Biological nitrogen removal and metabolic characteristics of a novel cold-resistant heterotrophic nitrification and aerobic denitrification Rhizobium sp. WS7

Evaluation of nitrogen removal performance and metabolic mechanism of a novel salt-tolerant strain Pseudomonas aeruginosa SH3

High salinity impedes efficient nitrogen removal from mariculture wastewater, which inhibits the colonization and nitrogen removal capabilities of nitrogen-removing microbes. This study aimed to isolate and characterize a salt-tolerant heterotrophic nitrification-aerobic denitrification bacterial strain. We evaluated 30 bacterial strains isolated from Portunus trituberculatus aquaculture ponds, among which Pseudomonas aeruginosa SH3 exhibited superior nitrogen removal efficiencies (99 % of NH4+-N, 71 % of NO2--N, and 85 % fof NO3--N at a salinity of 30 ‰) than the other strains. Single-factor experiments demonstrated that SH3 effectively removed either NH4+-N or NO2--N across various C/N ratios (10-20), pH levels (7-9), salinity levels (15-35 ‰), and temperatures (25-35 °C), highlighting its promising nitrogen removal capabilities under conditions suitable for mariculture. Genomic analysis showed that SH3 removes NH4+-N through ammonia assimilation and nitrification and converts NO2--N and NO3--N via denitrification and assimilatory nitrate reduction. Bioaugmentation with SH3 reduced the startup period by 14 d, addressing a common challenge of prolonged startup times in a moving-bed biofilm reactor used for nitrogen removal in marine recirculating aquaculture systems. Meanwhile, bioaugmentation maintained minimal fluctuations in nitrogen levels throughout the operational period, resulting in consistently low concentrations of NO2--N and NH4+-N, both below 1 mg/L. Therefore, strain SH3 exhibits robust nitrogen removal capabilities, demonstrating its practicality and reliability in mariculture wastewater treatment along with providing robust data support for industrial-scale applications.

Mechanistic insights into substituent-induced hydrolytic debromination and electron flow of bromophenols under nitrate-reducing conditions

Exogenous electron acceptors, such as nitrate, hold great potential for the bioremediation of wastewater contaminated with bromophenols (BPs). However, research into the mechanisms underlying BPs biodegradation remains in its early stages, particularly regarding the molecular structure and bioremediation performance. This study provides a comprehensive analysis of the mechanisms involved in BPs within a nitrate-reducing system, focusing on the molecular structure of BPs. Therefore, three up-flow bioreactors were operated for 187 days, achieving removal efficiencies of 100 %, 90.4 ± 0.6 % and 50.2 ± 2.8 % for ortho-bromophenol (2-BP), para-bromophenol (4-BP) and meta-bromophenol (3-BP), respectively. Hydrolytic dehalogenase (LinB) was found to play a critical role in BP metabolism. Molecular docking and density functional theory calculations revealed that the geometric structure and electronic effects of the Br-substituent significantly influenced LinB activity and BP reactivity, thereby affecting removal efficiencies. Notably, 2-BP, with a shorter orientation distance, was more readily catalyzed by LinB, as evidenced by metagenomic analyses showing significant increases in the abundance of N-transforming and BP-degrading genes. Furthermore, 2-BP and 4-BP stimulated more robust microbial responses, including dehalogenation (Thauera), denitrification (Delftia), and electron transport (Xanthomonadales). These results provide valuable insights into the environmental fate of BPs at the molecular level and how the Br-substituent influences microbial metabolism.

Heterotrophic nitrification-aerobic denitrification strains: An overlooked microbial interaction nexus in the anaerobic-swing-anoxic-oxic (ASAO) plug-flow system

This study aims to clarify the overlooked functions of heterotrophic nitrification-aerobic denitrification (HNAD) bacteria in a novel anaerobic-swing-anoxic-oxic (ASAO) continuous plug-flow system. The dissolved oxygen (DO) levels and aerated hydraulic retention time (HRT) varied in the swing zones, providing a more diverse redox environment. High nitrogen (85.0 %) and phosphorus (80.0 %) removal were achieved by enriched HNAD bacteria (e.g., Thauera and Malikia) and phosphate accumulating organisms (PAO, e.g., Rhodocyclus and Azonexus) under middle DO level (1.0-2.0 mg/L) and longer aerated HRT (5.0 h). More importantly, microbial network revealed that HNAD bacteria became a connection point for other functional microorganisms associated with pollutant metabolism, and promoted the cooperation and functional evolution of microbial communities. The microbial ecology analysis captured the high importance of homogeneous selection, diffusion restriction, and drift for microbial community assembly in the ASAO system. Among them, HNAD bacteria contributed to both deterministic and stochastic processes, whereas the community assembly of PAO was mainly affected by the deterministic processes. The upregulation of denitrification genes (i.e., napA, napB, nirS, norB and norC) further confirmed the nitrogen removal contribution of aerobic denitrification by HNAD bacteria. Through this study, a comprehensive analysis of microbial interactions in the ASAO system was achieved, providing valuable insights into the targeted regulation of functional microorganisms in wastewater biological treatment processes.

Performance and mechanisms of nitrogen removal from low-carbon source wastewater in an iron-carbon coupled biofilm airlift internal circulation sequencing batch reactor

An iron-carbon coupled biofilm airlift internal circulation sequencing batch reactor (IC-SBR) was constructed to treat low-carbon source wastewater. Single-factor experiments were used to determine the optimal operating conditions for the IC-SBR, with a hydraulic retention time (HRT) of 10 h, a dissolved oxygen (DO) concentration of 3 mg/L, a C/N ratio of 3, and an influent NH4+-N concentration of 50 mg/L, with average removal efficiencies of total nitrogen (TN) and total organic carbon (TOC) of 78.06% and 97.15%, respectively. Mechanistic studies of the IC-SBR indicated that iron-carbon selectively enriched nitrogen removal microorganisms and promoted nitrogen removal efficiency. Carbon sources affected the secretion of extracellular polymeric substances (EPS), enzyme activities, electron transport system activity, nitrogen removal gene abundance, and community structure of microorganisms in the IC-SBR. Microorganisms use EPS as a supplementary carbon source to ensure nitrogen removal efficiency when the carbon source is insufficient.

Characteristics of a heavy metal resistant heterotrophic nitrification-aerobic denitrification bacterium isolated from municipal activated sludge

The heterotrophic nitrification-aerobic denitrification (HNAD) is a new biological denitrification technology, the present study isolated a new HNAD strain named Cupriavidus metallidurans TX6 with heavy metal resistance. The gene expression, electron transport, enzyme activity and nitrogen removal property of strain TX6 were studied with different influencing factors. Strain TX6 has five nitrogen metabolism pathways (NH4+ → NH2OH → NO → NO2- → NH4+ → GOGAT/GDH; NH4+-N → NH2OH → NO → N2O → N2; NH4+ → NH2OH → NO → NO2- → NO3-; NO3- → NO2- → NH4+ → GOGAT/GDH; NO3-→ NO2- → NH4+ → GOGAT/GDH). Nitrogen balance analysis shows that 29 ± 4 mg/L of N was converted to intracellular nitrogen by assimilation and 50 ± 3 mg/L N loss may be attributed to aerobic denitrification. The results provide a theoretical basis for the HAND bacteria application in nitrogen removal from wastewaters containing heavy metals.

Electron-deficient wastewater treatment in membrane-aerated conductive biofilm reactor: Performance and mechanism

A membrane-aerated conductive biofilm reactor (MA-CBR) was constructed for carbon-limited wastewater treatment and to reduce the stress of the electric field on nitrous oxide reductase (NosZ). Counter-diffusion with an embedded aerobic layer declined the effect of current on NosZ (K00376) for N2O reduction. Other coding genes for denitrification in cathodic membrane aerated biofilms, including K02568, K00368, K15864, K02305, and K04561, were also positively affected by the electric field and significantly accumulate in Thauera. NH4+-N oxidation can occur at the anode and cathode (membrane aeration biofilm). This cathodic synergistic NH4+-N oxidation provided more electrons to be directly utilized by the denitrifying bacteria at the cathode. Compared to the MABR, the total nitrogen removal efficiency of MA-CBR increased by 5.68 mg/L, 11.02 mg/L, and 15.63 mg/L at voltages of 0.25 V, 0.50 V, and 0.75 V, respectively.

Fulvic acid mediated highly efficient heterotrophic nitrification-aerobic denitrification by Paracoccus denitrificans XW11 with reduced C/N ratio

Reducing the C/N ratio requirements for heterotrophic nitrification-aerobic denitrification (HNAD) is crucial for its practical application; however, it remains underexplored. In this study, a highly efficient HNAD bacterium, Paracoccus denitrificans XW11, was isolated. The HNAD characteristics of XW11 were studied, and the redox mediator fulvic acid (FA) was used to reduce the C/N requirements. Whole-genome sequencing revealed multiple denitrification genes in XW11; however, nitrification genes were not identified, because heterotrophic nitrification-related gene sequences were not included in the database. However, the nitrogen removal related enzyme activity test revealed complete nitrification and denitrification pathways. Reverse transcription PCR showed that the membrane-bound nitrate reductase (NarG), rather than the periplasmic nitrate reductase, was responsible for aerobic denitrification. The conventional nitrite reductase (NirS) also does not mediate nitrite denitrification. When the C/N ratio was 10, the ammonia removal efficiency of the Control was 71.71 % and the addition of FA increased it to 86.12 %. Transcriptomic analysis indicated electron flow from the carbon source to FA without proton transmembrane transport, and the presence of FA constructs another electron transfer system. The redox potential of oxidized FA/reduced FA is 0.3679 V, avoiding competition for electrons from Complex III. Thus, ammonia monooxygenase obtains electrons more easily, thereby promoting nitrification. The enzyme activity test of the nitrification process confirmed this view. In addition, NarG expression increased, and the denitrification process was enhanced. Overall, FA improved HNAD efficiency by facilitating electron transfer to the nitrogen dissimilation process, offering a novel approach to reduce the C/N requirement of HNAD.

Nitrate removal by a novel aerobic denitrifying Pelomonas puraquae WJ1 in oligotrophic condition: Performance and carbon source metabolism

Reducing nitrate contamination in drinking water has become a critical issue in urban water resource management. Here a novel oligotrophic aerobic denitrifying bacterium, Pelomonas puraquae WJ1, was isolated and purified from artificial lake sediments. For the first time, excellent aerobic denitrification capabilities were demonstrated. At a carbon-to‑nitrogen ratio of 5.0, strain WJ1 achieved 100.0 % nitrate removal and 84.92 % total nitrogen removal within 24 h, with no nitrite accumulation. PCR amplification and sequencing confirmed the presence of the denitrification genes napA, nirS, and nosZ in the strain. The nitrogen balance demonstrated that approximately 74.95 % of the initial nitrogen was eliminated as gaseous products under aerobic conditions. Furthermore, carbon balance analysis showed that most electron donors from strain WJ1 were directed towards oxygen, with limited availability for nitrate reduction. A combination of bio-ECO analysis and network modeling indicated that strain WJ1 has robust metabolic capabilities for diverse carbon sources and exhibits high adaptability to complex carbon environments. Overall, Pelomonas puraquae WJ1 removed approximately 45.89 % of the nitrates in raw water, demonstrating significant potential for practical applications in oligotrophic denitrification.

Enhancement of cold-adapted heterotrophic nitrification and denitrification in Pseudomonas sp. NY1 by cupric ions: Performance and mechanism

Cupric ions can restrain biological nitrogen removal processes, which comprise nitrite reductase and nitric oxide reductase. Here, Pseudomonas sp. NY1 can efficiently perform heterotrophic nitrification and aerobic denitrification with cupric ions at 15 °C. At optimal culturing conditions, low cupric ion levels accelerated nitrogen degradation, and ammonium and nitrite removal efficiencies increased by 2.33%-4.85% and 6.76%-12.30%, respectively. Moreover, the maximum elimination rates for ammonium and nitrite increased from 9.48 to 10.26 mg/L/h and 6.20 to 6.80 mg/L/h upon adding 0.05 mg/L cupric ions. Additionally, low cupric ion concentrations promoted electron transport system activity (ETSA), especially for nitrite reduction. However, high concentrations of cupric ions decreased the ETSA during nitrogen conversion processes. The crucial enzymes ammonia monooxygenase, nitrate reductase, and nitrite reductase possessed similarly trends as ETSA upon exposure to cupric ion. These findings deepen the understanding for the effect of cupric ions on nitrogen consumption and bioremediation in nitrogen-polluted waters.

In situ electron generation through Fe/C supported sludge coupled with a counter-diffusion biofilm for electron-deficient wastewater treatment: Binding properties and catalytic competition mechanism of nitrate reductase

A membrane-aerated biofilm-coupled Fe/C supported sludge system (MABR-Fe/C) was constructed to achieve in situ electron production for NO3--N reduction enhancement in different Fe/C loadings (10 g and 200 g). The anoxic environment formed in the MABR-Fe/C promoted a continual Fe2+release of Fe/C in 120 d operation (average Fe2+concentrations is 1.18 and 2.95 mg/L in MABR-Fe/C10 and MABR-Fe/C200, respectively). Metagenomics results suggested that the electrons generated from ongoing Fe2+ oxidation were transferred via the Quinone pool to EC 1.7.5.1 rather than EC 1.9.6.1 to complete the process of NO3--N reduction to NO2--N in Acidovorax, Ottowia, and Polaromonas. In the absence of organic matter, the NO3--N removal in MABR-Fe/C10 and MABR-Fe/C200 increased by 11.99 and 12.52 mg/L, respectively, compared to that in MABR. In the further NO2--N reduction, even if the minimum binding free energy (MBFE) was low, NO2--N in Acidovorax and Dechloromonas preferentially bind the Gln-residues for dissimilatory nitrate reduction (DNR) in the presence of Fe/C. Increasing Fe/C loading (MABR-Fe/C200) caused the formation of different residue binding sites, further enhancing the already dominant DNR. When DNR in MABR-Fe/C200 intensified, the TN in the effluent increased by 3.75 mg/L although the effluent NO3--N concentration was lower than that in MABR-Fe/C10. This study demonstrated a new MABR-Fe/C system for in situ electron generation to enhance biological nitrogen removal and analyzed the NO3--N reduction pathway and metabolic mechanism, thus providing new ideas for nitrogen removal in electron-deficient wastewater.

Anticancer drugs impact the performance and prokaryotic microbiome of an aerobic granular sludge system operated in a sequential batch reactor

Increased concerns exist about the presence of anticancer drugs in wastewater. However, knowledge of the impacts of anticancer drugs on the performance of the system and microbial communities during wastewater treatment processes is limited. We examined the effect of three anticancer drugs commonly detected in influents of wastewater treatment plants applied at three different concentration levels on the performance, efficiency of anticancer drug removal, and prokaryotic microbiome in an aerobic granular sludge system (AGS) operated in a sequential batch reactor (SBR). We showed that an AGS can efficiently remove anticancer drugs, with removal rates in the range of 53-100% depending on the type of drug and concentration level. Anticancer drugs significantly decreased the abundance of total bacterial and archaeal communities, an effect that was linked to reduced nitrogen removal efficiency. Anticancer drugs also reduced the diversity, altered the prokaryotic community composition, reduced network complexity, and induced a decrease of a wide range of predicted bacterial functions. Specific bacterial taxa responsive to the addition of anticancer drugs with known roles in nitrification and denitrification were identified. This study shows anticancer drugs should be monitored in the future as they can induce changes in the performance and microbiome of wastewater treatment technologies.

Multi-omics analysis to reveal key pathways involved in low C/N ratio stress response in Pseudomonas sp. LW60 with superior nitrogen removal efficiency

In practical engineering, nitrogen removal at low temperatures or low C/N ratios is difficult. Although strains can remove nitrogen well at low temperatures, there is no research on the performance and deep mechanism of strains under low C/N ratio stress. In this study, Pseudomonas sp. LW60 with superior nitrogen removal efficiency under low C/N ratio stress was isolated at 4 °C. With a C/N ratio of 2-10, the NH4+-N removal efficiency was 40.02 %-100 % at 4 °C. Furthermore, the resistance mechanism of Pseudomonas sp. LW60 to low C/N ratio stress was deeply investigated by multi-omics. The results of transcriptome, proteome, and metabolome revealed that the resistance of strain LW60 to low C/N ratio stress was attributed to enhanced central carbon metabolism, amino acid metabolism, and ABC transporters, rather than nitrogen removal pathways. This study isolated a strain with low C/N ratio tolerance and deeply explored its tolerance mechanism by multi-omics.

Explaining nitrogen turnover in sediments and water through variations in microbial community composition and potential function

Anthropogenic activities greatly impact nitrogen (N) biogeochemical cycling in aquatic ecosystems. High N concentrations in coastal aquaculture waters threaten fishery production and aquaculture ecosystems and have become an urgent problem to be solved. Existing microbial flora and metabolic potential significantly regulate N turnover in aquatic ecosystems. To clarify the contribution of microorganisms to N turnover in sediment and water, we investigated three types of aquaculture ecosystems in coastal areas of Guangdong, China. Nitrate nitrogen (NO3--N) was the dominant component of total nitrogen in the sediment (interstitial water, 90.4%) and water (61.6%). This finding indicates that NO3--N (1.67-2.86 mg/L and 2.98-7.89 mg/L in the sediment and water) is a major pollutant in aquaculture ecosystems. In water, the relative abundances of assimilation nitrogen reduction and aerobic denitrifying bacteria, as well as the metabolic potentials of nitrogen fixation and dissimilated nitrogen in fish monoculture, were only 61.0%, 31.5%, 47.5%, and 27.2% of fish and shrimp polyculture, respectively. In addition, fish-shrimp polyculture reduced NO3--N content (2.86 mg/L) compared to fish monoculture (7.89 mg/L), which was consistent with changes in aerobic denitrification and nitrate assimilation, suggesting that polyculture could reduce TN concentrations in water bodies and alleviate nitrogen pollution risks. Further analysis via structural equation modeling (SEM) revealed that functional pathways (36% and 31%) explained TN changes better than microbial groups in sediment and water (13% and 11%), suggesting that microbial functional capabilities explain TN better than microbial community composition and other factors (pH, O2, and aquaculture type). This study enhances our understanding of nitrogen pollution characteristics and microbial community and functional capabilities related to sediment-water nitrogen turnover in three types of aquaculture ecosystems, which can contribute to the preservation of healthy coastal ecosystems.

Nitrogen removal capability and mechanism of a novel heterotrophic nitrifying-aerobic denitrifying strain H1 as a potential candidate in mariculture wastewater treatment

The nitrogen removal performance and mechanisms of Bacillus subtilis H1 isolated from a mariculture environment were investigated. Strain H1 efficiently removed NH4+-N, NO2--N, and NO3--N in simulated wastewater with removal efficiencies of 85.61%, 90.58%, and 57.82%, respectively. Strain H1 also efficiently degraded mixed nitrogen (NH4+-N mixed with NO2--N and/or NO3--N) and had removal efficiencies ranging from 82.39 to 89.54%. Nitrogen balance analysis revealed that inorganic nitrogen was degraded by heterotrophic nitrification-aerobic denitrification (HN-AD) and assimilation. 15N isotope tracing indicated that N2O was the product of the HN-AD process, while N2 as the final product was only detected during the reduction of 15NO2--N. The nitrogen assimilation and dissimilation pathways by strain H1 were further clarified using complete genome sequencing, nitrification inhibitor addition, and enzymatic activity measurement, and the ammonium oxidation process was speculated as NH4+ → NH2OH → NO → N2O. These results showed the application prospect of B. subtilis H1 in treating mariculture wastewater.

Comparative genomic analysis of two Arctic Pseudomonas strains reveals insights into the aerobic denitrification in cold environments

BACKGROUND

Biological denitrification has been commonly adopted for the removal of nitrogen from sewage effluents. However, due to the low temperature during winter, microorganisms in the wastewater biological treatment unit usually encounter problems such as slow cell growth and low enzymatic efficiency. Hence, the isolation and screening of cold-tolerant aerobic denitrifying bacteria (ADB) have recently drawn attention. In our previous study, two Pseudomonas strains PMCC200344 and PMCC200367 isolated from Arctic soil demonstrated strong denitrification ability at low temperatures. The two Arctic strains show potential for biological nitrogen removal from sewage in cold environments. However, the genome sequences of these two organisms have not been reported thus far.

RESULTS

Here, the basic characteristics and genetic diversity of strains PMCC200344 and PMCC200367 were described, together with the complete genomes and comparative genomic results. The genome of Pseudomonas sp. PMCC200344 was composed of a circular chromosome of 6,478,166 bp with a G + C content of 58.60% and contained a total of 5,853 genes. The genome of Pseudomonas sp. PMCC200367 was composed of a circular chromosome of 6,360,061 bp with a G + C content of 58.68% and contained 5,801 genes. Not only prophages but also genomic islands were identified in the two Pseudomonas strains. No plasmids were observed. All genes of a complete set of denitrification pathways as well as various putative cold adaptation and heavy metal resistance genes in the genomes were identified and analyzed. These genes were usually detected on genomic islands in bacterial genomes.

CONCLUSIONS

These analytical results provide insights into the genomic basis of microbial denitrification in cold environments, indicating the potential of Arctic Pseudomonas strains in nitrogen removal from sewage effluents at low temperatures.

Efficient nitrogen removal by a novel extreme strain, Pseudomonas reactans WL20-3 under dual stresses of low temperature and high alkalinity: Characterization, mechanism, and application

Although many studies report the resistance of heterotrophic nitrification-aerobic denitrification (HN-AD) strains to single environmental stress, there is no research on its resistance to dual stresses of low temperature and high alkalinity. A novel bacterium Pseudomonas reactants WL20-3 isolated in this study showed removal efficiencies of 100%, 100%, and 97.76% for ammonium, nitrate, and nitrite, respectively, at 4 °C and pH 11.0. Transcriptome analysis revealed that the resistance of strain WL20-3 to dual stresses was attributed not only to the regulation of genes in the nitrogen metabolic pathway, but also to genes in other pathways such as the ribosome, oxidative phosphorylation, amino acid metabolism, and ABC transporters. Additionally, WL20-3 removed 83.98% of ammonium from actual wastewater at 4 °C and pH 11.0. This study isolated a novel strain WL20-3 with superior nitrogen removal under dual stresses and provided a molecular understanding of its tolerance mechanism to low temperature and high alkalinity.

Bioaugmentation of woodchip bioreactors by Pseudomonas nicosulfuronedens D1-1 with functional species enrichment

A novel heterotrophic nitrification and aerobic denitrification (HN-AD) bacterium D1-1 was identified as Pseudomonas nicosulfuronedens D1-1. Strain D1-1 removed 97.24%, 97.25%, and 77.12% of 100 mg/L NH₄⁺-N, NO₃^--N, and NO₂^--N, with corresponding maximum removal rates of 7.42, 8.69, and 7.15 mg·L^-1·h^-1, respectively. Strain D1-1 bioaugmentation enhanced woodchip bioreactor performance with an average NO₃^--N removal efficiency of 93.8%. Bioaugmentation enriched N cyclers along with increased bacterial diversity and predicted genes for denitrification, DNRA (dissimilatory nitrate reduction to ammonium), and ammonium oxidation. It also reduced local selection and network modularity from 4.336 to 0.934, resulting in predicted nitrogen (N) cycling genes shared by more modules. These observations suggested that bioaugmentation could enhance the functional redundancy to stabilize the NO₃^--N removal performance. This study provides insights into the potential applications of HN-AD bacteria in bioremediation or other environmental engineering fields, relying on their ability to shape bacterial communities.

Domestication and pilot-scale culture of mixed bacteria HY-1 capable of heterotrophic nitrification-aerobic denitrification

To further investigate the potential of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria for practical applications, the HN-AD mixed bacteria HY-1 were enriched and domesticated in this study. After five generations of domestication, the mixture was able to remove 98% of ammonia nitrogen (400 mg/L) and 81.9% of mixed nitrogen source (nitrate, nitrite). Changes in community structure in the domestication process of mixed microorganisms were studied using 16S rDNA-seq. The results indicated an increase in the abundance of Acinetobacter from 16.9% to 80%. The conditions for the expanded culture of the HY-1 were also optimized. Moreover, A pilot-scale expanded reactor with a capacity of 1000L was constructed, and the HY-1 was successfully expanded from 0.1L to 800L. The community structures of the HY-1 remained stable after the expanded culture, with Acinetobacter as the dominant species. Moreover, the HY-1 demonstrated adaptability to actual high ammonia nitrogen wastewater and showed potential for practical application.

High nitrous oxide (N2O) greenhouse gas reduction potential of Pseudomonas sp. YR02 under aerobic condition

Aerobic environments exist widely in wastewater treatment plants (WWTP) and are unfavorable for greenhouse gas nitrous oxide (N₂O) reduction. Here, a novel strain Pseudomonas sp. YR02, which can perform N₂O reduction under aerobic conditions, was isolated. The successful amplification of four denitrifying genes proved its complete denitrifying ability. The inorganic nitrogen (IN) removal efficiencies (NRE) were >98.0% and intracellular nitrogen and gaseous nitrogen account for 52.6-58.4% and 41.6-47.4% of input nitrogen, respectively. The priority of IN utilization was TAN > NO₃^--N > NO₂^--N. The optimal conditions for IN and N₂O removal were consistent, except for the C/N ratio, which is 15 and 5 for IN and N₂O removal, respectively. The biokinetic constants analysis indicated strain YR02 had high potential to treat high ammonia and dissolved N₂O wastewater. Strain YR02 bioaugmentation mitigated 98.7% of N₂O emission and improved 32% NRE in WWTP, proving its application potential for N₂O mitigation.

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

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