Intensification of phenol biodegradation by humic substances

Phenol biodegradation was carried out in a batch system by the bacterial strain Cupriavidus metallidurans in the presence of potassium humate that was prepared by alkaline extraction from oxyhumolite. The experiments were focused on the assessment of the humate effect on biodegradation activity of the tested bacterial strain. The achieved results demonstrated that the humate has a positive influence on the biodegradation of phenol and reduces the incubation time necessary for phenol removal. Higher biodegradation rate and more intensive growth were observed during the cultivation in presence of humate in comparison to the cultivation without its addition. Adsorption of the humate on bacterial biomass was observed as well. Subsequently, a phenol biodegradation testing in a continuous-flow system using a biofilm reactor was also carried out. Although the reactor was inoculated by C. metallidurans only, the microbial composition under an aerobic non-aseptic condition during this long-term cultivation changed. The phenol removal efficiency obtained in the biofilm reactor was higher than 92% when phenol concentration in a treated medium was 1200 mg l⁻¹.     

Enhanced molecular dimension of a humic acid induced by photooxidation catalyzed by biomimetic metalporphyrins

Synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinates of Mn(III) chloride [Mn-(TDCPPS)Cl] and iron(III) chloride [Fe-(TDCPPS)Cl] were employed as biomimetic catalysts in the photooxidative coupling of a terrestrial humic acid (HA). The changes in molecular dimension of HA induced by irradiation with UV light for different periods were followed by high-performance size-exclusion chromatography (HPSEC), with both spectrophotometric and refractive index (RI) detectors. Enhancement of apparent weight-average molecular weight (M(wa)) of sodium humate solutions at both pH 7 and 3.5, occurred after irradiation with UV light after 5.5 and 13 h by catalysis with either manganese or iron porphyrin. A significant increase in M(wa) values was also found when samples were kept in the dark for 8 and 11 days after the end of irradiation, thereby suggesting a progression of free-radicals coupling with time course after photoinduction. The enhancement of absorptivity of humic matter with catalyzed photooxidation was confirmed by the significant increase in apparent molecular mass as shown by the RI detector. The latter also indicated a slightly larger effect by iron-porphyrin than by manganese-porphyrin in the photooxidative coupling of humic molecules. These findings suggest that photooxidation may represent a valid alternative to oxidizing agents, such as H(2)O(2), in the polymerization of natural organic matter catalyzed by biomimetic metalporphyrins.     

Intramolecular catalysis of biomimetic Michael additions to cyclopentenones

A study of the Michael additon of n-propyl mercaptan to a series of cyclopentenones shows that intramolecular hydrogen bonding enhances the rate. The possible significance of this observation is discussed.     

Reduction of humic substances by halorespiring, sulphate-reducing and methanogenic microorganisms

Physiologically distinct anaerobic microorganisms were explored for their ability to oxidize different substrates with humic acids or the humic analogue, anthraquinone-2,6-disulphonate (AQDS), as a terminal electron acceptor. Most of the microorganisms evaluated including, for example, the halorespiring bacterium, Desulfitobacterium PCE1, the sulphate-reducing bacterium, Desulfovibrio G11 and the methanogenic archaeon, Methanospirillum hungatei JF1, could oxidize hydrogen linked to the reduction of humic acids or AQDS. Desulfitobacterium dehalogenans and Desulfitobacterium PCE1 could also convert lactate to acetate linked to the reduction of humic substances. Humus served as a terminal electron acceptor supporting growth of Desulfitobacterium species, which may explain the recovery of these microorganisms from organic rich environments in which the presence of chlorinated pollutants or sulphite is not expected. The results suggest that the ubiquity of humus reduction found in many different environments may be as a result of the increasing number of anaerobic microorganisms, which are known to be able to reduce humic substances.     

Evaluation of extractants for soil humic substances

Summary An evaluation of alkaline extractants was done by isotachophoresis and compared with infrared, ultraviolet and visible spectroscopic analysis. The electrophoretograms show that the humic acid extracted. This result is partially corroborated by the E₄/E₆ ratio. Differences in the carboxyl content and TRIS. In the pyrophosphate humic acid three fractions of high molecular weight were not extracted. This resultis partially corroborated by the E₄/E₆ ratio. Differences in the carboxyl content found by ir spectra of the TRIS humic acid and the NaOH humic acid were not shown in the isotachophoretic separation.     

Water-extractable humic substances enhance iron deficiency responses by Fe-deficient cucumber plants

The ability of Fe-deficient cucumber plants to use iron complexed to a water-extractable humic substances fraction (WEHS), was investigated. Seven-day-old Fe-deficient plants were transferred to a nutrient solution supplemented daily for 5 days with 0.2 μM Fe as Fe-WEHS (5 μg org. C mL^-1), Fe-EDTA, Fe-citrate or FeCl₃. These treatments all allowed re-greening of the leaf tissue, and partial recovery of dry matter accumulation, chlorophyll and iron contents. However, the recovery was faster in plants supplied with Fe-WEHS and was already evident 48 h after Fe supply. The addition of 0.2 μM Fe to the nutrient solution caused also a partial recovery of the dry matter and iron accumulation in roots of Fe-deficient cucumber plants, particularly in those supplied with Fe-WEHS. The addition of WEHS alone (5 μg org. C mL^-1, 0.04 μM Fe) to the nutrient solution slightly but significantly increased iron and chlorophyll contents in leaves of Fe-deficient plants; in these plants, dry matter accumulation in leaves and roots was comparable or even higher than that measured in plants treated with Fe-citrate or FeCl₃. After addition of the different iron sources for 5 days to Fe-deficient roots, morphological modifications (proliferation of lateral roots, increase in the diameter of the sub-apical zones and amplified root-hair formation) and physiological responses (enhanced Fe(III)-chelate reductase and acidification of the nutrient solution) induced by Fe deficiency, were still evident, particularly in plants treated with the humic molecules. The presence of WEHS caused also a further acidification of the nutrient medium by Fe-deficient plants. The Fe-WEHS complex (1 μM Fe) could be reduced by intact cucumber roots, at rates of reduction higher than those measured for Fe-EDTA at equimolar iron concentration. Plasma membrane vesicles, purified by two-phase partition from root microsomes of Fe-deficient plants, were also able to reduce Fe-WEHS. Results show that Fe-deficient cucumber plants can use iron complexed to water soluble humic substances, at least in part via reduction of complexed Fe(III) by the plasma membrane Fe(III)-chelate reductase of root cells. In addition, the stimulating effect of humic substances on H⁺ release might be of relevance for the overall response of the plants to iron shortage. This revised version was published online in June 2006 with corrections to the Cover Date.     

Determination of heavy metals in humic substances by instrumental photon activation analysis

Biological Trace Element Research - Photoactivation analysis is used for the determination of heavy metals in water and humic substances. Isolated humic acids serve as a carrier of environmental...     

厌氧条件下希瓦氏菌腐殖质还原对偶氮还原的影响

以希瓦氏菌属的3个代表种为研究对象,研究了在厌氧条件下腐殖质的存在对偶氮还原的影响。实验结果表明:3个代表菌株在厌氧条件下都有高效的偶氮还原和腐殖质还原功能,1mmol/L偶氮染料在24h内完全脱色,并且偶氮还原与电子供体氧化存在着紧密的偶联关系。腐殖质物质模式物2-磺酸蒽醌AQS在小于1~2mmol/L条件下能显著加速偶氮还原,12h就完全脱色,3mmol/L时18h完全脱色。但当浓度大于3mmol/L时则对偶氮还原产生明显抑制作用。另一腐殖质模式物2,6-双磺酸蒽醌AQDS其浓度在1~3mmol/L以内亦使脱色在12h内完成,4~6mmol/L时15h左右完成脱色。7~12mmol/L仍有一定的脱色促进作用,但随着浓度的提高,其促进作用也逐渐减弱。这说明腐殖质的确可以作为氧化还原中间体穿梭于电子供体与染料的偶氮双键之间促进偶氮还原。但当其浓度达到某一阈值时它就显出与偶氮键竞争电子的本质,从而使偶氮还原速率下降。原因在于他们的氧化还原电势的差异,导致细菌呼吸链的电子递体对腐殖质物质和偶氮键的亲和力不同,从而使不同腐殖质浓度对偶氮键还原产生了不同的影响。     

The effect of fire on soil humic substances

Summary High temperature effects on soil humic substances were investigated both in natural and laboratory conditions. Differential Thermal Analysis and pyrolysis show that only temperatures above 250°C produce changes in the humic acid fraction. The mean change is a loss of weight due to decarboxylation. Isotachophoretic studies also show that temperatures higher than 250°C produce alteration in the separation pattern of the different subfractions due to changes in the ‘core’ or/and in the amount of carboxyl and hydroxyl groups. Isotachophoregrams done on soil samples extracted from an area before and after fire show no differences. This result is taken as an indication that there was no direct effect of the temperature on the soil humic substances.     

Biostimulant activity of humic substances extracted from leonardites

Background and aims

Biostimulants are natural compounds that enhance plant growth and plant nutrient use efficiency. In this study, biostimulant effects of humic substances (HS) extracted from leonardites were analysed on the metabolism of maize plants grown in hydroponic conditions.

Methods

HS extracted from four leonardites were tested for their auxin-like and gibberellin-like activities. Then, 11 day old maize seedlings were treated for 48 h with five concentrations (0, 0.1, 0.5, 1, and 10 mg C L^?1) of HS. After sampling, root growth and morphology, glutamine synthetase (GS) activity, glutamate synthase (GOGAT) activity, total protein content, soluble sugars content, phenylalanine ammonia-lyase (PAL) activity, soluble phenols, and free phenolic acids were analysed.

Results

HS from leonardites had similar spectroscopic pattern, with small differences. The HS from the South Dakota lignite (HS_USA) had more carboxylic groups, whereas the three from Turkish mines had more aromatic and aliphatic structures. HS_USA best enhanced total root growth, root surface area, and proliferation of secondary roots. Plant nutrient use efficiency was enhanced by HS_4, HS_USA and HS_B, with increment of GS and GOGAT enzymes activity and total protein production. HS stimulated also PAL enzyme activity, followed by a higher production of total soluble phenols, p-hydroxybenzoic acid, p-coumarilic acid, and chlorogenic acid.

Conclusion

This study found that, although the activity of the HS depended on the origin of the leonardite, these compounds can be attributed to the biostimulant products, eliciting plant growth, nitrogen metabolism, and accumulation of phenolic substances.

     

Content of auxin-inhibitor-and gibberellin-like substances in humic acids

The content of auxin-, inhibitors-and gibberellin-like substances in freeze-dried humic acids was studied. The results indicate the existence of growth-promoting substances in humic acids, possibly corresponding to IAA or its precursors. Inhibitory activity is more marked during germination than during the growth process. The inhibitory effect caused by high concentration of humic acids could be due to an auxin-like action rather than an input per se of growth inhibitors. A significant amount of both free and conjugated gibberellin-like substances were observed.     

The disruption of Daphnia magna sodium metabolism by humic substances: mechanism of action and effect of humic substance source

Humic substances have important functions in aquatic systems. While these roles are primarily indirect, influencing the physicochemical environment, recent evidence suggests these materials may also have direct biological actions. This study investigated the mechanism by which humic substances perturb sodium metabolism in a freshwater invertebrate, the water flea Daphnia magna. Aldrich humic acid (AHA) stimulated the maximal rate of whole-body sodium influx (Jmax) when experimental pH was 6 and water calcium content was 0.5 mM. This effect persisted at pH 8 and 1 mM calcium but not at pH 8 in the absence of calcium. An indirect action of AHA on apical transporter activity was proposed to explain this effect. At pH 4 AHA promoted a linear sodium uptake kinetic relationship, attributed to altered membrane permeability due to enhanced membrane binding of humic substances at low pH. In contrast, a real-world natural organic matter sample had no consistent action on sodium influx, suggesting that impacts on sodium metabolism may be limited to commercially available humic materials. These findings question the applicability of commercially available humic substances for laboratory investigations and have significant implications for the study of environmental metal toxicity.     

Role of aliphatic and phenolic hydroxyl groups in uranyl complexation by humic substances

Relativistic density functional calculations of uranyl complexes with alcohols were carried out to study how phenolic and aliphatic hydroxyl groups of humic substances may contribute to uranyl complexation by humic substances. According to recent experimental work, blocking of phenolic OH groups decreases the loading capacity, but has no effect on the key geometric parameters of uranyl humate complexes. This can be understood on the basis of our calculations which showed uranium-oxygen distances to be very similar for complexes with rather different types of O-donor ligands, with average U-O_eq ∼ 237 pm for fivefold coordinated uranyl (VI) complexes, both for O⁻ and OH functional groups. Uranyl complexation by alcohol moieties seems unlikely at environmental conditions as a high pH is required for the deprotonation of these groups; we confirm an alternative complexation mechanism that overcomes the ligand deprotonation problem. Similarities in structures and energetic suggest that complexes of both aliphatic and phenolic alcoholates may well contribute in comparable fashion to the complexation of uranyl by humic acids.     

Degradation and transformation of humic substances by saprotrophic fungi: processes and mechanisms

Humic substances represent the main carbon reservoir in the biosphere, estimated at 1600 × 10¹⁵ g C. Due to their crucial role in reductive and oxidative reactions, sorption, complexation and transport of pollutants, minerals and trace elements, sustaining plant growth, soil structure and formation, and control of the biogeochemistry of organic carbon in the global ecosystem, humic substances are extremely important to environmental processes. Saprotrophic fungi active in the decomposition process of humic substances include mainly ascomycetes and basidiomycetes, which are both common in the upper layers of soils. White rot and litter decomposing fungi are the most important organisms in the degradation and mineralization of refractory organic matter (OM), whereas ascomycetes are mainly involved in the modification and polymerization of humic substances. The mechanisms of degradation probably involve mainly a variety of non specific oxidizing enzymes. This review provides an overview of the subject, while bridging two main disciplines: soil OM chemistry and fungal microbiology. It is aimed to highlight problems, unsolved questions and hypotheses.     

Inhibition of phosphatase activity by dissolved humic substances and hydrolytic reactivation by natural ultraviolet light

1. Phosphatases released extracellularly by aquatic micro-organisms often complex with humic compounds that are released from decomposing tissues of plants and imported in dissolved and colloidal forms to lakes and rivers. 2. Dissolved humic substances from several natural sources formed complexes with phosphatases of bacterial and algal origin and reduced hydrolytic activity by non-competitive inhibition. Restoration of the hydrolytic enzyme activities from the humic substances–enzyme complexes increased progressively over time when exposed experimentally to natural and artificial ultraviolet (UV) irradiance. 3. Greater phosphatase restoration occurred from humic acid–phosphatase complexes when humic acids were extracted from dissolved organic matter (DOM) of mixed natural plant sources, than when humic acids were isolated from a decomposing single plant species. 4. The data support a previously suggested hypothesis that phosphatases and other enzymes in aquatic ecosystems can complex with humic substances that dominate the DOM pool. These humic substances–enzyme complexes, in which the enzyme is temporarily inactivated, can be transported with water movements and displaced to other sites within the ecosystem. Upon exposure to UV irradiance in the photic zone, functional enzymes can be released. The potential for inactivation and storage of enzyme activity, relocation within the ecosystem, and subsequent reactivation holds important implications for regulation of nutrient cycling in fresh waters.     

Chemical characterization of humic substances extracted from organic-waste-amended soils

Humic substances were extracted from a soil treated, in a 4-year experiment, at different rates with a sludge from anaerobic treatment of combined civil and industrial wastes, and with agricultural manure. Elemental and chemical analyses, molecular weight (MW) distribution and infrared (IR) spectroscopy were performed on the purified humic acids (HA). Organic wastes significantly increased the HA content of the treated soils and improved CEC. The C/N, C/H and C/O ratios of HA extracted from the original wastes showed a higher degree of humification for sludge than for manure. This difference was also noticed for the C/N ratio of soil humic extracts, indicating a faster humification process for the sludges in soil. The content of oxygen-containing functional groups was lower than the ‘model’ HA reported in the literature, and even more so for HA from sludges, reflecting their anaerobic formation. MW distribution and E₄/E₆ ratios showed that the sludge material had a higher molecular complexity than manure, supporting the high degree of humification attributed to the former. HA extracted from sludge-treated soils revealed a molecular dimension increasing with the application doses of waste material. Infrared spectra showed that HA formed in soils after waste additions reflected the chemical composition of the original organic material, which was rich in aliphatic groups and peptides for sludge and in carbohydrates for manure. On the basis of this study, it is concluded that not only are organic waste additions able to build up the HA content in soils but the HA formed assume the chemical characteristics and the degree of humification of the original material.     

C-13 nuclear magnetic resonance spectroscopy of humic substances

Summary Evidence is presented from a preliminary study showing that C-13 N.M.R. spectroscopy is a useful new tool for the elucidation of the structure of soil organic matter.