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PubMed2002

Host selection as a downstream strategy: polyelectrolyte precipitation of beta-glucuronidase from plant extracts.

Host selection can be a strategy to simplify downstream processing for protein recovery. Advancing capabilities for using plants as hosts offers new host opportunities that have received only limited attention from a downstream processing perspective. Here, we investigated the potential of using a polycationic precipitating agent (polyethylenimine; PEI) to precipitate an acidic model protein (beta-glucuronidase; GUS) from aqueous plant extracts. To assess the potential of host selection to enhance the ease of recovery, the same procedure was applied to oilseed extracts of canola, corn (germ), and soy. For comparison, PEI precipitation of GUS was also evaluated from a crude bacterial fermentation broth. Two versions of the target protein were investigated--the wild-type enzyme (WTGUS) and a genetically engineered version containing 10 additional aspartates on each of the enzyme's four homologous subunits (GUSD10). It was found that canola was the most compatible expression host for use with this purification technique. GUS was completely precipitated from canola with the lowest dosage of PEI (30 mg PEI/g total protein), and over 80% of the initial WTGUS activity was recovered with 18-fold purification. Precipitation from soy gave yields over 90% for WTGUS but only 1.3-fold enrichment. Corn, although requiring the most PEI relative to total protein to precipitate (210 mg PEI/g total protein for 100% precipitation), gave intermediate results, with 81% recovery of WTGUS activity and a purification factor of 2.6. The addition of aspartate residues to the target protein did not enhance the selectivity of PEI precipitation in any of the systems tested. In fact, the additional charge reduced the ability to recover GUSD10 from the precipitate, resulting in lower yields and enrichment ratios compared to WTGUS. Compared to the bacterial host, plant systems provided lower polymer dosage requirements, higher yields of recoverable activity and greater purification factors.

Chemical Precipitation↗

PubMed2005

Quantitative validation of different protein precipitation methods in proteome analysis of blood platelets.

For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment.

Adult↗

PubMed1999

Precipitation of dilute chromatographic samples (ng/ml) containing interfering substances for SDS-PAGE.

SDS-PAGE of chromatographic fractions requires prior removal of salts, detergents, denaturants, or organic solvents which may perturb the electrophoretic separation. Likewise, to successfully visualize minute amounts of protein present in chromatographic fractions, they must often be concentrated before analysis by SDS-PAGE. In this study, we used a dye precipitation procedure for simultaneous removal of interfering substances and concentration of dilute samples (ng/ml) before analysis by SDS-PAGE. Nanogram amounts of protein (143 ng) were effectively precipitated with a pyrogallol red-molybdate reagent from commonly used chromatographic buffers containing various interfering solutes or solvents. Proteins were successfully precipitated from solution in the presence of organic solvents (acetonitrile, methanol, 2-propanol), chaotropic agents (6 M urea, 6 M guanidine-HCl), a protein stabilizer (40% sucrose), metal chelators (30 mM EDTA and 30 mM EGTA), or high salt (1.0 M NaCl). Detergents, at concentrations up to twice their critical micelle concentrations, from the nonionic class (Triton X-100, Tween 20) or from the zwitterionic class (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) did not inhibit protein precipitation. Some interference was observed when proteins were precipitated in the presence of ammonium sulfate (0. 5-2.0 M). Proteins did not precipitate in the presence of ionic detergents (SDS and cetyltrimethylammonium bromide). The sensitivity of the combined pyrogallol red-molybdate precipitation/SDS-PAGE procedure is approximately 7 ng. Two other methods of precipitating proteins (trichloroacetic acid and phenol-ether) both exhibited varying degrees of effectiveness, ranging from 714 to 7 ng/ml, in the precipitation of individual proteins. In summary, the pyrogallol red-molybdate protein precipitation procedure facilitates the SDS-PAGE analysis of dilute protein samples (ng/ml) from chromatographic fractions of various compositions. The method is useful for rapid pilot-scale protein fractionation and facilitates the ongoing propensity of researchers to work with minuscule amounts of protein.

Chemical Precipitation↗

PubMed1984

Conformation-specific precipitation of human alpha 2-macroglobulin by divalent zinc or calf thymus histone H3.

Highly purified native alpha 2-macroglobulin (alpha 2M), alpha 2M-trypsin, and alpha 2M-methylamine were compared in experiments designed to study protein precipitation. Significant turbidity developed within 30 min in solutions containing histone H3 and either alpha 2M-methylamine or alpha 2M-trypsin, as determined by absorbance at lambda = 550 nm. No turbidity was detected in solutions that contained histone H3 and native alpha 2M or histone H3 alone. Experiments with radioiodinated histone H3 or radioiodinated proteinase inhibitor confirmed that both the H3 and the alpha 2M "fast" forms (alpha 2M-methylamine, alpha 2M-trypsin) were present in the precipitates generated. As much as 70% of the 125I-alpha 2M-methylamine was recovered in the precipitate after incubation with a 120-fold molar excess of H3 (concentration of alpha 2M-methylamine, 0.28 microM). The ratio of histone to proteinase inhibitor by weight in the precipitate was approximately two. Under comparable conditions, somewhat less alpha 2M-trypsin precipitated from solutions containing H3 than did alpha 2M-methylamine; however, inactivation of the alpha 2M-trypsin with phenylmethylsulfonyl fluoride prior to incubation increased the level of precipitation significantly. Solutions containing poly-L-lysine (Mr approximately 13,000) instead of histone did not form precipitates with any of the forms of alpha 2M studied. In a second set of experiments, radioiodinated native alpha 2M, alpha 2M-trypsin, and alpha 2M-methylamine were incubated in solutions containing ZnCl2, BaCl2, CdCl2, CuSO4, MgCl2, or NiCl2 (concentration of divalent cation between 5 microM and 1.0 mM). Native alpha 2M was soluble in all of these salts. By contrast, alpha 2M-methylamine and alpha 2M-trypsin precipitated extensively from solutions containing greater than 100 microM ZnCl2. Precipitation was greater than 90% complete at 1 mM ZnCl2. A similar effect was not observed with any of the other divalent cations.

Cations, Divalent↗

PubMed1988

On the solubility of calcium deoxycholate: kinetics of precipitation and the effect of conjugated bile salts and lecithin.

In view of the low solubility of calcium deoxycholate and the possible induction of cholesterol precipitation in the gallbladder by calcium insoluble salts, we find it of interest to study the precipitation of calcium deoxycholate and its dependence on other bile components. The findings of these studies were as follows: (i) Precipitation of calcium deoxycholate from mixtures of calcium chloride and monomeric deoxycholate (at concentrations below the critical micelle concentration (CMC] is very slow even at relatively high CaCl2 concentrations (more than 20 days at 50 mM CaCl2). (ii) At higher deoxycholic acid (DOC) concentrations, precipitation of micellar DOC is faster and requires much lower calcium chloride concentrations. For any given calcium concentration, the rate of precipitation is maximal at an optimal DOC concentration. In solutions containing 150 mM NaCl, the maximal rate of precipitation occurs at about 10 mM DOC, almost independent of Ca2+ concentration. At lower ionic strength (10 mM NaCl), the optimal DOC concentration is 30 mM. These observations suggest that the most important factors in determining the rate of Ca(DOC)2 precipitation are (a) the ratio between calcium ions bound to the surface of a DOC micelle, and the [DOC] (the Ca2+/DOC binding ratio) and (b) the concentration of DOC micelles. (iii) In the presence of conjugated deoxycholates, the crystallization of calcium deoxycholate is inhibited. Phosphatidylcholine has a similar, although smaller, inhibitory effect. Upon precipitation of calcium deoxycholate from a mixed micellar system containing sodium deoxycholate, phosphatidylcholine and cholesterol, the latter two components spontaneously form vesicles. The anti-nucleating effect of PC and conjugated bile salts is explained in terms of "poisoning" of the crystallization process. In view of the latter results we conclude that under normal conditions calcium deoxycholate is not likely to precipitate in the gallbladder.

Bile Acids and Salts↗

PubMed1990

Acridine orange-induced precipitation of mouse testicular sperm cell DNA reveals new patterns of chromatin structure.

Precipitate resulting from interaction between certain intercalators, such as acridine orange (AO), and nucleic acids can be detected by electron microscopy. Formation of precipitate in nuclei of live cells is modulated by chromatin structure. Susceptibility of in situ DNA to precipitation was studied in mouse testicular germ cells during various stages of sperm maturation. DNA in round spermatid chromatin, similar to somatic cell euchromatin, was rather resistant to precipitation; the electron-dense precipitate was granular and randomly distributed. DNA in elongated spermatids was more susceptible to precipitation; the products were in the form of fibers. At early stages of spermatid maturation these fibers were distributed uniformly throughout the entire nucleus. At later stages, the products appeared as approximately 25-nm-thick fibers arranged longitudinally in arrays within the nucleus. With further cell maturation, fibers in the anterior portion of the nucleus appeared to fuse, forming homogeneously dense product. These fibrous products likely represent AO interactions with DNA in chromatin in which transition proteins had replaced histones. Changing patterns of these precipitated fibers likely reflect progressive stages of chromatin condensation, which starts at the center and anterior portion of the nucleus where the fibers coalesce. Mature sperm cell DNA, known to be complexed with protamines, was more resistant to AO-induced precipitation. The data suggest that precipitation induced by AO and monitored by electron microscopy may be a useful probe of nuclear chromatin structure.

Acridine Orange↗

PubMed1988

An analysis of the fluid phase C1q binding assay. The effect of endogenous C1q on the precipitation and detection of an immune complex model.

We examined the effect of endogenous C1q on the sensitivity of the fluid-phase C1q binding assay (C1qBA) in detecting an immune complex (IC) model, heat-aggregated IgG (HAIgG), at concentrations of 10-10,000 micrograms/ml sample. Results in normal human serum (NHS) or plasma (NHP) were compared with those in heat-inactivated NHS (NHS/56) in which most endogenous C1q was depleted by heat denaturation. Higher HAIgG concentrations were required in NHP and NHS to produce the same 125I-C1q precipitation seen in NHS/56. This decreased sensitivity varied from 70% at low HAIgG concentrations to 0% at high concentrations, as predicted for a large pool of endogenous C1q, in equilibrium with 125I-C1q, but in excess of that which could bind to all but the highest concentrations of IC model. In serum depleted of functional C1q on an immunoadsorbant of HAIgG, the precipitation of radiolabeled HAIgG under C1qBA conditions was concentration dependent and generated a saturation curve, showing that only a fraction of IC are usually precipitated in this assay. HAIgG precipitation was enhanced 1.4-fold in NHS/56 (8 micrograms C1q/ml) and three-fold in NHS (67 micrograms C1q/ml) suggesting that IC size is increased by endogenous C1q. In dual label experiments using 131I-HAIgG, the precipitation of 125I-C1q in NHS/56 was directly proportional to IC model precipitation, but markedly discordant in NHP, showing the measurement of IC in heat-inactivated sera superior to that in native serum. A comparison of the C1q:HAIgG ratio in PEG precipitates with that in samples, indicated that equilibrium was established between C1q and IC model. Thus the precipitation of 125I-C1q in the C1qBA represents (1) the fraction of total C1q bound to IC, and (2) the fraction of IC precipitated by PEG.

Antigen-Antibody Complex↗

PubMed1989

Structure-function relationships in the inorganic salt-induced precipitation of alpha-chymotrypsin.

alpha-Chymotrypsin (alpha CT) was used as a model protein to study the effects of salt-induced precipitation on protein conformation. Process parameters investigated included the type and amount of salt used to induce precipitation. The salts studied included Na2SO4, NaCl, NaBr, KBr and KSCN. Precipitate secondary structure content was examined via laser Raman spectroscopy. Conventional and saturation transfer electron paramagnetic resonance spectroscopy were employed to probe the tertiary structure of the active site in spin-labelled alpha CT precipitates. As the molal surface tension increment of the inducing salt increased, the beta-sheet content increased and the alpha-helix content decreased. There was no significant variation in secondary structure with the amount of salt used. The fraction of precipitate that recovered activity on redissolution was correlated with the change in secondary structure content. Spin-labelled precipitate spectra indicated that the active site remains unaltered during precipitation. Molecular modelling was employed to investigate how physical property of alpha CT were affected by these types of conformational change. Estimated physical property changes could not account entirely for observed deviations from current equilibrium theory for salt-induced precipitation. The spectroscopic observations were also combined with activity/solubility results to propose a mechanism for the salt-induced precipitation of globular proteins.

Animals↗

PubMed2004

Development of a calcium phosphate co-precipitate/poly(lactide-co-glycolide) DNA delivery system: release kinetics and cellular transfection studies.

One of the most common non-viral methods for the introduction of foreign deoxyribonucleic acid (DNA) into cultured cells is calcium phosphate co-precipitate transfection. This technique involves the encapsulation of DNA within a calcium phosphate co-precipitate, particulate addition to in vitro cell culture, endocytosis of the co-precipitate, and exogenous DNA expression by the transfected cell. In this study, we fabricated a novel non-viral gene transfer system by adsorbing DNA, encapsulated in calcium phosphate (DNA/Ca-P) co-precipitates, to biodegradable two- and three-dimensional poly(lactide-co-glycolide) matrices (2D-DNA/Ca-P/PLAGA, 3D-DNA/Ca-P/PLAGA). Co-precipitate release studies demonstrated an initial burst release over the first 48 h. By day 7, approximately 96% of the initially adsorbed DNA/Ca-P co-precipitate had been released. This was followed by low levels of co-precipitate release for 42 days. Polymerase chain reaction was used to demonstrate the ability of the released DNA containing co-precipitates to transfect SaOS-2 cells cultured in vitro on the 3D-DNA/Ca-P/PLAGA matrix and maintenance of the structural integrity of the exogenous DNA. In summary, a promising system for the incorporation and controlled delivery of exogenous genes encapsulated within a calcium phosphate co-precipitate from biodegradable polymeric matrices has been developed and may have applicability to the delivery of therapeutic genes and the transfection of other cell types.

Adsorption↗

PubMed2005

Characterization of adsorbent composition in co-removal of hexavalent chromium with copper precipitation.

Mechanisms of hexavalent chromium co-removal with copper precipitation by dosing Na2CO3 were studied with a series of well-designed batch tests using solutions containing 150 mg l-1 Cu(II) and 60 mg l-1 Cr(VI). It was found that direct precipitation of chromium through formation of copper-chromium bearing precipitates (in the form of CuCrO4) was one of the main mechanisms contributing to chromium co-removal at pH close to 5.0, and adsorption of chromium at a higher pH by freshly formed copper-carbonate precipitates (adsorbent) contributed to further chromium co-removal. Since, according to solubility products, neither copper-carbonate nor copper-hydroxide precipitates can be produced at pH around 5.0 for a pure 150 mg l-1 copper precipitation, characterization of copper-carbonate precipitates (adsorbent) was carried out through developing pC-pH curves of the systems by both equilibrium calculations and MINEQL+ 4.5 (a chemical equilibrium modeling software), and also through laboratory determination of the precipitate composition, such as gravimetric analyses, inorganic carbon percentage and EDAX spectrum analyses. CuCO3.Cu(OH)2, or a combination of CuCO3.Cu(OH)2 (in majority) and Cu(OH)2 (in minority) were suggested to be the major constituent of the precipitates obtained from the copper solution with Na2CO3 dosing.

Adsorption↗

PubMedDate not supplied

Does precipitation reduce tissue staining by indocyanine green dye solutions?

PURPOSE: Indocyanine green (ICG) dye precipitates when mixed with certain ophthalmic irrigation solutions. The purpose of this study is to investigate whether this precipitation reduces ICG staining of the anterior lens capsule. METHODS: ICG was diluted with each of the following solutions: BSS Plus, physiological saline, or Opeguard Neo. The products were then examined for green precipitate by light microscopy. The tissue staining capability of each ICG solution was tested at two different concentrations (0.5% and 0.0625%) in porcine lenses, regardless of whether the solution contained precipitate. RESULTS: Green precipitate was observed in both concentrations of ICG solutions diluted with BSS Plus, but not in the solutions diluted with either physiological saline or Opeguard Neo. As assessed with light microscopy, staining of the anterior lens capsule appeared weaker for all 0.0625% ICG solutions compared to the corresponding 0.5% ICG solutions. The precipitate that formed in the 0.5% ICG solution diluted with BSS Plus had little effect on the staining quality of the anterior lens capsule. In contrast, the 0.0625% ICG solution diluted with BSS Plus (w/precipitate) showed weaker staining in the lens capsule compared to the other two 0.0625% ICG solutions (w/o precipitate). CONCLUSION: These results suggest that precipitation of ICG may weaken its capability to stain the anterior lens capsule or other transparent ocular tissues. Therefore, ICG solutions that do not form a precipitate may be more capable of staining tissues at lower concentrations. As for other possibilities to explain the deterioration in staining, the effect of the composition of BSS Plus should also be considered.

Animals↗

PubMed2003

Estimating the precipitation potential in urine-collecting systems.

Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals causes severe maintenance problems and can strongly reduce the content of soluble phosphate. In this study, we present a computer model for estimating the precipitation potential (PP) in urine-collecting systems. Calculating the PP enables to predict the composition and mass concentration of precipitates. We used our computer model for investigating how urea hydrolysis and dilution with flushing water affect precipitation. In a previous study, we found that microbial urea hydrolysis (ureolysis) triggers precipitation and that the amount of precipitates is limited by calcium and magnesium. With the present simulations, we could confirm these findings. We determined that only a small fraction of urea has to be hydrolysed for reaching 95% of the maximum PP. Since urease-positive bacteria are abundant in urine-collecting systems, strong precipitation is very likely. In further simulations, we determined that struvite (MgNH(4)PO(4).6H(2)O) and hydroxyapatite (HAP, Ca(10)(PO(4))(6)(OH)(2)) are the main precipitate compounds. If urine is highly diluted with tapwater, calcite (CaCO(3)) occurs as well. HAP is the only calcium phosphate mineral, although several others were supersaturated. Additionally, the simulations indicated that urine dilution diminishes the risk of blockages, since the mass concentration of precipitates decreases with the volume of flushing water. Rainwater flushing is more effective than flushing with tapwater. Moreover, flushing with tapwater leads to high phosphate fixation, because the total amount of calcium and magnesium ions increases, while the total amount of phosphate keeps constant. Finally, we compared simulation results with field measurements and found good agreement at low and very high urine dilution.

Bacteria↗

PubMed1997

Characterization of calcium phosphates precipitated from simulated body fluid of different buffering capacities.

The purpose of this experiment was to study the properties of calcium phosphate precipitated from simulated body fluids (SBFs) with different buffering capacities. The Ca/P molar ratios of the precipitates were determined and the microstructure of a sintered precipitate was studied. The results indicate that the pH of the SBF increases during calcium phosphate precipitations, which affects the Ca/P molar ratios and chemical compositions of these precipitates. A precipitate with a Ca/P molar ratio close to the stoichiometric molar ratio of hydroxyapatite was obtained when the pH of the SBF was continuously adjusted to 7.26 during precipitation. This precipitate has a fine-grained and laminated microstructure after sintering at 1000 degrees C in air. It seems that SBF can be used as a tool to study apatite-like precipitation in vitro when the pH of the solution is carefully controlled.

Biocompatible Materials↗

PubMed2002

Urease activity in microbiologically-induced calcite precipitation.

The role of microbial urease in calcite precipitation was studied utilizing a recombinant Escherichia coli HB101 containing a plasmid, pBU11, that encodes Bacillus pasteurii urease. The calcite precipitation by E. coli HB101 (pBU11) was significant although its precipitation level was not as high as that by B. pasteurii. Addition of low concentrations (5-100 microM) of nickel, the cofactor of urease, to the medium further enhanced calcite precipitation by E. coli (pBU11). Calcite precipitation induced by both B. pasteurii and E. coli (pBU11) was inhibited in the presence of a urease inhibitor, acetohydroxamic acid (AHA). These observations on the recombinant urease have confirmed that urease activity is essential for microbiologically-induced calcite precipitation. Partially purified B. pasteurii urease was immobilized in polyurethane (PU) foam to compare the efficacy of calcite precipitation between the free and immobilized enzymes. The immobilized urease showed higher K(m) and lower V(max) values, which were reflected by a slower overall calcite precipitation. However, scanning electron micrographs (SEM) identified that the calcite precipitation occurred throughout the matrices of polyurethane. Furthermore, PU-immobilized urease retained higher enzymatic activities at high temperatures and in the presence of a high concentration of pronase, indicating that immobilization protects the enzyme activity from environmental changes.

Bacillus↗

PubMed1999

Mineral precipitation and porosity losses in granular iron columns.

As permeable reactive barriers containing zero-valent iron are becoming more widely used to remediate contaminated groundwaters, there remains much uncertainty in predicting their long-term performance. This study focuses on two factors affecting performance and lifetime of the granular iron media: plugging at the treatment zone entrance and precipitation in the bulk iron media. Plugging at the system entrance is due principally to mineral precipitation promoted by dissolved oxygen in the influent groundwater and is an issue in aerobic aquifers or in above-ground canister tests. Designs to minimize plugging in field applications where the groundwater is oxygenated include the use of larger iron particles and admixing sand of comparable size with the iron particles. Beyond the entrance zone, the groundwater in anaerobic and mineral precipitation leads to porosity losses in the bulk iron media, potentially reducing flow through the treatment zone. The nature of the mineral precipitation and the factors that affect extent of mineral precipitation have been examined by a variety of tools, including tracer tests, aqueous inorganic profiles, and surface analytical techniques. At short treatment times, porosity losses as measured by tracer tests are due mainly to Fe(OH)(2) precipitates and possible entrapment of a film of hydrogen gas on the iron surfaces. Over longer treatment times, precipitation of Fe(OH)(2) and FeCO(3) in low carbonate waters and of Fe(OH)(2), FeCO(3) and CaCO(3) in higher carbonate waters begin to dominate porosity losses. The control of pH within the iron media by addition of ferrous sulfide was shown not to reduce significantly calcium and carbonate precipitates, indicating that mineral precipitation is controlled by more than simple carbonate equilibrium considerations.

Chemical Precipitation↗

PubMed2000

Risk factors in falls among the elderly according to extrinsic and intrinsic precipitating causes.

The aim of this prospective cohort study was to identify the risk factors involved in falls in 190 elderly residents of two geriatric centres in Granada (Andalusia, Spain). Because different types of falls may be associated with different factors, falls were classified according to the precipitating cause, either extrinsic or intrinsic. The incidence density and the ratios for crude and adjusted density were calculated. Cox proportional risk analysis was used to calculate adjusted incidence density ratios. Of the 121 falls identified, 63 (52.1%) had a extrinsic precipitating cause, 43 (35.5%) had an intrinsic precipitating cause, and no precipitating cause was determined in 15 falls. The rate of falls with an extrinsic precipitating cause was 0.39 per person per year, while falls with an intrinsic precipitating cause showed a frequency of 0.27 per person per year. For falls with an extrinsic precipitating cause, the most significant risk factors were: age, diabetes mellitus, a history of falling, and treatment with neuroleptics or oral bronchodilators. The number of illnesses acted as a protective factor. For falls with an intrinsic precipitating cause, the independent risk factors were: age, diabetes, dementia, alterations of gait and balance, previous falls, and treatment with digitalins, neuroleptics or antidepressants. These results suggest that the susceptibility to a fall with an intrinsic precipitating cause is easier to identify and has a greater potential for being controlled.

Accidental Falls↗

PubMed2026

Increased precipitation decelerates temporal succession of grassland soil microbial communities.

Global precipitation regimes have been shifted in recent decades, imposing significant consequences in water-limited grassland ecosystems. However, the effects of increased precipitation on the succession of soil microbial communities remain unclear, mainly due to the scarcity of long-term experiments with time-series data. Here, we examined temporal succession of grassland soil microbial communities in a long-term increased precipitation experiment. Both soil microbial taxonomic and functional structures were significantly altered by increased precipitation. Increased precipitation significantly decelerated the succession rates of soil microbial functional structure (i.e. time-decay relationships). Consistent with the increased microbial decomposition and heterotrophic respiration, the abundances of soil microbial carbon decomposition genes were markedly enhanced by increased precipitation. Furthermore, increased precipitation stimulated genes involved in nutrient cycling processes, potentially promoting plant growth. Collectively, the contributions of stochastic processes in shaping microbial communities were increased under increased precipitation, suggesting that microbial successional trajectories may shift toward multiple alternative states characterized by greater stochasticity under future altered precipitation regimes.

Soil Microbiology↗

PubMed1996

Were kinetics of Archean calcium carbonate precipitation related to oxygen concentration?

Archean carbonates commonly contain decimetre- to metre-thick beds consisting entirely of fibrous calcite and neomorphosed fibrous aragonite that precipitated in situ on the sea floor. The fact that such thick accumulations of precipitated carbonate are rare in younger marine carbonates suggests an important change in the modes of calcium carbonate precipitation through time. Kinetics of carbonate precipitation depend on the concentration of inhibitors to precipitation that reduce crystallization rates and crystal nuclei formation, leading to kinetic maintenance of supersaturated solutions. Inhibitors also affect carbonate textures by limiting micrite precipitation and promoting growth of older carbonate crystals on the sea floor. Fe2+, a strong calcite-precipitation inhibitor, is thought to have been present at relatively high concentrations in Archean seawater because oxygen concentrations were low. The rise in oxygen concentration at 2.2-1.9 Ga led to the removal of Fe2+ from seawater and resulted in a shift from Archean facies, which commonly include precipitated beds, to Proterozoic facies, which contain more micritic sediment and only rare precipitated beds.

Calcium Carbonate↗