Kinetics of denitritification and denitratification in anoxic filters

Denitritification and denitratification in anoxic filters were performed to generate experimental data. Also, a kinetic model of denitratification that accounts for intrinsic biokinetics and hydrodynamic behavior of the biofilter is proposed. In denitritification, the simulated results are in good agreement with the experimental data; and a higher nitrite influent concentration gives a higher nitrite reduction efficiency if the denitrifying loading is kept the same. In denitratification, the intermediate nitrite tends to accumulate, and a higher denitrifying loading results in a higher nitrite effluent concentration. By inserting biological and physical parameter values into the kinetic model, the variations in distributed fractions of nitrate-reductase (f) and nitrite-reductase (1-f) with different denitrifying loadings can be estimated by fitting in experimental data. The estimated f increased with an increase in denitrifying loading, implying that a higher denitrifying loading results in a higher nitrite effluent concentration. From parametric sensitivity analyses, the parameter f is more sensitive than other biological and physical parameters. Accordingly, the proposed kinetic model of denitratification can be used to predict the treatment performance of anoxic filters appropriately. Copyright 1998 John Wiley & Sons, Inc.     

Consecutive reaction kinetics involving distributed fraction of methanogens in fluidized-bed bioreactors

A kinetic model involving the distributed fractions of acidogens and methanogens is proposed. To determine the fluxes and biochemical reaction rates of the substrate sucrose and its intermediates, volatile fatty acids (VFAs) in bulk liquid and within the biofilm, a kinetic model was developed by combining the solid-phase model with the liquid-phase model. The predicted substrate removal efficiencies of the conventional and tapered fluidized-bed bioreactors (CFB, TFBs) are in good agreement with the experimental results. The biofilm thickness in TFBs are thicker than that in CFB, resulting in performance enhancement with TFBs. The simulated results obtained from the kinetic model show that methanogenesis is the rate-limiting step of degradation of the simple organic compound (sucrose), and the chemical oxygen demand (COD) concentration in the effluent is mainly contributed by the intermediates VFAs. The distributed fractions of acidogens and methanogens determined experimentally are 0.4 and 0.6, respectively.     

Inferring the roles of vicariance,climate and topography in population differentiation in Salamandra algira (Caudata,Salamandridae)

Integrating information from species occurrence data, environmental variables and molecular markers can provide valuable insights about the processes of population persistence and differentiation. In this study, we present the most comprehensive overview of the evolutionary history of the North African salamander Salamandra algira (Caudata, Salamandridae) to date, including analyses of climatic and topographical variables, and sequences of two mitochondrial and two nuclear DNA fragments, with a special focus on Algerian populations, under‐represented in previous studies. Coalescent‐based phylogenetic analyses of mtDNA data recover four well‐supported population groups corresponding to described subspecies, with a western clade including populations in north‐western Morocco (with two subclades corresponding to the subspecies tingitana and splendens), and an eastern clade including populations from north‐eastern Morocco (subspecies spelaea) and Algeria (subspecies algira). Inferred split times between major clades date back to the Miocene, with additional splits within each major clade in the Plio‐Pleistocene. Present climatic (aridity) and topographical factors account for geographical discontinuities across population groups and help identify potential areas of secondary contact between clades corresponding to the subspecies tingitana and splendens in the Rif mountains in Morocco. Niche analysis indicates the absence of phylogenetic signal in the use of environmental space in this species.     

A 1,100-year-old founder effect mutation in IL12B gene is responsible for Mendelian susceptibility to mycobacterial disease in Tunisian patients

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare disorder predisposing apparently healthy individuals to infections caused by weakly virulent mycobacteria such as bacille Calmette–Guerin (BCG), environmental mycobacteria, and poorly virulent Salmonella strains. IL-12p40 deficiency is the first reported human disease due to a cytokine gene defect and is one of the deficiencies that cause MSMD. Nine mutant alleles only have been identified in the IL12B gene, and three of them are recurrent mutations due to a founder effect in specific populations. IL-12p40 deficiency has been identified especially in countries where consanguinity is high and where BCG vaccination at birth is universal. We investigated, in such settings, the clinical, cellular, and molecular features of six IL-12p40-deficient Tunisian patients having the same mutation in IL12B gene (c.298_305del). We found that this mutation is inherited as a common founder mutation arousing ~1,100 years ago. This finding facilitates the development of a preventive approach by genetic counseling and prenatal diagnosis especially in affected families.     

The North China Steptoean positive carbon isotope excursion and its global correlation with the base of the Paibian Stage (early Furongian Series), Cambrian

The use of carbon isotope excursion in Cambrian stratigraphical correlation is a standard practice at both the intercontinental and intracontinental scales. The Steptoean positive carbon isotope excursion (SPICE) is one of the prime examples in this regard in correlating the base of the Paibian Stage and Furongian Series. A lack of definite SPICE evidence in the North China craton has been a challenge in precision correlation between North China and other palaeo‐continents. This study provides new carbonates carbon isotope data from the type locality of the Changshan Formation in Hebei Province, North China. Our new δ13C_carb data provide new objective evidence for the presence of the SPICE in North China. The sampling section is relatively condensed, and the interval of the SPICE curve is less than one and half‐metres after analysing 64 samples (the sampling interval within the SPICE is less than 10 cm). The onset of the SPICE curve in Tangshan, Hebei, occurs in the barren interval between the Neodrepanura and Chuangia trilobite zones. Based on this study and previous work, this could imply the middle part of the Prochuangia‐Paracoosia trilobite Zone in North China and can be correlated with the base of the Paibian Stage and Furongian Series.     

OPTIMIZATION OF SALT CONCENTRATIONS FOR A HIGHER CAROTENOID PRODUCTION IN DUNALIELLA SALINA (CHLOROPHYCEAE)1

Dunaliella salina (Dunal) Teodor, when treated over 25 d with a wide range of NaCl salinities (0.6–4.5 M), showed its maximal growth potentialities at 1.5–3.0 M NaCl and was able to survive even at 4.5 M NaCl. Sodium concentrations increased significantly at the supraoptimal salinities, reaching up to 5 mmol · g^?1 dry weight (dwt) at 4.5 M NaCl. Interestingly, ability of D. salina to take up essential mineral nutrients was not impaired by increased salinity. As for growth, chl concentrations were maximal in the 1.5–3.0 M NaCl range. Interestingly, carotenoid concentrations increased with the increasing salinity. The highest values of total antioxidant activity (5.2–6.9 mg gallic acid equivalents [GAE] · g^?1 dwt), antiradical activity, and reducing power were measured at 1.5–3.0 M NaCl. As a whole, these results showed that at 1.5–3.0 M NaCl, D. salina produce appreciable antioxidant level. But, once it reaches its growth maximum, a salt addition up to 4.5 M could enhance its carotenoid yield.     

Mammalian Kinesin-3 Motors Are Dimeric In Vivo and Move by Processive Motility upon Release of Autoinhibition

Kinesin-3 motors drive the transport of synaptic vesicles and other membrane-bound organelles in neuronal cells. In the absence of cargo, kinesin motors are kept inactive to prevent motility and ATP hydrolysis. Current models state that the Kinesin-3 motor KIF1A is monomeric in the inactive state and that activation results from concentration-driven dimerization on the cargo membrane. To test this model, we have examined the activity and dimerization state of KIF1A. Unexpectedly, we found that both native and expressed proteins are dimeric in the inactive state. Thus, KIF1A motors are not activated by cargo-induced dimerization. Rather, we show that KIF1A motors are autoinhibited by two distinct inhibitory mechanisms, suggesting a simple model for activation of dimeric KIF1A motors by cargo binding. Successive truncations result in monomeric and dimeric motors that can undergo one-dimensional diffusion along the microtubule lattice. However, only dimeric motors undergo ATP-dependent processive motility. Thus, KIF1A may be uniquely suited to use both diffuse and processive motility to drive long-distance transport in neuronal cells.     

Antimicrobial and antioxidant activities of methanol extracts of <Emphasis Type="Italic">Evax pygmaea</Emphasis> (Asteraceae) growing wild in Tunisia

Antimicrobial activity of methanolic extracts obtained from the aerial parts of Evax pygmaea was tested against five bacteria and two strains of phytopathogenic fungi using the agar diffusion and broth microdilution methods. Antioxidant properties were evaluated through the ability of the different fractions to scavenge the stable ABTS (2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals. The TEAC (Trolox Equivalent Antioxidant Capacity) and IC₅₀ values of the fractions were calculated and compared. The experimental data indicated that all fractions exhibit moderate to appreciable antibacterial activities against all Gram-positive cocci and Gram-negative rods except Pseudomonas aeruginosa, but no antifungal activity was observed. Ethyl acetate and methanol fractions were found to cause significant free radical-scavenging effects in both assays. These results may suggest that E. pygmaea could be used as a natural preservative ingredient in the food and/or pharmaceutical industries.     

Biphenyl‐Type Neolignan Derivatives from the Twigs of Magnolia denudata and Their Anti‐Inflammatory Activity

Two new biphenyl‐type neolignan derivatives, 2‐[2‐(hydroxymethyl)‐1‐benzofuran‐5‐yl]‐4‐(prop‐2‐en‐1‐yl)phenol ( 1 ) and 2′‐ethoxy‐5,5′‐di(prop‐2‐en‐1‐yl)biphenyl‐2‐ol ( 2 ), were isolated from the twigs of Magnolia denudata, together with six known compounds ( 3 – 8 ). The structures of 1 and 2 were determined through extensive 1D‐ and 2D‐NMR and mass‐spectrometric analyses. Magnolol ( 6 ) and honokiol ( 7 ) exhibited potent inhibition (IC₅₀ values=4.4±0.2 and 0.71±0.13 μg/ml, resp.) of O$\rm{{_{2}^{{^\cdot} -}}}$ generation by human nutrophils in response to N‐formyl‐L ‐methionyl‐L ‐leucyl‐L ‐phenylalanine/cytochalasin B (fMLP/CB). In addition, 2‐[2‐(hydroxymethyl)‐1‐benzofuran‐5‐yl]‐4‐(prop‐2‐en‐1‐yl)phenol ( 1 ), 2′‐ethoxy‐5,5′‐di(prop‐2‐en‐1‐yl)biphenyl‐2‐ol ( 2 ), magnolol ( 6 ), and vanillic acid ( 8 ) inhibited fMLP/CB‐induced elastase release with IC₅₀ values=6.4±1.5, 2.4±0.4, 1.5±0.2, and 4.8±0.5 μg/ml, respectively.