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

Simultaneous aerobic nitrogen and phosphate removal capability of novel salt-tolerant strain, Pseudomonas mendocina A4: Characterization, mechanism and application potential

A salt-tolerant strain, Pseudomonas mendocina A4, was isolated from brackish-water ponds showing simultaneous heterotrophic nitrification-aerobic denitrification and phosphorus removal capability. The optimal conditions for nitrogen and phosphate removal of strain A4 were pH 7-8, carbon/nitrogen ratio 10, phosphorus/nitrogen ratio 0.2, temperature 30 °C, and salinity range of 0-5 % using sodium succinate as the carbon source. The nitrogen and phosphate removal efficiencies were 96-100 % and 88-96 % within 24 h, respectively. The nitrogen and phosphate removal processes were matched with the modified Gompertz model, and the underlying mechanisms were confirmed by the activities of key metabolic enzymes. Under 10 % salinity, the immobilization technology was employed to enhance the nitrogen and phosphate removal efficiencies of strain A4, achieving 87 % and 76 %, respectively. These findings highlight the potential application of strain A4 in both freshwater and marine culture wastewater treatment.

Nitrate removal from industrial wastewater using six newly isolated strains of aerobic heterotrophic denitrifiers in an attached growth

BACKGROUND

The objective of this study was to isolate specific heterotrophic aerobic denitrifying bacteria from a wastewater treatment plant and employ them in an attached growth system for wastewater denitrification.

METHODS

To isolate and screen aerobic denitrifiers, Denitrifying Medium (DM) and Screen Medium (GN) were utilized. The Polymerase Chain Reaction (PCR) technique and 16S rDNA sequencing were used to identify the isolates. The formation of biofilms by selected isolates on ceramic media was examined using a Scanning Electron Microscope (SEM). This study also investigated various variables for nitrate removal, including temperature, Carbon/Nitrogen ratio (C/N), and the carbon source. A series of experiments were conducted to gauge nitrate removal under optimal variable values.

RESULTS

Six purified strains exhibited the highest denitrification efficiency in less than 30 h. Pseudomonas species were chosen for additional experiments. Denitrification efficiencies ranged from a low of 71.4% (at a temperature of 30 °C, C/N ratio of 17, and citrate as the carbon source) to a high of 98.9% (at a temperature of 33 °C, C/N ratio of 8, and citrate as the carbon source). The average denitrification efficiency was 84.02%. Optimal nitrate removal occurred at temperatures around 30-31 °C and C/N ratios of approximately 5.8-6.5.

CONCLUSION

This study demonstrates that aerobic denitrifying bacteria can effectively remove nitrate from aqueous solutions.

Urban landscapes and legacy industry provide hotspots for riverine greenhouse gases: A source-to-sea study of the River Clyde

There is growing global concern that greenhouse gas (GHG) emissions from water bodies are increasing because of interactions between nutrient levels and climate warming. This paper investigates key land-cover, seasonal and hydrological controls of GHGs by comparison of the semi-natural, agricultural and urban environments in a detailed source-to-sea study of the River Clyde, Scotland. Riverine GHG concentrations were consistently oversaturated with respect to the atmosphere. High riverine concentrations of methane (CH₄) were primarily associated with point source inflows from urban wastewater treatment, abandoned coal mines and lakes, with CH₄-C concentrations between 0.1 - 44 µg l^-1. Concentrations of carbon dioxide (CO₂) and nitrous oxide (N₂O) were mainly driven by nitrogen concentrations, dominated by diffuse agricultural inputs in the upper catchment and supplemented by point source inputs from urban wastewater in the lower urban catchment, with CO₂-C concentrations between 0.1 - 2.6 mg l^-1 and N₂O-N concentrations between 0.3 - 3.4 µg l^-1. A significant and disproportionate increase in all GHGs occurred in the lower urban riverine environment in the summer, compared to the semi-natural environment, where GHG concentrations were higher in winter. This increase and change in GHG seasonal patterns points to anthropogenic impacts on microbial communities. The loss of total dissolved carbon, to the estuary is approximately 48.4 ± 3.6 Gg C yr^-1, with the annual inorganic carbon export approximately double that of organic carbon and four times that of CO_2, with CH₄ accounting for 0.03%, with the anthropogenic impact of disused coal mines accelerating DIC loss. The annual loss of total dissolved nitrogen to the estuary is approximately 4.03 ± 0.38 Gg N yr^-1 of which N₂O represents 0.06%. This study improves our understanding of riverine GHG generation and dynamics which can contribute to our knowledge of their release to the atmosphere. It identifies where action could support reductions in aquatic GHG generation and emission.

Systematic review: External carbon source for biological denitrification for wastewater

Nitrogen mitigation is serious environmental issue around the globe. Several methods for wastewater treatment have been introduced, but biological denitrification has been recommended, particularly with addition of the best external carbon source. The key sites of denitrification are wetlands; it can be carried out with different methods. To highlight the aforementioned technology, this paper deals to review the literature to evaluate biological denitrification and to demonstrate cost effective external carbon sources. The results of systematic review disclose the denitrification process and addition of different external carbon sources. The online literature exploration was accomplished using the most well-known databases, that is, science direct and the web of science database, resulting 625 review articles and 3084 research articles, published in peer-reviewed journals between 2015 and 2021 were identified in first process. After doing an in-depth literature survey and exclusion criteria, we started to shape the review from selected review and research articles. A number of studies confirmed that both nitrification and denitrification are significant for biological treatment of wastewater. The studies proved that the carbon source is the main contributor and is a booster for the denitrification. Based on the literature reviewed it is concluded that biological denitrification with addition of external carbon source is cost effective and best option in nitrogen mitigation in a changing world. Our study recommends textile waste for recovery of carbon source.

Nitrogen removal by Rhodococcus sp. SY24 under linear alkylbenzene sulphonate stress: Carbon source metabolism activity, kinetics, and optimum culture conditions

Artificial intervention combined with stress acclimation was used to screen a heterotrophic nitrifying-aerobic denitrifying (HN-AD) bacterial, strain Rhodococcus SY24, resistant to linear alkylbenzenesulfonic acid (LAS) stress. When LAS was<15 mg/L, strain SY24 performed better cell growth and carbon source metabolism activity. The maximum nitrification and denitrification rates of SY24 under LAS stress could reach 1.18 mg/L/h and 1.05 mg/L/h, respectively, which were 13.80 % and 8.81 % higher than those of the original strain CPZ24. Higher LAS tolerance was seen in the functional genes (amoA, nxrA, napA, narG, nirK, nirS, norB, and nosZ). Response surface modeling revealed that 2 mg/L LAS, sodium succinate as a carbon source, 190 rams, and carbon/nitrogen 11 were the ideal culture conditions for SY24 to nitrogen removal under the LAS environment. This study offered a new screening strategy for the functional species, and strain SY24 showed significant LAS tolerance and HN-AD potential.

Mix-cultured aerobic denitrifying bacteria augmented carbon and nitrogen removal for micro-polluted water: Metabolic activity, coexistence and interactions, and immobilized bacteria for reservoir raw water treatment

Less attention has been paid on the oligotrophic water body nitrogen treatment with mix-cultured aerobic denitrifying bacteria (Mix-CADB). In this study, three Mix-CADB communities were screened from the sediments of reservoirs. The nitrate and dissolved organic carbon (DOC) removal efficiencies of Mix-CADB communities were higher than 92 % and 91 %, respectively. Biolog results suggested that Mix-CADB communities displayed excellent carbon source metabolic activity. The nirS gene sequencing indicated that Pseudomonas sp. and Pseudomonas stutzeri accounted for more proportions in the core species of three Mix-CADB communities. The network model revealed that Pseudomonas sp. and Pseudomonas stutzeri mainly drove the total nitrogen and DOC removal of Mix-CADB communities. More importantly, the immobilized Mix-CADB communities could reduce >91 % nitrate in the adjusted reservoir raw water. Overall, this study showed that the three Mix-CADB communities could be regarded as potential candidates for the nitrogen treatment in oligotrophic water body ecosystems.

Efficacy of simultaneous hexavalent chromium biosorption and nitrogen removal by the aerobic denitrifying bacterium Pseudomonas stutzeri YC-34 from chromium-rich wastewater

The impact of high concentrations of heavy metals and the loss of functional microorganisms usually affect the nitrogen removal process in wastewater treatment systems. In the study, a unique auto-aggregating aerobic denitrifier (Pseudomonas stutzeri strain YC-34) was isolated with potential applications for Cr(VI) biosorption and reduction. The nitrogen removal efficiency and denitrification pathway of the strain were determined by measuring the concentration changes of inorganic nitrogen during the culture of the strain and amplifying key denitrification functional genes. The changes in auto-aggregation index, hydrophobicity index, and extracellular polymeric substances (EPS) characteristic index were used to evaluate the auto-aggregation capacity of the strain. Further studies on the biosorption ability and mechanism of cadmium in the process of denitrification were carried out. The changes in tolerance and adsorption index of cadmium were measured and the micro-characteristic changes on the cell surface were analyzed. The strain exhibited excellent denitrification ability, achieving 90.58% nitrogen removal efficiency with 54 mg/L nitrate-nitrogen as the initial nitrogen source and no accumulation of ammonia and nitrite-nitrogen. Thirty percentage of the initial nitrate-nitrogen was converted to N₂, and only a small amount of N₂O was produced. The successful amplification of the denitrification functional genes, norS, norB, norR, and nosZ, further suggested a complete denitrification pathway from nitrate to nitrogen. Furthermore, the strain showed efficient aggregation capacity, with the auto-aggregation and hydrophobicity indices reaching 78.4 and 75.5%, respectively. A large amount of protein-containing EPS was produced. In addition, the strain effectively removed 48.75, 46.67, 44.53, and 39.84% of Cr(VI) with the initial concentrations of 3, 5, 7, and 10 mg/L, respectively, from the nitrogen-containing synthetic wastewater. It also could reduce Cr(VI) to the less toxic Cr(III). FTIR measurements and characteristic peak deconvolution analysis demonstrated that the strain had a robust hydrogen-bonded structure with strong intermolecular forces under the stress of high Cr(VI) concentrations. The current results confirm that the novel denitrifier can simultaneously remove nitrogen and chromium and has potential applications in advanced wastewater treatment for the removal of multiple pollutants from sewage.

Nitrogen Removal Characteristics of a Cold-Tolerant Aerobic Denitrification Bacterium, Pseudomonas sp. 41

Nitrogen pollution of surface water is the main cause of water eutrophication, and is considered a worldwide challenge in surface water treatment. Currently, the total nitrogen (TN) content in the effluent of wastewater treatment plants (WWTPs) is still high at low winter temperatures, mainly as a result of the incomplete removal of nitrate (NO3−-N). In this research, a novel aerobic denitrifier identified as Pseudomonas sp. 41 was isolated from municipal activated sludge; this strain could rapidly degrade a high concentration of NO3−-N at low temperature. Strain 41 completely converted 100 mg/L NO3−-N in 48 h at 15 °C, and the maximum removal rate reached 4.0 mg/L/h. The functional genes napA, nirS, norB and nosZ were successfully amplified, which provided a theoretical support for the aerobic denitrification capacity of strain 41. In particular, the results of denitrification experiments showed that strain 41 could perform aerobic denitrification under the catalysis of NAP. Nitrogen balance analysis revealed that strain 41 degraded NO3−-N mainly through assimilation (52.35%) and aerobic denitrification (44.02%), and combined with the gene amplification results, the nitrate metabolism pathway of strain 41 was proposed. Single-factor experiments confirmed that strain 41 possessed the best nitrogen removal performance under the conditions of sodium citrate as carbon source, C/N ratio 10, pH 8, temperature 15–30 °C and rotation speed 120 rpm. Meanwhile, the bioaugmentation test manifested that the immobilized strain 41 remarkably improved the denitrification efficiency and shortened the reaction time in the treatment of synthetic wastewater.

Heterotrophic ammonium assimilation: An important driving force for aerobic denitrification of Rhodococcus erythropolis strain Y10

Studies on microbial ammonium removal have focused on the heterotrophic nitrification of microorganisms and have rarely studied the role of ammonium assimilation. In this study, Rhodococcus erythropolis strain Y10 with the capacity of aerobic denitrification was screened from the surface flow constructed wetlands that treat high-strength ammonium swine wastewater. Instead of through nitrification, this strain removed ammonium through heterotrophic ammonium assimilation, with the removal rate of 9.69 mg/L/h. The KEGG nitrogen metabolism pathway analysis combined with nitrogen balance calculation manifested that the removal of nitrate and nitrite by R. erythropolis Y10 was achieved through two pathways: 1) assimilation reduction to biomass nitrogen and 2) aerobic denitrification reduction to gaseous nitrogen. Ammonium addition improved the aerobic denitrification rate of nitrate and nitrite. The maximal reduction rates of nitrate and nitrite increased from 7.82 and 7.23 mg/L/h to 9.09 and 8.09 mg/L/h respectively, when 100 mg/L ammonium was separately added to 150 mg/L nitrate and nitrite. Furthermore, the removal efficiency of total nitrogen increased from 69.80% and 77.65% to 89.19% and 91.88%, respectively. Heterotrophic ammonium assimilation promoted the aerobic denitrification efficiency of Rhodococcus erythropolis strain Y10.

Nitrogen removal characteristics and potential application of the heterotrophic nitrifying-aerobic denitrifying bacteria Pseudomonas mendocina S16 and Enterobacter cloacae DS'5 isolated from aquaculture wastewater ponds

Two biosafety strains, identified as Pseudomonas mendocina S16 and Enterobacter cloacae DS'5, were isolated from freshwater aquaculture ponds and showed significant heterotrophic nitrification-aerobic denitrification abilities. Within 48 h, the inorganic nitrogen removal efficiencies in the two strains were 66.59 %-97.97 % (S16) and 72.27 %-96.44 % (DS'5). The optimal conditions for organic nitrogen removal of the two strains were temperature 20-35 °C and carbon/nitrogen (C/N) ratio 10-20 while using sodium citrate as the carbon source. Sequence amplification demonstrated the presence of the denitrification genes in both the two strains, and quantitative real-time PCR results showed that the coupled expression of nap + nar would improve the nitrate removal rate in S16. The nitrogen removal efficiencies of the two strains in immobilization culture systems were 79.80 %-98.58 % (S16) and 60.80 %-98.40 % (DS'5). This study indicated the great potential application of the two strains in aquaculture tail water treatment.

Revealing the effects of static magnetic field on the anoxic/oxic sequencing batch reactor from the perspective of electron transport and microbial community shifts

The effects of static magnetic field (SMF) on an anoxic/oxic sequencing batch reactor were investigated from the perspective of electron transport via determining the variations of reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD⁺) ratio, NADH concentration, electron transport system activity (ETSA), poly-β-hydroxybutyrate (PHB), extracellular polymeric substances (EPS), as well as the gene expression under different conditions. Moreover, the shifts of microbial community were also analyzed. The application of SMF with an appropriate intensity significantly improved the performance of the process, the abundance of the anoxic denitrifiers, and the activity of the aerobic denitrifiers. The NADH content, as well as ETSA were also enhanced, therefore, the total nitrogen removal efficiency of the process was increased. However, the overhigh SMF intensity resulted in the change of microbial community, meanwhile, had negative effects on the metabolism of microorganisms. Selecting a proper intensity is crucial for the SMF-enhanced biological wastewater treatment process.

Isolation and Identification of an Efficient Aerobic Denitrifying Pseudomonas stutzeri Strain and Characterization of Its Nitrite Degradation

Nitrogen pollution in water bodies is becoming increasingly serious, and how to remove nitrogen from water bodies economically and effectively has become a research hotspot. Especially in recent years, with the gradual expansion of aquaculture in China, the content of nitrite and other nitrogen-containing substances in water bodies has been increasing, which inhibits the growth of farm animals and is one of the causes of eutrophication in water bodies. In this study, a strain of bacteria was isolated from the sludge of an aquaculture fishpond and identified as Pseudomonas stutzeri, which can efficiently degrade nitrite. After continuous domestication in nitrite mixed solution, the nitrite nitrogen reduction capacity of P. stutzeri was significantly improved. Univariate experiments aiming to optimize the degradation conditions indicate that the optimal culture conditions for strain F2 are: medium with a carbon source of sodium succinate; C/N of 18; pH of 8; culture temperature of 28 °C; and shaking speed of 210 rpm in the shaker. Under the optimal culture conditions, the NO2−-N concentration of the culture solution was 300 mg/L, and the nitrite removal rate reached 98.67%. Meanwhile, the results of the nitrogen balance test showed that the strain converted 6.1% of the initial nitrogen into cellular organic nitrogen and 62.3% into gaseous nitrogen.

Role of heterotrophic nitrifiers and aerobic denitrifiers in simultaneous nitrification and denitrification process: A non-conventional nitrogen removal pathway in wastewater treatment

Bacterial species capable of performing both nitrification and denitrification in a single vessel under similar conditions have gained significance in the wastewater treatment scenario considering their unique character of performing the above reactions under heterotrophic and aerobic conditions respectively. Such a novel strategy often referred to as simultaneous nitrification and denitrification (SND) has a tremendous potential in dealing with various wastewaters having low C:N content, considering that the process needs very little or no external carbon source and oxygen supply thus adding to its cost-effective and environmentally friendly nature. Though like other microorganisms, heterotrophic nitrifiers and aerobic denitrifiers convert inorganic or organic nitrogen-containing substances into harmless dinitrogen gas in the wastewater, their ecophysiological role in the global nitrogen cycle is still not yet fully understood. Attempts to highlight the role played by the heterotrophic nitrifiers and aerobic denitrifiers in dealing with nitrogen pollution under various environmental operating conditions will help in developing a mechanistic understanding of the SND process to address the issues faced by the traditional methods of aerobic autotrophic nitrification-anaerobic heterotrophic denitrification.

Supplementation of Bile Acids and Lipase in Broiler Diets for Better Nutrient Utilization and Performance: Potential Effects and Future Implications – A Review

Bile acids are used for better emulsification, digestion and absorption of dietary fat in chicken, especially in early life. Similarly, exogenous lipases have also been used for the improvement of physiological limitation of the chicken digestive system. Owing to potential of both bile acids and lipases, their use has been increased in recent years, for better emulsification of dietary fat and improvement of growth performance in broilers. In the past, pancreatic lipases were used for supplementation, but recently, microbial lipase is getting attention in poultry industry as a hydrolysis catalyst. Bile acids strengthen the defence mechanism of body against bacterial endotoxins and also play a key role in lipid regulation and sugar metabolism as signaling molecules. It has been demonstrated that bile acids and lipases may improve feed efficiency by enhancing digestive enzyme activity and ultimately leading to better fat digestion and absorption. Wide supplemental range of bile acids (0.004% to 0.25%) and lipases (0.01% to 0.1%) has been used in broiler diets for improvement of fat digestibility and their performance. Combinations of different bile acids have shown more potential to improve feed efficiency (by 7.14%) even at low (0.008%) levels as compared to any individual bile acid. Lipases at a lower level of 0.03% have exhibited more promising potential to improve fat digestibility and feed efficiency. However, contradicting results have been published in literature, which needs further investigations to elucidate various nutritional aspects of bile acids and lipase supplementation in broiler diet. This review focuses on providing insight on the mechanism of action and potential application of bile acids and lipases in broiler diets. Moreover, future implications of these additives in poultry nutrition for enhancing nutrient utilization and absorption are also discussed.

Effect of the Aerobic Denitrifying Bacterium Pseudomonas furukawaii ZS1 on Microbiota Compositions in Grass Carp Culture Water

Background: Although functional bacteria are widely used in aquaculture water treatment, whether they affect the indigenous microbiota and whether the impact is persistent remain unclear. Therefore, we aimed to explore the denitrification effect of Pseudomonas furukawaii ZS1 isolated from a grass carp culture pond in nitrogen-rich aquaculture water, and determine whether its effect on the microbiota structure of the aquaculture water was persistent. Methods: Three each of treatment and control groups were set up, and P. furukawaii ZS1 was added to the treatment group. The concentrations of ammonia nitrogen, nitrite, and nitrate, and the pH of each sample were measured for eight consecutive days. Changes of microbiota composition in the water were analysed via high-throughput sequencing. Results: Ammonia, nitrite, and nitrate concentrations were substantially lower in the treatment group than in the control group. There were significant differences in the microbiota structure between treatment and control groups, especially on days 2–7 after adding P. furukawaii ZS1. Furthermore, significantly enriched bacterial genera in the treatment group were initially higher in number than inhibited genera, but subsequently reverted to being lower in number. Conclusions: These results provide theoretical guidance for the effective use of P. furukawaii ZS1 to control aquaculture water.

Culturable nitrogen-transforming bacteria from sequential sedimentation biofiltration systems and their potential for nutrient removal in urban polluted rivers

Novel heterotrophic bacterial strains—Bzr02 and Str21, effective in nitrogen transformation, were isolated from sequential sedimentation-biofiltration systems (SSBSs). Bzr02, identified as Citrobacter freundii, removed up to 99.0% of N–NH₄ and 70.2% of N–NO₃, while Str21, identified as Pseudomonas mandelii, removed up to 98.9% of N–NH₄ and 87.7% of N–NO₃. The key functional genes napA/narG and hao were detected for Bzr02, confirming its ability to reduce nitrate to nitrite and remove hydroxylamine. Str21 was detected with the genes narG, nirS, norB and nosZ, confirming its potential for complete denitrification process. Nitrogen total balance experiments determined that Bzr02 and Str21 incorporated nitrogen into cell biomass (up to 94.7% and 74.7%, respectively), suggesting that nitrogen assimilation was also an important process occurring simultaneously with denitrification. Based on these results, both strains are suitable candidates for improving nutrient removal efficiencies in nature-based solutions such as SSBSs.

Novel microbial nitrogen transformation processes in constructed wetlands treating municipal sewage: a mini-review

Traditionally nitrogen transformation in constructed wetlands (CWs) has been attributed to the activities of aerobic autotrophic nitrifiers followed by anoxic heterotrophic denitrifiers. However, the nitrogen balances in such systems are far from being explained as a large fraction of the losses remain unaccounted for. The classical nitrification-denitrification theory has been successfully employed in certain unit processes by culturing fast-growing bacteria, but the CWs offer an ideal environment for slow-growing bacteria that may be beneficially exploited to achieve enhanced nitrogen removal by manipulating the environmental conditions in their favor. In the last three decades, many novel microorganisms have been isolated from CWs that have led to the discovery of some other routes that have made researchers believe could play a significant role in nitrogen transformation processes. The increased understanding of novel discerned pathways like anaerobic ammonium oxidation (ANAMMOX), heterotrophic nitrification and aerobic denitrification, which are mediated by specialized bacteria has indicated that these microorganisms could be enriched by applying selection pressures within CWs for achieving high rates of nitrogen removal. Understanding these novel nitrogen transformation processes along with the associated microbial population can provide new dimensions to the design of CWs for enhanced nitrogen removal.

Efficient nitrate removal by Pseudomonas mendocina GL6 immobilized on biochar

The performance of nitrate removal by Pseudomonas mendocina GL6 cells immobilized on bamboo biochar was investigated. The results showed that immobilized bacterial cells performed better nitrate removal than the free bacterial cells, and the nitrate removal rate increased from 6.51 mg/(L·h) of free cells to 8.34 mg/(L·h) of immobilized cells. The nitrate removal of immobilized bacterial cells fitted well to the zero-order kinetics model. Moreover, bath experiments showed that immobilized bacterial cells displayed more nitrate removal capacity under different conditions than free bacterial cells due to the protection of biochar carrier. The subsequent mechanistic study suggested that biochar promoted the expression level of denitrification functional genes (napA and nirK) and electron transfer genes involved in denitrification (napB and napC), which resulted in the increase of nitrate removal efficiency. Thus, biochar-immobilized P. mendocina GL6 has much potential to remove nitrate from wastewater via aerobic denitrification.

Aerobic denitrifying bacterial communities drive nitrate removal: Performance, metabolic activity, dynamics and interactions of core species

Three novel mix-cultured aerobic denitrifying bacteria (Mix-CADB) consortia named D14, X21, and CL exhibited excellent total organic carbon (TOC) removal and aerobic denitrification capacities. The TOC and nitrate removal efficiencies were higher than 93.00% and 98.00%. The results of Biolog demonstrated that three communities displayed high carbon metabolic activity. nirS gene sequencing and ecological network model revealed that Pseudomonas stutzeri, Paracoccus sp., and Paracoccus denitrificans dominated in the D14, X21, and CL communities. The dynamics and co-existence of core species in communities drove the nutrient removal. Response surface methodology showed the predicted total nitrogen removal efficiency reached 99.43% for D14 community. The three Mix-CADB consortia have great potential for nitrogen-polluted aquatic water treatment because of their strong adaptability and removal performance. These results will provide new understanding of co-existence, interaction and dynamics of Mix-CADB consortia for nitrogen removal in nitrogen-polluted aquatic ecosystems.

Nitrate removal performances of a new aerobic denitrifier, Acinetobacter haemolyticus ZYL, isolated from domestic wastewater

A new aerobic denitrifying bacterium ZYL was isolated from domestic wastewater sludge and identified as Acinetobacter haemolyticus (similarity 99%) by the 16S rDNA sequencing analysis. The strain could use nitrate, nitrite and ammonium as the sole N-source for growth with a final product of N₂, demonstrating its good abilities for aerobic denitrification and heterotrophic nitrification. Single-factor experiment results showed that the effective removal of nitrate by strain ZYL occurred with carbon source sodium succinate, C/N 16-24, pH 5-9, temperature 20-40 °C, DO ≥ 4.84 mg/L. Ammonium was preferentially used by strain ZYL with nitrate and ammonium as the mixed nitrogen sources. According to nitrogen utilization, nitrogen balance analysis, enzyme assay and denitrifying gene amplification, nitrate was assimilated directly by the isolate for cell synthesis and also converted into N₂ through aerobic denitrification. All these make strain ZYL an ideal choice for treating nitrogen-containing wastewater.

Nitrate reduction by Paracoccus thiophilus strain LSL 251 under aerobic condition: Performance and intracellular central carbon flux pathways

The intracellular carbon metabolic flux pathways of denitrifying bacteria under aerobic conditions remain unclear. Here, a newly strain LSL251 was identified as Paracoccus thiophilus. Strain LSL251 removed 94.79% and 98.78% of total organic carbon and nitrate. 74.66% of nitrogen in culture system was lost as gaseous nitrogen. Moreover, ¹³C stable isotopic labeling and metabolic flux analyses revealed that the primary intracellular carbon metabolic pathways were the Entner-Doudoroff pathway and the tricarboxylic acid (TCA) cycle. Electrons are primarily donated as direct electron donor-NADH through the TCA cycle. Furthermore, response surface methodology modeled that the highest total nitrogen removal efficiency was 98.43%, where the optimal parameters were C/N ratio of 8.00, 32.98 °C, 50.18 rpm, and initial pH of 7.73. All together, these results have shed new lights on intracellular central carbon metabolic distribution and flux pathways of aerobic denitrifying bacteria.

Nitrifying and Denitrifying Microbial Communities in Centralized and Decentralized Biological Nitrogen Removing Wastewater Treatment Systems

Biological nitrogen removal (BNR) in centralized and decentralized wastewater treatment systems is assumed to be driven by the same microbial processes and to have communities with a similar composition and structure. There is, however, little information to support these assumptions, which may impact the effectiveness of decentralized systems. We used high-throughput sequencing to compare the structure and composition of the nitrifying and denitrifying bacterial communities of nine onsite wastewater treatment systems (OWTS) and one wastewater treatment plant (WTP) by targeting the genes coding for ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ). The amoA diversity was similar between the WTP and OWTS, but nosZ diversity was generally higher for the WTP. Beta diversity analyses showed the WTP and OWTS promoted distinct amoA and nosZ communities, although there is a core group of N-transforming bacteria common across scales of BNR treatment. Our results suggest that advanced N-removal OWTS have microbial communities that are sufficiently distinct from those of WTP with BNR, which may warrant different management approaches.

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.

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.