Biosorption and Bio-Kinetic Properties of Solar Saltern Halobacterial Strains for Managing Zn2+, As2+ and Cd2+ Metals

Bacillus mucilaginosus has already been proved to be capable of degrading silicate minerals, but it is not very clear about the molecular mechanisms of bacterial mineral weathering. To understand the relationship between bacterial weathering of minerals and bacterial secreted proteins, B. mucilaginosus was chosen to study the expression of its extracellular proteins in the process of weathering potassium minerals. This article reveals that certain secreted proteins, related to weathering of potassium minerals, can be induced under conditions such as bacterial nutritional deficiency and the existence of K-bearing rock powders. This suggests direct evidence of the metabolic changes of extracellular enzymes in bacteria during the process of weathering of potassium minerals. It was speculated that these secreted proteins, together with extracellular polymers like polysaccharides, may accelerate the weathering of potassium minerals, resulting in the release of K⁺ needed for the bacterial growth.     

Biological weathering of silicate minerals

Summary The abilities of biological systems to mobilize potassium from crystal lattices of primary silicate minerals were investigated. Root systems of pine seedlings grown in laboratory cultures and cultures of Aspergillus niger and mixed populations of soil micro-organisms were able to alter biotite mineral particles and cause release of potassium and other ions from mineral lattices. Mineral alterations by the microbial systems used are similar to alterations caused by oxalic, citric and other organic acids. The significance of the weathering processes observed is considered in relation to forest tree nutrition and soil formation     

Paenibacillus sp. Strain SB-6 Induces Weathering of Ca-montmorillonite: Illitization and Formation of Calcite

Investigation of the weathering of silicate minerals is helpful to understand the process of soil development, cycling of nutrient elements, and potential applications in fixation of carbon dioxide from the atmosphere through carbonate precipitation. In this study, weathering experiments of calcium-montmorillonite were conducted using Paenibacillus sp. strain SB-6 for 70 days. The results indicated that the Si⁴⁺, Al³⁺, Ca²⁺ and Na⁺ concentrations in the medium of the biotic experiments were evidently higher than those of the abiotic experiments, and that Paenibacillus sp. could help the transformation of partial montmorillonite into an illite–montmorillonite mixed-layer. In the process of illitization, K⁺ went into the interlayer of montmorillonite and hydrated Ca²⁺ and Na⁺ released from it. In the late stage of the experiments, the Ca²⁺ released from montmorillonite combined with carbonate ions generated by the bacterial metabolism, forming calcite.     

Silicate weathering in temperate forest soils: insights from a field experiment

Few studies of silicate mineral weathering have been conducted in carbonate-bearing temperate forest soils. With climate and vegetation held constant, we compared soil mineralogy and major element chemistry of soil waters from a carbonate-free temperate aspen forest site in the Cheboygan watershed, northern Michigan, with that from carbonate-containing soils from experimental tree-growth chambers (low- vs. high- fertility). All soils were well-drained sands (quartz, Na-rich plagioclase, and K-feldspar) with minor amounts of carbonate present only in the experimentally manipulated soils. The Na⁺ concentrations in soil waters corrected for atmospheric deposition (Na*) were used to compare relative rates of plagioclase feldspar weathering across sites. In natural soil water profiles, maximum concentrations of Na*, Si, and dissolved organic carbon (DOC) were observed by a depth of 15 cm, a soil zone free of carbonate minerals. Mean Na* and DOC concentrations were different in the three soils, and increased in the order natural soil < low-fertility chambers < high-fertility chambers. While low pH environments are generally viewed as enhancing weathering rates, here higher Na* appears to be related to high DOC, which is consistent with observed increases in active organic functional groups as pH increases. Our results suggest that under a specific vegetative cover, the soil carbon environment affects the weathering flux observed. Our study also suggests that disturbed soils provide an enhanced physical and chemical environment for weathering. Generalized silicate weathering models may benefit from including the enhancing effects of organic anions at moderate pH in addition to precipitation and temperature.     

A major role for nitrification in the weathering of minerals of brown acid forest soils

Experiments employing lysimeters and a comparison of soil leachates at >‐0.03 MPa and soil solutions extracted at ‐2.5 MPa showed the importance of nitrification in the weathering of minerals of brown acid forest soils (dys‐trochrept) which are formed over large areas in temperate climates.

Mineralization of litter from plants characteristic of such soils (in particular Festuca silvatica and Abies pectinata) produces large amounts of nitric acid. This bacterial nitrification is responsible for the solubilization of Ca²⁺, Mg²⁺, and K⁺ and must be involved in the slow weathering of minerals by acidolysis and in the biogeochemical cycling of Ca²⁺, Mg²⁺, and K⁺ in these soils. Soil solutions extracted at ‐2.5 MPa reflect much more the microbial activity than the leachates from soil and provide interesting information.     

Sr Isotope Tracing of Differences in the Effects of Microorganisms on Weathering of Calcite and Apatite

To study differences in the effects of microorganisms on weathering of calcite and apatite, one strain of Aspergillus niger (A. niger) and one strain of Penicillium glaucum (P. glaucum), which respectively contain the mixture of calcite and apatite were cultivated for 24 days in the sucrose-potato culture medium, supernatant was taken every three days from the culture medium, followed by the determination of Ca²⁺ and Sr²⁺ contents and Sr isotopic ratios. The results of measurement showed that the Sr isotope ratios in the supernatant from the culture medium are intermediate between those of the end-member constituents calcite and apatite (0.70721-0.70861). Results of isotope mixing equations to calculation showed that in the first 15 days A. niger played a dominant role in weathering of calcite in the apatite/calcite mixture. The contribution rate of apatite for Ca²⁺ in the solution increased from 39.0% on the 18th day to 61.6% on the 24th day; P. glaucum played a key role in weathering of apatite in the first 3 days. Ions dissolved from apatite account for 73.9% of the total. It is known from the results of Sr isotope tracing that in the prior period of fungus cultivation A. niger plays a key role in weathering of calcite while P. glaucum plays a key role in weathering of apatite. The ability of P. glaucum to weather calcite tends to intensify progressively over time. Therefore, Sr isotope tracing can be used to accurately recognize differences in the effects of microorganisms on weathering of minerals.     

Solubilization of Magnesium-Bearing Silicate Minerals and the Subsequent Formation of Glushinskite by Aspergillus niger

Microbes may play a substantial role in the weathering and alteration of minerals. However, not enough concerns have been realized about the complexity of microbe-mineral interactions. The present work reports the interactions between fungi and minerals with emphasis on the role of silicate minerals as the metal donor for the precipitation of secondary mineral. Herein, two magnesium-bearing silicate minerals with different structures, forsterite and talc, were added to the submerged cultures of Aspergillus niger (A. niger). It is shown that forsterite exhibits a better solubilization effect than talc, and the secondary mineral glushinskite only precipitates in the presence of forsterite substrates. Oxalic acid excreted by A. niger plays a key role in the biological leaching and mineralization processes. Moreover, the forsterite particles with certain size added to the cultures tend to inhibit the aggregation of fungal biomass, and therefore affect the morphology of A. niger aggregates in the submerged culture. With varying forsterite particle size, distinct fungal morphological forms including mycelial pellets and freely dispersed hyphae can be formed, which have a direct impact on fungal metabolism and ultimately result in varied crystallization habits of the neo-minerals. Particularly in the culture with ?40/+60 mesh forsterite particles, the mineralized glushinskite mainly exhibit tubular forms; whereas when forsterite particles were at ?100/+120 mesh or ?200 mesh, pyramidal prisms are obtained. We show that the environmental factors such as the particle size of mineral substrate could influence the fungal morphology and metabolic activities, thereby leading to different morphological neo-minerals. The dependence of biomineral morphology on the environmental factors can open up a novel avenue to understanding the microorganism-environment interactions.     

Genome-Wide Identification and Expression Profiling of the Shaker K⁺ Channel and HAK/KUP/KT Transporter Gene Families in Grape (<i>Vitis vinifera</i> L.)

Potassium (K⁺) is an essential macronutrient for plants to maintain normal growth and development. Shaker-like K⁺ channels and HAK/KUP/KT transporters are critical components in the K⁺ acquisition and translocation. In this study, we identified 9 Shaker-like K⁺ channel (VvK) and 18 HAK/KUP/KT transporter (VvKUP) genes in grape, which were renamed according to their distributions in the genome and relative linear orders among the distinct chromosomes. Similar structure organizations were found within each group according to the exon/intron structure and protein motif analysis. Chromosomal distribution analysis showed that 9 VvK genes and 18 VvKUP genes were unevenly distributed on 7 or 10 putative grape chromosomes. Three pairs of tandem duplicated genes and one pair of segmental duplicated genes were observed in the expansion of the grape VvKUP genes. Gene expression omnibus (GEO) data analysis showed that VvK and VvKUP genes were expressed differentially in distinct tissues. Various cis-acting regulatory elements pertinent to phytohormone responses and abiotic stresses, including K⁺ deficiency response and drought stress, were detected in the promoter region of VvK and VvKUP genes. This study provides valuable information for further functional studies of VvK and VvKUP genes, and lays a foundation to explore K⁺ uptake and utilization in fruit trees.     

Carbon dioxide consumption during soil development

Carbon is sequestered in soils by accumulation of recalcitrant organic matter and by bicarbonate weathering of silicate minerals. Carbon fixation by ecosystems helps drive weathering processes in soils and that in turn diverts carbon from annual photosynthesis-soil respiration cycling into the long-term geological carbon cycle. To quantify rates of carbon transfer during soil development in moist temperate grassland and desert scrubland ecosystems, we measured organic and inorganic residues derived from the interaction of soil biota and silicate mineral weathering for twenty-two soil profiles in arkosic sediments of differing ages. In moist temperate grasslands, net annual removal of carbon from the atmosphere by organic carbon accumulation and silicate weathering ranges from about 8.5 g m^–2 yr^–1 for young soils to 0.7 g M^–2 yr^–1 for old soils. In desert scrublands, net annual carbon removal is about 0.2 g m^–2 yr^–1 for young soils and 0.01 g m^–2 yr^–1 for old soils. In soils of both ecosystems, organic carbon accumulation exceeds CO₂ removal by weathering, however, as soils age, rates of CO₂ consumption by weathering accounts for greater amounts of carbon sequestration, increasing from 2% to 8% in the grassland soils and from 2% to 40% in the scrubland soils. In soils of desert scrublands, carbonate accumulation far outstrips organic carbon accumulation, but about 90% of this mass is derived from aerosolic sources that do not contribute to long-term sequestration of atmospheric carbon dioxide.     

In vitro weathering of phlogopite by ectomycorrhizal fungi

The ways in which ectomycorrhizal fungi benefit tree growth and nutrition have not been fully elucidated. Whilst it is most probably due to improved soil colonization, it is also likely that ectomycorrhizal fungi could be directly involved in nutrient cycling of soil reserves. This study assessed access by two species of ectomycorrhizal fungi to soil nonexchangeable K⁺ reserves. The incubation of ectomycorrhizal fungi in bi-compartment Petri dishes with phlogopite led to cation exchange reactions and to crystal lattice weathering. Paxillus involutus COU led to irreversible phlogopite transformations, while Pisolithus tinctorius 441 led to reversible ones. Simultaneous depletion in K⁺ and Mg²⁺ led to an enhanced weathering of phlogopite by P. tinctorius 441. The observation of phlogopite evolution shows that some specific Al³⁺ immobilization occurred under P. tinctorius 441. The data suggest that these bio-weathering mechanisms could be related to the release of fungal organic acids or other complex forming molecules.     

Potassium Translocation into the Root Xylem

Abstract: Potassium is the most abundant cation in cells of higher plants and plays vital roles in plant growth and develop ment. Since the soil is the only source of potassium, plant roots are well adapted to exploit the soil for potassium and supply it to the leaves. Transport across the root can be divided into three stages: uptake into the root symplast, transport across the symplast and release into the xylem. Uptake kinetics of potassium have been studied extensively in the past and sug gested the presence of high and low affinity systems. Molecular and electrophysiological techniques have now confirmed the existence of discrete transporters encoded by a number of genes. Surprisingly, detailed characterisation of the transpor ters using reverse genetics and heterologous expression shows that a number of the transporters (AKT and AtKUP family) func tion both in the low (μM) and high (mM) K⁺ range. Electrophy siological studies indicate that K⁺ uptake by roots is coupled to H⁺, to drive uptake from micromolar K⁺. However, thus far only Na⁺ coupled K⁺ transport has been demonstrated (HKT1). Ion channels play a major role in the exchange of potassium be tween the symplast and the xylem. An outward rectifying chan nel (KORC) mediates potassium release. Cloning of the gene en coding this channel (SKOR) shows that it belongs to the Shaker super-family. Both electrophysiological and genetic studies demonstrate that K⁺ release through this channel is controlled by the stress hormone abscisic acid. Interestingly, xylem par enchyma cells of young barley roots also contain a number of in ward rectifying K⁺ channels that are controlled by G-proteins. The involvement of G-proteins emphasises once more that po tassium transport at the symplast/xylem boundary is under hor monal control. The role of the electrical potential difference across the symplastxylem boundary in controlling potassium release is discussed.     

Characterisation of two distinct HKT1-like potassium transporters from Eucalyptus camaldulensis

Potassium is an essential macronutrient in higher plants. It plays an important physiological role in stoma movements, osmoregulation, enzyme activation and cell expansion. The demand for potassium can be substantial, especially when the plant concerned is a Eucalyptus tree in excess of 50 m tall. We have isolated two cDNAs, EcHKT1 and EcHKT2, from Eucalyptus camaldulensis (river red gum) which are expressed in leaves, stems and roots. These encode potassium transporter polypeptides with homology to the wheat K⁺-Na⁺ symporter, HKT1. EcHKT1 and EcHKT2 both complemented the K⁺-limited growth of an Escherichia coli K⁺-uptake-deficient triple mutant. EcHKT1 and EcHKT2also mediated Na⁺ and K⁺ uptake when expressed in Xenopus oocytes. A comparison of the EcHKT1 and EcHKT2 sequences and their transport properties indicated that these cDNAs represent two K⁺ transporters with distinct functional characteristics. The functional and structural conservation between these two E. camaldulensis genes and the wheat HKT1 suggests that they play an important, albeit elusive, physiological role.     

Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar

The rate of K⁺ leaching from soil minerals such as K-feldspar is believed to be too slow to provide agronomic benefit. Currently, theories and methods available to interpret kinetics of mineral processes in soil fail to consider its microfluidic nature. In this study, we measure the leaching rate of K⁺ ions from a K-feldspar-bearing rock (syenite) in a microfluidic environment, and demonstrate that at the spatial and temporal scales experienced by crop roots, K⁺ is available at a faster rate than that measured with conventional apparatuses. We present a device to investigate kinetics of mineral leaching at an unprecedented simultaneous resolution of space (~10¹-10² μm), time (~10¹-10² min) and fluid volume (~10⁰-10¹ mL). Results obtained from such a device challenge the notion that silicate minerals cannot be used as alternative fertilizers for tropical soils.     

Acclimation of potassium influx in rye (Secale cereale) to low root temperatures

The influx of K⁺(⁸⁶Rb⁺) into intact roots of rye (Secale cereale L. cv. Rheidal) exposed to a differential temperature (DT) between the root (8° C) and shoot (20° C) is initially reduced compared with warm-grown (WG) controls with both shoot and root maintained at 20° C. Over a period of 3 d, however, K⁺-influx rates into DT plants are restored to levels similar to or greater than those of the WG controls, the absolute rates of K⁺ influx being strongly dependent upon the shoot/root ratio. Acclimation in DT plants results in a reduction of K⁺ influx into the apical (0–2 cm) region of the seminal root which is associated with a compensatory increase in K⁺ influx into the more mature, basal regions of the root. Values of V _max and apparent K _m for K⁺ influx into DT plants were similar to those for WG plants at assay temperatures of 8° C and 20° C except for an increase in the apparent K _m at 8° C. The influx of K⁺ from solutions containing 0.6 mol·m^-3 K⁺ into both WG and DT plants was found to be linearly related to assay temperature over the range 2–27° C, and the temperature sensitivity of K⁺ influx to be dependent upon shoot/root ratio. At high shoot/root ratios, the ratio of K⁺ influx at 20° C:K⁺ influx at 8° C for WG plants approached a minimum value of 1.9 whereas that for DT plants approached unity indicating that K⁺ influx into DT plants has a large temperature-insensitive component. Additionally, when plants were grown in solutions of low potassium concentration, K⁺ influx into DT plants was consistently greater than that into WG plants, in spite of having a greater root potassium concentration ([K⁺]int). This result indicates some change in the regulation of K⁺ influx by [K⁺]int in plants exposed to low root temperatures. We suggest that K⁺ influx into rye seedlings exposed to low root temperatures is regulated by the increased demand placed on the root system by a proportionally larger shoot and that the acclimation of K⁺ influx to low temperatures may be the result of an increased hydraulic conductivity of the root system.Abbreviations DT differential temperature pretreatment - [K⁺]int root potassium concentration - [K⁺]ext potassium concentration of nutrient medium - WG warm-grown pretreatment     

Renal Proteinase-activated Receptor 2, a New Actor in the Control of Blood Pressure and Plasma Potassium Level

Proteinase-activated receptor 2 (PAR2) is a G protein-coupled membrane receptor that is activated upon cleavage of its extracellular N-terminal domain by trypsin and related proteases. PAR2 is expressed in kidney collecting ducts, a main site of control of Na⁺ and K⁺ homeostasis, but its function remains unknown. We evaluated whether and how PAR2 might control electrolyte transport in collecting ducts, and thereby participate in the regulation of blood pressure and plasma K⁺ concentration. PAR2 is expressed at the basolateral border of principal and intercalated cells of the collecting duct where it inhibits K⁺ secretion and stimulates Na⁺ reabsorption, respectively. Invalidation of PAR2 gene impairs the ability of the kidney to control Na⁺ and K⁺ balance and promotes hypotension and hypokalemia in response to Na⁺ and K⁺ depletion, respectively. This study not only reveals a new role of proteases in the control of blood pressure and plasma potassium level, but it also identifies a second membrane receptor, after angiotensin 2 receptor, that differentially controls sodium reabsorption and potassium secretion in the late distal tubule. Conversely to angiotensin 2 receptor, PAR2 is involved in the regulation of sodium and potassium balance in the context of either stimulation or nonstimulation of the renin/angiotensin/aldosterone system. Therefore PAR2 appears not only as a new actor of the aldosterone paradox, but also as an aldosterone-independent modulator of blood pressure and plasma potassium.     

Carrier-mediated Potassium Efflux Across the Cell Membrane of Red Beet

The flux ratio (influx/efflux) of K⁺ across the plasmalemma of beet cells at an external potassium concentration of 0.6 mm does not respond to changes of membrane potential in the manner expected for the free diffusion of ions. The K⁺ efflux is affected by the presence of adsorbed Ca²⁺, but is apparently unrelated to the electrical potential or to the net uptake of potassium. The K⁺ efflux is greater than the efflux of the sulfate and organic anions which are accumulated with potassium, and is partially dependent on the presence of external potassium. Thus the loss of ⁴²K from the cell does not appear to be a leakage of freely diffusing K⁺ ions, nor a leakage of ion pairs, but a carrier-mediated transport or exchange of potassium across the cell membrane.     

The effect of abscisic acid on the uptake of potassium and chloride into Avena coleoptile sections

Summary The effect of abscisic acid (ABA) on uptake of potassium (⁸⁶Bb⁺ or ⁴²K⁺) by Avena sativa L. coleoptile sections was investigated. ABA lowered the potassium uptake rate within 30 min after its application and inhibition reached a maximum (ca. 75%) after 2 h. The inhibition of K⁺ uptake increased with ABA concentration over a range of 0.03 to 10 g/ml ABA. At a higher K⁺ concentration (20 mM) the percentage inhibition decreased. The percentage inhibition of K⁺ uptake by ABA remained constant with external K⁺ varied from 0.04 to 1.0 mM. After a loading period in 20 mM K⁺ (⁸⁶Rb⁺), apparent efflux of potassium was only slightly increased by ABA. Experiments in which growth was greatly reduced by mannitol or by omission of indole-3-acetic acid from the medium indicated there was no simple quantitative correspondence between ABA inhibition of coleoptile elongation and ABA inhibition of K⁺ uptake. Chloride uptake was also inhibited by ABA but to a smaller degree than was K⁺ uptake. No specificity for counterions was observed for K⁺ uptake. Uptake of 3,0-methylglucose and proline were inhibited by ABA to a much smaller extent (14 and 11%) than that of K⁺, a result which suggests that ABA acts on specific ion uptake mechanisms.