Effects of Stocking Density on the Growth Performance, Physiological Parameters, Antioxidant Status and Lipid Metabolism of Pelteobagrus fulvidraco in the Integrated Rice-Fish Farming System.

Pelteobagrus fulvidraco is a freshwater fish commonly raised in rice fields, yet the optimal stocking density for this species remains unknown. Therefore, this study aimed to investigate the appropriate stocking density of P. fulvidraco in integrated rice-fish farming systems. Three different stocking densities--low density (LD, 125 g/m2), middle density (MD, 187.5 g/m2), and high density (HD, 250 g/m2)--were set up to evaluate P. fulvidraco's growth performance, stress indices, immune function, antioxidant status, and lipid metabolism after 90 days of farming. The results indicated that HD treatment had a detrimental effect on P. fulvidraco's growth parameters. HD treatment led to an increase in cortisol (Cor) and lactate (La) levels, but a decrease in glucose (Glu) content in serum. After 90 days of farming, an immune response accompanied by the increase of complement 3 (C3), C4, and immunoglobulin M (IgM) was observed in the HD group. Meanwhile, HD treatment induced oxidative stress and altered antioxidative status evidenced by the levels of catalase (CAT), glutathione peroxidase (Gpx), glutathione (GSH), malondialdehyde (MDA), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) in serum or liver. Additionally, the lipid metabolism-related genes including lipoprotein lipase (lpl), peroxisome proliferators-activated receptor (pparα), carnitine palmitoyltransferase-1 (cpt-1), and sterol regulatory element binding protein-1 (srebp-1) were markedly downregulated in the HD and/or MD group after 90 days of farming. In conclusion, this study contributes to a better understanding of P. fulvidraco's response to different stocking densities in integrated rice-fish farming systems. We suggest that the appropriate stocking density for P. fulvidraco in these farming systems should be below 250 g/m2, considering both fish growth and physiological responses.

Comparison of bacterial and fungal communities structure and dynamics during chicken manure and pig manure composting.

Composting is a sustainable and eco-friendly technology that turns animal waste into organic fertilizers. It remains unclear whether differences exist in the structure of microbial communities during different livestock manure composting. This study analyzed the dynamic change of bacterial and fungal communities, metabolic function, and trophic mode during chicken manure (CM) and pig manure (PM) composting based on 16S rRNA and ITS sequencing. Environmental factors were investigated for their impact on microbial communities. During composting, bacterial diversity decreased and then increased, while fungal diversity slightly increased and then decreased. Saccharomonospora and Aspergillus were the dominant genera and key microorganisms in CM and PM, respectively, which played crucial roles in sustaining the stability of the ecological network structure in the microbial ecology and participating in metabolism. Saccharomonospora gradually increased, while Aspergillus increased at first and then decreased. PM had better microbial community stability and more keystone taxa than CM. In CM and PM, the primary function of bacterial communities was metabolism, while saprotroph was the primary trophic mode of fungal communities. Dissolved organic carbon (DOC) was the primary factor influencing the structure and function of microbial communities in CM and PM. In addition to DOC, pH and moisture were important factors affecting the fungal communities in CM and PM, respectively. These results show that the succession of bacteria and fungi in CM and PM proceeded in a similar pattern, but there are still some differences in the dominant genus and their responses to environmental factors.

Remediation of the microecological environment of heavy metal-contaminated soil with fulvic acid, improves the quality and yield of apple.

The excessive application of chemical fertilizers and pesticides in apple orchards is responsible for high levels of manganese and copper in soil, and this poses a serious threat to soil health. We conducted a three-year field experiment to study the remediation effect and mechanism of fulvic acid on soil with excess manganese and copper. The exogenous application of fulvic acid significantly reduced the content of manganese and copper in soil and plants; increased the content of calcium; promoted the growth of apple plants; improved the fruit quality and yield of apple; increased the content of chlorophyll; increased the activity of superoxide dismutase, peroxidase, and catalase; and reduced the content of malondialdehyde. The number of soil culturable microorganisms, soil enzyme activity, soil microbial community diversity, and relative abundance of functional bacteria were increased, and the detoxification of the glutathione metabolism function was enhanced. The results of this study provide new insights that will aid the remediation of soil with excess manganese and copper using fulvic acid.

Unraveling the response of water quality and microbial community to lake water backflowing in one typical estuary of Lake Taihu, China.

To investigate the effect of lake water backflowing on the aquatic ecosystem in the estuary, surface water samples in the backflowing and unbackflowing areas were collected from one typical estuary of Lake Taihu, Xitiaoxi River. 16S rRNA sequencing and redundancy analysis were conducted to quantitatively elucidate the correlation between microbial community and water quality parameters. Results indicated lake water backflowing would affect the relative distribution of nitrogen species and increase the concentration of total nitrogen (TN) and nitrate, especially in the outlets of municipal sewage and agricultural drainage. For backflowing areas, more frequent water exchange could lower the seasonal fluctuation of the abundance and diversity of microbial community. RDA results showed crucial water quality parameters that greatly influence bacterial community were total organic carbon (TOC), total dissolved solids (TDS), salinity (SAL), ammonia, nitrate, TN for backflowing areas, and TOC, TDS, SAL, ammonia, TN without nitrate for unbackflowing areas. Verrucomicrobia, Proteobacteria, Microcystis, and Arcobacter were dominant with 27.7%, 15.7%, 30.5%, and 25.7% contribution to the overall water quality in backflowing areas. Chloroflexi, Verrucomicrobia, Flavobacterium, and Nostocaceae were dominant with 25.0%, 18.4%, 22.3%, and 11.4% contribution to the overall water quality in unbackflowing areas. And lake water backflowing might mainly affect the amino acid and carbohydrate metabolism based on the metabolism function prediction. A better understanding of the spatiotemporal changes in water quality parameters and microbial community was obtained from this research to comprehensively assess the effect of lake water backflowing on the estuarine ecosystem.

Aerobic co-composting of mature compost with cattle manure: Organic matter conversion and microbial community characterization.

The production of organic fertilizer by aerobic composting of cattle manure is an important way of its resource utilization. This study evaluated the effects of adding mature compost on the decomposition and microbial communities in the aerobic composting of cattle manure. The addition of mature compost shortens the composting cycle and results in a final lignocellulosic degradation rate of 35%. Metagenomic analysis showed that this was due to the proliferation of thermophilic and organic matter-degrading functional microorganisms, which enhanced the activity of carbohydrate-active enzymes. With the addition of mature compost, the microbial community exhibited stronger metabolic functions, especially carbohydrate and amino acid metabolism, which are the driving forces of organic matter degradation. This study deepens the understanding of organic matter conversion and microbial community metabolic functions when mature compost is used for livestock manure composting and provides a promising technology for livestock manure composting.

Impacts of high-quality coal mine drainage recycling for replenishment of aquatic ecosystems in arid regions of China: Bacterial community responses.

Coal mine water is usually recycled as supplementary water for aquatic ecosystems in arid and semiarid mining regions of China. To ensure ecosystem health, the coal mine water is rigorously treated using several processes, including reverse osmosis, to meet surface water quality standards. However, the potential environmental impacts of this management pattern on the ecological function of receiving water bodies are unclear. In this study, we built several microcosm water ecosystems to simulate the receiving water bodies. High-quality treated coal mine drainage was mixed into the model water bodies at different concentrations, and the sediment bacterial community response and functional changes were systematically investigated. The results showed that the high-quality coal mine drainage could still shape bacterial taxonomic diversity, community composition and structure, with a concentration threshold of approximately 50%. Moreover, both the Mantel test and the structural equation model indicated that the salinity fluctuation caused by the receiving of coal mine drainage was the primary factor shaping the bacterial communities. 10 core taxa in the molecular ecological network influenced by coal mine drainage were identified, with the most critical taxa being patescibacteria and g_Geothermobacter. Furthermore, the pathway of carbohydrate metabolism as well as signaling molecules and interactions was up-regulated, whereas amino acid metabolism showed the opposite trend. All results suggested that the complex physical-chemical and biochemical processes in water ecosystems may be affected by the coal mine drainage. The bacterial community response and underlying functional changes may accelerate internal nutrient cycling, which may have a potential impact on algal bloom outbreaks.

Biochar improved the composting quality of seaweeds and cow manure mixture and altered the microbial community.

The beneficial effects of biochar addition during composting have been proved for many feedstocks, like manures and crop straws. However, the effect of biochar on the quality of composting product with seaweed as the feedstock and the bacterial response has not been investigated. In this study, the wheat straw biochar addition on the quality of the composting product and the bacterial response was explored at the rate of 0-10%. The results showed that biochar addition at the optimal rate (5%, w/w) could increase the germination index and the ratio of the optical density of humic acid at 460 nm to that at 660 nm (E4/E6) of the composting product, which indicated the decreased biotoxicity and enhanced compost maturity. The significant increase of the nitrate nitrogen (NO3 --N) content of the composting product proved the improvement of N cycling during composting process with biochar addition. The bacterial community of composting product was shifted and the relative abundance of some beneficial taxa (e.g., Muricauda and Woeseia) was significantly increased with biochar addition. Furthermore, the relative abundance of some bacterial genes related to amino acid metabolism and carbohydrate metabolism was also increased with biochar addition. The results of our study provided the positive effect of biochar addition on the composting of seaweed and could help to produce high quality seaweed fertilizer by composting with biochar addition.

Microbial Community, Co-Occurrence Network Relationship and Fermentation Lignocellulose Characteristics of Broussonetia papyrifera Ensiled with Wheat Bran.

Broussonetia papyrifera has a high lignocellulose content leading to poor palatability and low digestion rate of ruminants. Thus, dynamic profiles of fermentation lignocellulose characteristics, microbial community structure, potential function, and interspecific relationships of B. papyrifera mixing with wheat bran in different ratios: 100:0 (BP100), 90:10 (BP90), 80:20 (BP80), and 65:35 (BP65) were investigated on ensiling days 5, 15, 30, and 50. The results showed that adding bran increased the degradation rate of hemicellulose, neutral detergent fiber, and the activities of filter paper cellulase, endoglucanase, acid protease, and neutral protease, especially in the ratio of 65:35. Lactobacillus, Pediococcus, and Weissella genus bacteria were the dominant genera in silage fermentation, and Pediococcus and Weissella genus bacteria regulated the process of silage fermentation. Compared with monospecific B. papyrifera silage, adding bran significantly increased the abundance of Weissella sp., and improved bacterial fermentation potential in BP65 (p < 0.05). Distance-based redundancy analysis showed that lactic acid bacteria (LAB) were significantly positive correlated with most lignocellulose content and degrading enzymes activities, while Monascus sp. and Syncephalastrum sp. were opposite (p < 0.05). Co-occurrence network analysis indicated that there were significant differences in microbial networks among different mixing ratios of B. papyrifera silage prepared with bran. There was a more complex, highly diverse and less competitive co-occurrence network in BP65, which was helpful to silage fermentation. In conclusion, B. papyrifera ensiled with bran improved the microbial community structure and the interspecific relationship and reduced the content of lignocellulose.

Comparison of composting factors, heavy metal immobilization, and microbial activity after biochar or lime application in straw-manure composting.

Composting is an efficient way of disposing agricultural solid wastes as well as passivating heavy metals (HMs). Herein, equivalent (3%) biochar (BC) or lime (LM) were applied in rice straw and swine manure composting, with no additives applied as control group (CK). The results indicated that both the additives increased NO3--N content, organic matter degradation, humus formation, and HM immobilization in composting, and the overall improvement of lime was more significant. In addition, the additives optimized the bacterial community of compost, especially for thermophilic and mature phase. Lime stimulated the growth of Bacillus, Peptostreptococcus, Clostridium, Turicibacter, Clostridiaceae and Pseudomonas, which functioned well in HM passivation via biosorption, bioleaching, or promoting HM-humus formation by secreting hydrolases. Lime (3%) as additive is recommended in swine manure composting to promote composting maturity and reduce HM risk. The study present theoretical guidance in improving composting products quality for civil and industrial composting.

[Identification of Bacterial Flora and Metabolic Function of Sediments in Different Channels of Duliujian River Basin, Tianjin].

Bacterial communities are highly sensitive to environmental changes, but their metabolic functions may be convergent under similar ecological conditions. In order to test this environmental attribute of the bacterial community and verify the feasibility in using the bacterial metabolic data to divide functional units at the river basin scale, the surface sediments in three continuous spatial units of the main stream (MS), left tributary (LT), and right tributary (RT) of the Duliujian River basin were selected as the research objects. Therefore, 16S rDNA high-throughput sequencing and the PICRUSt platform were used to analyze the bacterial diversity and metabolic function of sediments in different units. The results showed that there were no significant differences for the Shannon and Simpson indices between the different river channels (P>0.05); however, the bacterial diversity indices of Chao1, ACE, Observed_species, and PD_whole_tree of LT and RT were significantly higher than those of the MS (P<0.05). Moreover, the dominant bacterial phyla were not significantly different among the different river channels. In the present study, a total of 41 metabolic pathways were predicted based on the KEGG database, among which 34 metabolic pathways such as membrane transport, amino acid metabolism, and carbohydrate metabolism were significantly different. The functional metabolic abundance was higher in MS than that in RT and LT (P<0.05); however, there was no significant difference between those of RT and LT (P>0.05). Except for exchangeable phosphorus and nitrate nitrogen, there were no significant differences in other physicochemical properties among the different river channels (P>0.05). Furthermore, pH and iron/aluminum-phosphorus were found to significantly affect the bacterial structure, and SOM and TN were found to significantly affect the bacterial metabolic function. Overall, the sediments of MS and tributaries (LT and RT) of the river were clearly divided into level-1 and level-2 groups, indicating that the metabolic abundance of the bacterial community can be used as the key indicator in the division of functional units at the river basin scale. This study provided a theoretical basis and technical support for ecological functional division and management in coastal river basins.

The microbial mechanisms of enhanced humification by inoculation with Phanerochaete chrysosporium and Trichoderma longibrachiatum during biogas residues composting.

This study investigated effects of composite microbes (CMs) (Phanerochaete chrysosporium and Trichoderma longibrachiatum) on humification during co-composting of biogas residue, spent mushroom substrate and rice straw. Results showed that CMs inoculation elevated degradation ratios of cellulose, hemicellulose and lignin by 7.86%, 8.87% and 6.45%, and contents of humus and humic acid were correspondingly promoted by 15.5% and 23.6%, respectively. Relative abundances of bacteria associated with refractory macromolecules degradation (Flavobacterium, Anseongella and Actinomadura) and cellulolytic fungi (Hypocreales_Incertae_sedis, Hypocreaceae and Psathyrellaceae) were raised by CMs addition. Redundancy analysis demonstrated a positive correlation between microbial communities and temperature, fulvic acid and lignocellulose contents. Moreover, CMs inoculation promoted pathways of xenobiotics biodegradation and metabolism, and biosynthesis of other secondary metabolites, which was closely associated with lignocellulose degradation and humus formation. These results suggested that biological inoculation could enhance composting efficiency and improve compost quality, benefiting biogas residues composting.

Short-term biodrying achieves compost maturity and significantly reduces antibiotic resistance genes during semi-continuous food waste composting inoculated with mature compost.

Food waste (FW) is important object of resource utilization and source of antibiotic resistance genes (ARGs). This study investigated the effects of biodrying combined with inoculating mature compost (B&M) on the composting efficiency, succession of bacterial communities and their links with metabolism functions as well as the fate of ARGs during FW composting. The results showed that B&M could rapidly raise and maintain high relative abundance of Bacillaceae (66.59-94.44%) as well as composting temperature (45.86-65.86 â„ƒ), so as to achieve the final maturity of FW composting in a short time by regulating microbial carbohydrate (14.02-15.31%) and amino acid metabolism (10.33-12.47%). Network analysis demonstrated that high temperature could effectively inhibit the proliferation and spread of potential bacterial hosts of ARGs and integrons including Lactobacillaceae, Enterobacteriaceae, Leuconostocaceae and Corynebacteriaceae during the first two days of composting. As a result, B&M significantly reduced the absolute (72.09-99.47%) and relative abundances (0.31-2.44 logs) of nearly all ARGs especially ermB, tetM, blaCTX-M and blaOXA. Present study deepened the knowledge of ARGs variation, succession and metabolism functions of bacterial communities when B&M processes were used for FW composting, suggesting a promising technology for reducing the transmission risk of ARGs and reaching maturity of FW composting.

Bacterial Community Structure and Metabolic Function Succession During the Composting of Distilled Grain Waste.

Distilled grain waste (DGW) can be converted to organic fertilizer via aerobic composting process without inoculating exogenous microorganisms. To illustrate the material conversion mechanism, this study investigated the dynamic changes of bacterial community structure and metabolic function involved in DGW composting. Results showed that a significant increase in microbial community alpha diversity was observed during DGW composting. Moreover, unique community structures occurred at each composting stage. The dominant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota, Myxococcota, and Chloroflexi, whose abundance varied according to different composting stages. Keystone microbes can be selected as biomarkers for each stage, and Microbispora, Chryseolinea, Steroidobacter, Truepera, and Luteimonas indicating compost maturity. Co-occurrence network analysis revealed a significant relationship between keystone microbes and environmental factors. The carbohydrate and amino acid metabolism were confirmed as the primary metabolic pathways by metabolic function profiles. Furthermore, nitrogen metabolism pathway analysis indicated that denitrification and NH3 volatilization induced higher nitrogen loss during DGW composting. This study can provide new understanding of the microbiota for organic matter and nitrogen conversion in the composting process of DGW.

Substrate competition and microbial function in sulfate-reducing internal circulation anaerobic reactor in the presence of nitrate.

Nitrate and sulfate often coexist in organic wastewater. In this study, an internal circulation anaerobic reactor was conducted to investigate the impact of nitrate on sulfate reduction. The results showed that sulfate reduction rate dropped from 78.4% to 41.4% at NO3- /SO42- ratios ranging from 0 to 1.03, largely attributed to the inactivity of acetate-utilizing sulfate-reducing bacteria (SRB) and preferential usage of nitrate of propionate-utilizing SRB. Meanwhile, high nitrate removal efficiency was maintained and COD removal efficiency increased with nitrate addition. Enhancement of propionate and butyrate degradation based on Modified Gompertz model and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) analysis. Moreover, nitrate triggered the shift of microbial community and function. Twelve genera affiliated to Firmicutes, Bacteroidetes and Proteobacteria were identified as keystone genera via network analysis, which kept functional stability of the bacterial community responding to nitrate stress. Increased nitrate inhibited Desulfovibrio, but promoted the growth of Desulforhabdus. Both the predicted functional genes associated with assimilatory sulfate reduction pathway (cysC and cysNC) and dissimilatory sulfate reduction pathway (aprA, aprB, dsrA and dsrB) exhibited negative relationship with nitrate addition.

Organic matter- and temperature-driven deterministic assembly processes govern bacterial community composition and functionality during manure composting.

Although many studies have shown that microbial communities play important roles in organic waste composting due to the involvement of specific microbial taxa with metabolic functions, the underlying ecological processes of community assembly and governing factors remain elusive. Thus, a chicken manure composting experiment as a model system of microbially mediated organic waste composting was conducted. Ecological null modeling and metabolic functional prediction combined with electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to quantify assembly processes governing bacterial community composition and functions during composting. The results showed the predominant role of deterministic assembly processes in shifting community compositions both across and within composting stages. Stochastic assembly processes also concomitantly influenced microbial community compositions. Changes in the organic matter (OM) content and its chemical properties and temperature governed bacterial community assembly processes throughout the stages by selecting specific bacterial taxa such as Cardiobacteriales, Bacteroidales, and Lachnospiraceae on day 1, Firmicutes on days 6, 25 and 37, and Sphingobacteriales, Thermoactinomycetaceae, Actinobacteria, and Novibacillus on day 45. These taxa ultimately influenced community functions such as environmental information processing, carbohydrate and amino acid metabolism, cellular processes, and genetic information processes involved in composting. Taken together, this study indicates that deterministic assembly processes governed by OM content and quality as well as temperature influenced microbial community turnover and determined community functions during composting. These results are important for better understanding and predicting microbial-driven composting and for ultimately manipulating microorganisms for environmentally-friendly composting outcomes.

Metabolic function, trophic mode, organics degradation ability and influence factor of bacterial and fungal communities in chicken manure composting.

The metabolic function and organic degradation behavior of bacterial and fungal communities were detected in 60 days composting of chicken manure and pumice by using Biolog tools, PICRUSt and FUNGuild. Fungal diversity increased from 57 OTUs in fresh chicken manure to 109 OTUs in high temperature stage, while bacterial diversity decreased from 86 OTUs to 44 OTUs after composting treatment. The carbohydrates degradation ability of bacterial community was enhanced in the high temperature stage. Fungal community had relatively higher degradation rates of carboxylic acids and amino acids in the maturation stage. Saprotroph was the main trophic mode of fungal community during the incubation process. The fungal animal pathogen decreased from 12.5% to 1.2% after composting treatment. Bacterial community composition and substrates degradation rate were mainly influenced by redox potential, pH and moisture, while temperature was the main environmental factor influencing on organic degradation of fungal community.

Responses of enzymatic activity and microbial communities to biochar/compost amendment in sulfamethoxazole polluted wetland soil.

Biochar and compost, two common amendments, were rarely conducted to investigate their combined influence on enzymatic activities and microbial communities in organic-polluted wetlands. This article described the effects of biochar/compost on degradation efficiency of sulfamethoxazole (SMX) and ecosystem responses in polluted wetland soil during the whole remediation process. 1% biochar (SB1) increased degradation efficiency of SMX by 0.067% ascribed to the increase of dehydrogenase and urease. 5% biochar (SB5) decreased degradation efficiency by 0.206% due to the decrease of enzymes especially for dehydrogenase. 2% compost (SC2), 1% biochar & 2% compost (SBC3), both 10% compost (SC10) and 5% biochar & 10% compost (SBC15) enhanced degradation efficiency by 0.033%, 0.015% and 0.222%, respectively, due to the increase of enzymes and biomass. The degradation efficiency was positively related to biomass and enzymatic activities. High-throughput sequencing demonstrated that HCGs (SB5, SC10, SBC15) improved the bacterial diversities but reduced richness through introducing more exogenous predominance strains and annihilated several inferior strains, while LCGs (SB1, SC2, SBC3) exhibited lower diversities but higher richness through enhanced the RAs of autochthonal preponderant species and maintained some inferior species. Additionally, HCGs raised the RAs of amino and lipid metabolism gene but lowered those of carbohydrate compared with LCGs.

Effects of rhamnolipid and Tween-80 on cellulase activities and metabolic functions of the bacterial community during chicken manure composting.

Metabolism by microorganisms is the basis of composting. In this study, the dynamic changes in the enzyme activity levels, bacterial community structure, and metabolism functions were investigated during chicken manure composting with an added bio-surfactant (rhamnolipid) or chemical surfactant (Tween-80). The results showed that rhamnolipid and Tween-80 improved the quality of the finished compost in terms of the C/N ratio, water-soluble carbon content, germination index, E4/E6 ratio, and the cellulase activity, especially with Tween-80. Furthermore, the bacterial communities were determined by high-throughput sequencing, and their metabolism functions were evaluated using the PICRUSt and Biolog methods. Tween-80 greatly influenced the bacterial community structure, where it enhanced the abundances of bacteria that degrade cellulose and lignin (e.g., members of the order Bacillales) and the capacities for carbohydrate and amino acid metabolism. Network analysis also showed that the order Bacillales was closely related to the metabolism of characteristic carbon sources, especially carbohydrates.

Succession of organics metabolic function of bacterial community in response to addition of earthworm casts and zeolite in maize straw composting.

Succession and metabolism functions of bacterial communities were determined in maize straw composting with earthworm casts and zeolite addition by using high-throughput sequencing, Biolog and PICRUSt. Results showed that earthworm casts and zeolite addition increased the temperature, decreased NH4+ contents and affected bacterial community structure. The relative abundances of Firmicutes and Betaproteobacteria increased with earthworm casts and zeolite addition in the late stage. The abundances of genes related to carbohydrate metabolism, amino acid metabolism, and energy metabolism were increased by these two additives in the early stage, but decreased in the late stage. Network analysis demonstrated that members of Bacillaceae were identified as the keystone taxa. Temperature showed negative relationship with Georgenia, while NH4+ exhibited positive associations with Georgenia, Devosia, Ruania and Mycobacterium. These results indicated that earthworm casts and zeolite addition benefitted the keystone species and enhanced the metabolism capacity of bacterial community, thereby improved the quality of compost.

Improved performance of simultaneous nitrification and denitrification via nitrite in an oxygen-limited SBR by alternating the DO.

In this study, the performance of simultaneous nitrification and denitrification via nitrite was investigated by alternating the dissolved oxygen (DO) concentration in a sequencing batch reactor with the DO-control area and the non-control area. In addition, bacterial communities and their metabolic functions were analyzed by high-throughput sequencing technology and phylogenetic investigation of the communities by reconstruction of unobserved states (PICRUSt). The removal efficiencies of NH4+-N and total nitrogen via the nitrite pathway were 97.91 ±â€¯2.04% and 72.28 ±â€¯2.23%, respectively, by maintaining low DO levels (0.7 ±â€¯0.1 mg/L) in the DO-control area. PICRUSt analysis showed that the metabolic potential of the bacterial community for amino acids, nucleotides, coenzymes and inorganic ions decreased, while the relative abundance of key enzymes involved in nitrification and denitrification, and the relative population of denitrifying bacteria increased when the DO decreased from 1.2 ±â€¯0.2 mg/L to 0.7 ±â€¯0.1 mg/L.