Denitrification is an indispensable part of most sewage treatment systems. The biological denitrification process has attracted much attention in the past decades due to the advantages such as cost-effectiveness, process simplicity, and absence of secondary pollution. This review summarized the advances on biological denitrification processes in recent years according to the different physiological characteristics and denitrification mechanisms of denitrification microorganisms. The pros and cons of different biological denitrification processes developed based on nitrifying bacteria, denitrifying bacteria, and anaerobic ammonia-oxidizing bacteria were compared with the aim to identify the best strategy for denitrification in a complex wastewater environment. The rapid development of synthetic biology provides possibilities to develop highly-efficient denitrifying strains based on mechanistic understandings. Combined with the applications of automatic simulation to obtain the optimal denitrification conditions, cost-effective and highly-efficient denitrification processed can be envisioned in the foreseeable future.
Aerobiosis ; Denitrification ; Nitrification ; Nitrogen ; Waste Water

Heterotrophic nitrification-aerobic denitrification (HN-AD) is an enrichment and breakthrough theory of traditional autotrophic nitrification heterotrophic denitrification. Heterotrophic nitrification-aerobic denitrifiers with the feature of wide distribution, strong adaptability and unique metabolic mechanism have many special advantages, including fast-growing, rapid biodegradability and long lasting activity, which can rapidly remove ammonia nitrogen, nitrate nitrogen (NO₃⁻-N) and nitrite nitrogen (NO₂⁻-N) under aerobic conditions simultaneously. Therefore, HN-AD bacteria show the important potential for denitrification under extreme conditions with high-salt, low-temperature or high-ammonia nitrogen environment, and HN-AD bacteria attract extensive attention in the field of biological denitrification of wastewater. In this review, we first introduce the previously reported HN-AD bacterial species which have denitrification performance in the extreme environments and state their typical metabolic mechanism. Then, we systematically analyze the nitrogen removal characteristics and potential under extreme conditions. We also briefly describe the progress in the application of HN-AD bacterial. Finally, we outlook the application prospects and research directions of HN-AD denitrification technology.
Aerobiosis ; Bacteria ; Denitrification ; Heterotrophic Processes ; Nitrification ; Nitrites ; Nitrogen

Heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are aerobic microorganisms that can remove nitrogen under high-salt conditions, but their performance in practical applications are not satisfactory. As a compatible solute, trehalose helps microorganisms to cope with high salt stress by participating in the regulation of cellular osmotic pressure, and plays an important role in promoting the nitrogen removal efficiency of microbial populations in the high-salt environment. We investigated the mechanism of exogenous-trehalose-enhanced metabolism of HN-AD community under high-salt stress by starting up a membrane aerobic biofilm reactor (MABR) to enrich HN-AD bacteria, and designed a C₁₅₀ experimental group with 150 μmol/L trehalose addition and a C₀ control group without trehalose. The reactor performance and the community structure showed that NH₄⁺-N, total nitrogen (TN) and chemical oxygen demand (COD) removal efficiency were increased by 29.7%, 28.0% and 29.1%, respectively. The total relative abundance of salt-tolerant HN-AD bacteria (with Acinetobacter and Pseudofulvimonas as the dominant genus) in the C₁₅₀ group reached 66.8%, an 18.2% increase compared with that of the C₀ group. This demonstrated that trehalose addition promoted the enrichment of salt-tolerant HN-AD bacteria in the high-salt environment to enhance the nitrogen removal performance of the system. In-depth metabolomics analysis showed that the exogenous trehalose was utilized by microorganisms to improve proline synthesis to increase resistance to high-salt stress. By regulating the activity of cell proliferation signaling pathways (cGMP-PKG, PI3K-Akt), phospholipid metabolism pathway and aminoacyl-tRNA synthesis pathway, the abundances of phosphoethanolamine, which was one of the glycerophospholipid metabolites, and purine and pyrimidine were up-regulated to stimulate bacterial aggregation and cell proliferation to promote the growth of HN-AD bacteria in the high-salt environment. Meanwhile, the addition of trehalose accelerated the tricarboxylic acid (TCA) cycle, which might provide more electron donors and energy to the carbon and nitrogen metabolisms of HN-AD bacteria and promote the nitrogen removal performance of the system. These results may facilitate using HN-AD bacteria in the treatment of high-salt and high-nitrogen wastewater.
Nitrification ; Denitrification ; Trehalose ; Phosphatidylinositol 3-Kinases/metabolism* ; Heterotrophic Processes ; Salt Stress ; Nitrogen/metabolism* ; Aerobiosis ; Bioreactors/microbiology*

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.
Phosphorus ; Phosphates ; Wastewater ; Denitrification ; Waste Disposal, Fluid ; Nitrogen ; Bioreactors/microbiology* ; Nitrification ; Sewage

Anaerobic ammonium oxidation (ANAMMOX), as its essential advantages of high efficiency and low cost, is a promising novel biological nitrogen elimination process with attractive application prospects. Over the past two decades, many processes based on the ANAMMOX reaction have been continuously studied and applied to practical engineering, with the perspective of reaching 100 full-scale installations in operation worldwide by 2014. Our review summarizes various forms of ANAMMOX processes, including partial nitritation-ANAMMOX, completely autotrophic nitrogen removal over nitrite, oxygen limited autotrophic nitrification and denitrification, denitrifying ammonium oxidation, aerobic deammonification, simultaneous partial nitrification, ANAMMOX and denitrification, single-stage nitrogen removal using ANAMMOX and partial nitritation. We also compare the operating conditions for one-stage and two-stage processes and summarize the obstacles and countermeasures in engineering application of ANAMMOX systems, such as moving bed biofilm reactor, sequencing batch reactor and granular sludge reactor. Finally, we discuss the future research and application direction, which should focus on the optimization of operating conditions and applicability of the process to the actual wastewater, especially on automated control and the impact of special wastewater composition on process performance.
Ammonia ; chemistry ; Bioreactors ; Denitrification ; Nitrification ; Nitrites ; chemistry ; Nitrogen ; chemistry ; Oxygen ; chemistry ; Sewage ; chemistry ; Waste Disposal, Fluid ; methods ; Waste Water ; chemistry

Two types of mycorrhizae, orchid (OM) and arbuscular mycorrhizae (AM), were observed in the cortical cells of Botrychium ternatum roots. The vesicles or arbuscules of AM fungi were examined and the fresh or digestive pelotons by other species of basidiomycetes were also observed in the roots under light microscope. These symbioses were, as the genomic DNAs extracted from roots of B. ternatum reacted with the specific primers, confirmed with PCR technique, being added to more strong evidences. These discoveries were rarely happened in the roots, especially a fern in nature. OM was observed in the roots of B. ternatum collected from the nationwide areas, whereas AM was only in the roots of B. ternatum collected from Chung-Buk areas. It is speculated that OM are associated with the nitrogen cycle in Islands and the growth of B. ternatum in the inland of Central Korea is related to both the phosphate and nitrogen cycle in the nature. The results suggest that B. ternatum is a typical species with two types of mycorrhizae under various growing conditions.
Basidiomycota ; DNA ; Ferns ; Fungi ; Islands ; Korea ; Mycorrhizae ; Nitrogen Cycle ; Polymerase Chain Reaction ; Symbiosis

Anaerobic ammonia oxidation (Anammox) is one of the important discoveries in the field of environmental microbiology, and it plays an indispensible role in the nitrogen removal from wastewaters and the biogeochemical nitrogen cycle. Through review research progress in anaerobic ammonia oxidation, an Anammox special issue is published so as to find problems, explore applications and outlook developments. The special issue consists of reviews and original papers, mainly involving in the following aspects: i) enrichment of Anaerobic ammonia oxidation bacteria (AnAOB); ii) community analysis of AnAOB; iii) preservation of granular AnAOB sludge; iv) effect of organic matter on Anammox; v) application of Anammox process, etc.
Ammonia ; chemistry ; Bacteria, Anaerobic ; metabolism ; Environmental Microbiology ; Nitrogen ; chemistry ; Nitrogen Cycle ; Oxidation-Reduction ; Sewage ; microbiology ; Waste Disposal, Fluid ; Waste Water ; chemistry

Alpha-ketoglutarate (AKG) is a key molecule in the Krebs cycle determining the overall rate of the citric acid cycle of the organism. It is a nitrogen scavenger and a source of glutamate and glutamine that stimulates protein synthesis and inhibits protein degradation in muscles. AKG as a precursor of glutamate and glutamine is a central metabolic fuel for cells of the gastrointestinal tract as well. AKG can decrease protein catabolism and increase protein synthesis to enhance bone tissue formation in the skeletal muscles and can be used in clinical applications. In addition to these health benefits, a recent study has shown that AKG can extend the lifespan of adult Caenorhabditis elegans by inhibiting ATP synthase and TOR. AKG not only extends lifespan, but also delays age-related disease. In this review, we will summarize the advances in AKG research field, in the content of its physiological functions and applications.
Adenosine Triphosphate ; Adult ; Bone and Bones ; Caenorhabditis elegans ; Citric Acid Cycle ; Gastrointestinal Tract ; Glutamic Acid ; Glutamine ; Humans ; Insurance Benefits ; Metabolism ; Muscle, Skeletal ; Muscles ; Nitrogen ; Proteolysis

OBJECTIVE: p16INK4 and p15INK4B genes are known to be tumor suppressor genes which reside in p21 region of chromosome 9 and are related to cell cycle control as an inhibitor of cyclin-dependent-kinase. We designed this study to search for deletion and decreased expression of p16INK4 and p15INK4B genes in advanced ovarian carcinomas. METHODS: Polymerase chain reaction (PCR)-based analysis was performed to search for deletion of p16INK4 and p15INK4B using DNA extracted from frozen tissue in liquid nitrogen of thirty-one advanced ovarian carcinoma patients. The intensities of PCR bands were analyzed using an imaging densitometer to determine gene dosage in tumor samples and the relative gene dosage was calculated by comparing band intesity of p16INK4 or p15INK4B with that of beta-globin gene. Homozygous deletions were assigned to tumors in which the ratio was reduced to less than 25% in any one of exons of p16INK4 and p15INK4B. Immunohistochemical techniques were used to study the expression of p16INK4. p16-negative cells were characterized by the absence of nuclear staining, whereas cytoplasmic staining was variable. Clinico-pathologic features, complete remission rates and survivals were analyzed according to the status of p16INK4 and p15INK4B genes. RESULTS: Homozygous deletion of p16INK4 was detected in 12.9% of advanced ovarian carcinoma patients and that of p15INK4B in 35.5%. Clinico-pathologic features such as FIGO stage, histological grade, serum CA-125 levels were not different from groups with homozygously deleted p16INK4 and p15INK4B to those with normal genes. The survival of patients (13 [6-20] months) with homozygously deleted p16INK4 was significantly shorter than that (30 [8-52] months) of patients with normal p16INK4 (p=0.046; Log-rank test). CONCLUSION: These observations indicate that deletions of p16INK4 and p15INK4B gene might be involved in tumorigenesis of ovarian carcinoma and could be useful as a prognostic factor. A prospective, controlled study with more patients will be mandatory in the future.
beta-Globins ; Carcinogenesis ; Cell Cycle Checkpoints ; Chromosomes, Human, Pair 9 ; Cytoplasm ; DNA ; Exons ; Gene Dosage ; Genes, Tumor Suppressor ; Humans* ; Immunohistochemistry ; Nitrogen ; Polymerase Chain Reaction

The denitrifier method is widely used as a novel pretreatment method for the determination of nitrogen and oxygen isotope ratios as it can provide quantitative and high-sensitivity measurements. Nevertheless, the method is limited by relatively low measurement accuracy for δ18O. In this study, we analyzed the factors influencing the accuracy of δ18O determination, and then systematically investigated the effects of dissolved oxygen concentrations and nitrate sample sizes on estimates of the δ15N and δ18O of nitrate reference materials. The δ18O contraction ratio was used to represent the relationship between the measured difference and true difference between two reference materials. We obtained the following main results: (1) a gas-liquid ratio of 3:10 (v/v) in ordinary triangular flasks and a shaking speed of 120 r/min produced an optimal range (1.9 to 2.6 mg/L) in the concentration of dissolved oxygen for accurately determining δ18O, and (2) the δ18O contraction ratio decreased as nitrate sample size decreased within a certain range (1.0 to 0.1 μmol). Our results suggested that δ18O contraction is influenced mainly by dissolved oxygen concentrations in pure culture, and provided a model for improving the accuracy of oxygen isotope analysis.
Denitrification ; Nitrates/analysis* ; Oxygen Isotopes/analysis*