N. A. Kulikova

Mitigating Activity of Humic Substances: Direct Influence on Biota

Mitigating activity of HS can be defined as a phenomenon of lowering the adverse effects of contaminants toxicity and of those of abiotic stress factors such as unfavourable temperature, pH, salinity, etc. As a rule, it is related to the detoxifying properties of HS or to their beneficial effects on biota. This review focuses on the latter effects and considers the possible mechanisms of mitigating activity of humic materials in terms of biological activity of HS. The beneficial effects of HS on biota are segregated into the four categories according to the underlying mechanism of their action: an influence on the organism development; an enhancement in nutrient supply; catalysis of the biochemical reactions; and an antioxidant activity. The published data on the mentioned essential biological functions of HS are reviewed.

Estimation of uptake of humic substances from different sources by Escherichia coli cells under optimum and salt stress conditions by use of tritium-labeled humic materials.

ABSTRACT The primary goal of this paper is to demonstrate potential strengths of the use of tritium-labeled humic substances (HS) to quantify their interaction with living cells under various conditions. A novel approach was taken to study the interaction between a model microorganism and the labeled humic material. The bacterium Escherichia coli was used as a model microorganism. Salt stress was used to study interactions of HS with living cells under nonoptimum conditions. Six tritium-labeled samples of HS originating from coal, peat, and soil were examined. To quantify their interaction with E. coli cells, bioconcentration factors (BCF) were calculated and the amount of HS that penetrated into the cell interior was determined, and the liquid scintillation counting technique was used as well. The BCF values under optimum conditions varied from 0.9 to 13.1 liters kg−1 of cell biomass, whereas under salt stress conditions the range of corresponding values increased substantially and accounted for 0.2 to 130 liters kg−1. The measured amounts of HS that penetrated into the cells were 23 to 167 mg and 25 to 465 mg HS per kg of cell biomass under optimum and salt stress conditions, respectively. This finding indicated increased penetration of HS into E. coli cells under salt stress.

A new technique for tritium labeling of humic substances

Abstract Humic substances (HS) of different origins have been labeled with tritium by the thermal activation method. Specific radioactivity of labeled HS ( 3H-HS) was sufficiently high and varied from 0.14 to 0.6 TBq/g. Parent HS and 3H-HS were analyzed by size exclusion chromatography with radioactivity and UV detection. The results allowed concluding that (1) neither partial decomposition nor polymerization of HS occurred during labeling and (2) tritium labeled molecules have a regular distribution among HS fractions of different molecular weights. The performed correlation analysis revealed that there was no significant relationship between HS properties and specific radioactivity of the obtained 3H-HS. Thus universality of the developed technique for radioactive labeling of HS with tritium could be demonstrated.

Comparative Analysis of the Ligninolytic Potential of Basidiomycetes Belonging to Different Taxonomic and Ecological Groups

Screening of the ligninolytic activity of basidiomycetes from the Komarov Botanical Institute Basidiomycetes Culture Collection (LE-BIN), Russian Academy of Sciences, belonging to different taxonomic and ecological groups was performed. The patterns of the position of taxa of active producers of ligninolytic enzymes in the modern system of fungi were identified. Cluster analysis showed that the group of fungi with the greatest ligninolytic and degradation potential includes representatives of the families Pleurotaceae, Polyporaceae, and Phanerochaetaceae, which perform the first stages of wood decomposition. As a result, species of interest for the further study of their oxidative potential and use in biotechnology were selected.

Structure of Humic Acids Isolated by Sequential Alkaline Extraction from a Typical Chernozem

It was shown with the isolation of a humic acid (HA) preparation from a typical chernozem by sequential alkaline extraction as an example that the preparative yield of HAs decreased at each sequential extraction stage by 3–4 times. On the basis of studying the obtained preparations using elemental analysis, gel-penetration chromatography, and 13C NMR spectroscopy, the tendencies of the changes in the structural-group and molecular-weight compositions of the HAs from one extraction stage to the next one were revealed. The conclusion was drawn that a single extraction is sufficient for obtaining a representative HA sample.

A Comparative Characterization of Fungal Melanin and the Humin-like Substances Synthesized by Cerrena maxima 0275

Comparative studies of fungal melanin and two preparations of the high-molecular-weight humin-like substances formed during a solid-phase cultivation of the basidiomycete Cerrena maxima 0275 for 45 and 70 days were performed. The fungal melanin from Aspergillus niger and the humin-like substances synthesized by the basidiomycete C. maxima 0275 are similar in their physicochemical properties (elemental composition and behavior in acids and alkalis) and auxin-like activities. However, these biopolymers differ, essentially, at the structural level. According to IR spectroscopy data, the obtained humin-like substances display a higher similarity to natural humic acids and are more diverse in their functional groups compared with fungal melanins. Presumably, this is connected with the fact that laccase is involved in formation of humin-like substances; moreover, this enzyme is involved not only in the synthesis of these polymers, but also in their modification and degradation.

Use of Basidiomycetes in Industrial Waste Processing and Utilization Technologies: Fundamental and Applied Aspects (Review)

This review provides an analysis of recent data on the mechanisms of degradation of lignocellulosic materials and xenobiotics by basidiomycetes. Special attention is given to the analysis of the current state of research of ligninolytic enzymes and their involvement in the degradation of xenobiotics. Data on the practical use of basidiomycetes for bioconversion of industrial wastes are systematized. The most promising areas of bioconversion technologies are considered, such as contaminated water purification (including wastewater), cleanup of soils contaminated with heavy metals and xenobiotics, and degradation of difficult-to-degrade substrates (lignin and lignocellulose wastes, low-energy coal, and synthetic polymers).

Transformation of humic substances of highly oxidized brown coal by basidiomycetes Trametes hirsuta and Trametes maxima

The ability of white rot basidiomycetes Trametes hirsuta and Trametes maxima to transform coal humic substances (HS’s) under the conditions of solid phase cultivation in the presence or absence of an easily available source of carbon (glucose) has been studied. It was shown that during the growth of the fungal strains used in media containing HS’s, destructive and condensation processes of HS transformation proceeded simultaneously. Based on a comparative physicochemical analysis of the initial HS’s and HS’s trans-formed by the fungi, it was established that, despite the introduction of glucose may favor a deeper transformation of HS’s by basidiomycetes, the general direction of their modification is dominant reduction or oxidation and is determined by the physiological biochemical peculiarities of the strain used.

Label Distribution in Tissues of Wheat Seedlings Cultivated with Tritium-Labeled Leonardite Humic Acid.

Humic substances (HS) play important roles in the biotic-abiotic interactions of the root plant and soil contributing to plant adaptation to external environments. However, their mode of action on plants remains largely unknown. In this study the HS distribution in tissues of wheat seedlings was examined using tritium-labeled humic acid (HA) derived from leonardite (a variety of lignites) and microautoradiography (MAR). Preferential accumulation of labeled products from tritiated HA was found in the roots as compared to the shoots, and endodermis was shown to be the major control point for radial transport of label into vascular system of plant. Tritium was also found in the stele and xylem tissues indicating that labeled products from tritiated HA could be transported to shoot tissues via the transpiration stream. Treatment with HA lead to an increase in the content of polar lipids of photosynthetic membranes. The observed accumulation of labeled HA products in root endodermis and positive impact on lipid synthesis are consistent with prior reported observations on physiological effects of HS on plants such as enhanced growth and development of lateral roots and improvement/repairs of the photosynthetic status of plants under stress conditions.

Humic Substances Enhance Growth and Respiration in the Basidiomycetes Trametes Maxima Under Carbon Limited Conditions

Humic substances (HS) represent the major reservoir of carbon (C) in ecosystems, and their turnover is crucial for understanding the global C cycle. Although basidiomycetes clearly have a role in HS degradation, much less is known about the effect of HS on fungal traits. We studied the alteration of physiological, biochemical, and morphological characteristics of Trametes maxima in the presence of HS. Both complete medium and minimal (C-limited) medium mimicking natural environmental conditions were used. Adding HS led to increased biomass yield, but under C-limited conditions the effect was more apparent. This result indicated that HS were used as an additional substrate and agreed with data showing a greater penetration of tritium-labeled HS into the cell interior under C-limited conditions. Humic substances induced ultra-structural changes in fungal cells, especially under C limitation, including reducing the thicknesses of the hyphal sheath and cell wall. In the minimal medium, cellular respiration increased nearly three-fold under HS application, while the corresponding effect in complete medium was lower. In addition, in the presence of inhibitors, HS stimulated either the cytochrome or the alternative pathway of respiration, depending on presence or absence of glucose in the medium. Our results suggest that, under conditions mimicking the natural environment, HS may play three major roles: as a surplus substrate for fungal growth, as a factor positively affecting cell morphology, and as an activator of physiological respiration.