Model of ammonia volatilization from calcareous soils

A quantitative model of ammonia volatilization from the calcareous soil uppermost 1-cm layer was developed and tested. The model accounts for the following processes: ammonium-ammonia equilibration in the soil solution, cation exchange between calcium and ammonium which results in ammonium distribution between soil liquid and solid phases, nitrification of dissolved ammonium, distribution of ammonia between liquid and gaseous phases and diffusion of gaseous ammonia in the soil air. The combined effect of various characteristics such as soil pH, cation exchange capacity, water capacity and nitrification rate on ammonia losses from various soil types have been studied. The model was validated against experimental results of ammonia losses from different soils for its use as a predicting tool. The model shows that most of ammonia losses can be explained by the interactive effect of high soil pH and low cation exchange capacity. Computations show increased ammonia volatilization with decreasing soil water capacity. Increasing fertilizer application rate has a small effect on percentage of ammonia losses. Increased nitrification rate and shorter “lag” period of nitrification reduce ammonia losses considerably. Good agreement was obtained between model calculations and experimental results of ammonia volatilization from 13 soils.     

A system for coupled multiple-column separation of proteins

Purification of proteins is commonly a multiple-step process involving size exclusion, ion exchange, affinity, hydrophobic, and other modes of chromatography. In an effort to circumvent the laborious process of collecting the solutes from each column and reintroducing them onto a second column, a valving system is described that directs the samples eluted from a high-performance liquid chromatographic column through a detector with a high-pressure cell into either a second column or into storage loops of a multiloop value. This multiloop value is referred to as a high-pressure fraction collector. After development of the first column is complete, a second solvent can be directed to the second column or high-pressure fraction collector to elute the solutes back through the detector and onto any other column in the system. The process of eluting a sample from a column through a single detector and directing it to the high-pressure fraction collector or any other column in the system may be repeated a number of times. Such valving systems make it possible to chromatograph a single protein component on two or three columns in a short time.     

Supramolecular organization in streptococcal pericellular capsules is based on hyaluronan tertiary structures

Supramolecular organization involving a polyanionic glycan in a bacterial capsule (hyaluronan, HA, in streptococcal capsules) is revealed, for the first time, by electron-histochemical methodology previously used to elucidate ultrastructure in extracellular matrix. Capsular HA filaments thereby revealed closely resemble aligned linear structures demonstrated by similar technology in HA solution. These parallel arrays, spontaneously formed, are based on HA tertiary structures (beta sheet-like) which are stabilized by hydrophobic and hydrogen bonds. HA tertiary structures in aqueous solutions resist shear stress as shown by rheo-NMR. Thus, supramolecular HA wrapping covering many cells probably stabilizes chains of bacteria. Streptococci possibly templated the ordered structures since eukaryotic B6 cell HA did not produce similarly organized envelopes. Supramolecular organization in streptococcal and pneumococcal capsules are compared. Their glycans are very similar but the potential for HA-like tertiary structures is not present in the pneumococcal type 3 polysaccharide and chains of cells are not formed to the same extent by pneumococci. We suggest that the streptococcal capsule exemplifies a simple extracellular matrix analogous to those in animal connective tissues, which contain glycans (chondroitin, keratan, and dermochondan sulfates) of the HA family, capable of undergoing aggregation to similar tertiary structures.     

Rapid induction of large chromosomal deletions by a Cre/inverted loxP system in mouse ES Cell hybrids

Loss of heterozygosity by whole or partial loss of chromosomal regions is crucial to genetic disorders, cancers and diseases. It is difficult to analyze the mechanisms of pathogenesis caused by large-scale chromosomal abnormalities due to the extreme rarity of this mutagenesis. Using a Cre/inverted loxP system, we have generated a chromosome elimination cassette (CEC) that induces a selective loss of embryonic-stem-cell-derived chromosomes in undifferentiated embryonic stem cell-somatic cell hybrids. Here, due to the increased expression of Cre, rapid formation of Cre recombination products and immediate loss of CEC-tagged chromosomes were detected by fluorescence in situ hybridization. Cre also initiated intrachromosomal recombination between identical short sequences outside loxP, leading to large chromosomal deletions of CEC-tagged regions. The Cre-mediated antiparallel synapses likely act as a scaffold to bring the identical short sequences into close proximity for recombination. This CEC technology might allow better understanding of the modulator sequences responsible for the tangled structure formation and its solution mechanism, inducing mitotic recombination leading to chromosomal deletions.     

Determination of cation exchange capacity of woody plant roots using ammonium acetate extractant

Summary A rapid exchange procedure using ammonium acetate as an extractant was developed for measurement of cation exchange capacity (CEC) of plant roots. The CEC values obtained with 1∶100 and 1∶200 root/solution ratios were almost equal, though the values increased with length of the time of immersion in both the root/solution ratios. The method gave higher CEC values with fresh roots as compared to dried roots. However, dried milled and dried unmilled roots gave identical values.     

The relative impact of lichen symbiotic partners to repeated copper uptake

The relative impact of lichen photobiont and mycobiont was evaluated by submitting nine lichen species with: (i) different photobiont types; (ii) different lichen growth forms; and (iii) different nutrients, pH, humidity preferences; to a range of Cu concentrations (μM) supplied in repeated cycles to simulate the natural process of uptake under field conditions. The physiological performance of the photosystem II photochemical reactions was measured using F_v/F_m and the metabolic activity of the mycobiont was evaluated using ergosterol and intracellular K-loss as indicators. Lichens with higher cation exchange capacity showed higher intracellular Cu uptake and their ecology seemed to be associated with low-nutrient environments. Thus the wall and external matrix, mainly characteristic of the mycobiont partner, cannot be ignored as the first site of interaction of metals with lichens. No common intracellular Cu concentration threshold was found for the physiological impacts observed in the different species. Most physiological effects of Cu uptake in sensitive lichens occurred for intracellular Cu below 200 μg/g dw whereas more tolerant species were able to cope with intracellular Cu at least 3 times higher. Cyanobacterial lichens showed to be more sensitive to Cu uptake than green-algal lichens. Within the Trebouxia lichens, different species showed different sensitivities to Cu uptake, suggesting that the mycobiont may change the microenvironment close to the photobiont partner providing different degrees of protection. Despite the fact that the photobiont is the productive partner, the metabolic activity of the mycobiont of lichen species adapted to environments rich in nutrients, showed to be more sensitive to Cu uptake than the photochemical performance of the photobiont.     

喀斯特峰丛洼地植被演替过程中土壤养分的积累及影响因素

以桂西北环江县典型喀斯特峰丛洼地为对象,利用空间代替时间的方法,于2009年分析了植被演替过程中表层土壤(0～15 em)养分的变化及其主要控制因素.结果表明:随着植被正向演替(草地-灌丛-次生林-原生林),表层土壤的有机碳、全氮和全磷等含量显著增加,分别由演替初期(草地)的29.1、2.48和0.72 g·kg-1增加为演替后期(原生林)的73.9、8.10和1.6g·kg-1.土壤阳离子交换量与有机碳和全氮密切相关,是喀斯特土壤C、N积累的主要控制因素;凋落物中的P含量、C/P和N/P是土壤全磷积累的主要控制因素,较高的凋落物P含量、N/P以及较低的C/P有利于土壤中P的积累;而坡度、坡向和裸岩率等地形因子对土壤养分的影响较小.     

Chiral separation-based ligand exchange by open-tubular capillary electrochromatography

Chiral ligand-exchange enantioseparation of aliphatic and aromatic amino acids was successfully performed using a new open-tubular zwitterionic column with tentacle-type polymer stationary phase. The polymeric stationary phase was prepared using 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl), a new reactive monomer. The preparation procedure of the open-tubular column included silanization, in situ graft polymerization with HPMA-Cl, and l-histidine (l-His) modification. l-His was used as a chiral ligand-exchange selector and copper(II) as a central ion. Successful enantioseparation of six pairs of amino acid enantiomers was achieved with a buffer of 5 mM CuSO₄, 20 mM (NH₄)₂SO₄ at pH 3.0.     

Towards rationally designed biomanufacturing of therapeutic extracellular vesicles: impact of the bioproduction microenvironment

Extracellular vesicles (EVs), including exosomes, microvesicles, and others, have emerged as potential therapeutics for a variety of applications. Pre-clinical reports of EV efficacy in treatment of non-healing wounds, myocardial infarction, osteoarthritis, traumatic brain injury, spinal cord injury, and many other injuries and diseases demonstrate the versatility of this nascent therapeutic modality. EVs have also been demonstrated to be effective in humans, and clinical trials are underway to further explore their potential. However, for EVs to become a new class of clinical therapeutics, issues related to translation must be addressed. For example, approaches originally developed for cell biomanufacturing, such as hollow fiber bioreactor culture, have been adapted for EV production, but limited knowledge of how the cell culture microenvironment specifically impacts EVs restricts the possibility for rational design and optimization of EV production and potency. In this review, we discuss current knowledge of this issue and delineate potential focus areas for future research towards enabling translation and widespread application of EV-based therapeutics.     

Recent advances in polysaccharide bio-based flocculants

Natural polysaccharides, derived from biomass feedstocks, marine resources, and microorganisms, have been attracting considerable attention as benign and environmentally friendly substitutes for synthetic polymeric products. Besides many other applications, these biopolymers are rapidly emerging as viable alternatives to harmful synthetic flocculating agents for the removal of contaminants from water and wastewater. In recent years, a great deal of effort has been devoted to improve the production and performance of polysaccharide bio-based flocculants. In this review, current trends in preparation and chemical modification of polysaccharide bio-based flocculants and their flocculation performance are discussed. Aspects including mechanisms of flocculation, biosynthesis, classification, purification and characterization, chemical modification, the effect of physicochemical factors on flocculating activity, and recent applications of polysaccharide bio-based flocculants are summarized and presented.