Biodegradation of soil humic acids by Streptomyces viridosporus.

Biodegradation of soil humic acids by Streptomyces viridosporus ATCC 39115 growing in a mineral salts--glucose medium was demonstrated. This biodegradation accompanies bacterial growth and is, therefore, presumed to be a primary metabolic activity, but humic acids were not used as the sole source of carbon. This bacterial activity was enhanced when cells were shaken and within a pH range of 6.5-8.5. In further experiments, the relative abilities of S. viridosporus to mineralized [14C]melanoidin, used as synthetic humic acid, were also established. In contrast to the white rot fungus Phanerochaete chrysosporium, another microorganism exhibiting humic acid degrading activity at acidic pH, poor extracellular activities were found in culture medium of S. viridosporus, and veratryl alcohol does not result in increased humic acid degradation. In spite of some peroxidase activity measured in culture filtrates and analyzed by polyacrylamide gel electrophoresis, the humic acid degrading system of S. viridosporus, in these experimental conditions, seems to be cell associated.     

Complexation of trace metals with humic acids from soil,sediment and sewage

ABSTRACT

Metal—humate interactions in aqueous and terrestrial ecosystems control the speciation of trace metals and hence, their bioavailability and toxicity. The present study investigated the complexation interactions of copper, cadmium and lead, in their divalent states, with humic acids extracted from three different sources: the treated sewage from a treatment plant, Yamuna river bed sediment, and Yamuna river flood plain soil, all at Okhla, Delhi, employing ion selective electrode potentiometry. The conditional stability constants of the complexes were computed from Scatchard plots. The influences of the two important metal speciation factors, viz., pH and ionic strength of the reaction medium on the conditional stability constants were ascertained by investigating the reactions under three different pH: 5.0, 6.0 and 7.0 and three different ionic strengths: 0.01, 0.03 and 0.1. Stabilities of metal—humic acid (HA) complexes follow the order: Cu-HA > Pb-HA > Cd-HA for humic acids from any single source and are found to increase with a rise in pH and fall in a ionic strength of the medium. The humic acids extracted from the soil and the sediment emerged as stronger complexing agents, as compared to that extracted from sewage.     

Sugars in hydrolysates of fungal melanins and soil humic acids

Humic acids from four Brazilian topsoils of different origin and four fungal melanins, synthesized under two cultural conditions were subjected to a two step hydrolysis procedure and the released monosaccharides qualitatively and quantitatively determined by gas-liquid chromatography. The neutral sugars, glucose, galactose, mannose, arabinose, xylose, fucose, rhamnose and the alcohol sugar inositol, were detected in most of the soil humic acid samples. The fungal melanins showed the presence of glucose, galactose, mannose and arabinose. Ribose was present in two out of the eight samples tested. Some quantitative differences in the two types of humic polymers were noted and expected considering their origins. However, similarities were more apparent than differences and give further indication that melanic fungi may play a significant role in the formation of soil humic acids.     

Chemical and structural evolution of humic acids during organic waste composting

The effects of the composting process on the chemical and structural properties of humic acids have been studied in seven different organic waste mixtures from different origin. Only slight changes in elemental composition have been found in the humic acids after the composting process pointing to a more aromatic structure with higher proportions of oxygen and nitrogen. Functional groups were the most sensitive to the changes caused by the composting process showing a marked increase in the total acidity and phenolic, carboxyl and carbonyl groups. Gel permeation chromatography showed a slight increase in the average molecular weight of the humic acids. Infrared spectroscopy did not show important differences in humic acid structure but a clear decrease in the intensity of the bands in the region 3000–2850 cm^-1 corresponding to the aliphatic fractions. As a general result, the composting process yields humic acids in which the elemental and functional composition are closer to that of the more humified soil humic acids.     

外源腐殖酸对三种土壤磷吸附与解吸特性的影响

通过对3种土壤（红壤、棕壤和褐土）施入不同腐殖酸的室内培养试验,探讨了外源腐殖酸对不同土壤磷素吸附和解吸的影响。结果表明：与对照土壤相比,不同腐殖酸降低了3种供试土壤磷素的吸附量,其降低顺序为：褐土＞红壤＞棕壤;外源腐殖酸提高了红壤和棕壤磷素的解吸量和解吸率,提高的幅度与腐殖酸的种类有关;而腐殖酸对褐土磷素的解吸量则无明显促进作用。表明外源腐殖酸对3种土壤磷素吸附-解吸作用最强的为红壤,其次为棕壤,最弱的为褐土;同时表明腐殖酸可提高红壤和棕壤磷素的利用率。     

Enhancing pyrene mineralization in contaminated soil by the addition of humic acids or composted contaminated soil

The addition of composted PAH-contaminated soil to PAH-contaminated soil spiked with 14C-labeled pyrene resulted in rapid mineralization of pyrene (more than 57% after 21 days compared with 3.4% in un-amended soil). The addition of the humic acid fraction of the composted soil also increased the mineralization potential of the soil significantly, but to a lesser extent (37.5% mineralization after 106 days compared with 20.6% in unamended soil). Increasing the humic acid concentration increased mineralization up to a maximum of more than three times the unamended rate, after which the rate of pyrene mineralization decreased, possibly due to inhibitory pH or concentrations of salts. The amendment of PAH-contaminated soil with materials containing humic acids or humic acid extracts is suggested as a method of bioremediation.     

Fractal dimension of humic acids

Small-angle neutron scattering experiments have been made on solutions of humic acid aggregates with an acidity corresponding to pH 5.0 and at 0.1 M ionic strength. We observe power-law decay of the intensity over one decade of the scattering vector, Q, indicating that the aggregates are fractal. We explain the normalized intensity in the entire Q-range by assuming that the humic acid particles can be described by building units of a radial size, 25 Å, aggregated into clusters with an average radius of 400–500 Å. For humic acids obtained from two different sources, we determine the fractal dimension, D = 2.3 ± 0.1. For small values of Q, the measured data of one of the samples extend into the Guinier range giving an average radius of gyration of 320 ± 20 Å. Correspondence to: R. Österberg     

Chemical and infra-red spectroscopic study of humic and fulvic acids from composted poplar bark

Humic (HA) and fulvic (FA) acids were extracted from poplar bark after 12 and 30 months of composting and characterized through functional groups analysis and FT-IR spectra. The extraction and purification procedures were those recommended by the International Humic Substances Society (IHSS). Total acidity and COOH, total OH and CO contents of FA were always greater than those of the corresponding HA. Carboxyl groups were the major components of total acidity. Phenolic OH groups content of HA was always higher than that of the corresponding FA, whilst the alcoholic OH groups content was higher in FA than in HA. There were no significant differences between HA extracted after 12 and 30 months of composting, but some differences were shown by the corresponding FA.     

Amino acid distribution in some fungal melanins and of soil humic acids from Brazil

Summary Humic acids from four Brazilian topsoils of different origins and four soil fungal melanins, synthesized under two cultural conditions, were subjected to 6N HCl hydrolysis and their amino acid distribution patterns qualitatively and quantitatively determined. Both soil and fungal polymers showed similar patterns with aspartic acid, glutamic acid, glycine and alanine as the dominant amino acids. Some variations noted were more quantitative than qualitative, the similarities were more pronounced than differences, indicating that the fungal melanins may play a significant role in the formation of soil humic acid polymers. The humic acids of Brazilian soils had amino acid distribution patterns similar to those reported for humic acids of other tropical and temperate soils.     

Cleavage of humic acids bypenicillium frequentans

Summary Functional group content of undegraded humic acids was compared with that of humic acids which had been partially degraded by a strain ofPenicillium frequentans. It was found that cleavage of humic acids by this organism did not involve reduction of the carboxyl groups. It was suggested that one of the steps involved was hydrolysis of the ether bonds present in humic acids.     

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.     

Sorption of humic acids by bacteria

Capacity for sorption of humic acid (HA) from water solutions was shown for 38 bacterial strains. Isotherms of HA sorption were determined for the cells of 10 strains. The bonding strength between the cells and HA (k) and the terminal adsorption (Q _max) determined from the Langmuir equation for gram-positive and gram-negative bacteria were reliably different. Gram-positive bacteria sorbed greater amounts of HA than gram-negative ones (Q _max = 23 ± 10 and 5.6 ± 1.2 mg/m², respectively). The bonding strength between HA and the cells was higher in gram-negative bacteria than in gram-positive: k = 9 ± 5 and 3.3 ± 1.1 mL/mg, respectively.     

Isolation of soil Streptomyces strains capable of degrading humic acids and analysis of their peroxidase activity

Abstract Fifteen Streptomyces strains capable of decolorizing humic acids in presence of glucose were isolated from soil samples using the dilute suspension technique and spread on agar plates. Six strains, displaying a significant and stable activity, were selected for further characterization. Some features of these isolates (carbon source utilization, enzyme production, antibiotic resistance) were compared with those of the reference strain Streptomyces viridosporus ATCC 39115. Degradation properties studied in batch cultures at pH 7.0 showed that the catabolic activity on humic acids was generally stimulated by incubation with 100% oxygen and was cell surface-associated. Peroxidase activity from cell-free extracts was analysed by using the oxidation of N,N,N′,N′-tetramethyl-phenylene-diamine. PAGE analysis revealed the existence of two major types of peroxidases (molecular mass: about 39.2 and 61.6 kDa), dividing the strains into two groups. The role of cell surface-associated peroxidase activity in the breakdown of humic acids is discussed.     

Decomposition of humic acids by incubation in a soil water-extract under various conditions of oxygen availability

Summary Decomposition of humic acids suspended in a soil water-extract under various conditions of oxygen availability (aerobic, anaerobic, alternating aerobic/anaerobic) led to the formation of fulvic acids, lower molecular weight compounds, and humin, a more complex mixture of insoluble compounds. The transformation of humic acids and formation of new humic compounds were higher under aerobic conditions than under either anaerobic or alternating aerobic/anaerobic ones.Although subjected to decomposition under greatly differing conditions of oxygen availability, the residual humic acids showed essentially the same types of chemical alterations, an increase of functional groups containing oxygen and a decrease of hydrolysable ternary and quarternary fractions.     

Permeability of plant tissues to humic acids

Do od?ezaných větvi?ek r?zných rostlin pono?ených ?eznou plochou do roztoku humusové kyseliny proniká hnědě zbarvený roztok do cév a je v nich koagulován. Během týdne se cévní svazky zbarvily do vý?ky 1 a? 6 cm. V parenchymatických buňkách není mo?no p?ímo humusovou kyselinu zjistit; ale i buňky se ?lutě nebo hnědavě zbarvenou blanou jsou ?ivé (dají se plasmolysovat). Kyselina humusová zna?ená aktivním uhlíkem C¹⁴ se v rostlinách ?í?í celkem stejně v nesterilních i sterlních kulturách, a to rovně? p?edev?ím cévními svazky.     

Ratio of elements in humic acids as a source of information on the environment of soil formation

This paper considers the informative importance of one of the main features that characterize humic acids of soils at the diagnosis of the natural environment of their formation in both the present and the past. It is shown that the ratio of elements in the humic acids clearly corresponds to the landscape conditions and quantitative characteristics of climatic parameters. They persist over time and can serve as one of the reliable indicators in assessing the environment of different periods of paleogeographic history.     

Separation of low molecular weight humic acids with Sephadex G25

Summary A method is pressented using Sephadex G25 to separate the smallest molecules from a humic acid sample. This procedure can also be used to select a certain molecular range.