Fluorescence and bioluminescence analysis of sequential UV-biological degradation of p-cresol in water.

The photolysis and Penicillium tardum H-2 degradation of p-cresol in water containing humic acids was investigated by fluorescence and bioluminescence methods. Humic acids extracted from peat (the Vasuygan bog, Tomsk region of Russia) induce the phototransformation of p-cresol. The influence of humic acids on the phototransformation of p-cresol under different irradiation conditions was investigated. Comparison of the data on the KrCl* (lambda = 222 nm) and XeCl* (lambda = 308 nm) excilamps light showed that the most effective p-cresol degradation was observed with mercury lamp irradiation in the presence of humic acids.     

The role of UV‐irradiation pretreatment on the degradation of 2,4‐dichlorophenoxyacetic acid in water

The degradation of 2,4‐dichlorophenoxyacetic acid (2,4‐D) in water by the combination process of UV‐irradiation, humic acids and activated sludge treatment has been studied. The photoreaction rate of all irradiated samples was lowest for the sample irradiated at 308 nm (the XeCl excilamp) in the absence and in the presence of humic acids, and highest for the sample irradiated at 222 nm (the KrCl excilamp). Photolysis of 2,4‐D has been shown to enhance the subsequent microbial degradation. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of photochemical properties of compost humic-like materials

Humic-like acids (HLA) were extracted from compost at the beginning and after 70, 130 and 730 days of maturation in order to be investigated for their ability to induce the transformation of 2,4,6-trimethylphenol under irradiation at 365 nm. The rate of 2,4,6-trimethylphenol phototransformation in the presence of HLA (25 mg l(-1)) varied within HLA 0相似文献   

STIMULATION OF GROWTH IN SCENEDESMUS OBLIQUUS (CHLOROPHYCEAE) BY HUMIC ACIDS UNDER IRON LIMITED CONDITIONS1,2

Stimulatory affects of humic acids of molecular weight 30,000 or greater on iron-starved Scenedesmus obliquus (Turp.) Kütz. in association with bacteria were studied by growth and Fe uptake experiments. Humic acids stimulated growth of Fe-starved cells by decreasing the lag phase and extending the growth phase. Humic acids stimulated increased algal growth in medium containing EDTA as well as in medium containing no EDTA, indicating humic acids are not stimulating algal growth under Fe limiting conditions by creating a soluble Fe pool. Humic acids decreased Fe availability to Fe-starved S. obliquus. Iron bound to humic acids is unavailable for uptake by Fe-starved cells indicating growth stimulation is not due to chelation effects alone. Stimulation of growth is not a membrane phenomenon as humic acids show the same stimulatory effect when in contact with cells or separated by dialysis membrane. Humic acids also stimulate growth in the dark, with and without aeration, indicating use as a heterotrophic substrate. A photoheterotrophic mechanism is indicated by increased algal growth caused by illuminating cultures, containing humic acids but excluding CO₂.     

Rhizosphere humic acid interacts with root cell walls to reduce hydraulic conductivity and plant development

Humic acids are ubiquitous, organic-end-products of the chemical and microbial degradation of dead biota in soils throughout the world. Humic acids can be transported in soil water as heterogeneous, supra-molecular, colloidal-agglomerates. Humic acid accumulation in the rhizosphere of transpiring plants may chemically stimulate development by increasing root availability of mineral nutrients and/or growth regulatory biomolecules. This report introduces novel, physical mechanisms by which humic acid can also reduce plant development. Effects of humic acid addition to the root media of intact maize plants (Zea mays L.) on their growth, transpiration and resistance to water deficits were assayed, as were the effects of external humic acid on the hydraulic conductivity of excised primary-roots. Humic acid reduced shoot growth, transpiration and resistance to water stress but not root growth. Root hydraulic conductivity was reduced by up to 44% via a time-, concentration- and size-dependent fouling mechanism resulting from humic acid accumulation at root cell-walls. Thus, humic acid is shown, apparently for the first time, to be able to exert novel physical effects in addition to its known chemical effects on plant development.     

Effect of humic acids on the inhibition of pea choline esterase and choline acyltransferase with malathion

Humic acids in a concentration of up to 100 μg ml^-1 affect the activity of choline esterase of pea only weakly during sinapin (choline ester of sinapic acid) hydrolysis. The inhibition is stronger at higher concentrations. A similar course of inhibition with humic acids was also observed during the synthesis of sinapin catalysed with choline acyltransferase present in the same enzyme extract. The organophosphate malathion is a strong inhibitor of both the hydrolysis and the synthesis of sinapin. Thus, for example, at a 3.5 × 10^-5 M concentration it causes 85% inhibition of pea choline esterase. However, in combination with 100 μg of humic acids this inhibition decreases to about 8%. It was observed that humic acids prevent the inhibition of both the hydrolysis and the synthesis of sinapin with malathion even at low concentrations. The interaction of the organophosphate malathion with humic acids seems specific. Humic acids do not affect the inhibition of choline esterase with physostigmine or the inhibition of the hydrolysis and the synthesis of sinapin with chlorocholine chloride, alar and hexamine either. This is also true of the activation of the processes with the K⁺ ions. Humic acids represent competitive inhibitors of choline esterase. Malathion shows an acompetitive — noncompetitive character of the inhibition. The interaction of humic acids with malathion in the roots of the plants may also be assumed in the soil when malathion is applied as an insecticide.     

Influence of Naturally Occurring Humic Acids on Biodegradation of Monosubstituted Phenols by Aquatic Bacteria

Samples of the microbial community from Lake Michie, a mesotrophic reservoir in central North Carolina, were adapted to various levels (100 to 1,000 μg/liter) of natural humic acids in chemostats. The humic acids were extracted from water samples from Black Lake, a highly colored lake in the coastal plain of North Carolina. After adaptation, the microbial community was tested for its ability to degrade the monosubstituted phenols m-cresol, m-aminophenol, and p-chlorophenol. Adaptation to increasing levels of humic acids significantly reduced the ability of the microbial communities to degrade all three phenols. The decline in biodegradation was accompanied by a decrease in the number of specific compound degraders in the adapted communities. Short-term exposure of the community to increasing levels of humic acids had no significant effect on the ability of the community to degrade m-cresol. Thus the suppressive effect of humic acids on monosubstituted phenol metabolism was the result of long-term exposure to the humic materials. Increasing the levels of inorganic nutrients fed to the chemostats during the humic acid adaptation had little effect on the suppressive influence of the humic acids, indicating that nutrient limitation was probably not responsible for the metabolic suppression. The results of the study suggest that long-term exposure to humic acids can reduce the ability of microbial communities to respond to monosubstituted phenols.     

有机物质对土壤镉有效性的影响研究综述

土壤中的低分子有机酸和腐殖酸对镉的有效性有重要作用。根系分泌的低分子量有机酸能提高土壤镉的可提取率、移动性和生物有效性,但是更大分子量的有机酸EDTA却抑制植物对镉的吸收,腐殖酸促进土壤镉的溶解性;因腐殖酸组分和环境条件,腐殖酸能够促进也能抑制土壤镉活性,因此有必要深入研究影响腐殖酸固定镉的因素,以达到利用有机质抑制土壤镉活性的目的。     

Organic biogeochemistry of groundwater at a mountain coal mine

Measurements of dissolved organic matter (DOM), humic and fulvic acids, carbohydrates, tannins + lignins, phenols and amino acids were made in the groundwater permeating Reclamation site 2 at the Canmore Coal Mine (Alberta, Canada). Estimates of the number of bacteria present in the groundwater were also made using plate and direct count techniques. Temperature, pH, Eh, and oxygen content of the groundwater were measured on two occasions. DOM was very low in concentration (av. 1.62 mg/liter) and consisted principally of fulvic acid. Humic acids formed about 20% of DOM, carbohydrates 6%, tannins + lignins 4%, and trace compounds (phenols, amino acids, and proteins) 2%. Seasonal variations were observed, with tannins + lignins and carbohydrates reaching their highest concentration in the summer, and humic and fulvic acids, and DOM peaking in the winter. The organic composition of the groundwater upstream of the reclamation site did not differ significantly from groundwater sampled from within the reclamation site. Differences were observed, however, between ground and surface waters draining the site. No correlation between concentration and depth was observed. Large numbers of bacteria were found in groundwater using both plate count and direct count methods. Populations were only modestly correlated with the concentrations of organic compounds (r<0.9). Heterotrophic bacteria must have been dependent upon organic matter (both as DOM and as insoluble organic matter in the spoil) for growth, however. The groundwater bacteria studied appeared to be characterized by slow growth under adverse geological conditions with only low concentrations of labile organic compounds present.     

Effect and potential ecological significance of the interaction of humic acids with two aquatic extracellular proteases

1. The effects of humic acids and fulvic acids on an extracellular serine and metalloprotease purified from a strain of Aeromonas hydrophila isolated from a freshwater wetland were examined. The serine protease was inhibited by humic acids at pH and humic acid concentrations found naturally in the wetland where this strain of A. hydrophila was isolated. The metalloprotease was not inhibited by humic acids at any pH investigated. Fulvic acids had no effect upon either protease. 2. Inhibition of serine protease activity by humic acids was reversed by increasing the pH to 9, as well as increasing the ionic strength by addition of CaCl₂- It was concluded that the interaction between humic acids and the serine protease was primarily ionic. 3. The formation of a humic acid-serine protease complex increased the half-life of enzymatic activity in dilute solutions. Humic acids had no effect on the stability of the metalloprotease. 4. There was no clear effect of humic acids on the growth of A. hydrophila, indicating that either the serine protease is not involved in the rate-limiting step of growth or that sufficient activity exists even when the serine protease is inhibited by humic acids. 5. Increasing the enzymatic lifetime through association with humic acids may be an adaptive mechanism which could result in energy conservation due to a decreased requirement for protein synthesis.     

Humic Materials Offer Photoprotective Effect to Escherichia coli Exposed to Damaging Luminous Radiation

The behavior ofEscherichia coli immersed in aqueous systems amended with humic acids, under PAR, UV-A, UV-B, and simulated solar radiation was examined. Culturability, ability to elongate, functioning of the electron transport systems, and glucose uptake were assessed. Humic substances in the range from 1 to 50 mg L⁻¹ protected cells from photoinactivation. Decrease in culturability and cellular activities was significantly (p<0.05) less in the presence of humic material. However, humic acid were not used as nutrients. Neither irradiated nor nonirradiated humic solutions (50 mg L⁻¹) supported the growth of 10⁵ cells ml⁻¹. However, humic acids dissolved in 0.9% NaCl efficiently absorbed light over wavelengths from 270 to 500 nm. Also, a photoprotective effect against simulated sunlight was observed when humic acid were not in contact with but rather enveloped the cellular suspensions in double-wall microcosms. The protection afforded by humic acids against luminous radiation likely derives from their ability to absorb these radiations and hence reduces the amount of energy reaching the cells.     

The influence of topography on the nature of humic substances in soil organic matter at a site in the Atlantic Coastal Plain of South Carolina

The effect of topography on the nature of humic substances, isolated as water soluble organic carbon (WSOC), fulvic acid (FA), and humic acid (HA) was evaluated by comparing relative proportion and chemical characteristics of these fractions in upland and bottomland Coastal Plain soils in South Carolina. The fractions were characterized by elemental analysis and¹³C cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. The majority of humic substances occur as humic acids, with bottomland soils having higher HA/FA ratios when compared to upland soils. We found no significant differences between upland and bottomland humic substances with respect to yields of WSOC and fulvic acids, and in the C and N content of humic and fulvic acids. Carbon-13 CPMAS NMR spectroscopy revealed that the WSOC and fulvic acid fractions were composed largely of O-alkyl-C structures with bottomland soils having higher amounts of these groups. Humic acid C distribution was similar between upland and bottomland soils and was largely composed of aromatic groups. Our results demonstrate that topography influences the formation of humic acid and the structural and chemical properties of the various humic fractions.requests for offprints     

Interference of humic acids and DNA extracted directly from soil in detection and transformation of recombinant DNA from bacteria and a yeast.

A two-step protocol for the extraction and purification of total DNA from soil samples was developed. Crude DNA extracts (100 microliters from 5 g of soil) were contaminated with humic acids at concentrations of 0.7 to 3.3 micrograms/microliters, depending on the type of soil extracted. The coextracted humic acid fraction of a clay silt was similar to a commercially available standard humic acid mixture, as determined by electrophoretic mobility in agarose gels, UV fluorescence, and inhibition assays with DNA-transforming enzymes. Restriction endonucleases were inhibited at humic acid concentrations of 0.5 to 17.2 micrograms/ml for the commercial product and 0.8 to 51.7 micrograms/ml for the coextracted humic acids. DNase I was less susceptible (MIC of standard humic acids, 912 micrograms/ml), and RNase could not be inhibited at all (MIC, > 7.6 mg/ml). High inhibitory susceptibilities for humic acids were observed with Taq polymerase. For three Taq polymerases from different commercial sources, MICs were 0.08 to 0.64 micrograms of the standard humic acids per ml and 0.24 to 0.48 micrograms of the coextracted humic acids per ml. The addition of T4 gene 32 protein increased the MIC for one Taq polymerase to 5.12 micrograms/ml. Humic acids decreased nonradioactive detection in DNA-DNA slot blot hybridizations at amounts of 0.1 micrograms and inhibited transformation of competent Escherichia coli HB101 with a broad-host-range plasmid, pUN1, at concentrations of 100 micrograms/ml. Purification of crude DNA with ion-exchange chromatography resulted in removal of 97% of the initially coextracted humic acids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of humic acids in vitro

Humic acids are known for their overall positive health and productivity effects in animal feeding trials and, controversially, as an aetiological factor of cancer. We tried to assess the in vitro effect of humic acids from a selected source in Slovakia when used at recommended prophylactic dosage. We investigated antioxidant properties, enzymatic and non-enzymatic antioxidant defence system in liver mitochondria and cultured cancer cell lines in vitro. We observed a significant decrease in superoxide dismutase activity after humic acids treatment irrespective of dissolving in dimethyl sulphoxide or direct addition to mitochondria suspension in a respiration medium. Activities of other antioxidant enzymes measured, such as glutathione peroxidase and glutathione reductase, showed no significant differences from the control as well as the reduced glutathione content. Percentage of inhibition by humic acids of superoxide radical indicated lower efficacy compared with that of hydroxyl radical. Survival of six different cancer cells lines indicated that only the acute T lymphoblastic leukaemia cell line was sensitive to the tested humic acids. Despite relatively low solubility in aqueous solutions, humic acids from the selected source participated in redox regulation. By recapturing the radicals, humic acids reloaded the antioxidant defensive mechanism. Results from in vitro study conducted with humic acids from the natural source showed potential of these substances as promising immunity enhancing agents.     

Effects of Humic Acid on Protein Synthesis and Ion Uptake in Beet Discs

Humic acids stimulate the development of phosphate uptake-capacityin beet discs during ageing under aseptic conditions withoutaffecting phosphate uptake per se. Chloride uptake is inhibitedby humic acids as is the development of chloride uptake capacity.The uptake of proline and leuoine is not influenced by ageingin humic acid. While measurements of the incorporation of theseamino acids into the sub-cellular particles of discs indicatethat humic acid does not affect protein synthesis in general,the stimulation of invertase development during ageing doesshow a definite effect on some aspect of protein synthesis.     

High salt stress in wheat leaves causes retardation of chlorophyll accumulation due to a limited rate of protochlorophyllide formation

When exposed to salt stress, leaves from dark-grown wheat seedlings ( Triticum aestivum , cv. Giza 168) showed reduced accumulation of chlorophyll during irradiation. To elucidate the mechanism behind salt-influenced reduction of chlorophyll biosynthesis, we have investigated the effect of salt stress on the spectral forms of Pchlide, the phototransformation of Pchlide to Chlide, the Shibata shift, the regeneration of Pchlide and the accumulation of Pchlide from 5-aminolevulinic acid (ALA). We found that the phototransformation of Pchlide to Chlide was not affected by salt stress. The blue shift (Shibata shift) of newly formed Chlide was delayed both after flash irradiation and in continuous light. The reformation of Pchlide in darkness after a flash irradiation or after a period of 3-h irradiation was retarded in the salt-treated leaves. However, after a 20-h dark period, Pchlide was reformed even in salt-treated leaves but the formation of short-wavelength Pchlide was suppressed. Compared to controls, salt treatment also reduced the amount of Pchlide accumulated in leaves floated on ALA. The increase in the low temperature fluorescence emission spectrum at 735 nm, which occurred gradually during several hours of irradiation with continuous light in control leaves, was completely suppressed in salt-treated leaves. It is concluded that salt stress inhibits chlorophyll accumulation partly by reducing the rate of porphyrin formation but, as discussed, also by a possible reduction in the formation of chlorophyll-binding proteins.     

Differential exposure of aromatic amino acids in the red-light-absorbing and far-red-light-absorbing forms of 124-kDa oat phytochrome

The surface topography of aromatic amino acid residues and/or other hydrophobic groups of phytochrome has been investigated by ultraviolet absorption spectra and ultraviolet circular dichroism using phytochrome-cyclodextrin inclusion complexation. Three different types of cyclodextrins (alpha, beta and gamma) with varying hydrophobic cavity sizes, were used. Complexation resulted in significant changes in the circular dichroic signals of both the red-light-absorbing (Pr) and far-red-light-absorbing (Pfr) forms of phytochrome in the ultraviolet region at 222 nm, mid-ultraviolet at 280 nm and 300 nm and in the near-ultraviolet and visible regions at 365 nm and 670 mm, respectively, alpha- and beta-Cyclodextrins were markedly (1.7-4.5-fold) more effective in reducing the mid-ultraviolet CD signal of Pr than that of Pfr, indicating a differential inclusion of the aromatic amino acid residues. gamma-Cyclodextrin did not exhibit any significant differentiation. Secondary structure analysis of the phytochrome-cyclodextrin complexes revealed a considerable increase in the alpha-helical contents of both Pr and Pfr forms. The increase in the Pfr form (17-25%) was about twice that in the Pr form (8-9%), indicating a differential effect of complexation on the conformation of the phytochrome protein. Although the photostationary-state equilibrium of the phytochrome was not affected by the cyclodextrin complexation, the Pr----Pfr phototransformation rate was significantly increased. However, the Pfr----Pr photoreversion was not affected significantly. The results suggest a differential complexation of cyclodextrins with the Pr and Pfr forms of phytochrome as a result of a difference in accessibility of aromatic amino acids in the two forms. A detailed analysis of absorption difference spectra and circular dichroic spectra around 280 nm also revealed evidence for a difference in the exposure of aromatic amino acids.     

Water repellency of Casuarina windbreaks (Casuarina equisetifolia Forst.) caused by fungi in central Taiwan

The water repellent layer (WRL) in the Casuarina plantation near Taichung Harbor in central Taiwan is mainly due to the development of filamentous fungi. The hyphae of the isolated fungi and the metabolites of the TCHC-5 and TCHC-20 fungi are also significantly hydrophobic. In the soil layers, humic substances decrease the phosphorus fixation and contribute to the formation of WRL. The hydrophobic properties of humic substances are unfavorable for the nutrient cycling in this area. The water contact angles of fulvic acids and humic acids are pH-dependent. Increasing the solution pH value reduces the hydrophobic strength for fulvic acids and/or humic acids. TCHC-15 and TCHC-16 isolated fungi exude strong acidic metabolites (pH 2.7–3.0). This may result in polymerization and/or precipitation of fulvic acids and humic acids and increase the hydrophobic strength of the soil layers. Humic substances with aliphatic chains are the main components that form WRL in soils. Soil pH may be an indicator of the hydrophobic potential for organic matters.     

Py-GC/MS analysis of sediments from Lake Biwa,Japan: characterization and sources of humic acids

Humic substances extracted and purified from bottom sediments of northern Lake Biwa, Japan, in November 2012 and 2013 were characterized using elemental analysis, Fourier-transform infrared spectroscopy, hydrogen-1 nuclear magnetic resonance (¹H NMR) analysis, and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The infrared (IR) bands in the spectra of humic acids showed the presence of amide linkages and polysaccharides. Results of ¹H NMR analysis showed that the humic acids contained approximately twice the number of aliphatic protons as those in the Japanese soil standards used for comparison. Results of the Py-GC/MS analysis, which evaluates pyrolysis temperature dependency of the amount of pyrolysis products, showed that the generation of pyrolysis products in humic acids also differed from that in Japanese soil standards but was similar to that of phytoplankton in Lake Biwa. This analysis method is the first to provide extensive information about the chemical structure of humic substances; conventional Py-GC/MS provides limited information for a single temperature. Data suggest that humic acids in lake sediments are related to chemical characteristics of phytoplankton. Results shed new light on the origins of humic substances in deep-water-lake sediments and provide insights into material recycling in such sediments.     

Contrasting effects of solar UV radiation on dissolved organic sources for bacterial growth

The photochemical transformation of dissolved organic matter (DOM) in lakes and oceans has been shown to either reduce or enhance bacterial utilization. We compared the effects of UV radiation on the bacterial use of DOM in a wide range of lakes. Although complex DOM was converted in all irradiated samples into carboxylic acids that are readily utilized by bacteria, irradiation in several lakes resulted in a decreased ability of DOM to support bacterial growth. The effect of irradiation on the ability of DOM to promote bacterial growth was a positive function of the terrestrial humic matter, and a negative function of indigenous algal production. We suggest that the net effect of irradiation is a result of counteracting but concurrent processes rendering DOM either labile or recalcitrant. Humic DOM is predominantly transformed into forms of increased lability, whereas photochemical transformation into compounds of decreased bacterial substrate quality dominates in algal-derived DOM. Hence, solar-induced photochemical reactions interact with microbial degraders in different ways, depending on the origin and nature of the organic matter, affecting the transfer of energy within aquatic food webs, as well as the degradation and preservation of detrital organic matter, in different directions.