Aerobic denitrification by Paracoccus sp. YF1 in the presence of Cu(II)

Unlocking N2O respiratory pathways in Stutzerimonas stutzeri PRE-2: Implications for reducing N2O emissions from estuaries

Although nitrogen cycling in nitrogen-enriched estuaries is highly active, the reported nitrous oxide (N2O) emission factor (EF5e) values for N2O emissions in estuarine environments are usually low. Therefore, biological or abiotic mechanisms control the emission of N2O from estuarine ecosystems. In this study, a pure culture of N2O-reducing bacteria was isolated from Pearl River Estuary surface sediment and identified as Stutzerimonas stutzeri PRE-2. This strain displayed a high N2O reduction capability, and the average N2O reduction rate was 17.93 ± 0.43 μmol h-1 under anoxic conditions. This reduction of N2O was coupled with the stoichiometric consumption of acetate or lactate as electron donors, suggesting that microbial N2O reduction involves electron transport. Furthermore, N2O reduction can yield energy that supports microbial growth. Genomic analysis demonstrated that the strain Stutzerimonas stutzeri PRE-2 contains a complete pathway for the reduction of N2O to N2. Typical respiratory chain inhibitors did not significantly inhibit N2O reduction activity, demonstrating that the electron transfer pathway involved in N2O reduction is unique compared to the classic respiratory chain. The integrated evidence suggests that microbial N2O reduction by Stutzerimonas stutzeri PRE-2 involves N2O respiration and may play an important role in reducing N2O emissions in estuarine ecosystems.

Nano-Fe3O4/FeCO3 modified red soil-based biofilter for simultaneous removal of nitrate, phosphate and heavy metals: Optimization, microbial community and possible mechanism

The pollution of nitrogen, phosphorus and heavy metals in surface water is becoming more and more serious, affecting the safety of water quality. In this study, three biofilters were constructed using iron-modified red soil-based filler carriers (RSC, nano-Fe3O4@RSC, and FeCO3@RSC) combined with strain Zoogloea sp. ZP7 to simultaneously remove nitrate (NO3--N), phosphate (PO43--P), copper (Cu2+), and zinc (Zn2+). The long-term operation results showed that the three groups of biofilters could remove 85.0 %, 90.0 %, and 89.8 % of NO3--N, respectively. Furthermore, the addition of iron compounds enhanced the removal of PO43--P and the resistance to the stress of Cu2+ and Zn2+ in the biofilter. The analysis illustrated that iron modification improved the redox activity and zeta potential of RSC surface. The secondary structure analysis of the protein showed that the microbial secreted proteins were more compact on the surface of the iron-modified RSC, which facilitated the formation of biofilm on the carrier surface. In addition, the iron-modified RSC-based biofilter also showed excellent NO3--N and PO43--P removal efficiency in the treatment of actual surface water. The microbial community analysis results showed that Zoogloea became the dominant species in the biofilter. On the other hand, the presence of iron-reducing bacteria and the expression iron cycle-related genes may contribute to denitrification under low nutrient conditions.

Nitrogen fertilization and soil nitrogen cycling: Unraveling the links among multiple environmental factors, functional genes, and transformation rates

Anthropogenic nitrogen (N) inputs substantially influence the N cycle in agricultural ecosystems. However, the potential links among various environmental factors, nitrogen functional genes, and transformation rates under N fertilization remain poorly understood. Here, we conducted a five-year field experiment and collected 54 soil samples from three 0-4 m boreholes across different treatments: control, N-addition (nitrogen fertilizer) and NPK-addition (combined application of nitrogen, phosphorus and potassium fertilizers) treatments. Our results revealed pronounced variations in soil physiochemical parameters, metal concentrations and antibiotic levels under both N and NPK treatments. These alternations induced significant shifts in bacterial and fungal communities, altered NFG abundance and composition, and greatly enhanced rates of nitrate reduction processes. Notably, nutrients, antibiotics and bacteria exerted a more pronounced influence on NFGs and nitrate reduction under N treatment, whereas nutrients, metals, bacteria and fungi had a significant impact under NPK treatment. Furthermore, we established multidimensional correlations between nitrate reduction gene profiles and the activity rates under N and NPK treatments, contrasting with the absence of significant relationships in the control treatment. These findings shed light on the intricate relationships between microbial genetics and ecosystem functions in agricultural ecosystem, which is of significance for predicting and managing metabolic processes effectively.

Profile of Bacterial Communities in Copper Mine Tailings Revealed through High-Throughput Sequencing

Mine-tailing dumps are one of the leading sources of environmental degradation, often with public health and ecological consequences. Due to the complex ecosystems generated, they are ideal sites for exploring the bacterial diversity of specially adapted microorganisms. We investigated the concentrations of trace metals in solid copper (Cu) mine tailings from the Ovejería Tailings Dam of the National Copper Corporation of Chile and used high-throughput sequencing techniques to determine the microbial community diversity of the tailings using 16S rRNA gene-based amplicon sequence analysis. The concentrations of the detected metals were highest in the following order: iron (Fe) > Cu > manganese (Mn) > molybdenum (Mo) > lead (Pb) > chromium (Cr) > cadmium (Cd). Furthermore, 16S rRNA gene-based sequence analysis identified 12 phyla, 18 classes, 43 orders, 82 families, and 154 genera at the three sampling points. The phylum Proteobacteria was the most dominant, followed by Chlamydiota, Bacteroidetes, Actinobacteria, and Firmicutes. Genera, such as Bradyrhizobium, Aquabacterium, Paracoccus, Caulobacter, Azospira, and Neochlamydia, showed high relative abundance. These genera are known to possess adaptation mechanisms in high concentrations of metals, such as Cd, Cu, and Pb, along with nitrogen-fixation capacity. In addition to their tolerance to various metals, some of these genera may represent pathogens of amoeba or humans, which contributes to the complexity and resilience of bacterial communities in the studied Cu mining tailings. This study highlights the unique microbial diversity in the Ovejería Tailings Dam, including the discovery of the genus Neochlamydia, reported for the first time for heavy metal resistance. This underscores the importance of characterizing mining sites, particularly in Chile, to uncover novel bacterial mechanisms for potential biotechnological applications.

A novel derivative synchronous fluorescence method for the rapid, non-destructive and intuitive differentiation of denitrifying bacteria

It is challenging to differentiate bacteria residing in the same habitat by direct observation. This difficulty impedes the harvest, application and manipulation of functional bacteria in environmental engineering. In this study, we developed a novel method for rapid differentiation of living denitrifying bacteria based on derivative synchronous fluorescence spectroscopy, as exemplified by three heterotrophic nitrification-aerobic denitrification bacteria having the maximum nitrogen removal efficiencies greater than 90%. The intact bacteria and their living surroundings can be analyzed as an integrated target, which eliminates the need for the complex pre-processing of samples. Under the optimal synchronous scanning parameter (Δλ = 40 nm), each bacterium possesses a unique fluorescence spectral structure and the derivative synchronous fluorescence technique can significantly improve the spectral resolution compared to other conventional fluorescence methods, which enables the rapid differentiation of different bacteria through derivative synchronous fluorescence spectra as fast as 2 min per spectrum. Additionally, the derivative synchronous fluorescence technique can extract the spectral signals contributed by bacterial extracellular substances produced in the biological nitrogen removal process. Moreover, the results obtained from our method can reflect the real-time denitrification properties of bacteria in the biological nitrogen removal process of wastewater. All these merits highlight derivative synchronous fluorescence spectroscopy as a promising analytic method in the environmental field.

Insights into the nitrogen transformation mechanism of Pseudomonas sp. Y15 capable of heterotrophic nitrification and aerobic denitrification

Excessive nitrogen (N) discharged in water is a major cause of eutrophication and other severe environmental issues. Biological N removal via heterotrophic nitrification and aerobic denitrification (HN-AD) has drawn particular attention, owing to the merit of concurrent nitrification and denitrification inside one cell. However, the mechanisms underlying N transformation during HN-AD remain unclear. In the present study, the HN-AD strain Pseudomonas sp. Y15 (Y15) was isolated to explore the N distribution and flow, based on stoichiometry and energetics. The total N removal efficiency by Y15 increased linearly with C/N ratio (in the range of 5-15) to ∼96.8%. Of this, ∼32.2% and ∼64.6% were transformed into gas-N and biomass-N, respectively. A new intracellular N metabolic bypass (NO → NO2) was found, to address the substantial gaseous N production during HN-AD. Concering energetics, the large portion of the biomass-N is ascribed to the synthesis of the amino acids that consume low energy. Finally, two novel stoichiometric equations for different N sources were proposed, to describe the overall HN-AD process. This study deepens the fundamental knowledge on HN-AD bacteria and enlightens their use in treating N-contaminated wastewater.

Aerobic denitrifying bacterial-fungal consortium mediating nitrate removal: Dynamics, network patterns and interactions

In recent years, nitrogen removal by mixed microbial cultures has received increasing attention owing to cooperative metabolism. A natural bacterial-fungal consortium was isolated from mariculture, which exhibited an excellent aerobic denitrification capacity. Under aerobic conditions, nitrate removal and denitrification efficiencies were up to 100% and 44.27%, respectively. High-throughput sequencing and network analysis suggested that aerobic denitrification was potentially driven by the co-occurrence of the following bacterial and fungal genera: Vibrio, Fusarium, Gibberella, Meyerozyma, Exophiala and Pseudoalteromonas, with the dominance of Vibrio and Fusarium in bacterial and fungal communities, respectively. In addition, the isolated consortium had a high steady aerobic denitrification performance in our sub-culturing experiments. Our results provide new insights on the dynamics, network patterns and interactions of aerobic denitrifying microbial consortia with a high potential for new biotechnology applications.

Heterotrophic nitrification-aerobic denitrification performance of a novel strain, Pseudomonas sp. B-1, isolated from membrane aerated biofilm reactor

A heterotrophic nitrification-aerobic denitrification (HN-AD) strain isolated from membrane aerated biofilm reactor (MABR) was identified as Pseudomonas sp. B-1, which could effectively utilize multiple nitrogen sources and preferentially consume NH₄-N. The maximum degradation efficiencies of NO₃-N, NO₂-N and NH₄-N were 98.04%, 94.84% and 95.74%, respectively. The optimal incubation time, shaking speed, carbon source, pH, temperature and C/N ratio were 60 h, 180 rpm, sodium succinate, 8, 30 °C and 25, respectively. The strain preferred salinity of 1.5% and resisted heavy metals in the order of Mn²⁺ > Co²⁺ > Zn²⁺ > Cu²⁺. It can be preliminarily speculated from the results of enzyme assay that the strain removed nitrogen via full nitrification-denitrification pathway. The addition of strain into the conventional MABR significantly intensified the HN-AD performance of the reactor. The relative abundance of the functional bacteria including Flavobacterium, Pseudomonas, Paracoccus, Azoarcus and Thauera was obviously increased after the bioaugmentation. Besides, the expression of the HN-AD related genes in the biofilm was also strengthened. Thus, strain B-1 had great application potential in nitrogen removal process.

Ecophysiological and genomic analyses of a representative isolate of highly abundant Bacillus cereus strains in contaminated subsurface sediments

Bacillus cereus strain CPT56D-587-MTF (CPTF) was isolated from the highly contaminated Oak Ridge Reservation (ORR) subsurface. This site is contaminated with high levels of nitric acid and multiple heavy metals. Amplicon sequencing of the 16S rRNA genes (V4 region) in sediment from this area revealed an amplicon sequence variant (ASV) with 100% identity to the CPTF 16S rRNA sequence. Notably, this CPTF-matching ASV had the highest relative abundance in this community survey, with a median relative abundance of 3.77% and comprised 20%-40% of reads in some samples. Pangenomic analysis revealed that strain CPTF has expanded genomic content compared to other B. cereus species-largely due to plasmid acquisition and expansion of transposable elements. This suggests that these features are important for rapid adaptation to native environmental stressors. We connected genotype to phenotype in the context of the unique geochemistry of the site. These analyses revealed that certain genes (e.g. nitrate reductase, heavy metal efflux pumps) that allow this strain to successfully occupy the geochemically heterogenous microniches of its native site are characteristic of the B. cereus species while others such as acid tolerance are mobile genetic element associated and are generally unique to strain CPTF.

Simultaneous removal of high concentrations of ammonia nitrogen and calcium by the novel strain Paracoccus denitrificans AC-3 with good environmental adaptability

The novel Paracoccus denitrificans AC-3 strain was isolated and displayed outstanding purification capability for high concentrations of ammonia nitrogen (NH₄⁺-N) and calcium (Ca²⁺). Meanwhile, the strain exhibited excellent environmental adaptability within a wide pH range and high levels of NH₄⁺-N and Ca²⁺. Nitrogen balance analysis demonstrated that the pathways of NH₄⁺-N removal consisted of 80.12% assimilation and 16.60% heterotrophic nitrification aerobic denitrification (HNAD). In addition, Ca²⁺ was removed by forming calcium carbonate (CaCO₃) with carbonate (CO₃^2-) and bicarbonate (HCO₃^-). CO₃^2-and HCO₃^- were obtained from carbon dioxide (CO₂) hydration, which was catalyzed by carbonic anhydrase (CA) secreted by strain AC-3. The alkaline environment for carbonate precipitation was provided by CA and HNAD. The resulting CaCO₃ existed in the form of calcite and exhibited a unique morphology and elemental composition.

Simultaneous denitrification and phosphorus removal: A review on the functional strains and activated sludge processes

Eutrophication has attracted extensive attention owing to its harmful effects to the organisms and aquatic environment. Studies on the functional microorganisms with the ability of simultaneously nitrogen (N) and phosphorus (P) removal is of great significance for alleviating eutrophication. Thus far, several strains from various genera have been reported to accomplish simultaneous N and P removal, which is primarily observed in Bacillus, Pseudomonas, Paracoccus, and Arthrobacter. The mechanism of N and P removal by denitrifying P accumulating organisms (DPAOs) is different from the traditional biological N and P removal. The denitrifying P removal (DPR) technology based on the metabolic function of DPAOs can overcome the problem of carbon source competition and sludge age contradiction in traditional biological N and P removal processes and can be applied to the treatment of urban sewage with low C/N ratio. This paper reviews the mechanism of N and P removal by DPAOs from the aspect of the metabolic pathways and enzymatic processes. The research progress on DPR processes is also summarized and elucidated. Further research should focus on the efficient removal of N and P by improving the performance of functional microorganisms and development of new coupling processes. This review can serve as a basis for screening DPAOs with high N and P removal efficiency and developing new DPR processes in the future.

Antimicrobial peptide antibiotics inhibit aerobic denitrification via affecting electron transportation and remolding carbon metabolism

The harmful effects of antibiotics on biological denitrification have attracted widespread attention due to their excessive usage. Polymyxin B (PMB) as the typical antimicrobial peptides having been regarded as the "last hope" for treatment of multidrug-resistance bacteria, has also been detected in wastewater. However, little is known about the influence of PMB on aerobic denitrification. In this study, the impact of PMB on aerobic denitrification performance was investigated. Results showed 0.50 mg/L PMB decreased nitrate removal efficiency from 97.4% to 85.3%, and drove denitrifiers to transform more nitrate to biomass instead of producing gas-N. The live/dead staining method showed PMB damaged bacterial membrane. Transcriptome analysis further indicated the key enzymes participating in denitrification and aerobic respiratory chains were suppressed by PMB. To resist the PMB stress, denitrifiers formed thicker biofilm to protect cells from PMB damaging and thus remodeling the central carbon metabolism. Further investigation revealed denitrifiers have different preference on various carbon sources when PMB is present. Subsequently, the underlying mechanism of the distinctive carbon sources preference was explored by the combination of transcriptome and metabolism analysis. Overall, our data suggested denitrifiers have distinctive carbon sources preference under PMB treatment conditions, reminding us that carbon source selection should be cautious in practical applications.

Water recycle system in an artificial closed ecosystem - Lunar Palace 1: Treatment performance and microbial evolution

Water recycle systems have important implications to realize material circulation in biological regeneration life support systems, which is of significance for long-term space missions and future planetary base. Based on membrane biological activated carbon reactor (MBAR) technologies, the 'Lunar Palace 365' experiment established various treatment processes for condensate wastewater, domestic wastewater, urine, and used nutrient solutions. The 370-day operation data showed the COD_Mn index of purified condensate wastewater decreased to 0.74 ± 0.15 mg/L, which met the standards for drinking water quality. The average removal rate of organic contaminants in domestic wastewater by the MBAR was 85.7% ± 10.2%, and this MBAR also had a stable nitrification performance with effluent NO₃^--N concentrations fluctuating from 145.57 mg/L to 328.59 mg/L. Moreover, the purification of urine achieved the conversion of urea-N to NH₄⁺-N and thus the partial recovery of nitrogen. 16S rDNA sequencing results revealed the evolution of microbial diversity and composition during the long-term operation. Meiothermus, Rhodanobacter, and Ochrobactrum were the dominant microorganisms in various MBARs.

Hypothermia Pseudomonas taiwanensis J488 exhibited strong tolerance capacity to high dosages of divalent metal ions during nitrogen removal process

The nitrogen metabolic pathways of Pseudomonas taiwanensis J488 have not been confirmed from genomic function analysis and its divalent metal ion resistance remains poorly understood. In this study, the key denitrifying gene of Pseudomonas taiwanensis J488, nirB, was determined by draft genome sequencing. The nitrification of ammonium was insensitive to high concentrations of Ca(II), Mn(II), Zn(II), and Cd(II). Similarly, complete nitrite removal was achieved despite Mn(II) and Zn(II) reaching concentrations up to 30 mg/L. Furthermore, the efficiency of nitrate removal was significantly enhanced by 1.33%, 3.33%, 5.99%, and 1.53% with the addition of 0.5 mg/L Ca(II), 20 mg/L Mn(II), 5 mg/L Zn(II), and 2 mg/L Cd(II), respectively, comparison with the control. The bacterial growth in both nitrifying and denitrifying processes was substantially promoted by various dosages of divalent metal ions. These results indicate that divalent metal ions would not severely limit the capacity of strain J488 to purify nitrogen-polluted wastewater.

Simultaneous removal of nitrate, manganese, and tetracycline by Zoogloea sp. MFQ7: Adsorption mechanism of tetracycline by biological precipitation

A Mn(II) oxidizing-denitrifying and tetracycline (TC) removal bacterium Zoogloea sp. MFQ7 was isolated in this study. Nitrogen removal was 83.49% by nitrogen balance experiment. The maximum removal efficiencies of nitrate, Mn(II), and TC by strain MFQ7 within 96 h was 100.00, 74.56, and 63.59% at C/N of 2.0, pH of 7.0, Mn(II) of 20 mg L^-1, temperature of 30.0 °C, and TC of 0.2 mg L^-1. SEM illustrated that biogenic manganese oxides (BMO) was petal-like, XRD and XPS analyses confirmed that MnO₂ was the main component of BMO. Besides, the maximum adsorption capacity of BMO for TC was 52.21 mg g^-1. FTIR detected the changes in TC adsorption by BMO. Pseudo-second-order model (R² = 0.994) explained the adsorption kinetics of TC on BMO and Langmuir isotherm model (R² = 0.983) suggested that it was homogeneous adsorption, thermodynamics data (ΔG < 0, ΔH = 18.31 kJ mol^-1, ΔS = 72.8 J (mol*K)^-1) confirmed that adsorption was endothermic and spontaneous.

Effects of green synthesized and commercial nZVI on crystal violet degradation by Burkholderia vietnamiensis C09V: Dose-dependent toxicity and biocompatibility

The increasingly common remedial application of nanoscale zero-valent iron (nZVI) to alleviate specific contaminant issues may inadvertently lead to nZVI accumulation in wastewater. This is a potential concern, because the effect of nZVI on the common microbes essential for wastewater biotreatment is not known. This is further complicated when there are many ways available to synthesize nZVI, which may interreact with bacteria differently. Thus, in this study, the different effects of nZVI synthesized by Eucalyptus leaves (EL-nZVI) and a commercially synthesized nZVI on the biodegradation of crystal violet by Burkholderia vietnamiensis C09V (B.V. C09V) was studied. At high dose (1000 mg/L), EL-nZVI and commercial nZVI both significantly inhibited the removal of crystal violet by B.V. C09V, decreasing removal rates by 10.5 and 13.1% respectively. Optical density (OD₆₀₀) and soluble protein assays indicated that the growth of B.V. C09V improved under low doses (100 mg/L), but remained inhibited under high doses (500 and 1000 mg/L) of both commercial and EL-nZVI. Enzymes were also sensitive to nZVI, where the commercial variant exerted a greater effect on both the activity of lactate dehydrogenase (LDH) and superoxide dismutase (SOD) than EL-nZVI, indicating that EL-nZVI was less toxic than commercial nZVI. LIVE/DEAD staining also showed that the number of apoptotic cells was significantly higher when exposed to commercial nZVI rather than EL-nZVI. Furthermore, scanning electron microscopy (SEM) confirmed that direct contact between nZVI and cells at 1000 mg/L nZVI caused cell membrane disruption. Whereas, at 100 mg/L EL-nZVI, B.V. C09V grew better due to the formation of dense biofilms around the suspended EL-nZVI at a. Fourier transform infrared spectra (FTIR), confirmed an abundance of oxygen-containing functional groups on the surface of EL-nZVI which provided better biocompatibility than commercial nZVI. Overall, while dose was the most significant factor influencing nZVI toxicity, surface composition and morphology was also important. These new findings suggest chemical synthesis of metal nanoparticles should be replaced by biosynthetic routes to maintain viable microbial pollution during wastewater treatment.

Microbially induced calcium precipitation based simultaneous removal of fluoride, nitrate, and calcium by Pseudomonas sp. WZ39: Mechanisms and nucleation pathways

A simultaneous denitrifying and mineralizing bacterium, Pseudomonas sp. WZ39 was isolated for fluoride (F^-), nitrate (NO₃^--N), and calcium (Ca²⁺) removal. Strain WZ39 exhibited a remarkable defluoridation efficiency of 87.49% under a pH of 6.90, F^- and Ca²⁺ concentration of 1.99 and 201.88 mg L^-1, respectively. EEM, SEM-EDS, XRD, and FTIR analyses elucidated the chemical adsorption and co-precipitation with calcium salt contributed to the removal of F^-. The mechanisms of biomineralization were also investigated by determining the role of bound and unbound extracellular polymeric substances (EPS), cell wall, and calcium channel in nucleation. The results showed that bacteria can promote nucleation on the templates of cell walls or EPS through the electrostatic effect. The presence of the calcium channel blocker inhibited the transport of intracellular Ca²⁺ to the extracellular environment. The outcome of the present research can provide a theoretical basis for the understanding of MICP phenomenon and the efficient treatment of F^- containing groundwater.

Effect of aerobic/anoxic duration on the performance, microbial activity and microbial community of sequencing batch biofilm reactor treating synthetic mariculture wastewater

The effect of aerobic/anoxic duration on the performance, microbial community and enzymatic activity of sequencing batch biofilm reactor (SBBR) were investigated in treating mariculture wastewater. The microbial oxygen uptake rate and nitrifying rate gradually decreased with the aerobic/anoxic duration from 120/210 to 30/300 min, whereas the nitrite reducing rate and nitrate reducing rate had the opposite results. The activities of dehydrogenase, ammonia monooxygenase and nitrite oxidoreductase gradually decreased with the aerobic/anoxic duration from 120/210 to 30/300 min, but the activities of nitrate reductase and nitrite reductase had a gradual increment. The microbial nitrogen removal rates had similar changing trends to their corresponding enzymatic activities at different aerobic/anoxic duration. The variation of aerobic/anoxic duration obviously affected the microbial richness and diversity of SBBR. The co-occurrence, keystone taxa and significant difference of microbial community had some changes with the aerobic/anoxic duration from 120/210 to 30/300 min.

Biological stimulation with Fe(III) promotes the growth and aerobic denitrification of Pseudomonas stutzeri T13

Certain metal ions can contribute to the functional microorganisms becoming dominant by stimulating their metabolism and activity. Therefore, Pseudomonas stutzeri T13 was used to investigate the impacts of biological stimulation with certain metal ions on aerobic denitrifying bacteria. Results showed that with the addition of 0.036 mmol/L Fe³⁺ ions, the nitrogen-assimilation capacity of P. stutzeri T13 significantly increased by 43.99% when utilizing ammonium as the sole nitrogen source. Kinetic models were applied to analyze the role of Fe³⁺ ions in the growth, and results indicated that increasing Fe³⁺ ion concentrations decreased the decay rate. The maximum nitrate reduction rate increased from 9.55 mg-N L^-1 h^-1 to 19.65 mg-N L^-1 h^-1 with Fe³⁺ ion concentrations increasing from 0.004 to 0.036 mmol/L, which was due to the increased level of napA gene transcription and activity of nitrate reductase. This study provides a theoretical foundation for further understanding of the mechanism of Fe³⁺ ion stimulation of aerobic denitrification, benefiting the practicable application of aerobic denitrifiers.

Effects of copper and florfenicol on nirS- and nirK-type denitrifier communities and related antibiotic resistance in vegetable soils

Denitrification play an important role in nitrogen cycle and is affected by veterinary drugs entering agricultural soils. In the present study, the effects of copper and florfenicol on denitrification, related antibiotic resistance and environmental variables were characterized using real-time quantitative PCR (qPCR) and amplicon sequencing in a short-term (30 d) soil model experiment. Drug additions significantly decreased the nirS gene abundance (P < 0.05) but maximized the abundance of gene nirK in soil containing florfenicol and moderate copper levels (150 mg kg^-1). Surprisingly, copper additions decreased the fexB gene abundance, however, the abundance of gene pcoD significantly increased in soils containing florfenicol, moderate copper levels (150 mg kg^-1), and florfenicol and low copper levels (30 mg kg^-1), respectively (P < 0.05). Overall, the nirK-type community composition was more complex than that of nirS-type but Proteobacteria predominated (> 90%) in both communities. Correlation analysis indicated that the gene abundance of fexB was highly correlated with NH₄⁺-N (P < 0.05) and NO₃^--N (P < -0.01), and floR gene abundance was positively correlated with nirK (P < 0.01). Besides, the abundance of nirS-type genera Bradyrhizobium and Pseudomonas were obviously related to total organic matter (TOM), total nitrogen (TN) or total phosphorus (TP) (P < 0.05), while the abundance of nirK-type Rhizobium, Sphingomonas and Bosea showed a significantly correlated with TOM, TN or copper contents (P < 0.05). Taken together, copper and florfenicol contamination increased the possibility of durg resistance genes spread in agricultural soils through nitrogen transformation.

Nitrogen removal characteristics of a novel heterotrophic nitrification and aerobic denitrification bacteria, Alcaligenes faecalis strain WT14

Alcaligenes faecalis strain WT14 is heterotrophic nitrification and aerobic denitrification bacterium, newly isolated from a constructed wetland, and its feasibility in nitrogen removal was investigated. The result showed sodium citrate was more readily utilized by WT14 as a carbon source. The response surface methodology model revealed the highest total nitrogen removal by WT14 occurred at 20.3 °C, 113.5 r·min^-1, C/N 10.8, and pH 8.4. Under adapted environmental conditions, up to 55.9 mg·L^-1·h^-1 of ammonium nitrogen (NH₄⁺-N) was removed by WT14, and its NH₄⁺-N tolerance ability reached 2000 mg·L^-1. In addition to the reported high NH₄⁺-resistance of Alcaligenes faecalis, WT14 multiplied fast and had strong nitrate or nitrite removal capacity when high strength nitrate or nitrite was provided as the single nitrogen source; which differed from other Alcaligenes faecalis species. These results show WT14 is a novel strain of Alcaligenes faecalis and its nitrogen removal pathway will be carried out in the further study.

Application of a heavy metal-resistant Achromobacter sp. for the simultaneous immobilization of cadmium and degradation of sulfamethoxazole from wastewater

Little information is available regarding the kinetics, products, and pathways of simultaneous SMX degradation and Cd(II) immobilization from wastewater. In this study, a novel bacterium (Achromobacter sp. L3) with SMX degradation and Cd(II) immobilization capabilities was isolated. The boundary conditions of SMX degradation were as follows: initial pH 6-8, temperature 25-30 °C, and SMX concentration 10-40 mg/L^-1. The boundary conditions of Cd(II) immobilization were as follows: initial pH 7-9, temperature 25-35 °C, and SMX concentration 10-30 mg/L^-1. The maximum SMX degradation and Cd(II) removal were 91.98% and 100%, respectively. The SMX degradation and Cd(II) immobilization data fitted well with the pseudo-first-order kinetic model, indicating that the two pollutants conform to the same degradation rule. Moreover, the microbial degradation, sediment adsorption, and intermediates identified in the experiments were used to explore the mechanisms of SMX and Cd(II) removal. These results indicate that microbial removal and sediment adsorption play equally important roles in Cd(II) immobilization; however, microbial degradation plays a decisive role in SMX degradation. Furthermore, the relationship between aerobic denitrification, SMX degradation, and Cd(II) immobilization was proposed. These results may provide valuable insights for treatment of wastewater polluted by antibiotics and heavy metals.

A critical review of aerobic denitrification: Insights into the intracellular electron transfer

Aerobic denitrification is a novel biological nitrogen removal technology, which has been widely investigated as an alternative to the conventional denitrification and for its unique advantages. To fully comprehend aerobic denitrification, it is essential to clarify the regulatory mechanisms of intracellular electron transfer during aerobic denitrification. However, reports on intracellular electron transfer during aerobic denitrification are rather limited. Thus, the purpose of this review is to discuss the molecular mechanism of aerobic denitrification from the perspective of electron transfer, by summarizing the advancements in current research on electron transfer based on conventional denitrification. Firstly, the implication of aerobic denitrification is briefly discussed, and the status of current research on aerobic denitrification is summarized. Then, the occurring foundation and significance of aerobic denitrification are discussed based on a brief review of the key components involved in the electron transfer of denitrifying enzymes. Moreover, a strategy for enhancing the efficiency of aerobic denitrification is proposed on the basis of the regulatory mechanisms of denitrification enzymes. Finally, scientific outlooks are given for further investigation on aerobic denitrification in the future. This review could help clarify the mechanism of aerobic denitrification from the perspective of electron transfer.

Simultaneous nitrate, nickel ions and phosphorus removal in a bioreactor containing a novel composite material

This study presents the novel composite material TMCC/PAA/SA@Fe(TPSA), a bacteria immobilized carrier for use in bioreactor systems to enhance the simultaneous removal efficiency of nitrate, Ni(II) and phosphorus. The influence of various operational factors were evaluated on the performance of nitrate, phosphorus and Ni(II) removal. Results demonstrate that under optimum conditions of an hydraulic retention time (HRT) of 8 h and pH 7.0, nitrate and phosphorus removal reached nearly 100% and 61.7%, respectively. When the initial Ni(II) concentration was 1 mg/L, approximately 100% Ni(II) removal efficiency was achieved. Furthermore, the morphology and components of the TPSA immobilized bacterial pellets were analyzed to investigate the mechanism of simultaneous nitrate, Ni(II) and phosphorus removal. Microbial metabolism was more active in the experimental reactor compared with control, although high concentrations of Ni(II) could inhibit bacterial activity.

Effects of carbon nanotube on denitrification performance of Alcaligenes sp. TB: Promotion of electron generation, transportation and consumption

Multi-walled carbon nanotubes (MWCNTs) promote biodegradation in water treatment, but the effect of MWCNT on denitrification under aerobic conditions is still unclear. This investigation focused on the denitrification performance of MWCNT and its toxic effects on Alcaligenes sp. TB which showed that 30 mg/L MWCNTs increased NO₃^- removal efficiency from 84% to 100% and decreased the NO₂^-and N₂O accumulation rates by 36% and 17.5%, respectively. Nitrite reductase and nitrous oxide reductase activities were further increased by 19.5% and 7.5%, respectively. The mechanism demonstrated that electron generation (NADH yield) and electron transportation system activity increased by 14.5% and 104%, respectively. Cell membrane analysis found that MWCNT caused an increase in polyunsaturated fatty acids, which had positive effects on electron transportation and membrane fluidity at a low concentration of 96 mg/kg but caused membrane lipid peroxidation and impaired membrane integrity at a high concentration of 115 mg/L. These findings confirmed that MWCNT affects the activity of Alcaligenes sp. TB and consequently enhances denitrification performance.

Role of heterotrophic aerobic denitrifying bacteria in nitrate removal from wastewater

With the increase in industrial and agricultural activities, a large amount of nitrogenous compounds are released into the environment, leading to nitrate pollution. The perilous effects of nitrate present in the environment pose a major threat to human and animal health. Bioremediation provides a cost-effective and environmental friendly method to deal with this problem. The process of aerobic denitrification can reduce nitrate compounds to harmless dinitrogen gas. This review provides a brief view of the exhaustive role played by aerobic denitrifiers for tackling nitrate pollution under different ecological niches and their dependency on various environmental parameters. It also provides an understanding of the enzymes involved in aerobic denitrification. The role of aerobic denitrification to solve the issues faced by the conventional method (aerobic nitrification-anaerobic denitrification) in treating nitrogen-polluted wastewaters is elaborated.