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Potential Application of Plant-Microbe Interaction for Restoration of Degraded Ecosystems DOI: 10.4018/978-1-4666-8682-3.ch011
Abstract
Rapidly increasing human population, urbanization, industrialization, and mining activities have become
the serious environmental issue of today’s world. Conventional physico-chemical remediation methods
are highly expensive and generate secondary waste. However, bioremediation of contaminated ecosystems
using indigenous microbes and plants or amalgamation of both has been recognized as a cost effective
and eco-friendly method for remediation as well as restoration of polluted or degraded ecosystems.
Further, variety of pollutant attenuation mechanisms possessed by microbes and plants makes them
more feasible for remediation of contaminated land and water over physico-chemical methods. Plants
and microbes act cooperatively to improve the rates of biodegradation and biostabilization of environmental
contaminants. This chapter aims to emphasize on potential application of microbes and plants
to attenuate the organic and inorganic pollutants from the contaminated sites as well as eco-restoration
of mine degraded and jhum lands by way of biodegradation and phytoremediation technologies
Despite the fact that it is not a new phenomenon, environmental pollution remains the world’s most pressing problem and the leading cause of disease and death among humans. Through urbanization, industrialization, mining, and exploratory operations, humans are in the forefront of polluting the world ecosystem. Both developing and developed countries suffer this burden, while developed countries have done a better job of maintaining their environment due to their increased knowledge and rigorous legislation. Even though the world is upset about pollution, its damage persists due to the catastrophic long-term implications. This chapter covers the various types of pollution, as well as the causes and effects of pollution, and offers potential strategies for dealing with pollution in order to build a healthy and sustainable ecosystem. Pollution is impeding the economic development of coal reserves. The standards for environmental protection in developed countries are comparatively stricter than in developing countries. As a result, getting a mining license entails time-consuming procedures that cause delays. Indian authorities have also begun to impose tough environmental pollution regulations. Therefore, environmental issues can be fully avoided, although such solutions are costly.
Heavy metal pollution is a matter of serious concern worldwide. Movement of heavy metals starting from the extraction processes to their applications in a variety of industrial activities, results in their indiscriminate release in the environment. Prolonged exposure to these heavy metals can cause detrimental health effects in human as well as other living organisms. Heavy metals include a class of some highly toxic metals such as, Hg, Cd, Cr, Pb, Ni, Cu, and Zn. that are reported to have cytotoxic, carcinogenic, teratogenic, and mutagenic effects. Since, these heavy metals are nondegradable and have a tendency to accumulate in environment, their removal from aquatic and terrestrial system is required. Bioremediation is one of the promising techniques which can be used to remove these contaminants from water and soil using biological agents, including microorganisms (bacteria, fungi, and microalgae) and plants (phytoremediation). Microorganisms and plants are capable of taking up heavy metals from nature and use these toxic contaminants in their metabolic activities, or convert them to less/nontoxic forms. Thus, the microorganism- and plant-mediated treatment processes are widely accepted since these methods are based on natural mechanisms and also reduce the chances of generation of secondary pollutants as in the case of various conventional processes. This chapter thus studies the various bioremediation techniques for the removal of heavy metal from nature and will discuss the mechanisms of different biological agents used for the transformation of toxic heavy metals. Different methods for the assessment of heavy metals have been discussed for the effective monitoring of contaminants in nature. The review also presents the recent advances in the field of bioremediation in terms of use of plants and their metabolites, plant growth–promoting rhizobacteria and nanoparticles for efficient removal of heavy metals from contaminated sites.
Soil is among the most challenging ecosystems for microbiologists in terms of microbial diversity and community size. Prokaryotes are the most abundant organisms in the soil and constitute the largest component of the soil biomass. In their native ecosystem, microorganisms live under different kinds of interactions that decide their survival and functioning. Both positive and negative interactions may operate under natural conditions. While negative interactions are inhibitory for microbial growth and development; positive ones are among the beneficial and sometimes obligatory for the growth of some other microorganisms. Therefore, these soil microbial communities may affect plant growth and development in several ways. They may have a direct or indirect role in plant growth and development through the synthesis of different chemical regulators in the rhizosphere’s proximity. Under direct mechanisms, they help the plants in macro/micronutrient uptake as well as by modulating plant hormone levels. Indirectly microbes may boost plant health by declining the detrimental effects of the biotic as well as abiotic stress. Among them, understanding the microbe-mediated abiotic stress tolerance mechanisms in plants is one of the major challenges in the field of agricultural research. Abiotic stresses like chilling injury, drought, high temperature, heavy metal toxicity, and salinity pose a major constraint to plant growth and crop production under natural field conditions. Because of the global food demand and limited resources, it becomes essential to generate deeper insights into the stress-alleviating mechanisms and the approaches employed by the plants, so that they can be explored for sustainable agricultural plants.
Rhizosphere microbial diversity plays an important role in plant health and agricultural sustainability. Several scientific groups have developed a wide range of methodologies for analyzing the structure, diversity, and functions of microbial populations to better understand rhizosphere biology and rhizosphere–microbe interactions. In this chapter we will discuss some of the advanced molecular tools available to explore microbial diversity of rhizosphere.
Earth is enriched with diverse climate, weather, and natural resources responsible for variable flora and fauna. The temperature change and variation in physical and chemical environmental factors give rise to a diverse microbial community. Soil microorganisms play an essential role in plant growth by several means including nitrogen fixation, element solubilization, nutrient mobilization and uptake, and suppression of disease, etc. However, higher altitudes face the issues of lower crop productivity due to less availability of soil nitrogen. Studies of rhizosphere communities may explore the potential microbial candidates to enhance and improve crop yield. The earlier development in molecular biology and proteomic approaches has been energized to explore such microbial communities. This chapter aimed to provide the current scenario of proteomic approaches to study the rhizosphere biology of higher altitudes.
Phosphorus (P) is the second utmost significant element required by the plants only after nitrogen. It is necessary for plants to carry out major metabolic process, signal transduction, respiration, macromolecular biosynthesis, and energy transfer. Phosphorous is present in ample amount in the soil in both organic and inorganic forms; however, its bioavailability for the plants is very limited. Further, phosphatic fertilizers applied in the fields quickly transformed into insoluble forms. Therefore, again very little percentage of the applied phosphorus is available to plants, making continuous application of fertilizers necessary. Thus, the extensive use of chemical phosphatic fertilizers causes soil fertility reduction and environmental pollution. In this perspective, phosphate-solubilizing microorganisms (PSMs) provide an eco-friendly alternative for the farmers. Bacteria, cyanobacteria, and fungi are the major candidates of PSM. Although PSMs are commonly found in soil, their population may not be high enough to compete with other bacterial community and establish in the rhizosphere. Therefore, inoculation with higher concentration of PSM strains would be more beneficial for phosphate-solubilizing activity in the root environment. Penicillium, Aspergillus, Rhizopus, Fusarium, and Sclerotium are the most studied genera among phosphate-solubilizing fungus (PSF).
Chickpea (Cicer arietinum L.) is the third most important food legume in the world; its annual production is nearly about 11.5 million tons with an estimated land area of 14.56 million hectares. The chickpea is a multifunction crop and has huge nutritional value. From a microbiological point of view, it is a legume crop and harbor rhizobia in its root in the form of nodules. The chickpea also has a diverse microbial population including both bacterial and fungal species. These microbial communities especially bacterial genera play an important role in its growth and protection. In this chapter, we will discuss these microbial communities and their role in chickpea growth.
This chapter explains the overview of bioremediation; soil remediation and Polycyclic Aromatic Hydrocarbon (PAH); bioremediation and ecosystem services; oil-contaminated soil, motor oil-contaminated soil, and petroleum-contaminated soil during bioremediation process; the overview of phytoremediation; the strategies and issues of phytoremediation; and phytoremediation and Plant Growth Promoting Bacteria (PGPB). Bioremediation is one of the safest methods to effectively manage contaminated waste. Without chemicals, bioremediation allows the contaminated waste to be recycled in environmental settings. Phytoremediation applies many types of plants to remove, stabilize, and destroy the contaminants in the soil and groundwater. The chapter argues that bioremediation and phytoremediation are the green technologies that can help remove contaminants from natural resources and are effective on the remediation of contaminated sites.
Different industrial, mining, agricultural and domestic activities produce a huge amount of wastes as by-products, which contaminate soil, surface water, and groundwater and cause ecological problems. Natural and traditional techniques are not very much sufficient to manage such type of pollutants/contaminants. The most affected area of environment is soil that indirectly affects biological interaction between plants and microorganisms. There is a need of highly eco-friendly approach to remove and manage such pollutants. Phytoremediation is a technique which remediates the contaminated site with and by the environmental phenomenon. Plants are the main tool of remediation in this technique. Phytoremediation includes the plant-mediated remediation of pollutants, like metal, organic, and hazardous wastes by its subclasses phytodegradation, phytovolatilization, phytoextraction, etc. This chapter includes all the phytoremediation techniques used to treat different types of contaminant site. It is an environment-friendly green technique which focused on the combined use of more than one phytoremediation approach for the successful remediation of the polluted area under field conditions.
Coal mining exerts a long lasting impact on landscape, ecosystem and socio-cultural-economic considerations. Mining and its subsequent activities in Northeastern Coal fields, Margherita Assam has been resulted significant forest and top soil loss, acid mine drainage and soil and water pollution in the area. Keeping in view the above facts, eco-restoration of mine degraded land Margherita, Assam is urgent need of the hour. Coal mining exerts a long lasting impact on landscape, ecosystem and socio-cultural-economic considerations. Mining and its subsequent activities have been found to degrade the land to a significant extent. Overburden removal from the coal field results in significant forest and top soil loss. Most of the mining wastes are inert solid materials and toxic in nature. These toxic substances are inherently present in the ore, e.g. heavy metals such as iron, mercury, arsenic, lead, zinc, cadmium, etc (Guha Roy, 1991). These heavy metals leach out of the stored waste piles and contaminate immediate environment. However, some toxic chemicals are also found in waste, as they are added intentionally during extraction and processing. The major environmental impacts due to coal mining are changes in soil stratification, reduced biotic diversity, and alteration of structure and functioning of ecosystems; these changes ultimately influence water and nutrient dynamics as well as trophic interactions. Land degradation due to coal mining is the cumulative effect of air and water pollution, soil quality degradation and biodiversity loss (Sankar et al. 1993). This process works through a cycle known as land degradation cycle. The magnitude and impact of mining on environment varies from mineral to mineral and also depends on the potential of the surrounding environment to attenuate the negative effects of mining, geographical disposition of mineral deposits and size of mining operations. A list of minerals has been prepared by Department of Environment, which is supposed to have serious impact on environment. These minerals include coal, iron ore, zinc, lead, copper, gold, pyrite,
Bioremediation of organic pollutants is often a slow and incomplete process, potentially leading to the accumulation of toxic metabolites that can be flirt her introduced into the food chain. Plant-associated bacteria, such as endophytic bacteria (non-pathogenic bacteria that occur naturally in plants) and rhizospheric bacteria (bacteria that live on and near the roots of plants), have been shown to contribute to biodegradation of toxic organic compounds in contaminated soil and could have potential for improving phytoremediation. The combination of bioaugmentation and phytoremediation, resulting in rhizoremediation, could solve some of the problems encountered during the application of both individual techniques. The inoculation of pollutant-degrading bacteria on plant seed can be an important additive to improve the efficiency of phytoremediation or bioaugmentation. Genetic engineeering of endophytic and rhizospheric bacteria for use in plant-associated degradation of toxic compounds in soil is considered one of the most promising new technologies for remediation of contaminated environmental sites. Transgenic plants exhibiting biodegradation capabilities of microorganisms bring the promise of an efficient and environmental-friendly technology for cleaning up polluted soils.
We describe a new technique for sample preparation, accelerated solvent extraction (ASE), that combines elevated temperatures and pressures with liquid solvents. The effects of various operational parameters (i.e., temperature, pressure, and volume of solvent used) on the performance of ASE were investigated. The solvents used are those normally used for standard liquid extraction techniques like Soxhlet or sonication. We found the recoveries of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and total petroleum hydrocarbons from reference materials using ASE to be quantitative. The extraction time for 1-30-g samples is less than 15 min, and the volume of solvent is 1.2-1.5 times that of the extraction cell containing the sample. No evidence was seen for thermal degradation during the extraction of temperature-sensitive compounds.
Biodegradation of α, β, γ and δ hexachlorocyclohexane (HCH) isomers was studied in broth medium and soil microcosm by Bacillus circulans and Bacillus brevis isolated from contaminated soil. Degradation of α and γ isomers by both the bacterial isolates was higher than thermodynamically stable β and δ isomers. However, B. circulans was found more effective than B. brevis for β and δ isomers. Maximum rate of degradation was recorded at 150 mg/L followed by 100 and 50 mg/L. Soil microcosm study revealed maximum degradation of HCH isomers in the treatment containing natural soil, pesticide and bacterial inocula than the treatment having sterilised soil, pesticide and bacterial isolates. Chloride release was positively co-related with HCH degradation in broth medium as well as in soil microcosm, suggesting that B. circulans and B. brevis hold promising potential by having efficient enzyme(s) required for dechlorination of HCH from contaminated sites.
Increased soil pollution with heavy metals due to various human and natural activities has led to a growing need to address environmental contamination. Some remediation technologies have been developed to treat contaminated soil, but a biology-based technology, phytoremediation, is emerging. Phytoremediation includes phytovolatilization, phytostabilization, and phytoextraction using hyperaccumulator species or a chelate-enhancement strategy. To enhance phytoremediation as a viable strategy, microbiota from the rhizosphere can play an important role, but the use of genetic engineering can also increase the success of the technique. Here we review the key information on phytoremediation, addressing both potential and limitations, resulting from the research established on this topic.
Appendix A. Pollution of environment (land, water and atmosphere) has increased rapidly since the onset of the industrial revolution. Population increase has placed much strain on the environment as have large-scale logging, mining and other commercial activities. Mining earns valuable foreign exchange but pollutes the environment, especially the water and soil through exposure to its discharge (treated or otherwise). Toxic heavy metals are present in this dischar ge and thus contaminate the soil, vegetation, water systems and marine life. There is a need to minimise or eliminate these heavy metals from the eff luent as well as the mine site after closure. One eco-friendly and sustainable mode of toxic heavy metal removal is phytoremediation. This review outlines what phytoremediation is, the classes of phytoremediation, the pros and cons of phytoremediation, its application and its relevance and applicability to the PNG situation. Suggestions will be made as to the most suitable plants for selected disused sites in PNG.
Bacterial isolates from endosulfan-contaminated soil were grown in minimal medium and screened for endosulfan degradation. The isolate which used endosulfan and showed maximum growth was selected for detailed study. Maximum degradation in shake flask culture by Pseudomonas fluorescens was 92.80% of α and 79.35% of β endosulfan isomers in 15 days at 20 mg/L concentration, followed by 50 and 100 mg/L, while the corresponding values in static condition were 69.15 and 51.39%, respectively. Endosulfan concentration degradation declined significantly at 50 and 100 mg/L. Concomitant to degradation, release of chloride ion exhibited positive relation, while pH decreased from 7.0 to 4.53 in agitating and 7.0–5.18 in static condition. The soil microcosm study revealed maximum endosulfan degradation in sterilized soil amended with P. fluorescens. Endosulfan diol and endosulfan ether were among the products of endosulfan metabolism in broth culture, but only endosulfan ether was detected in the soil microcosm. Endosulfan sulphate, a persistent and toxic metabolite of endosulfan, was not detected in either case. The study showed that P. fluorescens could be used effectively for bioremediation of the pesticide contaminated sites.
An increase of organic waste coming from different humans and productive activities is a continuous concern, and their application in soil is proposed many times as a solution to disposal problem. In agricultural soil, this practice is actually more popular because of its contribution as a fertilizer and soil enhancement. Recently, increased interest has been focused on assessing the influence of organic waste added to the soil related to pesticides behavior. The studies carried out show that addition of organic matter and nutrient mainly can affect the adsorption, movement, and biodegradation of pesticides. This review shows the factors involved, trend, and result obtained with pesticide behavior in soil amendment. Contradictory trends are reported in the literature on the pesticides' fate. These are mainly because soil type differences, pesticide characteristics, and source amendment are difficult to organize in a tendency pattern, and can significantly complicate the understanding of pesticides fate.
Savannas growing on stony, old and nutrient-poor soils of southern Venezuela were severely disturbed by removal of the soil organic layers with bulldozers for road building. Introduced species Brachiaria decumbens, Brachiaria humidicola, Pueraria phaseoloides, and Calopogonium sp. were sown. The substrate was fertilized and limed. Plant cover, vesicular – arbuscular mycorrhizae colonization, spore number, and most probable number of propagulels in undisturbed savanna, disturbed nonrevegetated savanna, and six revegetated savannas were assessed. The perturbation reduced the mycorrhizal propagule number in comparison with the undisturbed savanna. In the nonrevegetated areas the mean percent ground cover 2 years after disturbance was low (0.04%). In revegetated areas an increase in mycorrhizal propagule number occurred and the mycorrhizal colonization of the sown species was high. In restored areas there was an increase in species of nonmycotrophic Amaranthaceae. The results support other predictions on the mycorrhizae in successional biomes, because in the extremely nutrient-poor soils studied the colonizing species were mainly mycotrophic. The reclamation program applied in disturbed areas was useful because it has allowed the recovery of vesicular – arbuscular mycorrhizal inoculum and there was an increase in the recolonization of native plants. Key words: disturbance, endomycorrhizae, revegetation, savanna, vesicular – arbuscular mycorrhizae.
Biodegradation is a natural process, where the degradation of a xenobiotic chemical or pesticide by an organism is primarily a strategy for their own survival. Most of these microbes work in natural environment but some modifications can be brought about to encourage the organisms to degrade the pesticide at a faster rate in a limited time frame. This capability of microbe is some times utilized as technology for removal of contaminant from actual site. Knowledge of physiology, biochemistry and genetics of the desired microbe may further enhance the microbial process to achieve bioremediation with precision and with limited or no scope for uncertainty and variability in microbe functioning. Gene encoding for enzyme has been identified for several pesticides, which will provide a new inputs in understanding the microbial capability to degrade a pesticide and develop a super strain to achieve the desired result of bioremediation in a short time.
Mutualisms may play an important role in the establishment and invasion success of introduced species, but their influence is little studied. To test whether a lack of root nodule symbionts may limit the performance of invasive legumes, seedlings of Cytisus scoparius were introduced to an old-field habitat and then either inoculated with Bradyrhizobium strains from existing C. scoparius populations, or left uninoculated. In two separate years, inoculation more than doubled average plant biomass. For uninoculated transplants, nodule formation was positively correlated with proximity to plants of the native legume Desmodium canadense, but not related to distance from a second legume species, Apios americana. Polymerase chain reaction assays and DNA sequencing confirmed that bacteria isolated from uninoculated C. scoparius plants were indistinguishable from Bradyrhizobium strains in root nodules of D. canadense. By contrast, bacterial strains associated with A. americana were never found in C. scoparius nodules. Transplants in seven other habitats across a 160 km region also showed a highly significant, fivefold biomass increase in response to inoculation. Thus, colonizing legumes can suffer from a scarcity of nodule symbionts. However, certain indigenous legumes may create favourable microhabitats for invasion, by increasing symbiont availability in their vicinity.
Varieties and consumption of pesticides worldwide have been increasing dramatically as increased human population and crop production. In this process pesticide misuses become more and more serious, which has resulted in heavy environmental pollution and health risk of humans. In order to safeguard human health, threatened species and ecosystems from pesticide pollution, the consumption and pollution of pesticides worldwide especially China were reviewed and documented in present study. Meanwhile, the development trend of pesticide varieties and consumption was also prospected and discussed. It was found that worldwide consumption structure of pesticides has undergone significant changes since 1960s. The proportion of herbicides in pesticide consumption increased rapidly and the consumption of insecticides and fungicides/bactericides declined. China has become the largest pesticide producer and exporter in the world. Pesticide pollution of air, water bodies and soils, and pesticide-induced deaths in China has been serious in past years. Bio-pesticides should be further developed in the future.
Tin mining is one of the oldest industries in Malaysia that have started since1820s. These mining activities have resulted in about 113,700 hectors of tin tailings throughout the peninsula that created numerous environmental problems such as threat to natural reserves due to landscape changes, damage to natural drainage, pollution and destruction of natural habitats The present study was carried out in old tin mining area Bestari Jaya (Batang Berjuntai old name), district Kuala Selangor in Selangor state. The purpose of this study is to get the ground information about environmental and contamination characteristics and also planning for future work. The mined out catchment covers an area of 323.74 hectors. Initially 92.61 hectors of downstream catchment were investigated which includes two mined out water ponds. These ponds flow downstream to River Ayer Hitam that ultimately ends up with River Selangor, 5 Km upstream of Batang Berjunti Water Treatment Plants SSP1 and SSP2 which are major water distributors to federal territory (Kuala Lumpur and Putrajaya) and Selangor state as well. Samples of soil and water were taken separately from fifteen locations of downstream catchment using Global Positioning System. In preliminary studies physio-chemical parameters and concentration of heavy metals Pb 2+ , Zn 2+ , Ni 2+ , Co 2+ , As 3+ , Cu 2+ , Fe 2+ , Mn 2+ , Sn 2+ were analyzed. The metals were extracted by nitric acid and hydrogen peroxide in a closed vessel microwave digestion system and analysed by using atomic absorption spectroscopy. The method was validated by using standard reference material (NIST SRM 4354, 1643e) and results were compared with interim national water quality standards for Malaysia and found that most of physio-chemical parameters and metals concentration exceeds the permissible limits set by interim national water quality standards for Malaysia. So it is concluded that Bestari Jaya ex-mining catchment has a high pollution potential due to mining activities and Sungai (River) Ayer Hitam, recipient of catchment water is a highly polluted river. Therefore extensive research needs to be carried out in order to evaluate possible environmental risk factors in the area. Different environmental aspects have also discussed in this paper for the future research during this project.
Disturbance of vegetation and soil may change the species composition of arbuscular mycorrhizal fungi (AMF), which may in turn affect plant species responses to AMF. Seasonal tropical forest in Mexico is undergoing rapid conversion to early-succes-sional forest because of increased wildfire and may require restoration. The responses of six early-and late-successional tree species were tested using early-and late-successional AMF inoculum. The plants were germinated in the shadehouse and received three inoculum treatments: (1) soil from a two-year-old burned site, (2) soil from a mature forest site, or (3) uninoculated controls. They were transplanted as seedlings to a site prepared by burning, and their growth was measured from September 1997 to November 2000. All six species had the greatest growth response to early-seral inoculum, but the response to late-seral inoculum varied. Two tree species, Ceiba pentandra and Guazuma ulmifolia, were smallest with late-seral inoculum, even smaller than the uninoculated plants, and the other species, Brosimum alicastrum, Havardia albicans, Acacia pennatula, and Leucaena leucocephala, had intermediate growth with late-seral inoculum. Of these, Brosimum, Havardia, and Ceiba occur in late-successional forest, and the others are early seral. Of the several growth measurements (height, cover, biomass, stem diameter), stem-diameter responses to inoculum were still significantly different into the third year for four of the species. The uninoculated plants became infected by residual inoculum in the burned experimental site within three months of transplanting, yet mycorrhizal responses persisted. The treatment size differences may be due to different species composition of the inocula. The early-seral inoculum was dominated by small-spored Glomus spp., while the late-seral inoculum had a higher density of large-spored Gigasporaceae. The latter are known from greenhouse experiments to pro-mote a smaller plant-growth response than Glomus. Mature forest trees may withstand the carbon drain from Gigasporaceae better than establishing seedlings, so the growth patterns we observed with inoculum source are consistent with a rapidly growing successional forest, followed by slower-growing mature forest. The results suggest that early-seral AMF should be used when seedlings are inoculated for restoration, even for late-seral tree species.
The objectives of this study were to analyze the total contents of Cd, Cr, Cu, Ni, Pb, and Zn in the freshwater sediments
and the arable and non-arable soils of Taiwan, and to compare the different digestion methods for their determination. Two
hundred and thirty-nine freshwater sediments were collected from the Fei-Tsui Reservoir Watershed (FTRW) in northern Taiwan.
Forty-two surface (0–15 cm) and subsurface (15–30 cm) soil samples were likewise collected from 21 representative arable soils
derived from various parent materials and with varying weathered degrees in different regions of Taiwan. In addition, one
hundred and ninety-four non-arable soils were collected from the different forest regions, industrial parks, resident areas,
and commercial areas. Several digestion methods including the aquaregia and different combinations of concentrated acids (HClO4, HNO3, H2SO4, or HF) were compared. All samples were digested both by the aqua regia method and the Baker and Amacher method for Cd, Cr, Cu, Ni, Pb, and Zn. The Reisenauer method was used for Cr and the Burau
method for Pb further. The results indicate that the best digestion methods to analyze the total contents of heavy metals
in the sediments and soils were recommended as follows: the Baker and Amacher method for Cd, Cr,Cu, Ni, and Zn; the Reisenauer
method for Cr, but for simplicity the Baker and Amacher method is also recommended as the flexible method for the total analysis
of Cr; the aqua regia method for Cu, Ni, and Zn; and the Burau method for Pb.
Somatic hybrids between the zinc hyperaccumulator Thlaspi caerulescens and Brassica napus were produced by electrofusion of protoplasts isolated from each species. Optimization of electrofusion parameters yielded
interspecies heteroplasmic fusion rates of up to 13%. Hybrids were selected by screening the growing calli for Zn tolerance.
In addition, a second novel selection technique was developed based on the observation that a high proportion of hybrid microcalli
grown in liquid media did not adhere to the wall of the culture vessel, while microcalli derived from parental cells did.
Seventeen from a total of 64 regenerated plants were conclusively verified as hybrids by AFLP DNA analysis. The hybrid plants
were grown in soil for up to 4 months, and at least five flowered. Several of these hybrids survived when grown on high-zinc
media.These hybridsaccumulated levels of zinc and cadmium that would have been toxic for B. napus. The data indicate that transfer of the trait for metal hyperaccumulation in plants is possible through somatic hybridization.
"Phytoremediation" know-how to do-how is rapidly expanding and is being commercialized by harnessing the phyto-microbial diversity. This technology employs biodiversity to remove/contain pollutants from the air, soil and water. In recent years, there has been a considerable knowledge explosion in understanding plant-microbes-heavy metals interactions. Novel applications of plant-associated microbes have opened up promising areas of research in the field of phytoremediation technology. Various metabolites (e.g., 1-aminocyclopropane-1-carboxylic acid deaminase, indole-3-acetic acid, siderophores, organic acids, etc.) produced by plant-associated microbes (e.g., plant growth promoting bacteria, mycorrhizae) have been proposed to be involved in many biogeochemical processes operating in the rhizosphere. The salient functions include nutrient acquisition, cell elongation, metal detoxification and alleviation of biotic/abiotic stress in plants. Rhizosphere microbes accelerate metal mobility, or immobilization. Plants and associated microbes release inorganic and organic compounds possessing acidifying, chelating and/or reductive power. These functions are implicated to play an essential role in plant metal uptake. Overall the plant-associated beneficial microbes enhance the efficiency of phytoremediation process directly by altering the metal accumulation in plant tissues and indirectly by promoting the shoot and root biomass production. The present work aims to provide a comprehensive review of some of the promising processes mediated by plant-associated microbes and to illustrate how such processes influence heavy metal uptake through various biogeochemical processes including translocation, transformation, chelation, immobilization, solubilization, precipitation, volatilization and complexation of heavy metals ultimately facilitating phytoremediation.
The aim of this work was to test Lupinus luteus plants, inoculated with metal resistant rhizobacteria, in order to phytostabilise metals in contaminated soils. The resistance to heavy metals of strains isolated from nodules of Lupinus plants was evaluated. The strain MSMC541 showed multi-resistance to several metals (up to 13.3 mM As, 2.2 mM Cd, 2.3 mM Cu, 9 mM Pb and 30 mM Zn), and it was selected for further characterization. Furthermore, this strain was able to biosorb great amounts of metals in cell biomass. 16S rDNA sequencing positioned this strain within the genus Serratia. The presence of arsenic resistance genes was confirmed by southern blot and PCR amplification. A rhizoremediation pot experiment was conducted using Lupinus luteus grown on sand supplemented with heavy metals and inoculated with MSMC541. Plant growth parameters and metal accumulation were determined in inoculated vs. non-inoculated Lupinus luteus plants. The results showed that inoculation with MSMC541 improved the plant tolerance to metals. At the same time, metal translocation to the shoot was significantly reduced upon inoculation. These results suggest that Lupinus luteus plants, inoculated with the metal resistant strain Serratia sp. MSMC541, have a great potential for phytostabilization of metal contaminated soils.
Experiments were carried out in Italy on the potential use of the hyperaccumulator Alyssum bertolonii in phytomining of ultramafic soils for Ni. In situ experimental plots at Murlo, Tuscany were fertilized with various regimes during a 2-year period. The best fertilizer treatment (N + K + P) gave a threefold increase of the biomass of reproductive matter to 9.0 t/ha without dilution of the unfertilized Ni content. A Ni content of 0.8% in dry matter (11% in ash), would give a Ni yield of 72 kg/ha without need of resowing for a further crop. There was no correlation between the age of a plant and its Ni content. The long-term cropping sustainability of the soils was simulated by sequential extractions with KH phthalate solutions at pH 2, 4 and 6 that showed a limiting available Ni content of 768 μg/g. Thus just over seven croppings at pH 6 in the rhizosphere would reduce the available Ni pool by 30%. A proposed model for phytomining involves harvesting the crop after 12 months and burning the material to produce a sulphur-free bio-ore with about 11% Ni. Utilising the energy of combustion is also discussed. It is considered that Alyssum bertolonii or other Alyssum species might be used for phytomining throughout the Mediterranean area including Anatolia, as well as in Western Australia and the western United States. The economic limits of phytomining are proposed and at current world prices, the technique would only be feasible for Ni and Co with plants of at least the same biomass as Alyssum. Plants of higher biomass and similar uptake potential as for Ni, could extend the limits to other elements.
The ability of a nonenzymic system containing CuII/pyridine/peroxide to decolorize structurally different synthetic dyes and to degrade selected PAHs was followed. An intense and rapid (after 1 h) decolorization has been obtained with phenol red (89%), Evans blue (95%) eosin yellowish (84%) and Poly B-411 (92%). The use of radical scavengers, thiourea and Superoxide dismutase, showed that hydroxyl radicals rather than Superoxide anions are involved in the decolorization. The intensive degradation of PAHs has been obtained after 24 h. Benzo[a]pyrene has also been degraded by the CuII/H2O2 peroxide system.
Over the last five decades pesticides have undoubtedly helped to increase agricultural production and control vectors of disease, however the environmental impact of long term agro-chemical use has been cause for concern along with the effects on human health. In Pesticides, Graham Matthews begins by looking at the developmental history of pesticides, and how crop protection was achieved before they were in use, how pesticides are registered for use and what happens to pesticides in food and the environment. Pesticide application and operator safety is investigated and the future of pesticides in light of the development of genetically modified crops is explored. Provides commercially important information for the agro-chemical industry. Addresses all aspects of public concern relating to human health and the environment, including spray drift, bystander, resident and worker exposure. Looks at the future of pesticides in light of the increasing prevalence of genetically modified crops. Collecting together the most recent research in the area in a single volume, this book is a vital resource for agricultural scientists, agronomists, plant scientists, plant pathologists, entomologists, environmental scientists, public health personnel, toxicologists, crop protection personnel and all those involved in the agrochemical industry and government pesticide registration and legislation.
Although some heavy metals are essential trace elements, most of them can be toxic to all forms of life at high concentrations due to formation of complex compounds within the cell. Unlike organic pollutants, heavy metals once introduced into the environment cannot be biodegraded. They persist indefinitely and cause pollution of air, water, and soils. Thus, the main strategies of pollution control are to reduce the bioavailability, mobility, and toxicity of metals. Methods for remediation of heavy metal-contaminated environments include physical removal, detoxification, bioleaching, and phytoremediation. Because heavy metals are increasingly found in microbial habitats due to natural and industrial processes, microorganisms have evolved several mechanisms to tolerate their presence by adsorption, complexation, or chemical reduction of metal ions or to use them as terminal electron acceptors in anaerobic respiration. In heavy metals, pollution abatement, microbial sensors, and transformations are getting increased focus because of high efficiency and cost effectiveness. The sources and impacts of heavy metal pollution as well as various remediation techniques are described.
There have been numerous instances reported when potentially recalcitrant compounds have been modified by microorganisms or completely mineralized by mixed communities or organisms; an example is pesticide biodegradation. Both situations rely upon the ability of microorganisms to transform compounds that they cannot utilize as sole sources of carbon and energy. This phenomenon of co-oxidation or co-metabolism has been fraught with confusion for many years as a result of the ambiguous use of terms and definitions. A redefinition of co-metabolism is proposed in an attempt to alleviate the problem: Co-metabolism--the transformation of a non-growth substrate in the obligate presence of a growth substrate or another transformable compound. The term 'non-growth substrate' describes compounds that are unable to support cell replication as opposed to an increase in biomass. This definition was devised primarily as a result of non-growth substrate metabolism studies with methane-utilizing bacteria. These studies are described in the text. The possible impact of endogenous polymer reserves on co-metabolic events is discussed. A number of examples where non-growth substrate metabolism is of environmental importance are presented, in particular the potential role of methane-oxidizing bacteria in the removal of CO from the environment. The evolutionary significance, if any, of fortuitous metabolism or co-metabolism is discussed, as are potential applications of these phenomena.
The use of synthetic pesticides has become an indispensable tool in agriculture for the control of pests. Therefore, the search for remedies and techniques for decontamination and detoxification of a pesticide-contaminated environment has become an important part of the research. Currently, bioremediation seems to be one of the most environmentally safe and cost-effective methods. In nature, the existence of abundant material resources can be used to degrade the environmental pesticide pollutants. At present, a number of microorganisms, capable of degrading pesticides, have been isolated and characterised. For insects, insecticide resistance-associated esterases have been purified and characterised from several insect species, and a new family of cytochrome P450 apparently associated with insecticide resistance in the tobacco budworm, was discovered. Generally, two bioremediation approaches have been used one directly based on microorganisms, and the other involved in isolated enzymes. For the former, in addition to using natural microorganism strains, with genetic techniques certain desirable biodegradation pathways from different organisms are brought together in a single host. However, because of their own limits, especially problems associated with releasing genetically altered microorganisms into the environment, the strategy based on enzymes seems more feasible. In the long term, collaborations between microbiologists, biochemists, and engineers will become increasingly important to efficiently dispose of the pesticide pollutants.
The use of genetically modified or native microorganisms and plants to degrade or remove pollutants has emerged as a powerful technology for in situ remediation. An understanding of the genetic basis of the mechanisms of how microorganisms and plants biodegrade pollutants and how they interact with the environment is important for successful implementation of this technology. Recent studies have demonstrated that microbes and transgenic plants produce pesticide-degradaing enzymes that can mineralize different groups of pesticides and their metabolites with greater efficiency. This review describes the most recent progress in biotechnological approaches for enhancing the capability of microorganisms and plants through the characterization and transfer of pesticide-degrading genes, induction of catabolic pathways, and display of cell surface enzymes.
Monocrotophos (dimethyl (E)-1-methyl-2-(methylcarbamoyl) vinyl phosphate, or MCP), an organophosphorus insecticide, was used as a sole phosphorus source by the microorganisms isolated from the soil. None of the isolates could utilize MCP as a sole source of carbon. Two of the potential microbial isolates, Pseudomonas aeruginosa F10B and Clavibacter michiganense subsp. insidiosum SBL 11, could utilize MCP as a sole source of phosphorus. Pseudomonas aeruginosa F10B showed a lag phase of 4 h, while in the case of C. michiganense subsp. insidiosum SBL 11, it was 8 h when cultured in the presence of MCP. The generation time for both strains was increased in the medium containing MCP. It was 2.15 h for P. aeruginosa F10B in MCP medium as compared with 1.29 h in basal medium, while in case of C. michiganense subsp. insidiosum SBL 11 it was increased to 3.4 h in MCP medium as compared with 1.28 h in basal medium. These two strains were able to degrade technical MCP in shake-flask culture up to 98.9 and 86.9%, respectively, and pure MCP up to 79 and 80%, respectively, within 24 h at 37°C. The optimal concentration of MCP required for the normal growth was 500 ppm. In the substrate preference study, Trisp-nitrophenyl phosphate was the most preferred substrate followed by paraoxon. The enzyme responsible for the break down of MCP was phosphotriesterase, which was localized on the membrane-bound fraction of the disrupted cells. The gene responsible for the production of phosphotriesterase (opd) in P. aeruginosa F10B was plasmid-borne.Key words: biodegradation, monocrotophos, phosphotriesterase, P. aeruginosa, C. michiganense subsp. insidiosum.Le monocrotophos (diméthyl (E)-1 méthyl-2-(méthylcarbinol) vinyl phosphate), MCP, un insecticide organophosphoré, a été utilisé comme seule source de phosphore par des microorganismes isolés du sol. Aucun de ces isolats ne pouvait utiliser le MCP comme seule source de carbone. Deux de ces isolats microbiens potentiels, Pseudomonas aeruginosa F10B et Clavibacter michiganense subsp. insidiosum SBL 11 pouvaient utiliser le MCP comme seule source de phosphore. En culture en présence de MCP, P. aeruginosa F10B affichait une phase de latence de 4 h, alors que dans le cas de C. michiganense subsp. insidiosum SBL 11, cette phase était de 8 h. Le temps de génération augmentait dans le milieu contenant du MCP. Dans le milieu avec MCP, le temps de génération du P. aeruginosa F10B était de 2, 15 h comparativement à 1, 29 h dans le milieu de base alors que dans le cas de C. michiganense subsp. insidiosum SBL11, le temps de génération augmentait à 3, 4 h dans le milieu MCP comparativement à 1, 28 h dans le milieu de base. Ces deux souches étaient capables de dégrader du MCP (grade technique) en culture dans des flacons avec agitation jusqu'à 98,9 et 86,9 % respectivement et du MCP pur jusqu'à 79 et 80 % respectivement en 24 h à 37° C. La concentration optimale de MCP pour assurer une croissance normale était de 500 ppm. Dans une étude de préférence de substrats, le meilleur substrat était le Trisp-nitrophényl phosphate suivi du paraoxon. L'enzyme responsable de la dégradation du MCP était la phosphotriestérase localisée dans la fraction liée à la membrane de cellules éclatées. Le gène responsable (opd) de la production de la phosphotriestérase chez P. aeruginosa F10B était localisé sur un plasmide.Mots clés : biodégradation, monocrotophos, phosphotriestérase, P. aeruginosa, C. michiganense subsp. insidiosum.[Traduit par la Rédaction]
We describe a new technique for sample preparation, accelerated solvent extraction (ASE), that combines elevated temperatures and pressures with liquid solvents. The effects of various operational parameters (i.e., temperature, pressure, and volume of solvent used) on the performance of ASE were investigated. The solvents used are those normally used for standard liquid extraction techniques like Soxhlet or sonication. We found the recoveries of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and total petroleum hydrocarbons from reference materials using ASE to be quantitative. The extraction time for 1−30-g samples is less than 15 min, and the volume of solvent is 1.2−1.5 times that of the extraction cell containing the sample. No evidence was seen for thermal degradation during the extraction of temperature-sensitive compounds.
Low-polarity organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) typically have very low solubilities (e.g., ppb) in water at ambient conditions because of water's high polarity (dielectric constant, [epsilon] = 80). However, the dielectric constant can be drastically lowered by raising the temperature of the water under moderate pressure with dramatic increases (e.g., to percent levels) in the solubility of low-polarity organics. For example, subcritical water at 250[degree]C and 50 bar has [epsilon] = 27, which allowed quantitative extractions of PAHs in 15 min from soil and urban air particulates. Decreasing the polarity of water by sequentially raising the extraction temperature from 50 to 250[degree]C (subcritical water) and finally to 400[degree]C (supercritical water if P > 221 bar) allowed class-selective extractions of polar organics (e.g., chlorinated phenols), low-polarity organics (e.g., PAHs), and nonpolar organics (alkanes) to be performed. Simple methods for using sub- and supercritical water for quantitative extraction of organics from environmental solids are presented. 30 refs., 6 figs., 5 tabs.
The herbicide isoproturon was degraded rapidly in a sandy loam soil under laboratory conditions (incubation temperature, 15°C; soil moisture potential, -33 kPa). Degradation was inhibited following treatment of the soil with the antibiotic chloramphenicol, but unaffected by treatment with cycloheximide, thus indicating an involvement of soil bacteria. Rapid degradation was not observed with other phenylurea herbicides, such as diuron, linuron, monuron or metoxuron incubated in the same soil under the same experimental conditions. Three successive applications of isoproturon to ten soils differing in their physicochemical properties and previous cropping history induced rapid degradation of the herbicide in most of them under laboratory conditions. There were, however, no apparent differences in ease of induction of rapid degradation between soils which had been treated with isoproturon for the last five years in the field and those with no pre-treatment history. A mixed bacterial culture able to degrade isoproturon in liquid culture was isolated from a soil in which the herbicide degraded rapidly.
The aim of this study was to isolate and characterize a bacterium capable of metabolizing endosulfan.
A endosulfan-degrading bacterium (strain ESD) was isolated from soil inoculum after repeated culture with the insecticide as the sole source of sulfur. Analysis of its 16S rRNA gene sequence, and morphological and physiological characteristics revealed it to be a new fast-growing Mycobacterium, closely related to other Mycobacterium species with xenobiotic-degrading capabilities. Degradation of endosulfan by strain ESD involved both oxidative and sulfur-separation reactions. Strain ESD did not degrade endosulfan when sulfite, sulphate or methionine were present in the medium along with the insecticide. Partial degradation occurred when the culture was grown, with endosulfan, in the presence of MOPS (3-(N-morpholino)propane sulphonic acid), DMSO (dimethyl sulfoxide), cysteine or sulphonane and complete degradation occurred in the presence of gutathione. When both beta-endosulfan and low levels of sulphate were provided as the only sources of sulfur, biphasic exponential growth was observed with endosulfan metabolism being restricted to the latter phase of exponential growth.
This study isolated a Mycobacterium strain (strain ESD) capable of metabolizing endosulfan by both oxidative and sulfur-separation reactions. The endosulfan-degrading reactions are a result of the sulfur-starvation response of this bacterium.
This describes the isolation of a Mycobacterium strain capable of degrading the insecticide endosulfan. This bacterium is a valuable source of enzymes for use in enzymatic bioremediation of endosulfan residues.
In the framework of a project aiming to phytoremediate heavy metal contaminated soils in the Apulia region, Southern Italy, a series of greenhouse experiments followed by field trials were performed in order to optimize heavy metal phytoextraction by Brassica napus. The effects of root colonization by Bacillus licheniformis BLMB1 and of addition of municipal solid waste (MSW) composts on the capacity of B. napus to tolerate and accumulate Cr, Cu, Pb and Zn were evaluated. B. napus was able to accumulate high amount of metals in greenhouse conditions, whereas it grew with difficulty or not at all in the open field, and metal accumulation in plant fractions was relatively low. The accumulation of metals in the plant fractions was in the order: Cr > Zn > Cu > Pb. The presence of either compost or B. licheniformis BLMB1 strain enhanced metal accumulation, Cr in particular, in the experimental conditions used. This effect can be useful in the phytoextraction of Cr from contaminated soils.
Research Highlights:
► The study area is highly polluted by heavy metals (HMs), Cr in particular.
► In the greenhouse, B. napus behaved as good accumulator for HMs, Cr in particular.
► In the field, the accumulation of HMs in plant parts of B. napus was relatively low.
► Compost and B. licheniformis enhanced B. napus accumulation of HMs, Cr in particular.
► The study suggest a very slow restoration of HMs contaminated soil by the studied B. napus.
Summary • There are few studies of the performance of species in restored vegetation communities. Here we report the results of a meta-analysis of 25 experiments concerned with species-rich grassland restoration on ex-arable land and agriculturally improved grasslands situated at a wide range of locations throughout lowland Britain. Differences in species’ performance were related to 38 physiological and morphological traits. • An experiment-adjusted performance index was calculated for each of the 58 species (13 grasses and 45 forbs). The performance index was calculated for the first 4 years after establishment together with a temporal trend. • Individual species showed large differences in performance indices. However, grasses consistently out-performed forbs. • We examined the linkage between species’ performance and traits according to four non-exclusive hypotheses. The ability to establish and persist in restored vegetation communities requires: (H1) good gap colonization ability; (H2) strong competitive capability; and (H3) ability to undergo vegetative regeneration. (H4) Successful species are generalists associated with fertile habitats. • Trait analyses supported all four hypotheses. Within the forbs, good establishment in the first year was linked to traits determining colonization ability: ruderality, percentage germination of seeds and autumn germination. However, traits linked to competitive ability, vegetative growth and seed bank persistence became increasingly important determinants of success with time. Species with generalist habitat requirements, and especially those associated with fertile soils, performed increasingly well with time. This reflects the development of a closed vegetation in which the ability to grow vigorously and out-compete other established plants is important. • Stress-tolerators, habitat specialists and species of infertile habitats performed badly. This may reflect high residual fertility in restored grasslands and particular niche requirements of these species. This may be a problem as grassland restoration often targets communities characterized by species with these traits and many are food plants of invertebrates of conservation value. • There were few significant correlations between the performance of the grasses and traits reflecting their overall good performance in comparison with the forbs. • This study has important implications for practical restoration programmes and policies. Efficiency might be increased by introducing only species with good performance, but this would lead to uniformity among restored grasslands and would diminish the benefits of habitat restoration for national and regional biodiversity. • Synthesis and applications. Future work should focus on practical methods to increase the successful establishment of the poor performing but desirable species, by (i) targeting restoration to low fertility soils, (ii) changing the abiotic environment or (iii) the ‘phased introduction’ of species several years after restoration, when both the plant community is more stable and the environmental conditions are more favourable for establishment.
Plant–soil interactions are the foundation of effective and sustained restoration of terrestrial communities and ecosystems. Recent advances in ecological science have greatly contributed to our understanding of the effects of soil conditions on plant community dynamics and our understanding of plant composition impacts on almost every aspect of soil structure and function. Although these theories provide important guidelines for the practice of restoration, they often fall short of providing the level of information required to make effective site-specific management decisions. This is largely because of ecology’s search for simple unifying theories and the resulting tendency to generalize from studies at one or only a few sites. An average effect or broad-scale simple relationship tends to provide a “one-size-fits-all” (or none) prescription for managers. Plant–soil interactions can vary greatly depending on their context (e.g., environmental conditions, management practices, time, neighboring community, interaction with other organisms). The ability to predict these context-dependent interactions between plants and soils can be developed by building upon existing general frameworks for understanding plant–soil interactions. Collaborations between researchers and managers can develop conceptual tools that allow us to understand and manage the variability and complexity of plant–soil interactions, simultaneously advancing theory and applicability.
Sediment analysis is very important ininvestigations of the heavy metal burden in theenvironment. In the present work various digestion andextraction procedures were evaluated in order toassess the extent of contamination with heavy metalsin sediments from the Moste hydroelectric reservoir.Total acid dissolution, aqua regia digestion andacetic acid extraction procedures were applied tosamples. Zn, Cd, Pb, Co, Ni, Cu and Cr were determinedby flame or electrothermal atomic absorptionspectrometry (FAAS, ETAAS) under optimized measurementconditions. A comparison of total acid dissolutionincluding hydrofluoric acid (HF) treatment and theaqua regia soluble fraction was made to estimatethe applicability of aqua regia digestion inanalysis of total metal concentrations in sediments.In general, good agreement of the results was observedfor Co, Pb, Cu and Zn, however for Cr, Ni and Cdsignificantly lower results were obtained in the aqua regia soluble fraction. In addition, an extraction procedure using 25% v/v acetic acid wasapplied for estimation of the extent of contaminationwith heavy metals originating from anthropogenicactivities. The results indicate that the sedimentsupstream of the reservoir are not contaminated, whilethe sediments from the hydroelectric reservoir showsa significant anthropogenic input of Ni, Zn and Pb,which corresponds well with pollution sources.
Sedum alfredii, a cadmium (Cd) and zinc (Zn) hyperaccumulator at a mine located in Qu Zhou City, Zhejiang Province, China, can accumulate
Cd and Zn exceeding 1,000 and 10,000mg kg−1, respectively in its shoot (dry weight) when growing under metal-contaminated habitats. Several strains of bacteria were
isolated from the rhizosphere of S. alfredii thriving in different Pb/Zn mines in Hunan Province and Zhejiang Province, China, which can resist high levels of heavy metals.
Among the different strains isolated, Burkholderia cepacia showed the highest ability in mobilizing Cd and Zn as well as resisting high concentrations of soluble Zn (500mg L−1). The soluble Zn concentration in the medium increased from 13 to 72 and 99% (p < 0.001) after bacterial inoculation in the medium supplemented with insoluble zinc oxide and zinc carbonate, respectively,
while pH dropped from 7 to 2.93. The soluble Cd concentration was also increased from 8 to 96% (p < 0.001), and pH decreased from 7 to 2.65. Short-chain organic acids were also analyzed and the results indicated that oxalic
acid, tartaric acid, formic acid and acetic acid had a significant correlation (p < 0.001) with the concentrations of Cd and Zn being mobilized during the assay. The present results implicated that certain
bacteria associated with metal hyperaccumulators could contribute significantly in mobilizing heavy metals, which would enhance
the phytoextraction process.
The effect of bensulfuron-methyl (BSM) on a soil microbial community in a model paddy microcosm was studied. Total bacterial numbers in the overlying water and surface soil were monitored for 2months after the application of BSM at the field rate and a ten-fold field rate. Pentachlorophenol (PCP) was used for comparison. Neither chemical affected the total bacterial numbers remarkably, either in the overlying water or in the surface soil. In contrast, the nitrification potential was significantly suppressed by the BSM application. The bacterial community structure, as evaluated by the denaturing gradient gel electrophoresis (DGGE) of PCR amplification products from bacterial 16S rDNA, was unaffected by the BSM treatments over 8weeks in the surface soil, compared with the control (no pesticide). In contrast, the surface soil exposed to PCP at a ten-fold field rate showed different patterns from the controls at 4weeks and 8weeks after application. The DGGE patterns of the overlying water were much more variable than those of the surface soil in any treatments. Cluster analysis showed that the BSM plots were classified within the same group as the control at 1week after application and that the BSM and PCP plots from 2weeks onward after application were grouped differently from the control. Of 22clones excised from the DGGE gels, 20clones belonged to the Proteobacteria and two belonged to the Verrucomicrobia. It was considered that the impact of BSM on the overall microbial community (total numbers, community structure of soil) was negligible, although BSM had an impact on some specific functions of the soil microbial community (nitrification) and a part of the community (overlying water).
Three strains of bacteria (designated as YBL1, YBL2, YBL3 respectively) capable of degrading isoproturon, 3-(4-isopropylphenyl)-1,
1-dimethylurea, were isolated from the soils of two herbicide plants. Based on the comparative analysis of the 16S rRNA gene,
and phenotypic and biochemical characterization, these strains were identified as Sphingobium sp. The optimum conditions for isoproturon degradation by these strains were pH 7.0, and temperature 30°C. Mg2+ (1mM) enhanced the isoproturon degradation rate, while Ni2+ and Cu2+ (1mmoll−1) inhibited isoproturon degradation significantly. These three strains also showed the ability to remove the residues of other
phenylurea herbicides such as chlorotoluron, diuron and fluometuron in mineral salt culture medium. The N-demethylation was the first step of degradation of dimethylurea-substituted herbicides. Strain YBL1 was found capable of
degrading both dimethylurea-substituted herbicides and methoxymethylphenyl-urea herbicides i.e. linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea).
Using the PCR method, partial sequences of the catechol 1,2-dioxygenase gene were obtained from these strains.
Chromate-reducing microorganisms with the ability of reducing toxic chromate [Cr(VI)] into insoluble trivalent chromium [Cr(III)]
are very useful in treatment of Cr(VI)-contaminated water. In this study, a novel chromate-reducing bacterium was isolated
from Mn/Cr-contaminated soil. Based on morphological, physiological/biochemical characteristics and 16S rRNA gene sequence
analyses, this strain was identified as Intrasporangium sp. strain Q5-1. This bacterium has high Cr(VI) resistance with a MIC of 17mmoll−1 and is able to reduce Cr(VI) aerobically. The best condition of Cr(VI) reduction for Q5-1 is pH 8.0 at 37°C. Strain Q5-1
is also able to reduce Cr(VI) in resting (non-growth) conditions using a variety of carbon sources as well as in the absence
of a carbon source. Acetate (1mmoll−1) is the most efficient carbon source for stimulating Cr(VI) reduction. In order to apply strain Q5-1 to remove Cr(VI) from
wastewater, the bacterial cells were immobilized with different matrices. Q5-1 cells embedded with compounding beads containing
4% PVA, 3% sodium alginate, 1.5% active carbon and 3% diatomite showed a similar Cr(VI) reduction rates to that of free cells.
In addition, the immobilized Q5-1 cells have the advantages over free cells in being more stable, easier to re-use and minimal
clogging in continuous systems. This study provides potential applications of a novel immobilized chromate-reducing bacterium
for Cr(VI) bioremediation.
Arsenic is a common contaminant in soils and water. It is well established that the fern Pteris vittata L. is an As hyperaccumulator and therefore has potential to phyroremediate As-polluted soils. Also, it is accepted that rhizosphere microflora play an enhancing role in plant uptake of metallic elements from soils. Studies showed that hydroponiclly grown P. Vittata accumulated arsenite more than the arsenate form of As apparently because arsenate and phosphate are analogues and therefore its absorption is inhibited by phosphate. The objective of this study was to determine whether addition of five different arsenate-reducing bacteria would enhance arsenic uptake by P. vittata grown in arsenic polluted soils in afield experiment. Results showed that addition of the As reducing bacteria promoted the growth of P. vittata, increased As accumulation, activated soil insoluble As, and reduced As leaching compared to the untreated control. Plant biomass increased by 53% and As uptake by 44%. As leaching was reduced by 29% to 71% depending on the As reducing bacterium. The results in their entirety permitted some insight into the mechanisms by which the arsenate reducing bacteria enhanced the effectiveness of P. vittata to remove As from the polluted soil.
Pesticides, where used correctly, can save up to 40% in crop losses; however, when pesticides are mal-, misor over-used the environmental and public health consequences can be very considerable. The United Nations has issued a list of chemicals that are banned or severely restricted in use; many of the chemicals on this list are pesticides. Whilst the use of highly persistent pesticides such as DDT has proved very effective in the eradication of diseases such as malaria, the adverse effects to the natural environment have been devastating - whole populations of birds have been eliminated.
Mineralization and degradation of 14C-ring-labelled isoproturon were investigated over 120 days under controlled laboratory conditions in three soils of eastern France chosen for their pH: a pelosol, a brown calcareous soil and a brown acid soil. Biological activity of the micro-flora was also measured by release of total CO2. Common metabolites of isoproturon found in the three soils were N-(4-isopropyl phenyl)N'methylurea and N-(4-(2-hydroxyisopropylphenyl))-N'methylurea. Moreover N-(4-isopropylphenyl)urea was also found in brown acid soil. Other residues were detected; one in the pelosol and two in the brown acid soil. Analysis of non identified product of pelosol only revealed a polar affinity by presence of hydroxy fonction. One of the residues found in brown acid soil was characterised by GC/MS as 4,4′-diisopropylazobenzene.