Biostimulation Of Soil Research Articles

Activity of Phosphatases in Soil Contaminated with PAHs

Polycyclic aromatic hydrocarbons (PAHs) upset the basic biological parameters of the soil, such as enzymatic activity, which can be used to identify the direction and intensity of organic and mineral substance transformation in the soil environment. The aim of this study was to determine the impact of soil contamination with naphthalene, phenanthrene, anthracene and pyrene at rates of 0–4000 mg kg−1 DM (dry matter) of soil on the activity of acid phosphatase and alkaline phosphatase. An analysis was also conducted on how some organic substances, such as cellulose, sucrose and compost at rates of 0 and 9 g kg−1 DM alleviate the PAH impact on the enzymes under study. The experiment was carried out in a laboratory with loamy sand as the soil material. Phosphatase resistance (RS) and soil resilience (RL) were calculated. The enzyme activity was found to depend significantly on the PAH rate, time of PAH deposition in soil and the type of organic substance added to the soil. The activity of acid and alkaline phosphatase increased with the degree of soil contamination with PAHs. Naphthalene had the greatest stimulating effect on enzyme activity. Biostimulation of soil with cellulose, sucrose and compost had a positive effect on acid and alkaline phosphatase activity, with cellulose and compost being the most effective in boosting acid and alkaline phosphatase activity, respectively. Naphthalene had the greatest effect on acid and alkaline phosphatase resistance and pyrene had the least effect. Low RL indices indicate that the presence of PAHs permanently disturbed the activity of acid and alkaline phosphatase.

Obtaining Plant and Soil Biostimulants by Waste Whey Fermentation

This work presents the design of a bioprocess as an integral solution for adding value to whey by converting it into high value-added products for environmental/agronomical purposes as biostimulants for both soils and plants . The core of the bioprocess is a fermentation by Lactobacillus rhamnosus, a bacterial species within the group of plant growth promoting bacteria (PGPB), followed by a physicochemical separation of the valuable products obtained. The soil biostimulant products obtained are lactic acid, peptides and free amino acids and the biomass of Lactobacillus rhamnosus. All of these products were purified and the residual fraction, mainly comprising inorganic elements with high sodium content, was removed in order to avoid soil fertility problems. These products were evaluated on their soil biostimulant and biocontrol capacity, thus protein hydrolysates and lactic acid induced microbial activity, lactic acid also showed an effect modifying microbial biodiversity, favouring bacterial genera recognized as growth plants promoter, and L. rhamonsus presented biocontrol activity against some phytopathogenic microorganisms. These results give rise to the formulation of products for environmental/agronomic application.

Active Biostimulation of Environmental Soils Contaminated with Petroleum Lubricants

A new idea, active biostimulation, was put forward that direct addition of microbial nutrients into unreadily biodegradable petroleum-based lubricants is possible to stimulate biodegradation of the lubricants when they enter the environment, thus to help in situ “active” bioremediation of lubricant-contaminated areas. In the present study, small amount of nutritious amino acids, viz. oleoyl glycine, lauroyl alanine and lauroyl glycine, as “active biostimulators” were doped into a petroleum lubricating oil, respectively. The biodegradation capacities of neat oil and the amino acid-doped oils in environmental soils under specific conditions were determined and their biodegradation kinetics simulated based on the exponential kinetics model. The results demonstrated that oleoyl glycine, lauroyl alanine and lauroyl glycine were efficient in boosting biodegradation of lubricating oils in soils. Furthermore, biodegradation of lubricating oils in soils were well modeled by the first-order exponential kinetics. The biodegradation kinetics for the amino acid-doped oils in soils clearly displayed greater biodegradation reaction rates and thereby shorter biodegradation half-lives.

Specific recruitment of soil bacteria and fungi decomposers following a biostimulant application increased crop residues mineralization.

Agriculture is undergoing important changes in order to meet sustainable soil management with respect to biodiversity (namely agroecology). Within this context, alternative solutions to mineral fertilizers such as agricultural biostimulants are thus promoted and being developed. The mechanisms by which some soil biostimulants sustain soil biological functioning and indirectly increase crop yields are still unknown. Our goal in the present study was to demonstrate if and to what extent the application of a soil biostimulant affects the soil heterotrophic microbial communities that are involved in organic matter decomposition and carbon mineralization. We hypothesized that the addition of a biostimulant results in changes in the composition and in the biomass of soil microbial communities. This in turn increases the mineralization of the organic matter derived from crop residues. We performed soil microcosm experiments with the addition of crop residues and a biostimulant, and we monitored the organic carbon (orgC) mineralization and the microbial biomass, along with the microbial community composition by sequencing 16S rRNA gene and ITS amplicons. The addition of a soil biostimulant caused a pH neutralizing effect and simultaneous enhancement of the orgC mineralization of crop residues (+ 400 μg orgC g-1 dry soil) and microbial biomass (+ 60 μg orgC g-1 dry soil) that were linked to changes in the soil microbial communities. Our findings suggest that the soil carbon mineralization enhancement in the presence of the biostimulant was supported by the specific recruitment of soil bacteria and fungi. Whereas archaea remained stable, several operational taxonomic units (OTUs) of indigenous soil bacteria and fungi were enriched and affiliated with known microbial decomposers such as Cytophagaceae, Phaselicystis sp., Verrucomicrobia, Pseudomonas sp., Ramicandelaber sp., and Mortierella sp., resulting in lower soil microbial richness and diversity.

Biostimulation of Atrazine-impacted Soil Using Cassava Peel Waste Considering the Associated Soil Bacteria

Biostimulation of Atrazine-impacted Soil Using Cassava Peel Waste Considering the Associated Soil Bacteria

Production of biostimulants from okara through enzymatic hydrolysis and fermentation with Bacillus licheniformis: comparative effect on soil biological properties

ABSTRACTIn this work okara (OK), a by-product of soy milk manufacturing, is submitted to an enzymatic hydrolysis and a fermentative process to produce different soil biostimulants (BS): EH, hydrolysate obtained by the enzymatic process; FHEB, fermentation broth with Bacillus licheniformis and the enzymes secreted during the fermentation; FHE, fermentation broth without bacteria and FH, the FHE hydrolysate in which enzymes were denatured. Enzymatic hydrolysates showed a different chemical composition compared with fermented hydrolysates and OK. It had a higher protein concentration as well as C, P and K. The proteins of OK were converted into peptides with a lower molecular weight, the fermented hydrolysates being those with the lowest molecular weight profile. The influences of hydrolysates and OK were tested in soil, finding that β-glucosidase, phosphatase and dehydrogenase activities were stimulated by every treatment. However, it was observed that EH produced a greater stimulation of dehydrogenase and phosphatase than both OK and fermented BS. The bacterial and fungal phospholipid fatty acids were also higher in soils amended with BS than those of the control and soils with OK. It has also been found that β-glucosidase, phosphatase and microbial biomass were dose-dependent in every treatment, but dehydrogenase only was dose-dependent in EH and OK treatments.

Evaluation of microbial population and functional genes during the bioremediation of petroleum-contaminated soil as an effective monitoring approach

This study investigated the abundance and diversity of soil n-alkane and polycyclic aromatic hydrocarbon (PAH)-degrading bacterial communities. It also investigated the quantity of the functional genes, the occurrence of horizontal gene transfer (HGT) in the identified bacterial communities and the effect that such HGT can have on biostimulation process. Illumina sequencing was used to detect the microbial diversity of petroleum-polluted soil prior to the biostimulation process, and quantitative real-time PCR was used to determine changes in the bacterial community and functional genes (alkB, phnAc and nah) expressions throughout the biostimulation of petroleum-contaminated soil. The illumine results revealed that γ-proteobacteria, Chloroflexi, Firmicutes, and δ-proteobacteria were the most dominant bacterial phyla in the contaminated site, and that most of the strains were Gram-negative. The results of the gene expression results revealed that gram-negative bacteria and alkB are critical to successful bioremediation. Failure to maintain the stability of hydrocarbon-degrading bacteria and functional gene will reduce the extend to which alkanes and PAHs are degraded. According to the results of the study, the application of a C:N:P ratio of was 100:15:1 in the biodegradation experiment resulted in the highest rate at which petroleum hydrocarbons were biodegraded. The diversity of pollutant-degrading bacteria and the effective transfer of degrading genes among resident microorganisms are essential factors for the successful biostimulation of petroleum hydrocarbons. As such, screening these factors throughout the biostimulation process represents an effective monitoring approach by which the success of the biostimulation can be assessed.

Soil Dehydrogenases as an Indicator of Contamination of the Environment with Petroleum Products.

The aim of the research was to compare the effects of various petroleum products, biodiesel, diesel oil, fuel oil and unleaded petrol on soil dehydrogenases, and to evaluate biostimulation with compost and urea in the restoration of homeostasis of the soil contaminated with these products. The obtained results allowed for defining the weight of dehydrogenases in monitoring of the environment subjected to pressure from petroleum hydrocarbons. The studies were carried out under laboratory conditions for 180 days, and loamy sand was the soil formation used in the experiment. The petroleum products were used in the following amounts: 0, 2, 4, 8 and 16 g kg−1 DM of soil. Indices of the influence of the petroleum product and the stimulating substance on the activity of dehydrogenases were calculated. It was proved that the petroleum products affect soil dehydrogenases in various ways. Biodiesel, diesel oil and fuel oil stimulate these enzymes, while petrol acts as an inhibitor. Among the substances tested regarding biostimulation of soils contaminated with petroleum products, compost is definitely more useful than urea, and therefore, the former should be used for the remediation of such soils. Stimulation of dehydrogenases by compost, both in contaminated and non-contaminated soils, proves that it may accelerate microbiological degradation of petroleum-derived contaminants.

Bioremediation of a petroleum hydrocarbon-contaminated Antarctic soil: Optimization of a biostimulation strategy using response-surface methodology (RSM)

Bioremediation is a biotechnological approach to clean up contaminated soils. Among bioremediation strategies, biostimulation is a simple method which involves the modification of the soil physicochemical conditions in order to enhance the biological degradation of contaminants. One of the most common ways to do this is by the addition of macronutrients, mainly Nitrogen (N) and Phosphorus (P). Optimization of the amounts of N and P for a soil biostimulation strategy represents a key step prior to its application to a full-scale process. In this work, the response-surface methodology (RSM) was applied to optimize a biostimulation process for a hydrocarbon-contaminated Antarctic soil, considering a Carbon:Nitrogen:Phosporus (C:N:P) ratio of 100:10:1 as a reference. A faced-centered central composite design was used to determine the levels of the variables that lead to the optimum response values. Flasks containing contaminated soil and receiving different N and P amounts were incubated at 15°C for 80days. Biological activity and hydrocarbon concentration were evaluated. Results predicted that for the soil used in this experiment, the addition of 0.183gN/kg and 0.0179g P/kg leads to the highest hydrocarbon removal efficiency. The resulting C:N:P ratio (100:17.6:1.73) was different from that taken as reference (100:10:1), highlighting the usefulness of such an optimization. The hydrocarbon concentration decreased from 1042 (±73) mgkg−1 to 470 (±37) mgkg−1 in the most efficient combination tested.

Physiological Studies on Apricot Trees Fertilization Grown in Ismailia Governorate 2-effect of Mineral (npk), Organic (compost) Fertilizers and Some Soil bio-stimulants on Growth and Nutritional Status of "Canino" Apricot Trees

THE EFFECT of mineral (NPK) soil application either alone or in … combination with organic (compost) and some soil bio-stimulants (EM, bio-fertilizer, humic acid and compost tea) on increment percentage in trunk diameter (ITD %), average length and thickness of new shoots (cm), average number of leaves per shoot, leaf area and its dry weight, leaf photosynthetic pigments and leaf mineral content of apricot "Canino" cv. budded on local apricot rootstock grown at El-Kassasien Horti. Res. Sta., Ismailia Governorate during two successive seasons of (2010&2011) and (2011&2012). The obtained results revealed that all vegetative growth parameters under study except organic fertilizer (compost) at 100 % level resulted in significant increase in trunk diameter (ITD %), average length and thickness of new shoots (cm), average number of leaves per shoot and leaf area and its dry weight during both seasons of study. The same treatments increased, also, leaf nutrient contents of N, P, K, Ca, Mg, Zn, Fe and Mn as well as leaf photosynthetic pigments (chlorophyll a, b and carotein). It could be concluded that all investigated NPK soil application in mineral form, organic (compost) fertilizers and some soil stimulants results in significant effect, however, the fertilization with mineral (NPK) at 100% level (T1) and mineral NPK in mineral form at 50% level + organic (compost) fertilizer at 50% level coupled with all tested soil stimulants (T13) were the most effective treatments for increasing vegetative growth parameters and leaf nutrient contents of "Canino" cv. Apricot trees.

Implications of polluted soil biostimulation and bioaugmentation with spent mushroom substrate (Agaricus bisporus) on the microbial community and polycyclic aromatic hydrocarbons biodegradation

Different applications of spent Agaricus bisporus substrate (SAS), a widespread agro-industrial waste, were investigated with respect to the remediation of a historically polluted soil with Polycyclic Aromatic Hydrocarbons (PAH). In one treatment, the waste was sterilized (SSAS) prior to its application in order to assess its ability to biostimulate, as an organic amendment, the resident soil microbiota and ensuing contaminant degradation. For the other treatments, two bioaugmentation approaches were investigated; the first involved the use of the waste itself and thus implied the application of A. bisporus and the inherent microbiota of the waste. In the second treatment, SAS was sterilized and inoculated again with the fungus to assess its ability to act as a fungal carrier. All these treatments were compared with natural attenuation in terms of their impact on soil heterotrophic and PAH-degrading bacteria, fungal growth, biodiversity of soil microbiota and ability to affect PAH bioavailability and ensuing degradation and detoxification. Results clearly showed that historically PAH contaminated soil was not amenable to natural attenuation. Conversely, the addition of sterilized spent A. bisporus substrate to the soil stimulated resident soil bacteria with ensuing high removals of 3-ring PAH. Both augmentation treatments were more effective in removing highly condensed PAH, some of which known to possess a significant carcinogenic activity. Regardless of the mode of application, the present results strongly support the adequacy of SAS for environmental remediation purposes and open the way to an attractive recycling option of this waste.

Biostimulation and Phytoremediation Treatment Strategies of Gasoline-Nickel Co-Contaminated Soil

This study investigated the potential effect of poultry dung (biostimulation) and stubborn grass (Sporobolus pyramidalis) (phytoremediation) on microbial biodegradation of gasoline and nickel uptake in gasoline-nickel-impacted soil. In addition, the potential stimulatory effects of nickel on hydrocarbon utilization were investigated over a small range of nickel concentrations (2.5–12.5 mg/kg). The results showed that an increase in nickel concentration increased hydrocarbon degraders in soil by a range of 8.4–17.2% and resulted in a relative increase in gasoline biodegradation (57.5–62.4%). Also, under aerobic conditions, total petroleum hydrocarbons’ (TPH) removal was 62.4% in the natural gasoline-nickel microcosm (natural attenuation), and a maximum of 78.5%, 85.7%, and 95.8% TPH removal was obtained in phytoremediation, biostimulation, and a combination of biostimulation- and phytoremediation-treated microcosms, respectively. First-order kinetics described the biodegradation of gasoline and nickel uptake very well. Half-life times obtained were 28.88, 18.24, 14.44, and 8.56 days for gasoline degradation under natural attenuation, phytoremediation, biostimulation, and combined biostimulation and phytoremediation treatment methods, respectively. The results indicate that these remediation methods have promising potential for effective remediation of soils co-contaminated with petroleum hydrocarbons and heavy metals.

Effects of nitrogen fertility and crop rotation on onion growth and yield, thrips densities, Iris yellow spot virus and soil properties

Onion thrips and Iris yellow spot virus (IYSV) are two primary yield reducing factors in onion production worldwide. Current management practices rely on heavy use of insecticides and fertilizers, threatening the sustainability of onion systems. Little is known about how cultural practices such as reduced fertility, soil biostimulants, and crop rotation affect onion yield, thrips densities, soil properties, and IYSV incidence. In a replicated field experiment, reduced nitrogen (N) (134kgNha−1, one-third the standard grower rate), slightly decreased yield and onion size. Adult thrips populations were 23 to 31% lower in the reduced as compared to standard N (402kgNha−1) and biostimulant treatment, respectively. Growing onions following a one year cycle in corn rather than wheat reduced onion thrips in one of two years. The addition of a biostimulant had no effect on soil properties, but may have slightly increased yield, attracted adult thrips, and increased thrips populations. IYSV incidence was not influenced by fertilizer rate or crop rotation. Soil microbial biomass and readily mineralizable carbon were greater following wheat, while soil nitrate (NO3−) accumulation was greater in standard N treatments. Soil microbial activity, as measured by dehydrogenase enzyme potential, may have been adversely affected by high N rates. Results suggest that reduced N, without biostimulant, sustained onion yields, decreased onion thrips densities and potential for IYSV incidence, created a more favorable soil environment for microbial activity, and reduced the risk of NO3− leaching

Microbiological Features and Bioactivity of a Fermented Manure Product (Preparation 500) Used in Biodynamic Agriculture

The fermented manure derivative known as Preparation 500 is traditionally used as a field spray in biodynamic agriculture for maintaining and increasing soil fertility. This work aimed at characterizing the product from a microbiological standpoint and at assaying its bioactive properties. The approach involved molecular taxonomical characterization of the culturable microbial community; ARISA fingerprints of the total bacteria and fungal communities; chemical elemental macronutrient analysis via a combustion analyzer; activity assays for six key enzymes; bioassays for bacterial quorum sensing and chitolipooligosaccharide production; and plant hormonelike activity. The material was found to harbor a bacterial community of 2.38 × 10(8) CFU/g dw dominated by Grampositives with minor instances of Actinobacteria and Gammaproteobacteria. ARISA showed a coherence of bacterial assemblages in different preparation lots of the same year in spite of geographic origin. Enzymatic activities showed elevated values of beta-glucosidase, alkaline phosphatase, chitinase, and esterase. The preparation had no quorum sensing-detectable signal, and no rhizobial nod gene-inducing properties, but displayed a strong auxin-like effect on plants. Enzymatic analyses indicated a bioactive potential in the fertility and nutrient cycling contexts. The IAA activity and microbial degradation products qualify for a possible activity as soil biostimulants. Quantitative details and possible modes of action are discussed.

Dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil microcosms amended with mushroom cultivation substrate

The potential of mushroom cultivation substrate (MCS) in bioremediation was examined in polycyclic aromatic hydrocarbon (PAH)-contaminated soil. After a 60-day incubation, 32.9% dissipation of the 15 studied PAHs was observed in MCS-amended microcosms, with anthracene, benzo(a)pyrene and benzo(a)anthracene being the most degradable PAHs. MCS significantly increased the abundance and changed the community compositions of bacteria, fungi and aromatic hydrocarbon degraders. Two species belonging to the Sordariomycetes of the Ascomycota were enriched in all MCS-treated soil samples, and coupled with the unique changes in the PAH profile, this implies the involvement of laccase-like enzymes. Limited improvement was observed after adding Pleurotus ostreatus, possibly because of its poor colonization of the soil. In addition, alfalfa appeared to antagonize the bioremediation effects of MCS. The results of this study suggest that MCS can be a cost-effective and green biostimulation agent, thereby providing support for the development of MCS-based biostimulation of PAH-contaminated soil.

Effects of Biostimulation on Growth of Indigenous Bacteria in Sub-Antarctic Soil Contamined with Oil Hydrocarbons

Effects of Biostimulation on Growth of Indigenous Bacteria in Sub-Antarctic Soil Contamined with Oil Hydrocarbons — In order to evaluate the efficiency of biostimulation of soil contaminated with oil hydrocarbons under sub-Antarctic conditions, a mesocosm study was initiated in May 2001 in the Kerguelen Archipelago (49°21'S, 70°13'E). The effects of temperature and fertilizer addition (Inipol EAP-22, Elf Atochem) on soil bacterial assemblages contaminated with hydrocarbons were studied in 6-l batches of subantarctic soil incubated in the dark. Six different conditions were used at three temperatures (4, 10 and 20°C): control, fertilizer (50 ml), diesel oil (100 ml), diesel oil (100 ml) + fertilizer (50 ml), Arabian light crude oil (100 ml) and crude oil (100 ml) + fertilizer (50 ml). Mesocosms were sampled on a regular basis over a seven-month period. All samples were analyzed for total bacteria, viable heterotrophic assemblages and hydrocarbon-utilising microflora. The results clearly showed a significant response of sub-Antarctic microbial soil communities to hydrocarbon contamination. Large increases in total, heterotrophic and hydrocarbon-utilising bacteria were observed

Enhanced Biodegradation of Petroleum Hydrocarbons in Contaminated Soil

Soil samples taken from a contaminated site in Northern Quebec, Canada, exhibited a low capacity for biodegradation of total petroleum hydrocarbons (TPH), despite a high capacity for the mineralization of aromatic hydrocarbons and a low toxicity of soil leachates as measured by Microtox assay. Toxicity assays directly performed on surface soil, including earthworm mortality and barley seedling emergence, indicated moderate to high levels of toxicity. Soil biostimulation did not improve the removal of petroleum hydrocarbons, while bioaugmentation of soil with a developed enrichment culture increased the efficiency of hydrocarbon removal from 20.4% to 49.2%. A considerable increase in the removal of TPH was obtained in a bioslurry process, enhancing the mass transfer of hydrocarbons from soil to the aqueous phase and increasing the efficiency of hydrocarbon removal to over 70% after 45 days of incubation. The addition of ionic or nonionic surfactants did not have a significant impact on biodegradation of hydrocarbons. The extent of hydrocarbon mineralization during the bioslurry process after 45 days of incubation ranged from 41.3% to 58.9%, indicating that 62.7% to 83.1% of the eliminated TPH were transformed into CO2 and water.

Enhanced Biodegradation of Petroleum Hydrocarbons in Contaminated Soil

Soil samples taken from a contaminated site in Northern Quebec, Canada, exhibited a low capacity for biodegradation of total petroleum hydrocarbons (TPH), despite a high capacity for the mineralization of aromatic hydrocarbons and a low toxicity of soil leachates as measured by Microtox assay. Toxicity assays directly performed on surface soil, including earthworm mortality and barley seedling emergence, indicated moderate to high levels of toxicity. Soil biostimulation did not improve the removal of petroleum hydrocarbons, while bioaugmentation of soil with a developed enrichment culture increased the efficiency of hydrocarbon removal from 20.4% to 49.2%. A considerable increase in the removal of TPH was obtained in a bioslurry process, enhancing the mass transfer of hydrocarbons from soil to the aqueous phase and increasing the efficiency of hydrocarbon removal to over 70% after 45 days of incubation. The addition of ionic or nonionic surfactants did not have a significant impact on biodegradation of hydrocarbons. The extent of hydrocarbon mineralization during the bioslurry process after 45 days of incubation ranged from 41.3% to 58.9%, indicating that 62.7% to 83.1% of the eliminated TPH were transformed into CO2 and water.

Effects of agricultural biostimulants on soil microbial activity and nitrogen dynamics

We investigated the effects of two commercially available soil biostimulants, designated Z93 and W91, on key microbial and nutrient cycling processes in the soil, by conducting short-term (1 week) and longer-term (8 weeks) soil incubations in the laboratory. In the short-term soil incubations, the two compounds differed in their effects on microbial activity: Z93 was effective over a wide range, stimulating substrate-induced respiration (SIR) and dehydrogenase activity (DHA) at remarkably low concentrations (0.5–500 nl/g soil); W91 stimulated SIR at these concentrations, but also inhibited DHA. In longer-term soil incubations, we amended batches of soil with either finely-ground alfalfa leaves, wheat straw, or added no amendments, to alter patterns of soil nitrogen mineralization and immobilization. We treated these soils with Z93 and W91 at two concentrations (0.005 and 0.5 μl/g soil), and incubated them for up to 8 weeks. These extremely low doses of both Z93 and W91 influenced soil SIR, DHA, and cellulase activity significantly ( P<0.05). Both compounds also influenced soil nitrogen dynamics significantly; the extent depending upon the quality of the organic amendments. In the alfalfa-amended soil there was a steep increase in NO 3-N concentration during the incubation due to the rapid mineralization of nitrogen-rich alfalfa material. However, in this soil, both Z93 and W91 reduced NO 3-N concentrations greatly after 56 days. In the straw-amended soil, mineral nitrogen concentrations were very low, probably due to rapid immobilization of nitrogen by microbial biomass. In this soil, treatment with both compounds decreased microbial biomass nitrogen and increased dissolved organic nitrogen (DON), relative to that in the controls. Our results suggest that the two biostimulants can stimulate both the breakdown and mineralization of soil organic materials, perhaps by selectively inhibiting or stimulating particular components of the microbial community, leading to lasting (8 weeks or longer) increases in soil nitrogen availability.

Monitoring the Size and Metabolic Activity of the Bacterial Community during Biostimulation of Fuel-Contaminated Soil using Competitive PCR and RT-PCR.

Efforts to understand and improve soil bioremediation are limited by our ability to determine how treatment variables affect microbial communities. A method was developed to monitor the density and metabolic activity of the total bacterial community in soil. This method was used to monitor the bacterial community in microcosms of Arctic soil after addition of N plus P to stimulate biodegradation of hydrocarbon contaminants. During 29 days of incubation, the total petroleum hydrocarbon level in the soil was reduced from 850 to 360 mg/g of soil. DNA and RNA were extracted from soil using a bead beating method, purified by ammonium acetate precipitation, and assayed by competitive PCR and RT-PCR assays with universal bacterial primers. The copy number of 16S rDNA in the soil microbial community was relatively stable and ranged from 1.7 x 109 to 4.5 x 109/g of soil throughout the incubation. The copy number of 16S rRNA changed substantially and ranged from 5.6 x 1010 to 1.0 x 1012/g of soil. The rRNA:rDNA ratio was highest during the phase of fastest hydrocarbon biodegradation. These results suggest that the treatment to stimulate hydrocarbon biodegradation did not substantially change the density of the bacterial community but did transiently increase its overall metabolic activity.