Activity Of Soil Bacteria Research Articles

Chemical Structure of Stabilizing Layers of Negatively Charged Silver Nanoparticles as an Effector of Shifts in Soil Bacterial Microbiome under Short-Term Exposure.

In this work, we have assessed the exposure of soil bacteria from potato monoculture to three types of silver nanoparticles (AgNPs) as well as silver ions (Ag+ ions) delivered in the form of silver nitrate and a commercially available fungicide. The diversity of the soil microbial community, enzymatic activity, and carbon source utilization were evaluated. It was found that only the fungicide significantly limited the abundance and activity of soil bacteria. Silver ions significantly reduced bacterial metabolic activity. In turn, one type of AgNPs prepared with the use of tannic acid (TA) increased bacterial load and activity. There was found in all AgNPs treated soils (1) a greater proportion of all types of persistent bacteria, i.e., Bacillus, Paenibacillus, and Clostridium; (2) a visible decrease in the proportion of Nocardioides, Arthrobacter, and Candidatus Solibacter; (3) almost complete depletion of Pseudomonas; (4) increase in the number of low-frequency taxa and decrease in dominant taxa compared to the control soil. Despite the general trend of qualitative changes in the bacterial community, it was found that the differences in the chemical structure of the AgNP stabilizing layers had a significant impact on the specific metabolic activity resulting from qualitative changes in the microbiome.

Green manure effect on the ability of native and inoculated soil bacteria to mobilize zinc for wheat uptake (Triticum aestivum L.)

PurposeGreen manuring can increase the plant available fraction of zinc (Zn) in soil, making it a potential approach to increase wheat Zn concentrations and fight human Zn deficiency. We tested whether green manure increases the ability of both the native soil bacteria and inoculated Zn solubilizing bacteria (ZSB) to mobilize Zn.MethodsWheat was grown in a pot experiment with the following three factors (with or without); (i) clover addition; (ii) soil x-ray irradiation (i.e. elimination of the whole soil biota followed by re-inoculation with the native soil bacteria); and (iii) ZSB inoculation. The incorporation of clover in both the irradiated and the ZSB treatments allowed us to test green manure effects on the mobilization of Zn by indigenous soil bacteria as well as by inoculated strains.ResultsInoculation with ZSB did neither increase soil Zn availability nor wheat Zn uptake. The highest soil Zn availabilities were found when clover was incorporated, particularly in the irradiated soils (containing only soil bacteria). This was partly associated with the stimulation of bacterial activity during the decomposition of the incorporated green manure.ConclusionThe results support that the activity of soil bacteria is intimately involved in the mobilization of Zn following the incorporation of green manure.

Influence of soil structure on the spread of Pseudomonas fluorescens in soil at microscale

AbstractFor over a half a century, researchers have been aware of the fact that the physical and chemical characteristics of microenvironments in soils strongly influence the activity, growth and metabolism of microorganisms. However, many aspects of the effect of soil physical characteristics, such as the pore geometry, remain poorly understood. Therefore, the objective of the present research was to determine the influence of soil pore characteristics on the spread of bacteria, observed at the scale relevant to microbes. Pseudomonas fluorescens was introduced in columns filled with 1–2 mm soil aggregates, packed at different bulk densities. Soil microcosms were scanned at 10.87 μm voxel resolution using X‐ray computed tomography (CT) to characterize the geometry of pores. Thin sections were prepared to determine the spread and colonization of bacteria. The results showed that average bacterial cell density was 174 cells mm−2 in soil with bulk density of 1.3 g cm−3 and 99 cells mm−2 in soil with bulk density of 1.5 g cm−3. Soil porosity and solid‐pore interfaces influence the spread of bacteria and their colonization of the pore space at lower bulk density, resulting in relatively higher bacterial densities in larger pore spaces. The study also demonstrates that thin sectioning of resin‐impregnated soil samples can be combined with X‐ray CT to visualize bacterial colonization of a 3D pore volume. This research therefore represents a significant step towards understanding how environmental change and soil management impact bacterial diversity in soils.Highlights We used a quantitative approach to study bacterial spread in soil at scales relevant to microbes. The rate of pseudomonas spread decreased with increased bulk density of soil. Soil porosity and soil‐pore interface influence Pseudomonas in lower bulk density soil. Soil structure with different pore characteristics effects spread and activity of bacteria in soil.

Effects of chitin degradation products N-acetylglucosamine and N,Nʹ-diacetylchitobiose on chitinase activity and bacterial community structure in an incubated upland soil

ABSTRACT Chitin, which is the polymer of N-acetylglucosamine (GlcNAc) linked by β1,4 glycoside bonds, has been reported as a soil amendment to mitigate plant soil diseases, increasing the population of chitin-degrading bacteria, and chitinolytic enzymatic activity in the soil. In some chitin-degrading bacteria, whose chitinolytic systems have been intensively studied, the chitin degradation product N,Nʹ-diacetylchitobiose {(GlcNAc)2} induces expression of genes for chitinases whereas GlcNAc does not. To evaluate the effects of these mono- and disaccharides on the population and activity of chitinolytic bacteria in soil, we investigated the chitinolytic enzyme activity and bacterial community structure in an incubated upland soil supplemented with GlcNAc or (GlcNAc)2. The added GlcNAc and (GlcNAc)2 (2 mg g−1) were consumed within 1 d when incubated at 25°C. Chitinase activity was induced by (GlcNAc)2 and chitin after 1-d and 7-d incubation, respectively, but not by GlcNAc. N-acetylglucosaminidase (GlcNAcase) activity was induced by GlcNAc but was lower than those by (GlcNAc)2 and chitin. Amplicon sequencing analysis targeting 16S rRNA genes demonstrated that both GlcNAc and (GlcNAc)2 significantly increased the rate of the order Bacillales, but the compositions of Bacillales differed from each other: the family Planococcaceae significantly increased in either GlcNAc- or (GlcNAc)2-added soil, but the genera Bacillus and Paenibacillus were increased mainly by GlcNAc and (GlcNAc)2, respectively. The family Streptomycetaceae of the order Actinomycetales was significantly increased by (GlcNAc)2 and chitin, but GlcNAc did not. Thus, GlcNAc and (GlcNAc)2, which were promptly consumed in the incubated soil, indicated partly similar but distinctive effects on chitinolytic enzyme activity and bacterial communities. Both aminosugars increased GlcNAcase activity and the population size of Planococcaceae. GlcNAc increased Bacillus. Chitinase activity and the populations of Paenibacillus and Streptomycetaceae, a number of strains of which are known as potent chitin-degraders, were increased by (GlcNAc)2, but not by GlcNAc.

Rapid Shifts in Bacterial Community Assembly under Static and Dynamic Hydration Conditions in Porous Media.

The complexity of natural soils presents a challenge to the systematic identification and disentanglement of governing processes that shape natural bacterial communities. Studies have highlighted the critical role of the soil aqueous phase in shaping interactions among soil bacterial communities. To quantify and improve the attributability of soil aqueous-phase effects, we introduced a synthetic and traceable bacterial community to simple porous microcosms and subjected the community to constant or dynamic hydration conditions. The results were expressed in terms of absolute abundance and show species-specific responses to hydration and nutrient conditions. Hydration dynamics exerted a significant influence on the fraction of less-abundant species, especially after extended incubation periods. Phylogenetic relationships did not explain the group of most abundant species. The ability to quantify species-level dynamics in a bacterial community offers an important step toward deciphering the links between community composition and functions in dynamic terrestrial environments.IMPORTANCE The composition and activity of soil bacteria are central to various ecosystem services and soil biogeochemical cycles. A key factor for soil bacterial activity is soil hydration, which is in a constant state of change due to rainfall, drainage, plant water uptake, and evaporation. These dynamic changes in soil hydration state affect the structure and function of soil bacterial communities in complex ways often unobservable in natural soil. We designed an experimental system that retains the salient features of hydrated soil yet enables systematic evaluation of changes in a representative bacterial community in response to cycles of wetting and drying. The study shows that hydration cycles affect community abundance, yet most changes in composition occur with the less-abundant species (while the successful ones remain dominant). This research offers a new path for an improved understanding of bacterial community assembly in natural environments, including bacterial growth, maintenance, and death, with a special focus on the role of hydrological factors.

Pea cultivar Blauwschokker for the phytostimulation of biodiesel degradation in agricultural soil

Phytoremediation is a cost-effective and ecologically friendly process that involves the use of plants to uptake, accumulate, translocate, stabilize, or degrade pollutants. The present study was conducted to demonstrate the potential of pea (Pisum sativum L. spp. sativum) cultivar Blauwschokker to phytostimulate biodiesel degradation in an agricultural soil, considering the influence of biological remediation on selected physiological parameters of plants and the amount and activity of soil microflora. Biodiesel was spiked into soil in dose of 50 g kg−1 of dry mass soil. The results of the study showed that the rate of biodiesel degradation in the vegetated soil was higher than that occurring by natural attenuation. At the same time, biodiesel showed a positive effect on the growth, development, and activity of soil bacteria and fungi. Moreover, the obtained results showed an improvement in physiological parameters of plants, including an increase in chlorophyll a and total chlorophyll content and higher relative water content in leaves in the presence of biodiesel.

The Abundance of Nitrogen Fixing, Nitrifying, Denitrifying and Ammonifying Bacteria in the Soil of Tropical Rainforests and Oil Palm Plantations in Jambi

Alterations in the use of land for oil palm plantations can change the domination and activity of soil bacteria. More specifically, alteration in soil microbial communities can directly affect soil ecosystem functioning, particularly with respect to carbon and nitrogen cycles. Nitrogen can be a limiting nutrient, and the availability of nitrogen in the soil environment becomes a major factor in controlling the production of biomass. This research project aimed at studying the abundance of nitrogen-fixing, nitrogen-oxidizing, nitrogen-reducing, and ammonifying bacteria based on their functional genes in the tropical rain forests of Taman Nasional Bukit Duabelas (TNBD) and the oil palm plantations in Sarolangun Jambi. Samples were collected in November 2015. Soil sampling was performed randomly at three points representing each area of ​​the tropical rainforests of TNBD and the seven- to eight-year-old oil palm plantations. Soil samples were collected using a soil sample core from 0–15 cm below the surface with depth strata of 0–5 cm, 5–10 cm, and 10–15 cm. Composite assessment was conducted on samples from each point corresponding to each respective depth strata. Soil samples were stored at -20oC prior to testing. Microbial abundance was measured using the most probable number (MPN) method. The abundance of microbes that play a role in nitrogen metabolism between strata of 5–10 cm and 10–15 cm does not appear to be different. The highest abundance of microbes in oil palm plantation land in Jambi was found in samples with nitrifying bacteria, later followed by denitrifying , nitrogen-fixing, and ammonifying bacteria. Ultimately, it was found that microbial abundance in oil palm plantations was higher than the corresponding rates in samples from tropical rainforests .

Influence of Organic Amendment on Microbial Activities and Growth of Pepper Cultured on Crude Oil Contaminated Niger Delta Soil

Land contamination with crude oil is one of the challenges of effective crop production in the Niger Delta Region of Nigeria. This condition is inherent thus creates the need for developing effective remedial methods of managing contaminated lands as well as improve crop production. This study was designed to assess the effect of Brewers Spent Grains (BSG) on microbial activities and growth of Capsicum annum L cultured in crude oil contaminated soil. The results have shown that depending on the level of contamination, crude affected both the physical and chemical attributes of soil. It increased the acidity from pH 5.67 to a range of 5.58 - 5.64 and the total organic carbon content from 0.05% to 0.14% - 0.21 while the total nitrogen and available phosphorus levels of soil were remarkably reduced from 0.39% to 0.21% - 0.28%, and from 0.036% to 0.028% - 0.032% respectively. Amendment of contaminated soil with BSG had variable influence on the microbial properties of test soil. It increases the heterotrophic activity of bacteria in soil while retarding the activities of nitrogen fixing bacteria (Nitrosomonas sp and Nitrobacter sp). However at a stimulating amendment level of 150g of BSG in a 0.208% level of contamination, the activities of hydrocarbon degrading bacteria was enhanced from the hitherto low number of 3.6 log CFU/g found in test soil to 6.2 log CFU/g obtained on the 6th week of the remediation period. This resulted in 62.09% hydrocarbon degradation in soil at the end of the 8-week remediation course. BSG amendment of the oil contaminated had clear but variable influence on some agronomic traits of the cultured pepper. Growth was generally promoted by the amendment and the most significant (P<0.05) growth attributes affected were the plant height, number of branches, leaves, flowers and fruits as well as the leaf area. Pepper seedlings exposed to 0.624% of oil and remedied with 300g (1.5%) had the highest number of flowers but the flower did develop into fruits. However plant exposed to 0.416% of oil contamination and remedied with 0.75% of BSG produced flowers that formed fruits. Although the cultured pepper plants exhibited necrotic spots, this study has shown that plants grow in crude oil contaminated soil if alternative source of nutrients is provided. This tend to grow more in lightly contaminated soil and remediation using BSG has proven to enhance the activities of microorganisms and subsequent degradation of hydrocarbons in contaminated soil. It is highly recommended for use as soil conditioner to unmask nutrients in contaminated soils.

Profiling 16S bacterial DNA and RNA: Difference between community structure and transcriptional activity in phenanthrene polluted sand in the vicinity of plant roots

Biodegradation of polycyclic aromatic hydrocarbons (PAH) in soil is mainly performed by endogenous bacteria. The density and activity of soil bacteria are usually increased in the rhizosphere. A compartmentalized device was used to follow biodegradation of phenanthrene and bacterial community structure as a function of distance from roots. Isolation of total DNA and RNA, followed by PCR-TTGE and RT-PCR-TTGE on a 16S rDNA partial sequence, was performed to describe the structure of bacterial community and of active species, respectively. After 4 weeks, active species profiles in the immediate vicinity of roots were the same as in non-planted treatment, with similar biodegradation efficiency (approx. 60%) whereas community structure clearly indicated that bacterial populations were different. On the opposite, at a furthest distance (6–9 mm) from the roots where biodegradation was lower, bacterial community structure was similar to the non-planted treatment whereas active species differed. A specie activity factor ( S af) was calculated for five relevant species to follow their transcriptional state in the rhizosphere and showed spatial variations as a function of species and distance from roots. We conclude that depending on distance from roots, the rhizosphere selected different bacterial communities, and different active species within these communities, resulting in different degradation values. Potential biases of molecular protocols used in this study are discussed as well as their relevance to describe the bacterial component of the rhizosphere involved in PAH biodegradation.

Chronic nitrogen enrichment affects the structure and function of the soil microbial community in temperate hardwood and pine forests

We examined how chronic nitrogen (N) enrichment of pine and hardwood forest stands has affected the relative abundance, functional capacity, and activity of soil bacteria and fungi. During Fall 2002 we collected one soil core (5.6 cm diameter; organic horizon plus 10 cm of mineral soil) from each of four 5 m×5 m subplots within the control, low N (5 g N m −2 per year), and high N (15 g N m −2 per year) plots in both the hardwood and pine stands at the Chronic Nitrogen Amendment Study at Harvard Forest. The samples were analyzed for total and active bacterial and fungal biomass, microbial catabolic response profiles, the activities of cellulolytic and ligninolytic enzymes, and total, labile and microbially derived organic carbon (C). Live, fine roots were also collected from the control and low N pine plots and analyzed for ectomycorrhizal fungal community composition and diversity. Active fungal biomass was 27–61% and 42–69% lower in the fertilized compared to control plots in the hardwood and pine stands, respectively. Active bacterial biomass was not greatly affected by N additions, resulting in significantly lower fungal:bacterial biomass ratios in the N-treated plots. This shift in microbial community composition was accompanied by a significant reduction in the activity of phenol oxidase, a lignin-degrading enzyme produced by white-rot fungi. In the pine stand, ectomycorrhizal fungal community diversity was lower in the low N-treated plot than in the control plot. Differences in ectomycorrhizal community structure were also detected between control and fertilized pine plots, including a reduction in those species with the highest relative frequencies in the control community. Finally, N enrichment altered the pattern of microbial substrate use, with the relative response to the addition of carboxylic acids and carbohydrates being significantly lower in the N-treated plots, even after the data were normalized to account for differences in microbial biomass. These patterns are consistent with lower decomposition rates and altered N cycling observed previously at this site.

Chronic nitrogen enrichment affects the structure and function of the soil microbial community in temperate hardwood and pine forests

We examined how chronic nitrogen (N) enrichment of pine and hardwood forest stands has affected the relative abundance, functional capacity, and activity of soil bacteria and fungi. During Fall 2002 we collected one soil core (5.6 cm diameter; organic horizon plus 10 cm of mineral soil) from each of four 5m×5 m subplots within the control, low N (5 g N m−2 per year), and high N (15 g N m−2 per year) plots in both the hardwood and pine stands at the Chronic Nitrogen Amendment Study at Harvard Forest. The samples were analyzed for total and active bacterial and fungal biomass, microbial catabolic response profiles, the activities of cellulolytic and ligninolytic enzymes, and total, labile and microbially derived organic carbon (C). Live, fine roots were also collected from the control and low N pine plots and analyzed for ectomycorrhizal fungal community composition and diversity. Active fungal biomass was 27–61% and 42–69% lower in the fertilized compared to control plots in the hardwood and pine stands, respectively. Active bacterial biomass was not greatly affected by N additions, resulting in significantly lower fungal:bacterial biomass ratios in the N-treated plots. This shift in microbial community composition was accompanied by a significant reduction in the activity of phenol oxidase, a lignin-degrading enzyme produced by white-rot fungi. In the pine stand, ectomycorrhizal fungal community diversity was lower in the low N-treated plot than in the control plot. Differences in ectomycorrhizal community structure were also detected between control and fertilized pine plots, including a reduction in those species with the highest relative frequencies in the control community. Finally, N enrichment altered the pattern of microbial substrate use, with the relative response to the addition of carboxylic acids and carbohydrates being significantly lower in the N-treated plots, even after the data were normalized to account for differences in microbial biomass. These patterns are consistent with lower decomposition rates and altered N cycling observed previously at this site.

The effects of large- and small-scale differences in soil temperature and moisture on bacterial functional diversity and the community of bacterivorous nematodes

This paper describes the effects of large-scale seasonal fluctuations as well as experimentally induced small-scale variations of soil temperature and moisture on the community of bacterivorous nematodes and the activity of soil bacteria from a Greek Mediterranean grassland. Our experiment spanned a 6-month period (July–December 1996), during which artificially created changes in temperature (1.4 °C) and moisture content of the soil (2.3%) were superimposed on seasonal variations of these variables. Functional diversity of soil bacteria was assessed using Biolog GN-plates. Bacterial diversity, richness and evenness as well as the mean oxidation of almost all Biolog substrate groups, were affected significantly by the seasonal fluctuations of soil temperature and moisture, and declined linearly from July to December. The substrates responsible for the differences in monthly soil samples were mainly carbohydrates and carboxylic acids. The small-scale experimental changes in temperature and moisture affected oxidation of only four out of the eight substrate groups. The effect of seasonality was also obvious on the diversity, evenness, richness and total density of soil bacterivorous nematodes, which exhibited higher values during the period September–October. The effect of experimental temperature and moisture modifications varied between the different nematode taxa. Acrobeles, Chiloplacus and Cephalobus responded significantly to small-scale temperature changes, while the responses of the other taxa, if any, were more complicated, depending on the interactive effect of both soil temperature and moisture. In any case, the experimental modifications of moisture alone did not induce significant changes in the structure of the nematode community. After comparing the community parameters of bacteria and bacterivorous nematodes, we conclude that there was no synchronised response between nematodes and their food resources.

The Biometric Analysis of Bacterial Cells in Soil

The biometric analysis of bacterial cells in soil by light, fluorescence, and scanning electron microscopy showed that their average size is 0.8 μm in diameter, 1.4 μm in length, and 0.7 μm3 in volume. In soil loci with enhanced microbiological activity (the rhizoplane of plants and the intestinal tract of soil invertebrates), the average size of bacterial cells was found to be 40% smaller than that of cells occurring in other parts of soil. This is the first experimental evidence showing that the metabolic activity of soil bacteria, their concentration, and allometric parameters are related.

Screening for In Vitro Antifungal Activity of Soil Bacteria Against Plant Pathogens

Antifungal bacteria for biological control of plant diseases or production of novel antibiotics to plant pathogens were isolated in 1997 from various soils of Ansung, Chunan, Koyang, and Paju in Korea. Sixty-four bacterial strains pre-screened from approximately 1,400 strains were tested on V-8 juice agar against eight plant pathogenic fungi using in vitro bioassay technique for inhibition of mycelial growth. Test pathogens were Aiternaria mali, Colletotrichum gloeosporioides, C. orbiculare, Fusarium oxysporum f. sp. cucumerinum, F oxysporum f. sp. lycopersici, Magnaporthe grisea, Phytophthora capsici, and Rhizoctonia solani. A wide range of antifungal activity of bacterial strains was found against the pathogenic fungi, and strain RC-B77 showed the best antifungal activity. Correlation analysis between inhibition of each fungus and mean inhibition of all eight fungi by 64 bacterial strains revealed that C. gloeosporioides would be best appropriate for detecting bacterial strains producing antibiotics with potential as biocontrol agents for plant pathogens.

Phage-host interactions in soil

Phages are abundant and ubiquitous in nature, and are therefore important components of microbial communities. They can impact on host populations in several ways, including predation and alteration of host phenotype by genetic interactions. The dynamic survival of phage populations in soil requires infective interactions with host populations which must be undergoing growth. Hence survival is limited by the activity of soil bacteria, and phage populations must adopt strategies to overcome periods of inactivity. One of the most effective strategies is the lysogenic cycle of temperate phages. It is argued here that lysogeny in soil has a distinct advantage over virulence for phage and host survival, as opposed to aquatic ecosystems where virulence seems a more successful strategy for phage populations.

Phage-host interactions in soil

Phages are abundant and ubiquitous in nature, and are therefore important components of microbial communities. They can impact on host populations in several ways, including predation and alteration of host phenotype by genetic interactions. The dynamic survival of phage populations in soil requires infective interactions with host populations which must be undergoing growth. Hence survival is limited by the activity of soil bacteria, and phage populations must adopt strategies to overcome periods of inactivity. One of the most effective strategies is the lysogenic cycle of temperate phages. It is argued here that lysogeny in soil has a distinct advantage over virulence for phage and host survival, as opposed to aquatic ecosystems where virulence seems a more successful strategy for phage populations.

Use of an Exotic Carbon Source To Selectively Increase Metabolic Activity and Growth of Pseudomonas putida in Soil

Respiration and growth of Pseudomonas putida PpG7, containing catabolic plasmid NAH7, was determined in three agricultural field soils amended with the carbon source salicylate. The addition of salicylate to soil significantly increased the population of PpG7. However, there was a lack of relationship between microbial numbers and activity as determined by evolution of CO(2). In soils containing 30 to 1,500 mug of salicylate per g, metabolic activities of PpG7 peaked between 18 and 42 h and population densities increased approximately 10-to 10-fold. However, the metabolic activity of PpG7 rapidly declined after salicylate was utilized, whereas peak population densities were maintained for the duration of the experiments (5 to 7 days). Thus, elevated population densities of PpG7 were represented by inactive cells. Soil type had only minor effects on respiration rates or growth curves of PpG7 when amended with comparable concentrations of salicylate. Respiration and growth rates were optimal at concentrations between 300 and 1,000 mug of salicylate per g in the test soils. At 1,500 to 2,500 mug/g, respiration and growth of PpG7 were initially suppressed, but after a short lag time both attained levels similar to or greater than those resulting from the use of lower concentrations of salicylate. The culturing of PpG7 on a salicylate-amended medium to induce salicylate-degradative enzymes did not affect the lag time before utilization of salicylate in soil. Although PpG7 competed well with fungi for the substrate, suppression of fungal populations with cycloheximide resulted in significantly increased population densities of PpG7 in two of three soils amended with salicylate. The beneficial activities of bacteria in soil are discussed in relation to population density, population metabolic activity, and selective carbon source utilization.

The Carcinogenic Hydrocarbon Benzo[&lt;italic&gt;a&lt;/italic&gt;]pyrene in the Soil

This report describes the content, distribution, and fate of the carcinogenic hydrocarbon benzo(a)pyrene (BP) in the soil of various USSR regions. Enormous BP content has been found in the soil of an oil refinery. The benzene extracts from this oil caused skin cancer in treated mice. There is more BP in the old areas of large cities than in the new. BP is found everywhere, but the rural sections have less than the urban ones. The background level of BP is 1-3 ..mu..g/kg and not more than 10 ..mu..g/kg. The main source of soil contamination by BP is its sedimentation from air, particularly from aircraft exhausts. Its content decreases with the distance from the ejection source (industrial center, airfield) but may spread to 3-5 km. The redistribution of BP across soil layers is shown and its migration into plants confirmed. Seasonal variations of BP content in soil are established. After introduction into soil with tars, BP may be determined quantitatively. Eventually its quantity decreases and, at the doses applied, attains within a year background values. The main factor of BP destruction is the activity of soil bacteria. 41 references, 10 tables.