Supersaturation of soil solutions with respect to gypsum

The products of activities of calcium and sulphate were calculated for solutions of 75 glasshouse soils. The majority of these products was found to be higher than the solubility product of gypsum, thus indicating that these soil solutions were possibly supersaturated. In another investigation, soil solutions were examined to determine whether such high activity products could be really attributed to supersaturation. By means of ultracentrifuging of solutions of glasshouse soils, it could be established that the solutions were practically free of sulphate-bearing colloidal particles. Some solutions contained calcium-bearing colloidal particles, but the quantities of calcium contained in these particles were too small to substantially influence the calcium activity. Addition of gypsum crystals to soil solutions led to crystallization of so much calcium and sulphate that the products of the activities of calcium and sulphate dropped from values that can be listed as high to values approaching the solubility product of gypsum. The results obtained demonstrate the occurrence of supersaturation of soil solutions with respect to gypsum. It is further postulated that the presence of humic substances in the soil solution is responsible for this supersaturation. The possible occurrence of supersaturation with respect to gypsum in soils other than glasshouse soils is discussed.     

Polyphenol‐solubility alters amyloid fibril formation of α‐synuclein

Amyloid fibril formation is associated with various amyloidoses, including neurodegenerative diseases such as Alzheimer''s and Parkinson''s diseases. Amyloid fibrils form above the solubility of amyloidogenic proteins or peptides upon breaking supersaturation, followed by a nucleation and elongation mechanism, which is similar to the crystallization of solutes. Many additives, including salts, detergents, and natural compounds, promote or inhibit amyloid formation. However, the underlying mechanisms of the opposing effects are unclear. We examined the effects of two polyphenols, that is, epigallocatechin gallate (EGCG) and kaempferol‐7─O─glycoside (KG), with high and low solubilities, respectively, on the amyloid formation of α‐synuclein (αSN). EGCG and KG inhibited and promoted amyloid formation of αSN, respectively, when monitored by thioflavin T (ThT) fluorescence or transmission electron microscopy (TEM). Nuclear magnetic resonance (NMR) analysis revealed that, although interactions of αSN with soluble EGCG increased the solubility of αSN, thus inhibiting amyloid formation, interactions of αSN with insoluble KG reduced the solubility of αSN, thereby promoting amyloid formation. Our study suggests that opposing effects of polyphenols on amyloid formation of proteins and peptides can be interpreted based on the solubility of polyphenols.     

WINTER PHYTOPLANKTON BLOOMS UNDER ICE ASSOCIATED WITH ELEVATED OXYGEN LEVELS1

Many shallow lakes in north temperate zones experience reduced dissolved oxygen concentration under ice. However, some shallow lakes display supersaturated dissolved oxygen concentrations (>20 mg·L ^{? 1}) in late winter under conditions of maximum ice thickness. During the winters of 1996, 1997, and 1999, we collected phytoplankton samples from Arrowwood Lake near Pingree, North Dakota to determine whether a specific alga was involved in dissolved oxygen supersaturation in this lake. Although dissolved oxygen supersaturation was not observed during this period, we did observe an increase in dissolved oxygen concentration that was associated with a phytoplankton bloom during late February and early March in both 1996 and 1997. In 1996, the bloom was composed of the dinoflagellate, Peridinium aciculiferum (Lemm.) Lemm. and several species of cryptomonads. A similar bloom of P. aciculiferum was followed by a bloom of several species of euglenoids in 1997. In contrast, P. aciculiferum was only a minor component of the winter phytoplankton, dissolved oxygen concentrations remained low, and no bloom event was observed in 1999. Statistical analyses indicated a significant relationship (r_s = 0.57, P = 0.019) between dissolved oxygen levels and the density of the dinoflagellate, P. aciculiferum, but no significant relationship between dissolved oxygen levels and densities of other phytoplankton. These results suggest that the elevated levels of dissolved oxygen are associated with the dinoflagellate, P. aciculiferum. This bloom was most likely the result of an excystment event rather than a general growth response.     

KINETICS OF GROWTH AND DEATH IN ANABAENA FLOS-AQUAE (CYANOBACTERIA) UNDER LIGHT LIMITATION AND SUPERSATURATION

The kinetics of population growth and death were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown at light intensities ranging from limitation to photoinhibition (5 W·m⁻² to 160 W·m⁻²) in a nutrient-replete turbidostat. Steady-state growth rate (μ, or dilution rate, D) increased with light intensity from 0.44·day⁻¹ at a light intensity of 5 W·m⁻² to 0.99·day⁻¹ at 20 W·m⁻² and started to decrease above about 22 W·m⁻², reaching 0.56·day⁻¹ at 160 W·m⁻². The Haldane function of enzyme inhibition fit the growth data poorly, largely because of the unusually narrow range of saturation intensity. However, it produced a good fit (P < 0.001) for growth under photoinhibition. Anabaena flos-aquae died at different specific death rates (γ) below and above the saturation intensity. When calculated as the slope of a v_x⁻¹ and D⁻¹ plot, where v_x and D are cell viability (or live cell fraction) and dilution rate, respectively; γ was 0.047·day⁻¹ in the range of light limitation and 0.103·day⁻¹ under photoinhibition. Live vegetative cells and heterocysts, either in numbers or as a percentage of the total cells, showed a peak at the saturation intensity and decreased at lower and higher intensities. The ratio of live heterocysts to live vegetative cells increased with intensity when light was limiting but decreased when light was supersaturating. In cells growing at the same growth rate, the ratio was significantly lower under light inhibition than under subsaturation and the cell N:C ratio was also lower under inhibition. The steady-state rate of dissolved organic carbon (DOC) production increased with light intensity. However, its production as a percentage of the total C fixation was lowest at the optimum intensity and increased as the irradiance decreased or increased. The rate and percentage was significantly higher under photoinhibition than limitation in cells growing at the same growth rate. About 22% of the total fixed carbon was released as DOC at the highest light intensity. No correlation was found between the number of dead cells and DOC.     

Interaction effects of zooplankton and CO2 on phytoplankton communities and the deep chlorophyll maximum

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CO2 Saturation and Trophic Shift Induced by Microbial Metabolic Processes in a River-Dominated Ocean Margin (Tropical Shallow Lagoon,Chilika, India)

An effort has been made for the first time in Asia's largest brackish water lagoon, Chilika, to investigate the spatio-temporal variability in primary productivity (PP), bacterial productivity (BP), bacterial abundance (BA), bacterial respiration (BR) and bacterial growth efficiency (BGE) in relation to partial pressure of CO₂ (pCO₂) and CO₂ air–water flux and the resultant trophic switchover. Annually, PP ranged between 24 and 376 µg C L^?1 d^?1 with significantly low values throughout the monsoon (MN), caused by light limitation due to inputs of riverine suspended matter. On the contrary, BP and BR ranged from 11.5 to 186.3 µg C L^?1 d^?1 and from 14.1 to 389.4 µg C L^?1 d^?1, respectively, with exceptionally higher values during MN. A wide spatial and temporal variation in the lagoon trophic status was apparent from BP/PP (0.05–6.4) and PP/BR (0.10–18.2) ratios. The seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter inputs via rivers, enhanced the bacterial metabolism during the MN, as evident from the high pCO₂ (10,134 µatm) and CO₂ air–water flux (714 mm m^?2 d^?1). Large variability in BGE and BP/PP ratios especially during MN led to high bacteria-mediated carbon fluxes which was evident from significantly high bacterial carbon demand (BCD >100% of PP) during this season. This suggested that the net amount of organic carbon (either dissolved or particulate form) synthesized by primary producers in the lagoon was not sufficient to satisfy the bacterial carbon requirements. Lagoon sustained low to moderate autotrophic–heterotrophic coupling with annual mean BCD of 231% relative to the primary production, which depicted that bacterioplankton are the mainstay of the lagoon biogeochemical cycles and principal players that bring changes in trophic status. Study disclosed that the high CO₂ supersaturation and oxygen undersaturation during MN was attributed to the increased heterotrophic respiration (in excess of PP) fuelled by allochthonous organic matter. On a spatial scale, lagoon sectors such as south sector, central sector and outer channel recorded “net autotrophic,” while the northern sector showed “net heterotrophic” throughout the study period.     

Strong acids induce amyloid fibril formation of β2-microglobulin via an anion-binding mechanism

Amyloid fibrils, crystal-like fibrillar aggregates of proteins associated with various amyloidoses, have the potential to propagate via a prion-like mechanism. Among known methodologies to dissolve preformed amyloid fibrils, acid treatment has been used with the expectation that the acids will degrade amyloid fibrils similar to acid inactivation of protein functions. Contrary to our expectation, treatment with strong acids, such as HCl or H₂SO₄, of β₂-microglobulin (β2m) or insulin actually promoted amyloid fibril formation, proportionally to the concentration of acid used. A similar promotion was observed at pH 2.0 upon the addition of salts, such as NaCl or Na₂SO₄. Although trichloroacetic acid, another strong acid, promoted amyloid fibril formation of β2m, formic acid, a weak acid, did not, suggesting the dominant role of anions in promoting fibril formation of this protein. Comparison of the effects of acids and salts confirmed the critical role of anions, indicating that strong acids likely induce amyloid fibril formation via an anion-binding mechanism. The results suggest that although the addition of strong acids decreases pH, it is not useful for degrading amyloid fibrils, but rather induces or stabilizes amyloid fibrils via an anion-binding mechanism.     

Heparin‐induced amyloid fibrillation of β2‐microglobulin explained by solubility and a supersaturation‐dependent conformational phase diagram

Amyloid fibrils are fibrillar deposits of denatured proteins associated with amyloidosis and are formed by a nucleation and growth mechanism. We revisited an alternative and classical view of amyloid fibrillation: amyloid fibrils are crystal‐like precipitates of denatured proteins formed above solubility upon breaking supersaturation. Various additives accelerate and then inhibit amyloid fibrillation in a concentration‐dependent manner, suggesting that the combined effects of stabilizing and destabilizing forces affect fibrillation. Heparin, a glycosaminoglycan and anticoagulant, is an accelerator of fibrillation for various amyloidogenic proteins. By using β₂‐microglobulin, a protein responsible for dialysis‐related amyloidosis, we herein examined the effects of various concentrations of heparin on fibrillation at pH 2. In contrast to previous studies that focused on accelerating effects, higher concentrations of heparin inhibited fibrillation, and this was accompanied by amorphous aggregation. The two‐step effects of acceleration and inhibition were similar to those observed for various salts. The results indicate that the anion effects caused by sulfate groups are one of the dominant factors influencing heparin‐dependent fibrillation, although the exact structures of fibrils and amorphous aggregates might differ between those formed by simple salts and matrix‐forming heparin. We propose that a conformational phase diagram, accommodating crystal‐like amyloid fibrils and glass‐like amorphous aggregates, is important for understanding the effects of various additives.     

High performance DNA nano-carriers of carbonate apatite: multiple factors in regulation of particle synthesis and transfection efficiency

Increasing attention is being paid on synthetic DNA delivery systems considering some potential life-threatening effects of viral particles, for development of gene-based nanomedicine in the 21st century. In the current nonviral approaches, most of the efforts have been engaged with organic macromolecules like lipids, polymers, and peptides, but comparatively fewer attempts were made to evaluate the potential of inorganic materials for gene delivery. We recently reported that biodegradable nanoparticles of carbonate apatite are highly efficient in transfecting a wide variety of mammalian cells. Here we show that a number of parameters actively regulate synthesis of the nanoparticles and their subsequent transfection efficacy. Development of "supersaturation", which is the prerequisite for generation of such particles, could be easily modulated by reactant concentrations, pH of the buffered solution, and incubation temperatures, enabling us to establish a flexible particle generation process for highly productive trans-gene delivery. Carbonate incorporation into the particles have been proposed for generating nano-size particles resulting in cellular uptake of huge amount of plasmid DNA as well as endosome destabilization facilitating significant release of DNA from the endosomes.     

Formation of Peptide Bonds from Metastable versus Crystalline Phase: Implications for the Origin of Life

Formation of peptide bonds was attempted bythermal activation of dry amino acids from aqueous solutionthat simulated prebiotic evaporative environments. Theevaporation trend of amino acids solutions shows abifurcation and can lead to either a crystalline phase(near equilibrium) or a metastable non-crystalline phase(far from equilibrium). Only amino acids in this metastablephase are able to form peptide bonds by thermal activationat temperatures that are generated by solar radiationtoday. We suggest that this metastable phase is the idealinitial material to trigger amino acid assemblage withprotein-like structure because provide the driving force(supersaturation) for an intense interaction betweenmonomers of different amino acids and allows activation ofthese monomers in plausible prebiotic conditions.