Aerobic Denitrification Ability Research Articles

Simultaneous removal of calcium, phosphorus, and bisphenol A from industrial wastewater by Stutzerimonas sp. ZW5 via microbially induced calcium precipitation (MICP): Kinetics, mechanism, and stress response

The biological treatment of complex industrial wastewater has always been a research hotspot. In this experiment, a salt-tolerant strain Stutzerimonas sp. ZW5 with aerobic denitrification and biomineralization ability was screened, and the optimum conditions of ZW5 were explored by kinetics. The removal efficiencies of nitrate (NO3--N), bisphenol A (BPA), phosphorus (PO43--P), and calcium (Ca2+) were 94.47%, 100%, 98.87%, and 83.04%, respectively. The removal mechanism of BPA was the adsorption of microbial induced calcium precipitation (MICP) and extracellular polymeric substances (EPS). Moreover, BPA could weaken the electron transfer ability and growth metabolism of microorganisms and affect the structure of biominerals. At the same time, the stress response of microorganisms would increase the secretion of EPS to promote the process of biomineralization. Through nitrogen balance experiments, it was found that the addition of BPA would lead to a decrease in the proportion of gaseous nitrogen. This experiment offers novel perspectives on the treatment of industrial effluents and microbial stress response. Environmental ImplicationNitrate and PO43--P in industrial wastewater led to eutrophication of water bodies, and BPA has a negative effect on the endocrine of aquatic organisms. In this experiment, a salt-tolerant strain ZW5 capable of efficient aerobic denitrification and biomineralization was screened. The strain ZW5 produced alkalinity in denitrification to promote the MICP, and BPA was adsorbed by hydrogen bonding and pore interaction through MICP and EPS. It was further studied that BPA would cause strain ZW5 to secrete more EPS and improve the MCIP. This experiment offers new insights into industrial wastewater treatment and the stress response of microorganisms.

Hydroxylamine supplementation accelerated the rates of cell growth, aerobic denitrification and nitrous oxide emission of Pseudomonas taiwanensis EN-F2

Hydroxylamine can disrupt the protein translation process of most reported nitrogen-converting bacteria, and thus hinder the reproduction of bacteria and nitrogen conversion capacity. However, the effect of hydroxylamine on the denitrification ability of strain EN-F2 is unclear. In this study, the cell growth, aerobic denitrification ability, and nitrous oxide (N2O) emission by Pseudomonas taiwanensis were carefully investigated by addition of hydroxylamine at different concentrations. The results demonstrated that the rates of nitrate and nitrite reduction were enhanced by 2.51 and 2.78 mg/L/h after the addition of 8.0 and 12.0 mg/L hydroxylamine, respectively. The N2O production from nitrate and nitrite reaction systems were strongly promoted by 4.39 and 8.62 mg/L, respectively, through the simultaneous acceleration of cell growth and both of nitrite and nitrate reduction. Additionally, the enzymatic activities of nitrate reductase and nitrite reductase climbed from 0.13 and 0.01 to 0.22 and 0.04 U/mg protein when hydroxylamine concentration increased from 0 to 6.0 and 12.0 mg/L. This may be the main mechanism for controlling the observed higher denitrification rate and N2O release. Overall, hydroxylamine supplementation supported the EN-F2 strain cell growth, denitrification and N2O emission rates.

Insight into the Cold Adaptation Mechanism of an Aerobic Denitrifying Bacterium: Bacillus simplex H-b.

Psychrophilic bacteria with aerobic denitrification ability have promising potential for application in nitrogen-contaminated wastewater treatment, especially under cold conditions. A better understanding of the cold adaptation mechanism during aerobic denitrification would be beneficial for the practical application of this type of functional bacterium. In this study, Bacillus simplex H-b with good denitrification performance at 5°C was used to investigate the corresponding cold tolerance mechanism. Transcriptomics and nitrogen removal characterization experiments were conducted at different temperatures (5°C, 20°C, and 30°C). At low temperatures, more nitrogen was utilized for assimilation, accompanied by the accumulation of ATP and extracellular polymeric substances (EPS), rather than transforming inorganic nitrogen in the dissimilation pathway. In addition, the proportion of unsaturated fatty acids was higher in strains cultured at low temperatures. At the molecular level, the adjustment of membrane transport, synthesis of cofactors and vitamins, and transcriptional regulators might contribute to the survival of the strain under cold conditions. Moreover, nucleotide precursor synthesis, translation, and oxidative and temperature stress response mechanisms also enhanced the resistance of strain H-b to low temperatures. The results suggest that combining multiple regulatory mechanisms and synergistic adaptation to cold stress enabled the growth and relatively high nitrogen removal rate (27.22%) of strain H-b at 5°C. By clarifying the mechanism of regulation and cold resistance of strain H-b, a theoretical foundation for enhancing the application potential of this functional bacterium for nitrogen-contaminated wastewater treatment was provided. IMPORTANCE The newly isolated aerobic denitrifying bacterium Bacillus simplex H-b removed various forms of inorganic nitrogen (nitrate, nitrite, and ammonium) from wastewater, even when the temperature was as low as 5°C. Although this environmentally functional bacterium has been suggested as a promising candidate for nitrogen-contaminated water treatment at low temperatures, understanding its cold adaptation mechanism during aerobic denitrification is limited. In this study, the cold tolerance mechanism of this strain was comprehensively explained. Furthermore, a theoretical basis for the practical application of this type of functional bacterium for nitrogen removal in cold regions is provided. The study expands our understanding of the survival strategy of psychrophilic bacteria and hence supports their further utilization in wastewater treatment applications.

Characteristics of a novel heterotrophic nitrification and aerobic denitrification bacterium and its bioaugmentation performance in a membrane bioreactor

A novel bacteria with heterotrophic nitrification and aerobic denitrification ability was obtained from a membrane bioreactor (MBR) and identified as Acinetobacter sp. TSH1. The nitrogen removal characteristics, nitrogen balance analysis, kinetic characteristics, and enhanced biological treatment in MBR of the novel isolated strain TSH1 were determined. Results showed that strain TSH1 could remove approximately 96.6% of NH4+-N, 82.9% of NO2−-N and 98.7% of NO3−-N in 24 h, and the corresponding maximum removal rates were 3.64 mg-N/(L·h), 1.77 mg-N/(L·h) and 3.94 mg-N/(L·h). The nitrogen balance analysis indicated that most of NH4+-N (62.6%) and NO3−-N (71.9%) were transformed to gaseous nitrogen. The kinetic experiments showed that strain TSH1 had a high Km of 151.64 mg-NH4+-N/L and 203.25 mg-NO3--N/L. The enhanced biological treatment of synthetic wastewater in MBR showed that the strain TSH1 can significantly improve the nitrogen removal efficiency.

Simultaneous nitrification and aerobic denitrification by a novel isolated Ochrobactrum anthropi HND19

The study aimed to isolate a novel strain with heterotrophic nitrification and aerobic denitrification ability and evaluate the nitrogen removal characteristics. Results showed that Ochrobactrum anthropi HND19 could remove approximately 98.6% of NH4+-N (104.3 mg·L-1) and 97.6% of NO3−-N (98.6 mg·L-1), and the removal rates achieved 4.28 and 4.01 mg-N/(L·h) by heterotrophic nitrification and aerobic denitrification. The optimal incubate conditions of strain HND19 were 120 rpm (shaking speed), 5 ‰ (salinity), 30 °C (temperature), 7.5 (C/N ratio) with sodium acetate as carbon resource. And the removal efficiency of the total nitrogen (TN) realized 73.4% under the optimal conditions. Functional genes (hao, napA, nirK, norB, and nosZ) involved in the nitrogen removal processes were successfully amplified from strain HND19. These findings indicate that the strain HND19 possesses great application feasibility in treating wastewater with high-intensity nitrogen.

Combined Remediation of Eutrophic Water by Phoslock® and Aerobic Denitrifying Bacteria

Nitrogen and phosphorus are the leading causes of water eutrophication, and it is challenging to remove nitrogen and phosphorus effectively through a single water remediation method. In this study, an aerobic denitrifying bacterium (AD-19) isolated from eutrophic water was used to construct an immobilized biofilm and combined with Phoslock® to remove nitrogen and phosphorus from the water. The phosphorus control efficiency of Phoslock®, nitrogen removal performance of the denitrifying bacteria, and combined remediation performance for the eutrophic water were studied. The results demonstrated that the removal rate of PO43--P in the simulated eutrophic water reached 95% with a dosing ratio of 80 (mass ratio of Phoslock® to PO43--P), and phosphorus release from sediment was effectively inhibited at the same time. Strain AD-19, which was identified as Pseudomonas sp. Using the 16S rDNA method, had a good heterotrophic nitrification and aerobic denitrification ability, and more than 97% of the nitrogen was removed when NH4+-N or NO3--N was used as the nitrogen source. The feasibility of the combined remediation of the eutrophic water was demonstrated using a lake simulation device. Furthermore, this technique was used to restore a eutrophic pond in a park in Wuhan city. After 16 days of treatment, the water quality indices for nitrogen and phosphorus were improved from worse than Grade Ⅴ to Grade Ⅲ (GB 3838-2002, Ministry of Environmental Protection of China, 2002) and remained stable for more than 270 days, indicating that Phoslock® combined with the immobilized biofilm could quickly and effectively restore eutrophic water as well as maintain the water quality for long periods.

Simultaneous aerobic removal of phosphorus and nitrogen by a novel salt-tolerant phosphate-accumulating organism and the application potential in treatment of domestic sewage and aquaculture sewage

Phosphorus (P) and nitrogen (N) pollution are the worldwide challenging problem. In the present study, a new salt-tolerant phosphate-accumulating organism (PAO) was isolated and identified as Bacillus subtilis GHSP10. Strain GHSP10 did not produce hemolysin and showed high susceptibility to antibiotics. The favorable phosphorus removal C/N ratios, P/N ratios, temperature, salinities, pH values and shaking speeds of strain GHSP10 were 10–20, 0.1–0.2, 28 °C, 0–3%, 7.5–8.5 and 100–250 r/min. Besides, strain GHSP10 could conduct heterotrophic nitrification–aerobic denitrification and the maximal removal efficiencies of ammonium, nitrite and nitrate were 99.52%, 81.10% and 95.84% respectively. Moreover, the phosphorus removal process of strain GHSP10 was achieved under entirely aerobic conditions, and glycogen and poly-β-hydroxybutyrate could provide energy source for the phosphorus removal process of strain GHSP10. The amplification of ppk, hao, napA, narG, nirK genes as well as the expression of polyphosphate kinase helped to reveal the removal pathways of phosphorus and nitrogen, providing theoretical support for the phosphorus removal, nitrification and aerobic denitrification abilities of strain GHSP10. Furthermore, efficient removal of phosphorus and nitrogen from both domestic sewage and aquaculture sewage could be accomplished by strain GHSP10. This study may provide a hopeful candidate strain for simultaneous removal of phosphorus and nitrogen pollution from both freshwater sewage and saline sewage.

Nitrogen Removal Performance and Nitrogen/Carbon Balance of Oligotrophic Aerobic Denitrifiers

Due to the problems of low nitrogen removal efficiency and unclear electron transfer during biological denitrification treatment of an oligotrophic drinking water reservoir, the nitrogen removal characteristics, environmental adaptability, and electron transfer during denitrification were systematically studied using the aerobic denitrifier Acinetobacter junii ZMF5, which has efficient nitrogen removal ability. The results showed that:① Strain ZMF5 exhibited efficient heterotrophic nitrification and aerobic denitrification ability, with an ammonia removal rate of 0.211 mg·(L·h)-1 and a nitrate removal rate of 0.236 mg·(L·h)-1, and the nitrification intermediates were not accumulated during the treatment process. ② According to analysis of the nitrogen removal efficiency and growth kinetics of strain ZMF5, the strain can effectively utilize different types of carbon source, and show efficient nitrogen removal efficiency under the conditions of low C/N, low pH, and low temperature. ③ Analysis of nitrogen balance showed that carboxylate compound, compared with carbohydrate, could promote the process of aerobic denitrification and change the nitrogen removal pathway of strain ZMF5, i.e., 38.81% of nitrogen was transformed into gas, higher than the 29.81% for assimilation. ④ Analysis of carbon balance indicated that most carbon sources were used as electron donors in the denitrification process, but fewer electrons were used for nitrate reduction, and with respect to different carbon sources, electron transfer to the nitrate respiratory chain was regulated by different reduction potentials, electron donor abundance, and molecular weight. Acinetobacter junii ZMF5 could be used to control nitrogen pollution in drinking water reservoirs.

Characterization of aerobic denitrification genome sequencing of Vibrio parahaemolyticus strain HA2 from recirculating mariculture system in China

A novel halophilic bacterium capable of heterotrophic nitrification–aerobic denitrification was isolated from the polyethylene fiber of a recirculating aquaculture system and identified Vibrio parahaemolyticus HA2. In this study, the degradation rate of ammonia nitrogen, nitric nitrogen and nitrite nitrogen were 99.06%, 97.35% and 34.91% respectively, and the pH increases furtherly proved existing denitrification during the growth of strain HA2. Genome sequencing showed that the ammonia monooxygenase (AMO), periplasmic nitrate reductase (NAP), nitrite reductase (NIR), nitric oxide reductase (NOR), hydroxylamine oxidase (HAO) and nitrous oxide reductase (N2OR) of strain HA2 were associated with the progress of nitrification and denitrification. Utilization of nitrite and nitrate as well as existence of NAP gene further proved aerobic denitrification ability of strain HA2. The aim is indicating great potential of strain HA2 for future full-scale applications in aquaculture

Nitrate removal characteristics and 13C metabolic pathways of aerobic denitrifying bacterium Paracoccus denitrificans Z195

Strain Z195 was isolated and identified as Paracoccus denitrificans. Z195 exhibited efficient aerobic denitrification and carbon removal abilities, and removed 93.74% of total nitrogen (TN) and 97.81% of total organic carbon.71.88% of nitrogen was lost as gaseous products.13C-metabolic flux analysis revealed that 95% and 132% of the carbon fluxes entered the Entner-Doudoroff (ED) pathway and tricarboxylic acid (TCA) cycle, respectively. Electrons produced by carbon metabolism markedly promoted the processes of nitrogen metabolism process and aerobic respiration. A response surface methodology model demonstrated that the optimal conditions for the maximum TN removal were a C/N ratio of 7.47, shaking speed of 108 rpm, temperature of 31 °C and initial pH of 8.02. Additionally, the average TN and chemical oxygen demand removal efficiencies of raw wastewater were 89% and 91%, respectively. The results give new insight for understanding metabolic flux analysis of aerobic denitrifying bacteria.

Denitrification Process and N2O Production Characteristics of Heterotrophic Nitrifying Bacterium Pseudomonas aeruginosa YL

Because of the massive discharge of nitrogenous wastewater, the eutrophication of a water body is becoming increasingly serious, and how to effectively remove nitrogen from this wastewater remains an urgent problem to be solved. In this study, due to disadvantages in the traditional biological nitrogen removal process, such as complex and long procedures, high energy consumption, weak impact resistance, and N2O release, the nitrogen removal theory by heterotrophic nitrification was further analyzed by discussing the physiological-biochemical, heterotrophic nitrification-aerobic denitrification, and N2O production characteristics of a high-efficiency heterotrophic nitrifying bacteria Pseudomonas aeruginosa YL. Results show that the strain YL had an eminent heterotrophic nitrification and aerobic denitrification ability, and NH4+-N, NO2--N, and NO3--N with concentration of 100 mg·L-1 could be completely removed during the 24-hour incubation period. There was almost no intermediate product in the process of heterotrophic nitrification, however when NO3--N was used as nitrogen source, the accumulation of NO2--N reached 25.55 mg·L-1. Meanwhile, the successful expression of denitrification genes napA, nirK, and nosZ further confirmed the aerobic denitrification ability of strain YL. Gaseous nitrogen products accounted for about 30%-40% of removed TN in the heterotrophic nitrification-aerobic denitrification process by strain YL, and N2 was the main denitrification product. When NH4+-N, NO2--N, and NO3--N were used as the sole nitrogen source, N2 production amounted to 3.46, 3.49, and 3.36 mg, respectively. In contrast, only small amounts of N2O were produced in the denitrification process by strain YL, and the total amount was 6.63 μg when NH4+-N was the nitrogen source, which was much lower than in the cases of NO2--N and NO3--N as the sole nitrogen source. In addition, high C/N, low pH, high temperature, high NH4+-N, and high NO2--N conditions could result in more N2O generation. Nevertheless, most environmental factors had little effect on N2O production of strain YL, and the maximum N2O production was significantly lower than that of short-cut nitrification system and autotrophic nitrification system. These results demonstrated that strain YL exhibited excellent abilities of nitrogen removal, N2O emission control, and tolerance to environmental conditions, and could be an effective candidate for treating wastewater without secondary air pollution.

APPLICATION OF ALCALIGENES FAECALIS NO. 4 FOR TREATMENT OF HIGH-STRENGTH AMMONIUM WASTEWATER

Biological ammonium removal from wastewater requires coupling of nitrification and denitrification processes in respective aerobic and anaerobic conditions. This difference in environmental requirements pose a big challenge in the design of systems intended to effect both nitrification and denitrification processes. Alcaligenes faecalis strain No. 4, however, has both heterotrophic nitrification and aerobic denitrification abilities in aerobic conditions, eliminating the need to provide anaerobic conditions for denitrification. Batch and continuous experiments in a mixed culture of A. faecalis No. 4 and activated sludge were performed to examine ammonium removal and microbial stability of No. 4 in aerobic reactors. At an inflow ammonium load of 500 mg L-1 d-1 in continuous experiment, the ammonium removal rate (21 mg L-1 h-1), under No. 4, was approximately 2 times higher than that of the control (i.e., without No. 4), and the denitrification ratio was approximately 66%. The proportion of intracellular nitrogen converted from removed ammonium in the continuous mixed culture was reduced, compared to control batch and continuous cultures. These results demonstrated stable growth as well as the heterotrophic nitrification-aerobic denitrification abilities of No. 4 in activated sludge systems.

The Nitrogen-Removal Efficiency of a Novel High-Efficiency Salt-Tolerant Aerobic Denitrifier, Halomonas Alkaliphile HRL-9, Isolated from a Seawater Biofilter.

Aerobic denitrification microbes have great potential to solve the problem of NO3−-N accumulation in industrialized recirculating aquaculture systems (RASs). A novel salt-tolerant aerobic denitrifier was isolated from a marine recirculating aquaculture system (RAS) and identified as Halomonas alkaliphile HRL-9. Its aerobic denitrification performance in different dissolved oxygen concentrations, temperatures, and C/N ratios was studied. Investigations into nitrogen balance and nitrate reductase genes (napA and narG) were also carried out. The results showed that the optimal conditions for nitrate removal were temperature of 30 °C, a shaking speed of 150 rpm, and a C/N ratio of 10. For nitrate nitrogen (NO3−-N) (initial concentration 101.8 mg·L−1), the sole nitrogen source of the growth of HRL-9, the maximum NO3−-N removal efficiency reached 98.0% after 24 h and the maximum total nitrogen removal efficiency was 77.3% after 48 h. Nitrogen balance analysis showed that 21.7% of NO3−-N was converted into intracellular nitrogen, 3.3% of NO3−-N was converted into other nitrification products (i.e., nitrous nitrogen, ammonium nitrogen, and organic nitrogen), and 74.5% of NO3−-N might be converted to gaseous products. The identification of functional genes confirmed the existence of the napA gene in strain HRL-9, but no narG gene was found. These results confirm that the aerobic denitrification strain, Halomonas alkaliphile HRL-9, which has excellent aerobic denitrification abilities, can also help us understand the microbiological mechanism and transformation pathway of aerobic denitrification in RASs.

Simultaneous removal of nitrogen and phosphorous by heterotrophic nitrification-aerobic denitrification of a metal resistant bacterium Pseudomonas putida strain NP5

A novel strain NP5 with efficient heterotrophic nitrification, aerobic denitrification and phosphorus accumulation ability was isolated and identified as Pseudomonas putida strain NP5. The removed ammonium and phosphate were mainly converted into intracellular components by assimilation, and negligible nitrification intermediates and N2O were accumulated during heterotrophic nitrification. In addition, the optimal conditions for nutrient removal were: succinate as carbon source, C/N 10, P/N 0.2, temperature 30 °C, salinity 0% and shaking speed 160 rpm. Besides, strain NP5 possessed an exceptional heavy metal and nanoparticles resistance. Cr6+ was found to be the most toxic among the tested metals, and it could be removed simultaneously. Moreover, an obvious phosphorus release was observed under anaerobic condition, and repeated exposure to the anaerobic/aerobic conditions could significantly improve the nutrient removal. Furthermore, the successful expression of key enzymes for nitrogen and phosphorous removal provided additional evidence for possibility of simultaneous nitrification, denitrification and phosphorus removal.

Characterization of Aerobic Denitrifying Bacterium Pseudomonas mendocina Strain GL6 and Its Potential Application in Wastewater Treatment Plant Effluent.

To remove nitrate in wastewater treatment plant effluent, an aerobic denitrifier was newly isolated from the surface flow constructed wetland and identified as Pseudomonas mendocina strain GL6. It exhibited efficient aerobic denitrification ability, with the nitrate removal rate of 6.61 mg (N)·L−1·h−1. Sequence amplification indicated that the denitrification genes napA, nirK, norB, and nosZ were present in strain GL6. Nitrogen balance analysis revealed that approximately 74.5% of the initial nitrogen was removed as gas products. In addition, the response surface methodology experiments showed that the maximum removal of total nitrogen occurred at pH 7.76, C/N ratio of 11.2, temperature of 27.8 °C, and with shaking at 133 rpm. Furthermore, under the optimized cultivation condition, strain GL6 was added into wastewater treatment plant effluent and the removal rates of nitrate nitrogen and total nitrogen reached 95.6% and 73.6%, respectively. Thus, P. mendocina strain GL6 has high denitrification potential for deep improvement of effluent quality.

Denitrification-Potential Evaluation and Nitrate-Removal-Pathway Analysis of Aerobic Denitrifier Strain Marinobacter hydrocarbonoclasticus RAD-2

An aerobic denitrifier was isolated from a long-term poly (3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV-supported denitrification reactor that operated under alternate aerobic/anoxic conditions. The strain was identified as Marinobacter hydrocarbonoclasticus RAD-2 based on 16S rRNA-sequence phylogenetic analysis. Morphology was observed by scanning electron microscopy (SEM), and phylogenetic characteristics were analyzed with the API 20NE test. Strain RAD-2 showed efficient aerobic denitrification ability when using NO3−-N or NO2−-N as its only nitrogen source, while heterotrophic nitrification was not detected. The average NO3−-N and NO2−-N removal rates were 6.47 mg/(L·h)and 6.32 mg/(L·h), respectively. Single-factor experiments indicated that a 5:10 C/N ratio, 25–40 °C temperature, and 100–150 rpm rotation speed were the optimal conditions for aerobic denitrification. Furthermore, the denitrifying gene napA had the highest expression on a transcriptional level, followed by the denitrifying genes nirS and nosZ. The norB gene was found to have significantly low expression during the experiment. Overall, great aerobic denitrification ability makes the RAD-2 strain a potential alternative in enhancing nitrate management for marine recirculating aquaculture system (RAS) practices.

Biological nitrogen removal and metabolic characteristics of a novel aerobic denitrifying fungus Hanseniaspora uvarum strain KPL108

A novel aerobic denitrifying fungal strain KPL108 was isolated from the sediment of Jinpen drinking water reservoir and identified as Hanseniaspora uvarum. Strain KPL108 removed 99% of nitrate without nitrite accumulation under aerobic conditions, while the total organic carbon removal efficiency was 93%. KPL108 expressed fungal specific denitrifying gene p450nor. Nitrogen balance exhibited that approximately 92% of the initial nitrate was removed as gaseous products. Based on 13C-isotope labeling tracer, pentose phosphate pathway and tricarboxylic acid cycle were highly active in intracellular central carbon metabolism of strain KPL108. Response surface methodology revealed that the maximum total nitrogen removal efficiency occurred with the optimized parameters: C/N ratio of 6.4, pH of 8.2, 28.5 °C and 109.7 rpm. Collectively, the results from the present study indicate that strain KPL108 has aerobic denitrification ability, which has a great potential application for nitrogenous wastewater treatment.

Substrates removal and growth kinetic characteristics of a heterotrophic nitrifying-aerobic denitrifying bacterium, Acinetobacter harbinensis HITLi7T at 2 °C

In order to investigate the heterotrophic nitrification and aerobic denitrification ability of Acinetobacter harbinensis HITLi7T at 2 °C, both the growth parameters and substrates utilization characteristics were tested and appropriated kinetic models were obtained in this study. Under the initial concentration of 5 mg/L, the maximum NH4+-N and NO3−-N degradation rates were 0.076 mg NH4+-N/L/h and 0.029 mg NO3−-N/L/h, respectively. At the simultaneous presence of 2.5 mg/L NH4+-N and NO3−-N, the maximum nitrate removal rate increased to 0.054 mg NO3−-N/L/h (1.86 folds), while a slight decrease was observed in NH4+-N removal. Two double-substrate models, Contois-Contois (1) for NH4+-N and TOC, Monod-Contois (2) for NO3−-N and TOC matched well with the experimental data. The kinetic parameters were determined as μmax1 = 0.095 h−1, BA1 = 0.012 mg/L, BT1 = 0.784 g TOC/g biomass (R12 = 0.9997), and μmax2 = 0.032 h−1, KN2 = 0.375 mg/L, BT2 = 1.108 g TOC/g biomass (R22 = 0.9731) by multiple regression equation.

Nitrogen removal and metabolic profiling of a cold-adaptive and biofilm producing paddy soil bacterium Cupriavidus sp. PDN31

ABSTRACTTo assess the physiology and low temperature adaptability of the key players of nitrification and denitrification, denitrifying bacteria were isolated and characterized from the selected paddy fields. Bacterial strains belonging to Cupriavidus and Ochrobactrum sp. were explored through the selective screening of heterotrophic nitrifying and aerobic denitrifying bacteria. The direct implication of nitrate removal in the natural sample was estimated by taking the nitrate supplemented soil as well as the enriched culture. A more prominent cold-adaptive bacterium was identified as Cupriavidus sp. PDN31. The utilization of ammonium, nitrate, and nitrite and the presence of nitrous oxide reductase (nosZ) gene, catalyses the first step of the denitrification conferred its heterotrophic nitrification and aerobic denitrification ability. The ammonium, nitrate, and nitrite removal efficiency of PDN31 was found to be 92.1%, 93.5%, and 99.8%, respectively. The functional traits, evaluated from metabolizing various nitrogen substrates (Biolog) suggested its ability to utilize some sources as L-arginine, L-asparagine, L-cysteine, L-glutamic Acid, L-glutamine, L-histidine, L-citrulline and N-acetyl-L glutamic acid. The adaptive behaviour of PDN31 with its ability to remove nitrogen and induced biofilm production under low temperature regime makes it a suitable candidate among the plethora of microorganism resided in any agriculture environment.

Isolation and characterization of heterotrophic nitrifying and aerobic denitrifying Klebsiella pneumoniae and Klebsiella variicola strains from various environments.

We sought to isolate novel heterotrophic nitrifying and aerobic denitrifying Klebsiella pneumoniae and Klebsiella variicola strains from various natural environments and characterize their nitrogen removal processes. Ten novel Klebsiella strains with heterotrophic nitrification and aerobic denitrification abilities, including seven K. pneumoniae and three K. variicola, were successfully isolated from faeces, sewage, plant surfaces and sludge. A 1674-bp fragment of the hydroxylamine oxidase (hao) gene was successfully amplified from the novel strains. The removal rates of ammonium, nitrate and nitrite of the seven K. pneumoniae isolates were 96·42-97·38%, 61·27-82·78% and 100%, respectively, and the corresponding degradation ratios were 4·82-6·49 (higher than previously reported for K. pneumoniae CF-S9 and EGD-HP19-C), 1·15-1·38 and 1·48-3·33mgl-1 h-1 , respectively. The removal rates of ammonium, nitrate and nitrite of the three K. variicola isolates were 95·01-96·15%,68·60--78·37% and 100%, respectively, and the corresponding degradation ratios were 4·79-9·5, 1·14-1·74 and 1·67-4·44mgl-1 h-1 , respectively. The K. variicola strain sd-3 from sludge exhibited the best heterotrophic nitrification and aerobic denitrification abilities among the isolates. Meanwhile, the results of simultaneous nitrification and denitrification assays with all isolated strains showed that ammonium was removed prior to nitrate or nitrite. Our results indicate that K. pneumoniae and K. variicola (isolated from a novel natural environment) play an important role in the Earth's nitrogen cycle in various natural environments. This study is one of only a few works to successfully isolate K. pneumoniae with heterotrophic nitrification and aerobic denitrification abilities in various natural environments. The physiological characterization K. variicola as having abilities to heterotrophically nitrify and aerobically denitrify is the first to be reported. Moreover, this study may provide alternative microbial resources for the removal of nitrogen from wastewater.