Yu. A. Zavgorodnyaya

Effects of humic acids on the growth of bacteria

The influence of humic acids of different origins on the growth of bacterial cultures of different taxa isolated from the soil and the digestive tracts of earthworms (Aporrectodea caliginosa)—habitats with contrasting conditions—was studied. More than half of the soil and intestinal isolates from the 170 tested strains grew on the humic acid of brown coal as the only carbon source. The specific growth rate of the bacteria isolated from the intestines of the earthworms was higher than that of the soil bacteria. The use of humic acids by intestinal bacteria confirms the possibility of symbiotic digestion by earthworms with the participation of bacterial symbionts. Humic acids at a concentration of 0.1 g/l stimulated the growth of the soil and intestinal bacteria strains (66 strains out of 161) on Czapek’s medium with glucose (1 g/l), probably, acting as a regulator of the cell metabolism. On the medium with the humic acid, the intestinal bacteria grew faster than the soil isolates did. The most active growth of the intestinal isolates was observed by Paenibacillus sp., Pseudomonas putida, Delftia acidovorans, Microbacterium terregens, and Aeromonas sp.; among the soil ones were the representatives of the Pseudomonas genus. A response of the bacteria to the influence of humic acids was shown at the strain level using the example of Pseudomonas representatives. The Flexom humin preparation stimulated the growth of the hydrocarbon-oxidizing Acinetobacter sp. bacteria. This effect can be used for creating a new compound with the elevated activity of bacteria that are destroyers of oil and oil products.

Biochemical degradation of soil humic acids and fungal melanins

Studies were conducted to compare properties and biodegradation of fungal melanins from Aspergillus niger and Cladosporium cladosporiodes with those of humic acids from soils and brown coal. Compared to the humic acids the fungal melanins contained more functional groups, were less hydrophilic and had relatively high molecular weights. Under the conditions of incubation the melanins were found to be more readily degradable than the humic acids studied. The changes in elemental composition, optical parameters and the decrease of molecular weight, observed for both fungal melanins during degradation, made them more similar to soil humic acids.

Stimulating effect of earthworm excreta on the mineralization of nitrogen compounds in soil

The effect of excreta of earthworm species Aporrectodea caliginosa and Eisenia fetida on the mineralization of nitrogen compounds in soils has been studied. A single application of excreta obtained from three earthworms in one day increased the formation of nitrate nitrogen compounds in the soil by 10–50%. The application of ammonium nitrogen (in the form of NH4Cl) in amounts equivalent to the ammonium nitrogen content in the daily excreta of three earthworms had the same effect on the mineralization of nitrogen compounds. The effect of earthworm excreta, as well as the effect of ammonium nitrogen, on the nitrification process was an order of magnitude higher than their contribution to the formation of nitrates due to the oxidation of the introduced ammonium. Hence, ammonium—an important component of the earthworm excreta—can exert a stimulating effect on nitrification processes in the soil and produce long-term cumulative effects that are much more significant than the direct effect of this nitrogen compound.

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 (Qmax) 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 (Qmax = 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.

Earthworms as modifiers of the structure and biological activity of humic acids

Passage of humic acids (HAs) through the digestive tract of the earthworm, Eisenia fetida andrei, resulted in a decrease in molecular masses of the HAs. The effect of earthworm-modified HAs on individual bacteria and on bacterial communities as a whole is different from the effect of native HAs. Modified HA probably induces and regulates microbial successions in soils and composts in a different manner than the native HA, suppressing or stimulating different groups of microorganisms. These results may explain why the positive effects of commercial humates in real soil ecosystems, unlike model communities, attenuate rapidly.

Hydrocarbon contamination of arctic tundra soils of the Bol’shoi Lyakhovskii Island (the Novosibirskie Islands)

Data on the distribution of the components of oil products that have accumulated in the arctic tundra soils of the Bol’shoi Lyakhovskii Island (the Novosibirskie Islands) under the impact of technogenic loads are analyzed. The examined soils differ in the vertical and lateral distribution patterns of the methanenaphthenic and naphthenic hydrocarbons and in the degree of their transformation. This is determined by the position of particular soils in the catenas and by the sorption of particular hydrocarbon compounds in the soils. The portion of light molecular-weight hydrocarbons in the upper horizons decreases by two-ten times in comparison with the deeper soil layers. In the lateral direction, the twofold difference in the contents of the methane-naphthenic and naphthenic hydrocarbons in the upper horizons is seen. The degree of transformation of the hydrocarbons under the impact of microbiological processes depends on the aeration conditions, the depth of permafrost table, the composition of oil products, and the soil organic matter content.

Effect of activated charcoal on bioremediation of diesel fuel-contaminated soil

Elevated plant and microbial toxicity throughout the season was found in field experiments on bioremediation of diesel fuel (DF)-contaminated soil (4.5%). This was an indication of the presence of mobile toxic DF components and their metabolites. Introduction of granulated activated charcoal (GAC) was shown to decrease the bio- and phytotoxicity of petroleum-contaminated soil, resulting in a sharp increase in the abundance of petroleum degraders (both aboriginal and inoculated ones), as well as to create conditions for improved growth at the stage of post-treatment by phytoremediation. In spite of short-time deceleration of DF degradation, more complete decrease of hydrocarbon concentrations occurred in the presence of GAC, while simultaneous introduction of the sorbent and a biopreparation (and association of mesophilic petroleum-degrading strains) provided the best results. In these variants the concentration of petroleum hydrocarbons decreased to 0.19–0.21 and 0.13–0.14%, respectively, which was 1.5 and 2 times lower than the values for unsupplemented control. Thus, GAC introduction during bioremediation of DF-contaminated soils increases the efficiency of remediation and localizes the pollutants in the treated layer, which decreases the risk of their penetration into groundwater during in situ soil treatment.

Spatial variation of benzo[a]pyrene and agrozem properties in the vicinity of the Yuzhno-Sakhalinsk thermal power plant

The spatial variability of the density, moisture, pH, humus, and benzo[a]pyrene contamination in a structural-metamorphic agrozem within the impact zone of the Yuzhno-Sakhalinsk thermal power plant has been considered. The correlation of the benzo[a]pyrene content with the humus and density in the plow horizon has been revealed. The necessary numbers of sampling points for different problems of ecological monitoring have been planned.

Migration of Elements in Podzolic Soils of the Meshchera Lowlands (Vladimir Region, Russia): Laboratory Experiment

The study of the mobility of elements under dynamic conditions, when the material from each of soil horizons is regarded as a separate adsorption-precipitation chromatographic column allowed us make quantitative estimates of the migration of elements using coefficients of interaction as extraction and retention coefficients. The results that were obtained during the modeling experiment made it possible to compile mobility sequences of elements in soil horizons.

Quantitation of Ergosterol as a Mycorrhizal Symbiosis Biomarker

Several procedures for the detection of mycorrhizal fungi in plant roots are available. Direct microscopic assessment is labor-consuming and subjective [1], and therefore indirect methods for estimating the rate of mycorrhization have been proposed. These methods are based on assays for various components of fungal cells, such as chitin [2] and phospholipid fatty acids [3]. The first approach is relatively simple but takes into account both living and dead fungal biomass, whereas the second method is labour-consuming and requires expensive equipment. Ergosterol is another biomarker of fungal biomass [4, 5], which undergoes rapid decay after the death of fungi and can therefore be regarded as an indicator of living fungal biomass [6]. Ergosterol is not a component of plant cells [7, 8], which has allowed its use as a mycorrhiza biomarker for assessing mycorrhization of roots with arbuscular mycorrhiza [9], ectomycorrhiza [10–12], and ericoid mycorrhiza [13, 14]. Conventional procedures for ergosterol quantitation in roots and soil are labour-consuming, as they involve thermal processing, long-term shaking, centrifugation, and a liquid–liquid extraction. The procedure proposed by Beni et al. [15] does not require thermal processing, employs solid-phase extraction (SPE), and provides for rapid analysis. The authors of the procedure used it for ergosterol quantitation in poorly humified forest litter. The organic component of these samples is similar to plant tissues with regard to susceptibility to chemical processing. The aim of this study was to adapt the procedure [15] to ergosterol quantitation in fine plant roots and to assess this parameter in a series of plant species from mountain tundra ecosystems. Sample collection for analysis. Fine roots (<1 mm) of various plants were collected in the mountain tundra of the Avrorin Polar Alpine Botanical Garden– Institute (the Khibiny mountain range, Murmansk oblast). Ergosterol was determined in roots of several plant species with different mycorrhiza types and some species characterized by the absence of mycorrhizal symbiosis (Table 1). Plants were excavated together with a soil monolith, from which the fine roots were washed out, weighted, and frozen for transporting to the laboratory. Roots of each plant species (0.5–2 g wet weight) were collected from different soil monoliths in three to five replicates. Procedure modification. The original procedure [15] was modified taking into account the availability of analytical equipment (chromatographic system and column, and SPE column) and specific features of the substrate to be analyzed (plant roots). Parameters of the original procedure and modifications are listed in Table 2. Reduction of sample weight to 0.5–2 g fresh (frozen) roots was explained by the complication of collecting roots from individual plant species in multidominant natural plant communities. The substrate used in the original procedure (poorly humified forest litter) was less resistant to processing, and therefore КОН concentration in the methanol solution used for extraction was increased from 0.07 to 0.2 M in order to achieve a higher degree of cell wall destruction and to extract maximum amounts of ergosterol. As reported in [16], this concentration is sufficient for ergosterol extraction from plant tissue-associated fungi. Since the buffering capacity of the extracts was low, their neutralization was performed under control of pH in order to prevent degradation of the SPE column. According to [17], the retention of hydrophobic components on C-18 columns is most efficient at pH 6–8. An acetonitrile–water mixture (90 : 10 vol/vol) was used as the eluent in HPLC system, instead of 100% methanol used in the original procedure. The calibration curve of optical density versus ergosterol concentration (Sigma-Aldrich, >95% purity) was verified in the range of 0 to 10 μg. Spiking was used for procedure validation: a non-spiked mixed sample of fine roots from cereal plants and similar samples spiked with ergosterol (4.0 and 8.0 μg/g) were analyzed. Analytical procedure. A sample (0.5–2 g) of frozen fine roots was placed in a 100-mL conical glass f lask, suspended in 50 mL of 0.2 M КОН solution in СН3ОН, put onto a rotary shaker for 1 h, and then