Inhibitory factors affecting the process of enhanced biological phosphorus removal (EBPR) – A mini-review

Enhanced biological phosphorus removal (EBPR) technology has been widely considered as a key strategy in preventing eutrophication and recognized as the advancing front of research in wastewater treatment. The key to keep its high efficiency in biological phosphorus removal is to optimize the operation and management of the system. Previous research in this field has undoubtedly improved understanding of the factors hindered overall efficiency of EBPR. However, it is obvious that much remains to be learnt. This paper attempts to review the fundamental understanding in factors inhibiting the stability and reliability of the EBPR systems in the state-of-the-art research. In view of modeling the EBPR systems, an appropriate extension of the current mechanistic models with these inhibitory factors is recommended in order to better simulate and predict the behavior of full-scale and lab-scale EBPR plants. From the perspectives of the further mechanistic and multi-factors study, the direction of denitrifying dephosphatation and granules/biofilms are also discussed. This comprehensive overview will not only help us to understand the overall mechanism of the EBPR process, but also benefit the researchers and engineers to consider all the possible factors affecting the process in the urban sewage treatment plants.     

Functional Identification of the Hypoxanthine/Guanine Transporters YjcD and YgfQ and the Adenine Transporters PurP and YicO of Escherichia coli K-12

The evolutionarily broad family nucleobase-cation symporter-2 (NCS2) encompasses transporters that are conserved in binding site architecture but diverse in substrate selectivity. Putative purine transporters of this family fall into one of two homology clusters: COG2233, represented by well studied xanthine and/or uric acid permeases, and COG2252, consisting of transporters for adenine, guanine, and/or hypoxanthine that remain unknown with respect to structure-function relationships. We analyzed the COG2252 genes of Escherichia coli K-12 with homology modeling, functional overexpression, and mutagenesis and showed that they encode high affinity permeases for the uptake of adenine (PurP and YicO) or guanine and hypoxanthine (YjcD and YgfQ). The two pairs of paralogs differ clearly in their substrate and ligand preferences. Of 25 putative inhibitors tested, PurP and YicO recognize with low micromolar affinity N⁶-benzoyladenine, 2,6-diaminopurine, and purine, whereas YjcD and YgfQ recognize 1-methylguanine, 8-azaguanine, 6-thioguanine, and 6-mercaptopurine and do not recognize any of the PurP ligands. Furthermore, the permeases PurP and YjcD were subjected to site-directed mutagenesis at highly conserved sites of transmembrane segments 1, 3, 8, 9, and 10, which have been studied also in COG2233 homologs. Residues irreplaceable for uptake activity or crucial for substrate selectivity were found at positions occupied by similar role amino acids in the Escherichia coli xanthine- and uric acid-transporting homologs (XanQ and UacT, respectively) and predicted to be at or around the binding site. Our results support the contention that the distantly related transporters of COG2233 and COG2252 use topologically similar side chain determinants to dictate their function and the distinct purine selectivity profiles.     

Computational Oral Absorption Simulation for Low‐Solubility Compounds

Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the Henderson–Hasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the Nernst–Brunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed.     

Computational Fluid Dynamics Analysis of Upper Airway Changes after Protraction Headgear and Rapid Maxillary Expansion Treatment

Clinically, it is common for Class III patients with maxillary skeletal deficiency, which may result in a variety of adverse consequences. Protraction headgear and rapid maxillary expansion (PE) is an effective treatment, but its effect on upper airway hydrodynamics has not been reported. The main purpose of this study was to evaluate the changes of the flow in the upper airway after PE by computational fluid dynamics (CFD). The sample includes fifteen patients (6 males, 9 females, age 11.00 ± 1.00) and the paired T-test was used to analyze the differences between the measured data before and after treatment. The maximum flow velocity decreased from 8.42 ± 0.16 m/s to 6.98 ± 0.36 m/s (p < 0.05), and the maximum shear force decreased from 3.72 ± 1.48 Pa to 2.13 ± 0.18 Pa. The maximum negative pressure decreased from −101.78 ± 33.60 Pa to 58.15 ± 9.16 Pa, only the changes of velopharynx and glossopharynx were statistically significant; while the maximum resistance decreased from 140.88 ± 68.68 Pa/mL/s to 45.95 ± 22.96 Pa/mL/s. PE can effectively reduce the airflow resistance of the upper airway and the probability of airway collapse, thus improving the patient’s ventilation function.     

Crown alterations induced by decline: a study of relationships between growth rate and crown morphology in beech (Fagus sylvatica L.)

One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells.     

流行性感冒季节性的基本原因和模型理论

流行性感冒（流感）在世界范围内每年造成（300～500）万例严重疾病和（25～50）万例死亡。流感可造成严重的公共卫生和经济问题。流感流行和爆发都是以流感季节为特征。因为与甲型流感病毒相关疾病的发病率和死亡率水平较高,因此本研究从病毒学、流行病学、生物学和数学等方面重点讨论甲型流感季节性的基本原因和模型理论。     

Systematic development of computational models for the catalytic site in galactose oxidase: impact of outer-sphere residues on the geometric and electronic structures

A systematic in silico approach has been employed to generate sound, experimentally validated active-site models for galactose oxidase (GO) using a hybrid density functional, B(38HF)P86. GO displays three distinct oxidation states: oxidized [Cu(II)-Y*]; semireduced [Cu(II)-Y]; and reduced [Cu(I)-Y]. Only the [Cu(II)-Y*] and the [Cu(I)-Y] states are assumed to be involved in the catalytic cycle, but their structures have not yet been determined. We have developed several models (1-7) for the [Cu(II)-Y*] state that were evaluated by comparison of our computational results with experimental data. An extended model system (6) that includes solvent molecules and second coordination sphere residues (R330, Y405, and W290) is essential to obtain an experimentally correct electronic structure of the active site. The optimized structure of 6 resulted in a five-coordinate Cu site with a protein radical centered on the Tyr-Cys cofactor. We further validated our converged model with the largest model (7) that included additional outer-sphere residues (Q406, H334, Y329, G513, and T580) and water molecules. Adding these residues did not affect significantly the active site's electronic and geometric structures. Using both 6 and 7, we explored the redox dependence of the active-site structure. We obtained four- and three-coordinate Cu sites for [Cu(II)-Y] and [Cu(I)-Y] states, respectively, that corroborate well with the experimental data. The relative energies of these states were validated by a comparison with experimental redox potentials. Collectively, our computational GO models well reproduce the physicochemical characteristics of the individual states, including their redox behaviors.     

一株拮抗赤霉病的小麦内生细菌的筛选和抑菌活性

对安徽省淮北市小麦植株根、茎、叶中内生细菌的数量进行了调查和筛选,并测定了其抑菌活性.小麦根、茎和叶中的内生细菌的数量分别为7.01×105、4.26×105和0.94×105CFU·g-1鲜重.从健康小麦植株体内分离到131株内生细菌,通过对峙实验,筛选到6株对禾谷镰刀菌有拮抗作用的菌株,占所分离内生细菌总数的4.58%.来自根系组织中的菌株HB022的抑菌效果最佳,抑菌半径为17.0mm.根据形态特征、生理生化特性和16SrDNA序列分析,将菌株HB022初步鉴定为多粘类芽孢杆菌(Paenibacillus polymyxa).抑菌试验结果表明,100倍稀释的菌株HB022无菌发酵滤液对禾谷镰刀菌菌丝生长具有明显抑制作用,5倍稀释的无菌发酵滤液可完全抑制禾谷镰刀菌分生孢子萌发.可见,内生细菌HB022具有潜在生防应用前景.     

Circadian clock effects on cellular proliferation: Insights from theory and experiments

Oscillations of the cellular circadian clock have emerged as an important regulator of many physiological processes, both in health and in disease. One such process, cellular proliferation, is being increasingly recognized to be affected by the circadian clock. Here, we review how a combination of experimental and theoretical work has furthered our understanding of the way circadian clocks couple to the cell cycle and play a role in tissue homeostasis and cancer. Finally, we discuss recently introduced methods for modeling coupling of clocks based on techniques from survival analysis and machine learning and highlight their potential importance for future studies.