifying and denitrifying bacteria.

The metabolic network response and tolerance mechanism of Thalassia hemprichii under high sulfide based on widely targeted metabolome and transcriptome

Costal eutrophication leads to increased sulfide levels in sediments, which has been identified as a major cause of the global decline in seagrass beds. The seagrass Thalassia hemprichii, a dominant tropical species in the Indo-Pacific, is facing a potential threat from sulfide, which can be easily reduced from sulfate in porewater under the influence of global climate change and eutrophication. However, its metabolic response and tolerance mechanisms to high sulfide remain unclear. Thus, the current study investigated the physiological responses and programmed metabolic networks of T. hemprichii through a three-week mesocosm experiment, integrating physiology, stable isotope, widely targeted metabolomics, transcriptomics, and microbial diversity assessments. High sulfide reduced the sediment microbial diversity, while increased sediment sulfate reduced bacterial abundance and δ34S. The exposure to sulfide enhanced root δ34S while decreased leaf δ34S in T. hemprichii. High sulfide was shown to inhibit photosynthesis via damaging PSII, which further reduced ATP production. In response, abundant up-regulated differentially expressed genes in energy metabolism, especially in oxidative phosphorylation, were activated to compensate high energy requirement. High sulfide also promoted autophagy by overexpressing the genes related to phagocytosis and phagolysosome. Meanwhile, metabolomic profiling revealed that the contents of many primary metabolites, such as carbohydrates and amino acids, were reduced in both leaves and roots, likely to provide more energy and synthesize stress-responsive secondary metabolites. Genes related to nitrate reduction and transportation were up-regulated to promote N uptake for sulfide detoxification. High sulfide levels specifically enhanced thiamine in roots, while increased jasmonic acid and flavonoid levels in leaves. The distinct differences in metabolism between roots and leaves might be related to sulfide levels and the growth-defense trade-off. Collectively, our work highlights the specific mechanisms underlying the response and tolerance of T. hemprichii to high sulfide, providing new insights into seagrass strategies for resisting sulfide.

Effects of polyethylene, polylactic acid, and tire particles on the sediment microbiome and metabolome at high and low temperatures

Global warming has led to a high incidence of extreme heat events, and the frequent occurrence of extreme heat events has had extensive and far-reaching impacts on wetland ecosystems. The widespread distribution of plastics in the environment, including polyethylene (PE), polylactic acid (PLA), and tire particles (TPs), has caused various environmental problems. Here, high-throughput sequencing techniques and metabolomics were used for the first time to investigate the effects of three popular microplastic types: PE, PLA, and TP, on the sediment microbiome and the metabolome at both temperatures. The microplastics were incorporated into the sediment at a concentration of 3% by weight of the dry sediment (wt/wt), to reflect environmentally relevant conditions. Sediment enzymatic activity and physicochemical properties were co-regulated by both temperatures and microplastics producing significant differences compared to controls. PE and PLA particles inhibited bacterial diversity at low temperatures and promoted bacterial diversity at high temperatures, and TP particles promoted both at both temperatures. For bacterial richness, only PLA showed inhibition at low temperature; all other treatments showed promotion. PE, PLA, and TP microplastics changed the community structure of sediment bacteria, forming two clusters at low and high temperatures. Furthermore, PE, PLA, and TP changed the sediment metabolic profiles, producing differential metabolites such as lipids and molecules, organic heterocyclic compounds, and organic acids and their derivatives, especially TP had the most significant effect. These findings contribute to a more comprehensive understanding of the potential impact of microplastic contamination.IMPORTANCEIn this study, we added 3% (wt/wt) microplastic particles, including polyethylene, polylactic acid, and tire particles, to natural sediments under simulated laboratory conditions. Subsequently, we simulated the sediment microbial and ecosystem responses under different temperature conditions by incubating them for 60 days at 15°C and 35°C, respectively. After synthesizing these results, our study strongly suggests that the presence of microplastics in sediment ecosystems and exposure under different temperature conditions may have profound effects on soil microbial communities, enzyme activities, and metabolite profiles. This is important for understanding the potential hazards of microplastic contamination on terrestrial ecosystems and for developing relevant environmental management strategies.

Temperature-dependent effects of microplastics on sediment bacteriome and metabolome

The increasing prevalence of microplastics in the environment has become a concern for various ecosystems, including wetland ecosystems. Here, we investigated the effects of three popular microplastic types: polyethylene, polylactic acid, and tire particles at 5 °C and 25 °C on the sediment microbiome and metabolome at the 3% (w/w) level. Results indicated that temperature greatly influenced catalase and neutral phosphatase activities, whereas the type of microplastic had a more significant impact on urease and dehydrogenase activities. The addition of microplastic, especially tire particles, increased microbial diversity and significantly altered the microbial community structure and metabolic profile, leading to the formation of different clusters of microbial communities depending on the temperature. Nonetheless, the effect of temperature on the metabolite composition was less significant. Functional prediction showed that the abundance of functional genes related to metabolism and biogeochemical cycling increased with increasing temperature, especially the tire particles treatment group affected the nitrogen cycling by inhibiting ureolysis and nitrogen fixation. These observations emphasize the need to consider microplastic type and ambient temperature to fully understand the ecological impact of microplastics on microbial ecosystems.

New insights into the sustainable use of co-pyrolyzed dredged sediment for the in situ remediation of Cd polluted sediments in coastal rivers

The remediation of Cd-polluted sediment in coastal rivers is essential because of its potential hazards to river and marine ecosystems. Herein, a co-pyrolysis product of contaminated dredged sediment (S@BC) was innovatively applied to cap and immobilize Cd-contaminated sediment in coastal rivers in situ, and their remediation efficiencies, mechanisms, and microbial responses were explored based on a 360 d incubation experiment. The results showed that although S@BC immobilization and capping restrained sediment Cd release to the overlying water, S@BC capping presented a high inhibitory efficiency (66.0% vs. 95.3% at 360 d). Fraction analysis indicated that labile Cd was partially transformed to stable fraction after remediation, with decreases of 0.5%- 32.7% in the acid-soluble fraction and increases of 5.0%- 182.8% in the residual fraction. S@BC immobilization and capping had minor influences on the sediment bacterial community structure compared to the control. S@BC could directly adsorb sediment mobile Cd (precipitation and complexation) to inhibit Cd release and change sediment properties (e.g., pH and cation exchange capacity) to indirectly reduce Cd release. Particularly, S@BC capping also promoted Cd stabilization by enhancing the sediment sulfate reduction process. Comparatively, S@BC capping was a priority approach for Cd-polluted sediment remediation. This study provides new insights into the remediation of Cd-contaminated sediments in coastal rivers.

Electrochemical treatment of aquaculture wastewater effluent and optimization of the parameters using response surface methodology

The electrocoagulation (EC) and electrooxidation (EO) processes are employed widely as treatment processes for industrial, agricultural, and domestic wastewater. In the present study, EC, EO, and a combination of EC + EO were evaluated as methods of removing pollutants from shrimp aquaculture wastewater. Process parameters for electrochemical processes, including current density, pH, and operation time were studied, and response surface methodology was employed to determine the optimum condition for the treatment. The effectiveness of the combined EC + EO process was assessed by measuring the reduction of targeted pollutants, including dissolved inorganic nitrogen species, total dissolved nitrogen (TDN), phosphate, and soluble chemical oxygen demand (sCOD). Using EC + EO process, more than 87% reduction was achieved for inorganic nitrogen, TDN, and phosphate, while 76.2% reduction was achieved for sCOD. These results demonstrated that the combined EC + EO process provided better treatment performance in removing the pollutants from shrimp wastewater. The kinetic results suggested that the effects of pH, current density, and operation time were significant on the degradation process when using iron and aluminum electrodes. Comparatively, iron electrodes were effective at reducing the half-life (t_1/2) of each of the pollutants in the samples. The application of the optimized process parameters on shrimp wastewater could be used for large-scale treatment in aquaculture.

Gaoshiqia sediminis gen. nov., sp. nov., isolated from coastal sediment

A Gram-stain-negative, facultative anaerobic, motile, rod-shaped and orange bacterium, designated A06^T, was obtained off the coast of Weihai, PR China. Cells were 0.4-0.5×0.6-1.0 µm in size. Strain A06^T grew at 20-40 °C (optimum, 33 °C), at pH 6.0-8.0 (optimum, pH 6.5-7.0) and in the presence of 0-8 % NaCl (w/v) (optimum, 2 %). Cells were oxidase and catalase positive. Menaquinone-7 was detected as the major respiratory quinone. The dominant cellular fatty acids were identified as C_15:0 2-OH, iso-C_15:0, anteiso-C_15:0 and iso-C_15:1  ω6c. The DNA G+C content of strain A06^T was 46.1 mol%. The polar lipids were phosphatidylethanolamine, one aminolipid, one glycolipid and three unidentified lipids. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain A06^T is a member of the family Prolixibacteraceae and exhibited the highest sequence similarity to Mangrovibacterium diazotrophicum DSM 27148^T (94.3 %). Based on its phylogenetic and phenotypic characteristics, strain A06^T is considered to represent a novel genus in the family Prolixibacteraceae, for which the name Gaoshiqia gen. nov. is proposed. The type species is Gaoshiqia sediminis sp. nov., with type strain A06^T (=KCTC 92029^T=MCCC 1H00491^T). The identification and acquisition of microbial species and genes in sediments will help broaden the understanding of microbial resources and lay a foundation for its application in biotechnology. Strain A06^T uses an enrichment method, so the isolation of strain A06^T is of great significance to the enrichment of marine microbial resources.

Satellite taxa regulated the response of constructed wetlands microeukaryotic community to changing hydraulic loading rate

Revealing how species interaction and assembly processes structure the core and satellite microeukaryotic subcommunities in an engineering environment is crucial for understanding how biodiversity influences system function. By investigating the core and satellite microeukaryotic subcommunities in constructed wetlands (CWs), we depicted an integrated distribution pattern of microeukaryotic communities in the CWs with different hydraulic loading rates (HLRs). Surprisingly, our results suggested that high HLR reduced the diversity and network stability of the microeukaryote community in CW. The stochastic process becomes more important with the increased HLR. In addition, satellite and core taxa varied inconsistently under different HLRs except for niche breadth. And the changes in all taxa were consistent with those in satellite taxa. Satellite taxa, but not core taxa, was an important driver in shaping the dynamics of microeukaryotic communities and played an important role in maintaining the stability of the microeukaryotic community. Overall, our results not only fill a gap in understanding the microeukaryotic community dynamics and its basic drivers of CWs under different HLRs but also highlights the particular importance of satellite microeukaryotes in mediating biogeochemical cycles in CWs ecosystems.

Comparison of nitrogen removal performance and mechanism from low-polluted wastewater by constructed wetlands with two oxygen supply strategies: Tidal flow and intermittent aeration

Due to dissolved oxygen (DO) limited nitrogen removal efficiency in constructed wetlands (CWs), two representative oxygen-suppling CWs, i.e., tidal flow constructed wetlands (TFCWs) and intermittently aerated constructed wetlands (IACWs) were proposed to compare the effect of oxygen supply strategies on the nitrogen removal performance and mechanism. Results showed that the removal efficiencies of NH₄⁺-N and COD in IACWs were as high as 90.35-97.14% and 91.14-92.44%, respectively. In terms of TN, TFCWs (83.82%) showed a significantly higher removal efficiency than IACWs, and this result was derived with the flooded/drained phase (FP/DP) ratio of 21 h:3 h in TFCWs, because rhythmic FP and DP formed a high oxygen gradient at different depths of the system, which intensified the nitrification and denitrification simultaneously. The potential nitrifying and denitrifying bacteria (e.g., Nitrospira, Azospira, Haliangium, Bradyrhizobium and Arenimonas) were enriched more significantly in TFCWs compared with IACWs, as well as Bacillus for simultaneous nitrification and denitrification, which promoted nitrogen transformation together. Also, the results of molecular ecological network analysis showed that bacterial community structure in IACWs was more complex and robust than in TFCWs, because there were obviously more nodes and links as well as a higher proportion of negative interference. However, the relationship between genera in TFCWs was closer depending on shorter path distances, and the keystone genus (Nitrosomonas) in related to nitrification was considered to play an important role in nitrogen transformation performance.

Effects of Bellamya purificata Cultivation at Different Stocking Densities on the Dynamics and Assembly of Bacterial Communities in Sediment

To optimize the integrated multi-trophic aquaculture (IMTA) model, improve the efficiency of resource utilization, and reduce environmental pollution, Bellamya purificata, as a potential bioremediation species, was studied to investigate the effect of B. purificata culture on the dynamics and assembly of bacterial communities in sediment. Four experimental groups were established at four different densities: 0, 234.38, 468.75, and 937.5 g/m² (represented as CON, LD, MD, and HD, respectively). Each group was with three replicates. The 16S ribosomal RNA (rRNA) high-throughput sequencing was used to evaluate the composition, function, and assembly of bacterial communities in sediment. B. purificata cultivation significantly altered the composition and function of the bacterial communities in sediment; at high stocking density, it significantly decreased anaerobic and increased aerobic organic matter decomposition, whereas at low stocking density, it decreased the number of bacteria involved in sulfate reduction and inhibited the denitrification process. B. purificata decreased direct competition and promoted collaboration or niche sharing in bacterial communities, especially at the high stocking density. Moreover, B. purificata cultivation resulted in greater changes in the environmental factors. Variations in dissolved oxygen, pH, total nitrogen, nitrate, and nitrite levels were closely related to the altered composition and function of the bacterial communities. Stochastic processes dominated the bacterial community assembly in the sediment and B. purificata cultivation had limited impacts on the bacterial community assembly. The study provided a reference for the dynamics and assembly of bacterial communities in sediment with different densities of B. purificata cultivation and we hope that the findings will provide a theoretical reference for the optimization of IMTA and improve management strategies for B. purificata polyculture.

Quantitative comparison of clamworm (Perinereis aibuhitensis) and crab (Macrophthalmus japonicus) burrowing effects on nitrogen and phosphorus dynamics at the sediment-water interface

Exploring nitrogen and phosphorus dynamics in estuarine ecosystems is of great significance for understanding the nutrient cycle in terrestrial and marine ecosystems. However, the ecological functions of common species remain unclear because there is a dearth of observational data. To quantitatively compare the bioturbation effects of the clamworm Perinereis aibuhitensis and crab Macrophthalmus japonicus on the migration of nitrogen and phosphorus in the sediment-pore water-overlying water interfaces, an indoor experiment was carried out using microcosms containing substrate, water, and living specimens collected from the Dagu Estuary, China. The physical structure of the sediments was greatly altered by both clamworms and crabs, and the amount of suspended particulate matter in the overlying water was in the order: crab > clamworm > control groups. Sediments, especially the 0-2 cm layer, were continuously mineralized under bioturbation, releasing NH₃-N, NO₂^--N, NO₃^--N, and dissolved total phosphorus. During the experiment, the release rate of NH₃-N (2.45 mg L^-1 to 10.23 mg L^-1), NO₂^--N (0.25 mg L^-1 to 7.34 mg L^-1), NO₃^--N (0.02 mg L^-1 to 6.03 mg L^-1), and dissolved total phosphorus (0.07 mg L^-1 to 0.16 mg L^-1) in the crab group was higher than that in the clamworm group (NH₃-N, 0.93 mg L^-1 to 6.11 mg L^-1; NO₂^--N, 0.51 mg L^-1 to 6.18 mg L^-1; NO₃^--N, 0.01 mg L^-1 to 5.24 mg L^-1, and dissolved total P, 0.04 mg L^-1 to 0.08 mg L^-1). Our findings indicate that crabs might play a more important role in promoting nitrogen and phosphorus migration than clamworms because of their stronger bioturbation strategies in sediments. Bioturbation by both clamworms and crabs reduced nitrogen and phosphorus accumulation in surface sediments and accelerated organic matter mineralization in the sediments, which may promote nutrient recycling in estuarine ecosystems.

Application of an integrated loach-plant-substrate-microbes non-aerated saturated vertical flow constructed wetlands: Mechanisms of pollutants removal and greenhouse gases reduction

This study established an integrated loach-plant-substrate-microbes non-aerated saturated vertical flow constructed wetlands (VFCWs) to enhance pollutants removal efficiencies and reduce greenhouse gas emissions simultaneously. The results of the VFCWs experiment indicated that the removal efficiencies of chemical oxygen demand, total phosphorous, and total nitrogen in loach systems were significantly higher than those of non-loach systems, achieving 59.16%, 35.98%, and 40.96%, respectively. The CH₄ and N₂O emission fluxes were also significantly reduced in the integrated system, resulting in lower global warming potential (GWP) and GWP per unit of pollutants removal. Loaches promoted the transportation of oxygen, facilitated the re-contact and utilization of sediments, reduced CH₄ emission, and enhanced nitrogen conversion and phosphorus accumulation. Increased bioavailable carbon and nitrate-nitrogen in the integrated system improved the abundance of denitrifying bacteria, which supported complete denitrification, reducing N₂O emissions with high pollutant removal.

A review on algal-bacterial symbiosis system for aquaculture tail water treatment

Aquaculture is one of the fastest growing fields of global food production industry in recent years. To maintain the ecological health of aquaculture water body and the sustainable development of aquaculture industry, the treatment of aquaculture tail water (ATW) is becoming an indispensable task. This paper discussed the demand of environmentally friendly and cost-effective technologies for ATW treatment and the potential of algal-bacterial symbiosis system (ABSS) in ATW treatment. The characteristics of ABSS based technology for ATW treatment were analyzed, such as energy consumption, greenhouse gas emission, environmental adaptability and the possibility of removal or recovery of carbon, nitrogen and phosphorus as resource simultaneously. Based on the principle of ABSS, this paper introduced the key environmental factors that should be paid attention to in the establishment of ABSS, and then summarized the species of algae, bacteria and the proportion of algae and bacteria commonly used in the establishment of ABSS. Finally, the reactor technologies and the relevant research gaps in the establishment of ABSS were reviewed and discussed.

Effect of Electrode Distances on Remediation of Eutrophic Water and Sediment by Sediment Microbial Fuel Cell Coupled Floating Beds

Efficient and sustainable technologies for cleaning of contaminated water and sediments are in urgent demand. In this study, a new type of sediment microbial fuel cell coupled floating bed (FB-SMFC) was developed to repair eutrophic water and sediment in a cleaner way. The effect of electrode spacing on the power generation capacity and the synchronous remediation of pollutants from eutrophic water and sediment were studied. When the electrode distance was 60 cm, the maximum power generation and pollutant removal effects were obtained. At the end of the experiment, the maximum output voltage was 0.4 V, and the chemical oxygen demand (COD_Cr, potassium dichromate method), total nitrogen (TN), and total phosphorus (TP) contents in the overlying water were 8 mg/L, 0.7 mg/L, and 0.39 mg/L. The corresponding removal rates were 88.2%, 78.8%, and 59.0%, respectively. The removal rates of organic matter and TN in the sediment were 12.8% and 86.4%, respectively, and the fixation rate of TP was 29.2%. Proteobacteria was the dominant phylum of bacteria in the sediment and anode. Many anaerobic bacteria were found in the overlying water, which facilitated denitrification. Overall, the results of this research revealed a highly efficient and reliable strategy for eutrophic water and sediment remediation, aquatic ecosystems restoration, and human health protection.

Polychaete Bioturbation Alters the Taxonomic Structure, Co-occurrence Network, and Functional Groups of Bacterial Communities in the Intertidal Flat

Polychaetes are important benthic macrofauna that lives in sediments, usually in intertidal flats with high organic content and high sulfide. It has been suggested that polychaete bioturbation could perform environmental remediation. During the process, the microbial community plays important roles. Here, we used high-throughput sequencing technology to study the bioturbation effects on the bacterial community in the polychaete (Perinereis aibuhitensis) burrows at different tidal positions in intertidal flat. The results showed that the bacterial communities were dramatically influenced by the polychaete bioturbation. The ACE, Chao, and Shannon indices of the polychaete burrows increased in summer. Dominant phyla in the polychaete burrows were Proteobacteria, Campilobacterota, Desulfobacterota, Chloroflexi, and Bacteroidota, and the dominant bacterial families were Sulfurvaceae, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, Desulfobulbaceae, and Sulfurimonadaceae. Results of linear discriminant analysis effect size (LEfSe) showed that groups that include organic matter degraders, such as Bacteroidota, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, and groups that include sulfur oxidizers, such as Campilobacterota, Sulfurovaceae, Rhodobacteraceae, Desulfobulbaceae, and Sulfurimonadaceae, were significantly increased due to the polychaete bioturbation. The polychaete bioturbation reduced the complexity of the bacterial co-occurrence network while increased its modularity and homogeneity. The polychaete bioturbation also changed the functional groups, which significantly enhanced in functional groups of aerobic nitrite oxidation, nitration, dark thiosulfate oxidation, dark sulfur oxidation, and dark sulfite oxidation, while nitrogen respiration and nitrate respiration decreased. These results provide insight into the impact of bacterial communities under the intertidal polychaete bioturbation.

Enhancing robustness of halophilic aerobic granule sludge by granular activated carbon at decreasing temperature

High salinity seriously inhibits the growth and metabolism of microorganisms, resulting in poor settleability, excessive biomass loss and low treatment efficiency of biological wastewater treatment systems. The development of halophilic aerobic granular sludge (HAGS) is a feasible strategy for addressing this challenge. However, there are problems with the granulation of HAGS and the stability of granules at decreasing temperatures. In this study, granular activated carbon (GAC) with a large specific surface area and good biocompatibility was used to enhance the robustness of HAGS. The results showed that the addition of GAC shortened the granulation time from 60 d (control system) to 35 d (GAC-addition system). The proteins contents of extracellular polymeric substances (EPS) in the GAC-addition system was significantly higher (p < 0.05) than that in the control system during granulation. Satisfactory NH₄⁺-N and chemical oxygen demand (COD) removal efficiencies reached more than 96% in both systems at 18-26 °C. When the operating temperature was lower than 15 °C, the GAC-addition system exhibited better NH₄⁺-N removal performance (>80%) than the control system (<60%). Moreover, the abundance of almost all nitrogen metabolism-related genes in the GAC-addition system was higher than that in the control system. During the granulation process, the enrichment of functional microorganisms, including family Flavobacteriaceae, Rhodobacteraceae, and Cryomorphaceae, may promote the production of EPS by significantly upregulating (p < 0.05) the metabolic pathway "Signaling Molecules and Interaction" in the GAC-addition system. The overexpression of the nitrogen assimilation gene glnA in heterotrophic bacteria (Halomonas and Marinobacterium) may promote the conversion of inorganic nitrogen to extracellular proteins to adapt to the decreased operational temperature. Our findings confirm that GAC addition is a simple but effective strategy to accelerate granulation and enhance the robustness of HAGS in saline wastewater treatment.

Effects of bioturbation by tubificid worms on biogeochemical processes, bacterial community structure and diversity in heterotrophic wetland sediments

Bioturbation activity of tubificid worms has been recognized as a key process influencing organic matter processing and nutrient cycling in benthic aquatic ecosystems. This activity is expected to modify benthic microbial communities by affecting the physical and chemical environment in sediments. Nevertheless, quantifications of bacterial community changes associated with bioturbation in freshwater ecosystems are still lacking. The present study aimed at evaluating the impact of tubificid worms on bacterial community structure using NGS approach (16S metabarcoding) and long (6 months) laboratory experiments on four heterotrophic wetland sediments. Worm bioturbation activity significantly stimulated biogeochemical processes at the water-sediment interface but only had a marginally significant effect on bacterial community structures. Yet, bacterial diversity was consistently reduced in presence of worms. Such decrease could be associated with the stimulation of organic matter mineralization by worms, leading to a reduction of the diversity of trophic niches available for bacterial species. The slight changes in bacterial community structures induced by bioturbation did not appear to control biogeochemical processes. Thus, the stimulation of biogeochemical processes by worm bioturbation was more associated with a stimulation of the initial bacterial community than with a drastic change in bacterial communities induced by worms.

Keystone Species and Niche Differentiation Promote Microbial N, P, and COD Removal in Pilot Scale Constructed Wetlands Treating Domestic Sewage

The microbial characteristics related to nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) removal were investigated in three pilot scale constructed wetlands (CWs). Compared to horizontal subsurface flow (HSSF) and surface flow (SF) CWs, the aerobic vertical flow (VF) CW enriched more functional bacteria carrying genes for nitrification (nxrA, amoA), denitrification (nosZ), dephosphorization (phoD), and methane oxidation (mmoX), while the removal of COD, total P, and total N increased by 33.28%, 255.28%, and 299.06%, respectively. The co-occurrence network of functional bacteria in the HSSF CW was complex, with equivalent bacterial cooperation and competition. Both the VF and SF CWs exhibited a simple functional topological structure. The VF CW reduced functional redundancy by forming niche differentiation, which filtered out keystone species that were closely related to each other, thus achieving effective sewage purification. Alternatively, bacterial niche overlap protected a single function in the SF CW. Compared with the construction type, temperature, and plants had less effect on nutrient removal in the CWs from this subtropical region. Partial least-squares path modeling (PLS-PM) suggests that high dissolved oxygen and oxidation-reduction potential promoted a diverse bacterial community and that the nonkeystone bacteria reduced external stress for functional bacteria, thereby indirectly promoting nutrient removal.

Responses of bacterial communities and organic matter degradation in surface sediment to Macrobrachium nipponense bioturbation

The excessive accumulation of organic matter (OM) in sediments in aquaculture ponds is a potential environmental threat due to the risk of endogenous water pollution and eutrophication. From the perspective of inhibiting OM accumulation to prevent endogenous water pollution, the present study investigated the OM degradation states, variations of bacterial communities and basic environmental factors in sediments with/without Macrobrachium nipponense treatment/control groups in triplicate for effects of bioturbation on OM degradation in 90-day incubation. The total organic carbon (TOC) and total nitrogen (TN) in the M. nipponense treatment were higher than in the control at the 30th and 60th days, while no significant differences between treatment and control were found at the end of the experiment. Significantly higher oxidation-reduction potential (ORP) and more extensively degraded OM were observed in the M. nipponense treatment. Eleven significantly differential bacterial taxa were enriched in the sediments of M. nipponense treatment, of which eight (Actinobacteria, Chitinophagales, Chitinophagaceae, Flavihumibacter, Marinilabiliaceae, Cytophaga xylanolytica group, Christensenellaceae, and Christensenellaceae R-7 group) were significantly correlated with at least two OM degradation indicators. The functional groups chemoheterotrophy, aerobic chemoheterotrophy, xylanolysis, ureolysis, and intracellular parasites were enhanced by M. nipponense and were negatively correlated with OM degradation indictors. Overall, the M. nipponense bioturbation effectively increased the ORP to provide better conditions for OM degradation, altered the taxonomic composition and functional groups to enhance the bacterial ability for OM degradation, and finally promoted the OM degradation of the surface sediment in an artificial aquaculture system.

The bioturbation effect of the snail Bellamya aeruginosa on phosphorus immobilisation by drinking water treatment residue in sediment: A long-term continuous flow test

This study used a relatively long-term (350 d) continuous flow test to determine the bioturbation effect of a benthic macroinvertebrate (the snail Bellamya aeruginosa) on sediment internal phosphorus (P) pollution control by in-situ immobilisation using drinking water treatment residue (DWTR) as the inactivating agent. The results showed that DWTR substantially reduced P concentration in overlying water, had a limited effect on other overlying water properties, and tended to reduce nitrogen release from the sediment. Variations in overlying water properties induced by DWTR were generally not associated with snail activity or population density. However, the snails were found to promote DWTR burial and induce DWTR mixing within the sediment, indicating that bioturbation could change the distribution of P inactivating agents in sediment. The mobility of P was closely related to oxalate extractable aluminium, iron, and P (Al_ox, Fe_ox, and P_ox, respectively) in sediments at different depths. Typically, mobile P was stable at a relatively low level when the total content of Al_ox and Fe_ox was >0.750 mmol g^-1 or when the ratio of P_ox to (Al_ox + Fe_ox) was <0.05. Given these results, recommended practices include repeated dosing of the immobilising agents at intervals determined by the relationships among mobile P, P_ox, Al_ox, and Fe_ox in the sediment, especially for Al- and Fe-based agents such as DWTR. Overall, the effect of bioturbation on the stability of in-situ P immobilisation in sediment should be fully considered during long-term pollution control.

Microbial community and interspecies interaction during grazing of ark shell bivalve (Scapharca subcrenata) in a full-scale bioremediation system of mariculture effluents

A novel biological approach using ark shell bivalves as potential species for remediation of effluents was studied to determine the microbial community interspecies interaction and nutrient cycling in a restoration system of mariculture effluents. A field study showed that Scapharca subcrenata was the main driver of the microbial community's interspecies-interaction (PERMANOVA, R = 0.0572, P = 0.005) in the treatment zone (TZ). Analysis of co-occurrence networks based on random matrix theory (RMT) indicated that the network's complexity parameters were enhanced in the TZ and disrupted in the control zone (CZ) due to eutrophic disturbances. Concurrently, the TZ was correlated with more profound network modifications (i.e., higher modularity, total nodes (n), cohesion, and proportion of positive links), suggesting that S. subcrenata influenced microbial interspecies interactions in the system. Similarly, the co-occurring networks of generalists Proteobacteria (OTU2037) at genus Anaerospora and Actinobacteria (OTU9660) at genus Candidatus aquiluna for anaerobic ammonia-oxidation (ANAMMOX) were highly significant in the TZ. The top-down and bottom-up forces of S. subcrenata influenced the removal efficiency of nitrogenous compounds by reducing 81.51% of nitrite (NO₂^--N), 84.61% of total ammonium nitrogen (TAN) and 72.78% of nitrate (NO₃^--N). Generally, the introduction of ark shell bivalve (S. subcrenata) to the system as a biofilter provides a very low-cost bioremediation technology that could be one of the best restorations and remediation tools for mariculture effluents.

Multiple draft tubes airlift loop membrane bioreactor as an efficient system for acidic 7-amino cephalosporanic acid (7-ACA) wastewater treatment

In this study, a lab-scale multiple draft tubes airlift loop membrane bioreactor (Mt-ALMBR) was used for treating acidic 7-amino cephalosporanic acid (7-ACA) wastewater under different pHs (3.54-6.20) and hydraulic retention time (HRT) (48 h, 36 h, 24 h and 16 h). During about 200 days operation, under HRT of 48 h and pH condition about 6.0, the optimum average COD and BOD₅ removal rates were reach to 84.4 ± 2.1% and 94.9 ± 0.8%, and the highest 7-ACA removal rate also observed as 77.6%. Biodegradation, membrane rejection, hydrolysis and sludge adsorption were the four main pathways of 7-ACA removal. With the increase of pH, biodegradation, membrane rejection and hydrolysis had significant positive impacts on 7-ACA removal, while adsorption had a negative impact. Moreover, mathematical models for 7-ACA removal rate and pH were calculated to guide the operation of Mt-ALMBR. Biodegradation was the main pathway to remove 7-ACA when pH was >4.17.

Chromosome-level genome assembly of the razor clam Sinonovacula constricta (Lamarck, 1818)

Bivalves, a highly diverse and the most evolutionarily successful class of invertebrates native to aquatic habitats, provide valuable molecular resources for understanding the evolutionary adaptation and aquatic ecology. Here, we reported a high-quality chromosome-level genome assembly of the razor clam Sinonovacula constricta using Pacific Bioscience single-molecule real-time sequencing, Illumina paired-end sequencing, 10X Genomics linked-reads and Hi-C reads. The genome size was 1,220.85 Mb, containing scaffold N50 of 65.93 Mb and contig N50 of 976.94 Kb. A total of 899 complete (91.92%) and seven partial (0.72%) matches of the 978 metazoa Benchmarking Universal Single-Copy Orthologs were determined in this genome assembly. And Hi-C scaffolding of the genome resulted in 19 pseudochromosomes. A total of 28,594 protein-coding genes were predicted in the S. constricta genome, of which 25,413 genes (88.88%) were functionally annotated. In addition, 39.79% of the assembled genome was composed of repetitive sequences, and 4,372 noncoding RNAs were identified. The enrichment analyses of the significantly expanded and contracted genes suggested an evolutionary adaptation of S. constricta to highly stressful living environments. In summary, the genomic resources generated in this work not only provide a valuable reference genome for investigating the molecular mechanisms of S. constricta biological functions and evolutionary adaptation, but also facilitate its genetic improvement and disease treatment. Meanwhile, the obtained genome greatly improves our understanding of the genetics of molluscs and their comparative evolution.

Habitat filtering shapes the differential structure of microbial communities in the Xilingol grassland

The spatial variability of microorganisms in grasslands can provide important insights regarding the biogeographic patterns of microbial communities. However, information regarding the degree of overlap and partitions of microbial communities across different habitats in grasslands is limited. This study investigated the microbial communities in three distinct habitats from Xilingol steppe grassland, i.e. animal excrement, phyllosphere, and soil samples, by Illumina MiSeq sequencing. All microbial community structures, i.e. for bacteria, archaea, and fungi, were significantly distinguished according to habitat. A high number of unique microorganisms but few coexisting microorganisms were detected, suggesting that the structure of microbial communities was mainly regulated by species selection and niche differentiation. However, the sequences of those limited coexisting microorganisms among the three different habitats accounted for over 60% of the total sequences, indicating their ability to adapt to variable environments. In addition, the biotic interactions among microorganisms based on a co-occurrence network analysis highlighted the importance of Microvirga, Blastococcus, RB41, Nitrospira, and four norank members of bacteria in connecting the different microbiomes. Collectively, the microbial communities in the Xilingol steppe grassland presented strong habitat preferences with a certain degree of dispersal and colonization potential to new habitats along the animal excrement- phyllosphere-soil gradient. This study provides the first detailed comparison of microbial communities in different habitats in a single grassland, and offers new insights into the biogeographic patterns of the microbial assemblages in grasslands.

Bioturbation effect of fortified Daqu on microbial community and flavor metabolite in Chinese strong-flavor liquor brewing microecosystem

Traditional spontaneous fermentation in microecosystem with microbial successions and environmental variables results in inconsistent quality of fermented foods. We therefore propose the directional bioturbation for microbiota regulation and metabolites production in food fermentation. Here, we revealed the bioturbation effect of fortified Daqu on microbial community based on taxonomic composition, co-occurrence network, and metabolic potential, using Chinese strong-flavor liquor fermentation as a microecosystem. According to principal coordinate analysis, microbial communities were obviously influenced by the bioturbation of fortified Daqu. More specifically, bioturbation increased the abundances of Caproiciproducens, Clostridium, Aspergillus, Candida, Methanobacterium, and Methanosarcina, while decreased that of Lactobacillus. Meanwhile, higher abundances of most genes that encoding enzymes involved in interspecies hydrogen transfer between hexanoic acid bacteria and methanogens were observed in the bioturbated ecosystem by PICRUSt approach. Additionally, co-occurrence analysis showed that bioturbation increased the diversity and complexity of interspecies interactions in microecosystem, which contributed to higher production of flavor metabolites such as hexanoic acid, ethyl hexanoate, and hexyl hexanoate. These results indicated that the bioturbation of fortified Daqu is feasible for flavor metabolism by interspecies interactions of functional microbiota in liquor fermentation. Taken together, it is of great importance for regulating Chinese liquor and even other foods fermentation by bioturbation.

Bacterioplankton community in response to biological filters (clam, biofilm, and macrophytes) in an integrated aquaculture wastewater bioremediation system

Integrated systems with appropriate bio-filters can be used to treat aquaculture effluents. However, the information on bio-filters that alters the ecological functions of the bacterioplankton community (BC) in biodegradation of the aquaculture effluents remains controversial. In this study, we implemented a comprehensive restoration technology combined with bio-filters [biofilm, clam (Tegillarca granosa), and macrophytes (Spartina anglica)] to investigate their influence on the stability of the BC and nutrient removal. We found that the diversity of BC was linked with biogeochemical factors in processing and upcycling nitrogen-rich effluents into high-value biomass. The BC exhibited significant distinct patterns in the bio-filter areas. Potential biomarkers for constrained harmfully algae-bacteria (Nitriliruptoraceae, Bacillales, and Rhodobacteraceae) and nutrient removal were significantly higher in the bio-filters areas. The bio-filters significantly promoted the restoration effects of N and P balance by reducing 82.34% of total nitrogen (TN) and 81.64% of total phosphorus (TP) loads at the water interface. The main mechanisms for TN and TP removal and nutrient transformation were achieved by assimilation and absorption by the emergent macrophytes (Spartina anglica). The bio-filters significantly influenced the biodegradability and resolvability of particulate organic matter through ammonification, nitrification, and denitrification of microbes, which meliorated the nutrient removal. Beside bio-filter effects, the BC was significantly controlled by abiotic factors [nitrate (NO₃^--N), dissolved oxygen (DO), total nitrogen (TN), and water temperature (WT)], and biotic factors (chlorophyll ɑ and green algae). Our study revealed that the co-existence system with bio-filters may greatly improve our understanding on the ecological functions of the BC in aquaculture systems. Overall, combined bio-filters provide an opportunity for the development of efficient and optimized aquaculture wastewater treatment technology.

The role of the freshwater oligochaete Limnodrilus hoffmeisteri in the distribution of Se in a water/sediment microcosm

Selenite(IV) and selenate(VI) are the major species of Se in the seleniferous aquatic ecosystem. The redistribution of Se in the water/sediment microcosm by bioturbation remains largely unknown. In this study, the redistribution of Se in the water/sediment microcosm by the benthic oligochaete Limnodrilus hoffmeisteri was assessed. The worms were exposed to 2-40 μg/g dry weight of Se(IV) or Se(VI) in the sediment (diet) for 2 months. The changes in the Se levels in different compartments of the microcosm (sediment, overlying water, and worms) were quantified after 2 weeks and 2 months. The subcellular distribution of Se in the worms were also evaluated. Finally, the volatilization of Se from the two Se sources was estimated. The results showed that Se concentration in the overlying water and Se bioaccumulation in the worms were increased with Se levels in the sediments. Approximately 1.6-9.8% of Se was volatilized in the absence of the worms and was intensified in the presence of the worms (2.1-25.7%). The subcellular distribution witnessed high levels of Se in the cell debris (>60%). Se(IV) and Se(VI) differ in their bioaccumulation, redistribution and the effects on the growth of the worms. Our results suggest that the bioturbation by benthos play an essential role in the redistribution of Se in the water/sediment microcosm.

The application of bioturbators for aquatic bioremediation: Review and meta-analysis

Human activities introduce significant contamination into aquatic systems that impact biodiversity and ecosystem function. Many contaminants accumulate, and remediation options are now required worldwide. One method for bioremediation involves the application of macrofauna to stimulate microbial ecosystem processes including contaminant removal. However, if we are to confidently apply such a technique, we need clarity on the effect of bioturbators on different contaminants and how these vary under different environmental scenarios. Here we used a systematic review and meta-analysis to analyse current knowledge on the activities of bioturbating macrofauna in contaminated sediments and quantify how bioturbation-bioremediation changes depend on the taxonomic group, the aquatic ecosystem and important environmental variables. Three common contaminant classes were reviewed and analysed: metals, nutrients (i.e. ammonia and phosphorous) and polycyclic aromatic hydrocarbons (PAH). In addition, meta-regressions were calculated to estimate the effect of environmental and experimental design variables on effect sizes. Meta-analytic results revealed that deeper burrowing and more active sediment surface animals (e.g. polychaetes) increased metal release from sediments, nutrients and oxygen uptake by microbial fractions in comparison to bioturbators that inhabit shallower depths in sediments. In addition, there was a different effect of bioturbators on response variables in different aquatic systems. Finally, bioturbator effects on nutrient and metal release appeared modulated by context-specific variables such as temperature, pH, sediment grain size, animal density and experimental duration. Our findings highlight critical knowledge gaps such as field applications, less studied macrobenthic fauna and the incorporation of molecular approaches. Our results provide the first quantitative synthesis of the effects of bioturbators on contaminant fate and the variables that need to be considered for the optimization of this method as a viable approach for sediment remediation and contaminant management in aquatic systems.