Salt-tolerant plant growth-promoting bacteria as a versatile tool for combating salt stress in crop plants.

Soil salinization poses a great threat to global agricultural ecosystems, and finding ways to improve the soils affected by salt and maintain soil health and sustainable productivity has become a major challenge. Various physical, chemical and biological approaches are being evaluated to address this escalating environmental issue. Among them, fully utilizing salt-tolerant plant growth-promoting bacteria (PGPB) has been labeled as a potential strategy to alleviate salt stress, since they can not only adapt well to saline soil environments but also enhance soil fertility and plant development under saline conditions. In the last few years, an increasing number of salt-tolerant PGPB have been excavated from specific ecological niches, and various mechanisms mediated by such bacterial strains, including but not limited to siderophore production, nitrogen fixation, enhanced nutrient availability, and phytohormone modulation, have been intensively studied to develop microbial inoculants in agriculture. This review outlines the positive impacts and growth-promoting mechanisms of a variety of salt-tolerant PGPB and opens up new avenues to commercialize cultivable microbes and reduce the detrimental impacts of salt stress on plant growth. Furthermore, considering the practical limitations of salt-tolerant PGPB in the implementation and potential integration of advanced biological techniques in salt-tolerant PGPB to enhance their effectiveness in promoting sustainable agriculture under salt stress are also accentuated.

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.

Effects of continuous low-speed biogas agitation on anaerobic digestion of high-solids pig manure: Performance and microbial community.

This study aimed to investigate effects of continuous low-speed biogas agitation on the anaerobic digestion (AD) performance and microbial community of high-solids pig manure (total solids content of 10%). Our results reveal that at a biogas agitation intensity of 1.10 L/g feed VS/d, CH4 production increased by 16.67% compared to the non-agitated condition, the removal efficiency of H2S reached 63.18%, and the abundance of Methanosarcina was the highest. The presence of Hungateiclostridiaceae was associated with H2S concentrations. An increasing biogas agitation intensity led to an elevated pH and a decreased oxidation-reduction potential (ORP). Acetate concentrations, pH, and ORP values indicated changes in H2S concentrations. Sedimentibacter demonstrates the potential to indicate biogas agitation intensity and pH. We demonstrate that continuous low-speed biogas agitation effectively increases CH4 production and reduces H2S concentrations in AD of high-solids pig manure, offering a potential technical pathway for developing AD processes for high-solids pig manure, it also demonstrates that AD process can reduce the risk of pathogen and parasite transmission.

Efficient transformation of hydroxylamine from wastewater after supplementation with sodium carbonate or calcium bicarbonate.

Hydroxylamine is a highly reactive inorganic nitrogen compound that not only has a toxic effect on microorganisms, but also makes wastewater treatment more difficult, which in turn damages the environment and even endangers human health. This study reported a new method for converting of hydroxylamine by adding sodium carbonate or calcium bicarbonate to the hydroxylamine-polluted wastewater. The conversion efficiency of hydroxylamine was more than 99% in the presence of sodium carbonate or calcium bicarbonate under the reaction conditions of 25 °C, C/N ratio 15, and dissolved oxygen 7.4 mg/L. And its maximal conversion rate can reach 3.49 mg/L/h. This method overcomes various shortcomings of the reported hydroxylamine removal technologies that require a large material dosage and high cost. The technology in this report has many advantages: low cost, 'green' environmental protection, easy market promotion, and high economic benefits.

Hydroxylamine and nitrite are removed effectively by Streptomyces mediolani strain EM-B2.

Biological nitrogen removal is primarily conducted by bacteria and fungi rather than actinomycetes. However, accumulations of nitrite and hydroxylamine could significantly impair the biological nitrogen removal process. A strain of Streptomyces mediolani, termed EM-B2, was isolated from a cow dung fermentation biogas digester. The strain removed more than 99% of ammonium and 78% of total nitrogen in the presence of glucose and under environmental conditions of 30 °C, a carbon/nitrogen ratio of 15, 7.4 mg/L dissolved oxygen and a pH range of 7.5-9.0. Maximal removal rates were 2.29 mg/L/h for ammonium, 1.90 mg/L/h for nitrate and 2.01 mg/L/h for nitrite. The removal efficiencies of hydroxylamine and total nitrogen peaked at 81.48% and 60.38%, respectively. Notably, hydroxylamine and nitrite were never detected during the heterotrophic nitrification and aerobic denitrification. Nitrate rather than nitrite was accumulated from the process of hydroxylamine oxidation. These findings indicate that S. mediolani strain EM-B2 performs heterotrophic nitrification and aerobic denitrification, and can be used to remove hydroxylamine and nitrite from wastewater.

Investigating the effect of copper and magnesium ions on nitrogen removal capacity of pure cultures by modified non-competitive inhibition model.

Copper, a common heavy metal, may be beneficial for or poisonous to microbial activity. The objective of this study was to determine the effect of different copper ion concentrations on the nitrogen removal performance of Arthrobacter arilaitensis strain Y-10 and Pseudomonas taiwanensis strain J488. The non-competitive inhibition model was employed to evaluate the 50% inhibition concentrations (IC50 values) of copper ions toward the pure strains. In the absence of magnesium ions, a low concentration of copper (0.1 mg/L) significantly enhanced the ammonium removal ability of strain Y-10 and its removal efficiency increased by 10.88% compared with the control treatment. Copper ranging from 0 to 0.1 mg/L had no significant effect on the ammonium removal capacity of strain J488. After adding 9.90 mg/L of magnesium to the basal medium, the effects of copper on nitrification of ammonium or denitrification of nitrate or nitrite were also assessed. In these conditions, 0.25 mg/L copper ions could strongly inhibit the ammonium, nitrate and nitrite removal activities for strain Y-10. For strain J488, no clear deterioration in ammonium removal efficiency was observed at copper ion concentrations below 0.5 mg/L, but 0.25 mg/L copper ions significantly inhibited nitrate and nitrite removal efficiencies, which were only 45.88% and 6.35%, respectively. The IC50 values of copper ions for nitrate and nitrite removal by strain Y-10 were 0.195 and 0.090 mg/L respectively; for strain J488, the IC50 values were 0.175 and 0.196 mg/L. The magnesium ions could improve the cell growth, nitrogen removal efficiency and copper ion resistance of bacteria.

Simultaneous nitrification and denitrification with different mixed nitrogen loads by a hypothermia aerobic bacterium.

Microorganism with simultaneous nitrification and denitrification ability plays a significant role in nitrogen removal process, especially in the eutrophic waters with excessive nitrogen loads. The nitrogen removal capacity of microorganism may suffer from low temperature or nitrite nitrogen source. In this study, a hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was selected to determine the simultaneous nitrification and denitrification ability with mixed nitrogen source at 15 °C. The sole nitrogen removal efficiencies of strain Y-11 in simulated wastewater were obtained. After 24 h of incubation at 15 °C, the ammonium nitrogen fell below the detection limit from an initial value of 10.99 mg/L. Approximately 88.0 ± 0.33% of nitrate nitrogen was removed with the initial concentration of 11.78 mg/L and the nitrite nitrogen was not detected with the initial concentration of 10.75 mg/L after 48 h of incubation at 15 °C. Additionally, the simultaneous nitrification and denitrification nitrogen removal ability of P. tolaasii strain Y-11 was evaluated using low concentration of mixed NH4+-N and NO3--N/NO2--N (about 5 mg/L-N each) and high concentration of mixed NH4+-N and NO3--N/NO2--N (about 100 mg/L-N each). There was no nitrite nitrogen accumulation at the time of evaluation. The results demonstrated that P. tolaasii strain Y-11 had higher simultaneous nitrification and denitrification capacity with low concentration of mixed inorganic nitrogen sources and may be applied in low temperature wastewater treatment.

[Identification and characterization of a hypothermia nitrite bacterium Pseudomonas tolaasii Y-11].

OBJECTIVE: Denitrifying bacteria play an important role in the biological nitrogen removal process. However, there are few studies about hypothermia nitrite denitrifying bacteria. We isolated a hypothermia and aerobic nitrite-denitrifying bacterium (named as Y-11) from the long-term flooded paddy soil. Aims of this paper were to clarify the phylogeny and denitrifying characteristics of strain Y-11. METHODS: Morphological observation, specific phospholipid fatty acid and 16S rRNA analysis were employed to identify strain Y-11. Denitrification characteristics of strain Y-11, such as temperature, shaking speed, initial pH and carbon source were investigated by using shaking culture in Erlenmeyer flask. RESULTS: Strain Y-11 with high removal efficiency of nitrite and total nitrogen was identified as Pseudomonas tolaasii. The optimum conditions of Y-11 effectively removing nitrite nitrogen and total nitrogen were: initial pH7.0; 15 degrees C; shaking speed 200 r/min; inoculum size 1.5 x 10(8) CFU per 100 mL medium; sodium acetate as carbon source; and nitrite nitrogen 10 mg/L. Strain Y-11 can remove nitrite nitrogen and total nitrogen up to 100% and 61.28% within 48 h. CONCLUSION: Strain Y-11 was identified as Pseudomonas tolaasii with its potential nitrite polluted water treatment during early winter and late spring.

Exopolysaccharide production by salt-tolerant bacteria: Recent advances, current challenges, and future prospects.

Natural biopolymers derived from exopolysaccharides (EPSs) are considered eco-friendly and sustainable alternatives to available traditional synthetic counterparts. Salt-tolerant bacteria inhabiting harsh ecological niches have evolved a number of unique adaptation strategies allowing them to maintain cellular integrity and assuring their long-term survival; among these, producing EPSs can be adopted as an effective strategy to thrive under high-salt conditions. A great diversity of EPSs from salt-tolerant bacteria have attracted widespread attention recently. Because of factors such as their unique structural, physicochemical, and functional characteristics, EPSs are commercially valuable for the global market and their application potential in various sectors is promising. However, large-scale production and industrial development of these biopolymers are hindered by their low yields and high costs. Consequently, the research progress and future prospects of salt-tolerant bacterial EPSs must be systematically reviewed to further promote their application and commercialization. In this review, the structure and properties of EPSs produced by a variety of salt-tolerant bacterial strains isolated from different sources are summarized. Further, feasible strategies for solving production bottlenecks are discussed, which provides a scientific basis and direct reference for more scientific and rational EPS development.

Bacterial valorization of lignin for the sustainable production of value-added bioproducts.

As the most abundant aromatic biopolymer in the biosphere, lignin represents a promising alternative feedstock for the industrial production of various value-added bioproducts with enhanced economical value. However, the large-scale implementation of lignin valorization remains challenging because of the heterogeneity and irregular structure of lignin. General fragmentation and depolymerization processes often yield various products, but these approaches necessitate tedious purification steps to isolate target products. Moreover, microbial biocatalytic processes, especially bacterial-based systems with high metabolic activity, can depolymerize and further utilize lignin in an eco-friendly way. Considering that wild bacterial strains have evolved several metabolic pathways and enzymatic systems for lignin degradation, substantial efforts have been made to exploit their potential for lignin valorization. This review summarizes recent advances in lignin valorization for the production of value-added bioproducts based on bacterial systems. Additionally, the remaining challenges and available strategies for lignin biodegradation processes and future trends of bacterial lignin valorization are discussed.

Bacterial Pigments as a Promising Alternative to Synthetic Colorants: From Fundamentals to Applications.

Pigments find widespread application in the fields of food, medicine, textiles, and cosmetics. At present, synthetic colorants dominate the global pigment market. However, the environmental and health hazards associated with synthetic colorants have spurred extensive research on eco-friendly and safe alternatives. Natural pigments are particularly intriguing for meeting consumer demands and sustainable development, as they not only exhibit various vibrant color shades without discernible toxic side effects but also offer additional healthful features such as antibacterial, antioxidant, anticancer, and antiviral properties compared with their synthetic counterparts. Among natural sources, bacterial strains share distinct advantages for large-scale pigment production because of their intrinsic robustness of cellular metabolic systems. This review comprehensively outlines the bacterial sources, extraction and purification methods, structural characteristics, biological activities, and potential applications of typical pigments, including but not limited to violacein, indigoidine, melanin, carotenoids, prodigiosin, and rhodopsin. Additionally, it underscores the primary obstacles to the development and production of bacterial pigments for commercial applications, discussing feasible strategies for overcoming production bottlenecks. This work also provides valuable insights for the scientific and rational advancement of bacterial pigment development.

Review of the mechanisms involved in dissimilatory nitrate reduction to ammonium and the efficacies of these mechanisms in the environment.

Dissimilatory nitrate reduction to ammonium (DNRA) is currently of great interest because it is an important method for recovering nitrogen from wastewater and offers many advantages, over other methods. A full understanding of DNRA requires the mechanisms, pathways, and functional microorganisms involved to be identified. The roles these pathways play and the effectiveness of DNRA in the environment are not well understood. The objectives of this review are to describe our current understanding of the molecular mechanisms and pathways involved in DNRA from the substrate transfer perspective and to summarize the effects of DNRA in the environment. First, the mechanisms and pathways involved in DNRA are described in detail. Second, our understanding of DNRA by actinomycetes is reviewed and gaps in our understanding are identified. Finally, the effects of DNRA in the environment are assessed. This review will help in the development of future research into DNRA to promote the use of DNRA to treat wastewater and recover nitrogen.

[Research progress of nanoscale zero-valent iron in synergistic combinations of denitrifying bacteria for nitrate removal].

Nitrate (NO3--N) is a common inorganic nitrogen pollutant in water. Excessive NO3--N can lead to water eutrophication and threaten human health. Nanoscale zero-valent iron (nZVI) has attracted much attention in NO3--N removal due to its high specific surface and excellent electron donor properties. The combination of nZVI and denitrifying bacteria (DNB) demonstrates high efficiency in converting NO3--N into N2. This approach not only substantially enhances the removal rate of NO3--N but also exhibits superior environmental sustainability compared with conventional chemical denitrification methods. Accordingly, it holds substantial promise for mitigating NO3--N pollution and warrants further exploration in the pollution control. Therefore, it is necessary to understand the interaction mechanism between nZVI and DNB for NO3--N removal. This paper details the factors affecting the removal of NO3--N by nZVI combined with DNB, reviews the latest research progress in this field, elaborates on the interaction mechanism between nZVI and DNB for NO3--N removal, and discusses the challenges and future research directions of NO3--N removal by nZVI combined with DNB. This review aims to provide a theoretical basis for the development of efficient approaches for the remediation of NO3--N pollution.

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

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

Bacillus thuringiensis EM-A1: A novel bacterium for high concentration of ammonium elimination with low nitrite accumulation.

The biological elimination of high concentration of ammonium from wastewater has attracted increasing attention in recent years. However, few studies on the efficient elimination of high concentration of ammonium by a single bacterium have been reported. Here, the efficient elimination of NH4+-N (>99%) and total nitrogen (TN) (>77%) were attained by Bacillus thuringiensis EM-A1 under 150 rpm at pH 7.2 with sodium succinate and a carbon/nitrogen ratio of 15 at 30 °C with an inoculum size (as measured by absorbance at 600 nm) of 0.2. Strain EM-A1 effectively eliminated 100 mg/L of inorganic nitrogen with maximal NH4+-N, NO3--N, and NO2--N elimination rates of 4.88, 2.57, and 3.06 mg/L/h, respectively. The elimination efficiencies of NH4+-N were 99.87% and 97.13% at initial concentrations of 500 and 1000 mg/L, respectively. Only 0.91 mg/L of NO2--N was accumulated with the elimination of 1000 mg/L NH4+-N. A concentration of 5 mg/L exogenous hydroxylamine was toxic and further inhibited heterotrophic nitrification and aerobic denitrification (HN-AD). The NH4+-N and NO2--N elimination capacities of strain EM-A1 were specifically inhibited by 2-Octyne (OCT) over 4 µmol/L and diethyldithiocarbamate (DDC) over 0.5 mmol/L, respectively. Above 25 mg/L procyanidin (PCY) inhibited the bioconversion of NO3--N and NO2--N. The results demonstrated that strain EM-A1 had HN-AD capacity under halophilic conditions, and has great potential for use in the treatment of nitrogen pollution wastewater; this study also provides new insights into this strain's nitrogen elimination mechanism, helping advance environmental biotechnology.

Efficient detoxication of hydroxylamine and nitrite through heterotrophic nitrification and aerobic denitrification by Acinetobacter johnsonii EN-J1.

The co-existence of hydroxylamine (NH2OH) and nitrite (NO2 --N) can aggravate the difficulty of wastewater treatment. The roles of hydroxylamine (NH2OH) and nitrite (NO2 --N) in accelerating the elimination of multiple nitrogen sources by a novel isolated strain of Acinetobacter johnsonii EN-J1 were investigated in this study. The results demonstrated that strain EN-J1 could eliminate 100.00% of NH2OH (22.73 mg/L) and 90.09% of NO2 --N (55.32 mg/L), with maximum consumption rates of 1.22 and 6.75 mg/L/h, respectively. Prominently, the toxic substances NH2OH and NO2 --N could both facilitate nitrogen removal rates. Compared with the control treatment, the elimination rates of nitrate (NO3 --N) and NO2 --N were enhanced by 3.44 and 2.36 mg/L/h after supplementation with 10.00 mg/L NH2OH, and those of ammonium (NH4 +-N) and NO3 --N were improved by 0.65 and 1.00 mg/L/h after the addition of 50.00 mg/L NO2 --N. Furthermore, the nitrogen balance results indicated that over 55.00% of the initial total nitrogen was transformed into gaseous nitrogen by heterotrophic nitrification and aerobic denitrification (HN-AD). Ammonia monooxygenase (AMO), hydroxylamine oxidoreductase (HAO), nitrate reductase (NR), and nitrite reductase (NIR), which are essential for HN-AD, were detected at levels of 0.54, 0.15, 0.14, and 0.01 U/mg protein, respectively. All findings confirmed that strain EN-J1 could efficiently execute HN-AD, detoxify NH2OH and NO2 --N, and ultimately promote nitrogen removal rates.

Enhanced heterotrophic nitrification and aerobic denitrification performance of Glutamicibacter arilaitensis EM-H8 with different carbon sources.

Different carbon sources for Glutamicibacter arilaitensis EM-H8 were evaluated for ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and nitrite nitrogen (NO2--N) removal. Strain EM-H8 could rapidly remove NH4+-N, NO3--N and NO2--N. The highest removal rates measured for different forms of nitrogen with different carbon sources were 5.94 mg/L/h for NH4+-N with sodium citrate, 4.25 mg/L/h for NO3--N with sodium succinate, and 3.88 mg/L/h for NO2--N with sucrose. The Nitrogen balance showed that strain EM-H8 could convert 77.88% of the initial nitrogen into nitrogenous gas when NO2--N was selected as the sole nitrogen source. The presence of NH4+-N increased the removal rate of NO2--N from 3.88 to 4.02 mg/L/h. In an enzyme assay, ammonia monooxygenase, nitrate reductase and nitrite oxidoreductase were detected at 0.209, 0.314, and 0.025 U/mg protein, respectively. These results demonstrate that strain EM-H8 performs well for nitrogen removal, and shows excellent potential for simple and efficient removal of NO2--N from wastewater.

Klebsiella oxytoca (EN-B2): A novel type of simultaneous nitrification and denitrification strain for excellent total nitrogen removal during multiple nitrogen pollution wastewater treatment.

The poor total nitrogen (TN) removal rate achieved using microorganisms to treat wastewater polluted with multiple types of nitrogen was improved using a novel simultaneous nitrification and denitrification strain (Klebsiella oxytoca EN-B2). Strain EN-B2 rapidly eliminated ammonium, nitrate, and nitrite, giving maximum elimination rates of 4.58, 7.46, and 7.83 mg/(L h), respectively, equivalent to TN elimination rates of 4.35, 6.92, and 7.11 mg/(L h), respectively. The simultaneous nitrification and denitrification system gave ammonium and nitrite elimination rates of 7.14 and 9.17 mg/(L h), respectively, and a TN elimination rate ≥ 9.0 mg/(L h). Nitrogen balance calculations indicated that 51.22 %, 31.62 % and 46.82 % of TN in systems containing only ammonium, nitrite, and nitrate, respectively, were lost as nitrogenous gases. The ammonia monooxygenase, hydroxylamine oxidoreductase, nitrate reductase and nitrite reductase enzyme activities were determined. The results indicated that strain EN-B2 can be used to treat wastewater polluted with multiple types of nitrogen.

[Denitrifying phosphate accumulating organisms and its mechanism of nitrogen and phosphorus removal].

Water eutrophication poses great threats to protection of water environment. Microbial remediation of water eutrophication has shown high efficiency, low consumption and no secondary pollution, thus becoming an important approach for ecological remediation. In recent years, researches on denitrifying phosphate accumulating organisms and their application in wastewater treatment processes have received increasing attention. Different from the traditional nitrogen and phosphorus removal process conducted by denitrifying bacteria and phosphate accumulating organisms, the denitrifying phosphate accumulating organisms can simultaneously remove nitrogen and phosphorus under alternated anaerobic and anoxic/aerobic conditions. It is worth noting that microorganisms capable of simultaneously removing nitrogen and phosphorus absolutely under aerobic conditions have been reported in recent years, but the mechanisms remain unclear. This review summarizes the species and characteristics of denitrifying phosphate accumulating organisms and the microorganisms capable of performing simultaneous nitrification-denitrification and phosphorous removal. Moreover, this review analyzes the relationship between nitrogen removal and phosphorus removal and the underlying mechanisms, discusses the challenges of denitrifying phosphorus removal, and prospects future research directions, with the aim to facilitate process improvement of denitrifying phosphate accumulating organisms.

Nitrogen removal characterization and functional enzymes identification of a hypothermia bacterium Pseudomonas fragi EH-H1.

A novel hypothermic strain, Pseudomonas fragi EH-H1, was found to effectively perform heterotrophic nitrification and aerobic denitrification at 15 °C. This strain could consume 100 %, 100 % and 99.95 % of ammonium (54.90 mg∙L-1), nitrate (56.12 mg∙L-1) and nitrite (54.15 mg∙L-1), accompanied by peak removal rates of 5.51, 3.63 and 3.14 mg/L/h, respectively. The ammonium was removed preferentially during simultaneous nitrification and denitrification. Notably, the elimination rate of the toxic nitrite nitrogen remained approximately 3.14 mg/L/h, whether supplemented with ammonium or not. Stepwise inhibition experiments revealed that the key enzymes of ammonia monooxygenase (AMO) and nitrite oxidoreductase (NiR) for nitrification and denitrification coexisted in strain EH-H1. AMO, nitrate reductase and NiR were successfully expressed and detected at 0.637, 0.239 and 0.018 U/mg proteins, respectively. Overall, strain EH-H1 had an outstanding ability to remove nitrogen at low temperatures and could provide guidance for cryogenic wastewater treatment.