Biodegradation of halogenated organic compounds.

In this review we discuss the degradation of chlorinated hydrocarbons by microorganisms, emphasizing the physiological, biochemical, and genetic basis of the biodegradation of aliphatic, aromatic, and polycyclic compounds. Many environmentally important xenobiotics are halogenated, especially chlorinated. These compounds are manufactured and used as pesticides, plasticizers, paint and printing-ink components, adhesives, flame retardants, hydraulic and heat transfer fluids, refrigerants, solvents, additives for cutting oils, and textile auxiliaries. The hazardous chemicals enter the environment through production, commercial application, and waste. As a result of bioaccumulation in the food chain and groundwater contamination, they pose public health problems because many of them are toxic, mutagenic, or carcinogenic. Although synthetic chemicals are usually recalcitrant to biodegradation, microorganisms have evolved an extensive range of enzymes, pathways, and control mechanisms that are responsible for catabolism of a wide variety of such compounds. Thus, such biological degradation can be exploited to alleviate environmental pollution problems. The pathways by which a given compound is degraded are determined by the physical, chemical, and microbiological aspects of a particular environment. By understanding the genetic basis of catabolism of xenobiotics, it is possible to improve the efficacy of naturally occurring microorganisms or construct new microorganisms capable of degrading pollutants in soil and aquatic environments more efficiently. Recently a number of genes whose enzyme products have a broader substrate specificity for the degradation of aromatic compounds have been cloned and attempts have been made to construct gene cassettes or synthetic operons comprising these degradative genes. Such gene cassettes or operons can be transferred into suitable microbial hosts for extending and custom designing the pathways for rapid degradation of recalcitrant compounds. Recent developments in designing recombinant microorganisms and hybrid metabolic pathways are discussed.     

Recombinant entomopathogenic agents: a review of biotechnological approaches to pest insect control

Although the use of chemical pesticides has decreased in recent years, it is still a common method of pest control. However, chemical use leads to challenging problems. The harm caused by these chemicals and the length of time that they will remain in the environment is of great concern to the future and safety of humans. Therefore, developing new pest control agents that are safer and environmentally compatible, as well as assuring their widespread use is important. Entomopathogenic agents are microorganisms that play an important role in the biological control of pest insects and are eco-friendly alternatives to chemical control. They consist of viruses (non-cellular organisms), bacteria (prokaryotic organisms), fungi and protists (eukaryotic organisms), and nematodes (multicellular organisms). Genetic modification (recombinant technology) provides potential new methods for developing entomopathogens to manage pests. In this review, we focus on the important roles of recombinant entomopathogens in terms of pest insect control, placing them into perspective with other views to discuss, examine and evaluate the use of entomopathogenic agents in biological control.     

Role of modern chemistry in sustainable arable crop protection

Organic chemistry has been, and for the foreseeable future will remain, vitally important for crop protection. Control of fungal pathogens, insect pests and weeds is crucial to enhanced food provision. As world population continues to grow, it is timely to assess the current situation, anticipate future challenges and consider how new chemistry may help meet those challenges. In future, agriculture will increasingly be expected to provide not only food and feed, but also crops for conversion into renewable fuels and chemical feedstocks. This will further increase the demand for higher crop yields per unit area, requiring chemicals used in crop production to be even more sophisticated. In order to contribute to programmes of integrated crop management, there is a requirement for chemicals to display high specificity, demonstrate benign environmental and toxicological profiles, and be biodegradable. It will also be necessary to improve production of those chemicals, because waste generated by the production process mitigates the overall benefit. Three aspects are considered in this review: advances in the discovery process for new molecules for sustainable crop protection, including tests for environmental and toxicological properties as well as biological activity; advances in synthetic chemistry that may offer efficient and environmentally benign manufacturing processes for modern crop protection chemicals; and issues related to energy use and production through agriculture.     

Fate of Pesticides in the Environment and its Bioremediation

The present paper is an overview of the presence and fate of pesticides as persistent organic pollutants in the environment as well as of the potential for their detoxification, also combined with chemical and physical treatment. It contains information gathered from a range of currently available sources. The fate of pesticides in the environment is analyzed considering the processes that determine their persistence and mobility, grouped into transport, transfer and transformation processes. Few pesticide characteristics such as persistence, mobility and biodegradability are emphasized. The fate of a pesticide and the potential for its persistence and mobility from the site of application are considered to be affected by the chemical and physical properties of the pesticide, site characteristics such as soil and groundwater individuality, climate and local weather conditions, biological population, and the handling practices of the pesticide user. Bioremediation, as one of the most environmentally‐sound and cost‐effective methods for the decontamination and detoxification of a pesticide‐contaminated environment is discussed especially considering the factors affecting the biodegradability of pesticides such as biological factors and the characteristics of the chemical compounds. In situ and ex situ bioremediation as possible types of bioremediation activities are weighted up. Also, the paper includes some considerations for developing strategies regarding the choice of bioremediation technology, as well as advantages and disadvantages of the bioremediation of environmental components polluted with pesticides.     

海洋生物活性物质与害虫防治

由于有机合成杀虫剂的生态毒性影响和害虫抗药性的发展,目前世界范围的注意力集中于可生物降解和对环境友好的天然害虫控制剂的研究应用上.海洋是生物活性物质的巨大宝库,也是开发害虫控制剂的新来源.本文综述了海洋生物资源、海洋杀虫活性物质的主要类型及海洋活性物质生物筛选技术的发展方向,并简述了海洋源杀虫剂的应用发展前景.     

Coupling microbial catabolic actions with abiotic redox processes: A new recipe for persistent organic pollutant (POP) removal

The continuous release of toxic persistent organic pollutants (POPs) into the environment has raised a need for effective cleanup methods. The tremendous natural diversity of microbial catabolic mechanisms suggests that catabolic routes may be applied to the remediation of POP-contaminated fields. A large number of the recalcitrant xenobiotics have been shown to be removable via the natural catabolic mechanisms of microbes, and detailed biochemical studies of the catabolic methods, together with the development of sophisticated genetic engineering, have led to the use of synthetic microbes for the bioremediation of POPs. However, the steric effects of substituted halogen moieties, microbe toxicity, and the low bioavailability of POPs still deteriorate the efficiency of removal strategies based on natural and synthetic catabolic mechanisms. Recently, abiotic redox processes that induce rapid reductive dehalogenation, hydroxyl radical-based oxidation, or electron shuttling have been reasonably coupled with microbial catabolic actions, thereby compensating for the drawbacks of biotic processes in POP removal. In this review, we first compare the pros and cons of individual methodologies (i.e., the natural and synthetic catabolism of microbes and the abiotic processes involving zero-valent irons, advanced oxidation processes, and small organic stimulants) for POP removal. We then highlight recent trends in coupling the biotic–abiotic methodologies and discuss how the processes are both feasible and superior to individual methodologies for POP cleanup. Cost-effective and environmentally sustainable abiotic redox actions could enhance the microbial bioremediation potential for POPs.     

Distinguishing between the metabolome and xenobiotic exposome in environmental field samples analysed by direct-infusion mass spectrometry based metabolomics and lipidomics

Environmental metabolomics is increasingly used to investigate organismal responses to complex chemical mixtures, including waste water effluent (WWE). In parallel, increasingly sensitive analytical methods are being used in metabolomics studies, particularly mass spectrometry. This introduces a considerable, yet overlooked, challenge that high analytical sensitivity will not only improve the detection of endogenous metabolites in biological specimens but also exogenous chemicals. If these often unknown xenobiotic features are not removed from the “biological” dataset, they will bias the interpretation and could lead to incorrect conclusions about the biotic response. Here we illustrate and validate a novel workflow classifying the origin of peaks detected in biological samples as: endogenous, xenobiotics, or metabolised xenobiotics. The workflow is demonstrated using direct infusion mass spectrometry-based metabolomic analysis of testes from roach exposed to different concentrations of a complex WWE. We show that xenobiotics and their metabolic products can be detected in roach testes (including triclosan, chloroxylenol and chlorophene), and that these compounds have a disproportionately high level of statistical significance within the total (bio)chemical changes induced by the WWE. Overall we have demonstrated that this workflow extracts more information from an environmental metabolomics study of complex mixture exposures than was possible previously.     

Exploring molecular mechanisms in chemically induced cancer: complementation of mammalian DNA repair defects by a prokaryotic gene

Exposure of man to chemical agents can occur intentionally, as in the treatment of disease, or inadvertently because the environment contains a wide range of synthetic or naturally occurring chemicals. The alkylating agents are a diverse group of compounds (Fig. 1) and comprise a good example of such xenobiotics, since much is known about their occurrence, and their biological effects include carcinogenicity, mutagenicity, toxicity and teratogenicity. Exposure to potentially carcinogenic alkylating agents such as nitrosamines may occur occupationally, from cigarette smoke, from certain foodstuffs and even endogenously through the ingestion of the appropriate precursor chemicals.¹ At the other extreme, the cytotoxic effects of agents such as the chloroethylating nitrosamides or mustards have been exploited in the design of certain antitumour drugs.² The effectiveness of antitumour agents and the other, mostly adverse, biological effects of alkylating agents have been ascribed to their ability to damage cellular macromolecules, in particular DNA. This review concentrates on investigations carried out over the past two years on the role of DNA damage in carcinogenesis, but we shall see how recent advances in this area of research have also led to a better understanding of the mechanisms of the cytotoxic effects of alkylating antitumour agents.     

Genetic manipulations of microorganisms for the degradation of hexachlorocyclohexane

Abstract: Hexachlorocyclohexane (HCH) is an organochlorine insecticide which has been banned in technologically advanced countries. However, it is still in use in tropical countries for mosquito control and thus new areas continue to be contaminated. Anaerobic degradation of HCH isomers have been well documented but until recently there have been only a few reports on aerobic microbial degradation of HCH isomers. The isolation of these microbes made it possible to design experiments for the cloning of the catabolic genes responsible for degradation. We review the microbial degradation of HCH isomers coupled with the genetic manipulations of the catabolic genes. The first part discusses the persistence of residues in the environment and microbial degradation while the second part gives an account of the genetic manipulations of catabolic genes involved in the degradation.     

Genetic engineering and sustainable production of ornamentals: current status and future directions

Through the last decades, environmentally and health-friendly production methods and conscientious use of resources have become crucial for reaching the goal of a more sustainable plant production. Protection of the environment requires careful consumption of limited resources and reduction of chemicals applied during production of ornamental plants. Numerous chemicals used in modern plant production have negative impacts on human health and are hazardous to the environment. In Europe, several compounds have lost their approval and further legal restrictions can be expected. This review presents the more recent progress of genetic engineering in ornamental breeding, delivers an overview of the biological background of the used technologies and critically evaluates the usefulness of the strategies to obtain improved ornamental plants. First, genetic engineering is addressed as alternative to growth retardants, comprising recombinant DNA approaches targeting relevant hormone pathways, e.g. the gibberellic acid (GA) pathway. A reduced content of active GAs causes compact growth and can be facilitated by either decreased anabolism, increased catabolism or altered perception. Moreover, compactness can be accomplished by using a natural transformation approach without recombinant DNA technology. Secondly, metabolic engineering approaches targeting elements of the ethylene signal transduction pathway are summarized as a possible alternative to avoid the use of chemical ethylene inhibitors. In conclusion, molecular breeding approaches are dealt with in a way allowing a critical biological assessment and enabling the scientific community and public to put genetic engineering of ornamental plants into a perspective regarding their usefulness in plant breeding.     

细菌分解代谢转座子研究

近年来 ,随着人工合成化学物质大量进入环境 ,现已在环境中发现了新的适应性的细菌对有机污染物的代谢机制。许多分解代谢基因与插入元件或转座子相连 ,因此 ,分解代谢基因可以在细菌间快速传播。这种快速传播有利于新的降解途径的产生。因此 ,这种代谢全能性可以被开发并在生物修复污染环境中起到关键作用     

Recent developments in molecular techniques for identification and monitoring of xenobiotic-degrading bacteria and their catabolic genes in bioremediation

The pollution of soil and water with xenobiotics is widespread in the environment and is creating major health problems. The utilization of microorganisms to clean up xenobiotics from a polluted environment represents a potential solution to such environmental problems. Recent developments in molecular-biology-based techniques have led to rapid and accurate strategies for monitoring, discovery and identification of novel bacteria and their catabolic genes involved in the degradation of xenobiotics. Application of these techniques to bioremediation has also improved our understanding of the composition, phylogeny, and physiology of metabolically active members of the microbial community in the environment. This review provides an overview of recent developments in molecular-biology-based techniques and their application in bioremediation of xenobiotics.     

Quantifying Synergy: A Systematic Review of Mixture Toxicity Studies within Environmental Toxicology

Cocktail effects and synergistic interactions of chemicals in mixtures are an area of great concern to both the public and regulatory authorities. The main concern is whether some chemicals can enhance the effect of other chemicals, so that they jointly exert a larger effect than predicted. This phenomenon is called synergy. Here we present a review of the scientific literature on three main groups of environmentally relevant chemical toxicants: pesticides, metal ions and antifouling compounds. The aim of the review is to determine 1) the frequency of synergy, 2) the extent of synergy, 3) whether any particular groups or classes of chemicals tend to induce synergy, and 4) which physiological mechanisms might be responsible for this synergy. Synergy is here defined as mixtures with minimum two-fold difference between observed and predicted effect concentrations using Concentration Addition (CA) as a reference model and including both lethal and sub-lethal endpoints. The results showed that synergy occurred in 7%, 3% and 26% of the 194, 21 and 136 binary pesticide, metal and antifoulants mixtures included in the data compilation on frequency. The difference between observed and predicted effect concentrations was rarely more than 10-fold. For pesticides, synergistic mixtures included cholinesterase inhibitors or azole fungicides in 95% of 69 described cases. Both groups of pesticides are known to interfere with metabolic degradation of other xenobiotics. For the four synergistic metal and 47 synergistic antifoulant mixtures the pattern in terms of chemical groups inducing synergy was less clear. Hypotheses in terms of mechanisms governing these interactions are discussed. It was concluded that true synergistic interactions between chemicals are rare and often occur at high concentrations. Addressing the cumulative rather than synergistic effect of co-occurring chemicals, using standard models as CA, is therefore regarded as the most important step in the risk assessment of chemical cocktails.     

Molecular mechanisms of genetic adaptation to xenobiotic compounds.

Microorganisms in the environment can often adapt to use xenobiotic chemicals as novel growth and energy substrates. Specialized enzyme systems and metabolic pathways for the degradation of man-made compounds such as chlorobiphenyls and chlorobenzenes have been found in microorganisms isolated from geographically separated areas of the world. The genetic characterization of an increasing number of aerobic pathways for degradation of (substituted) aromatic compounds in different bacteria has made it possible to compare the similarities in genetic organization and in sequence which exist between genes and proteins of these specialized catabolic routes and more common pathways. These data suggest that discrete modules containing clusters of genes have been combined in different ways in the various catabolic pathways. Sequence information further suggests divergence of catabolic genes coding for specialized enzymes in the degradation of xenobiotic chemicals. An important question will be to find whether these specialized enzymes evolved from more common isozymes only after the introduction of xenobiotic chemicals into the environment. Evidence is presented that a range of genetic mechanisms, such as gene transfer, mutational drift, and genetic recombination and transposition, can accelerate the evolution of catabolic pathways in bacteria. However, there is virtually no information concerning the rates at which these mechanisms are operating in bacteria living in nature and the response of such rates to the presence of potential (xenobiotic) substrates. Quantitative data on the genetic processes in the natural environment and on the effect of environmental parameters on the rate of evolution are needed.     

Soil microbes and the availability of soil nutrients

It is likely to provide plants with their necessary nutrients using chemical and biological fertilization. Although chemical fertilization is a quick method, it is not recommendable economically and environmentally, especially if overused. Biological fertilization is the use of soil microbes including arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria to inoculate plants. It has been proved that biological fertilization is an efficient method to supply plants with their necessary nutrients. It is economically and environmentally recommendable, because it results in sustainability. In this article, some of the most important details including the mechanisms and processes regarding the effects of soil microbes on the availability and hence uptake of nutrients by plant are reviewed. Such details can be important for the selection and hence production of microbial inoculums, which are appropriate for biological fertilization.     

Linking long-term toxicity of xeno-chemicals with short-term biological adaptation

Understanding the mechanisms of long-term toxicities of chemicals is challenging. The present review discusses evidence suggesting that the biological adaptation to acute xenobiotic exposure could lead in the long run to toxic side effects. Upon acute exposure, hydrophobic xenobiotics are sequestered in the adipose tissue, which consequently protects other organs. However, this could also lead to the persistence of these xenochemicals and to a chronic low level internal exposure. The intrinsic properties of the xenobiotic detection and metabolism systems could also account for long-term toxicity. Indeed, hydrophobic xenochemicals are metabolized into more hydrophilic compounds; the first step of this pathway consists in the “activation” of the parent compound into a more reactive intermediate by cytochromes P450 activity. Those intermediates can be extremely reactive with DNA and proteins and thus could lead to toxic side effects that may become significant over time. Furthermore, recent evidence suggests that xenobiotic receptors also display endogenous functions. It is likely that repeated exposure to xenobiotics disrupts those endogenous functions with possibly dire cellular consequences. Altogether, The hypothesis presented here proposes that one mechanism for long-term toxicity stems from cumulative side effects due to the repeated activity of adaptive pathways triggered by acute intoxication.     

Laboratory evolution of catabolic enzymes and pathways

The laboratory evolution of environmentally relevant enzymes and proteins has resulted in the generation of optimized and stabilized enzymes, as well as enzymes with activity against new substrates. Numerous methods, including random mutagenesis, site-directed mutagenesis and DNA shuffling, have been widely used to generate variants of existing enzymes. These evolved catabolic enzymes have application for improving biodegradation pathways, generating engineered pathways for the degradation of particularly recalcitrant compounds, and for the development of biocatalytic processes to produce useful compounds. Regulatory proteins associated with catabolic pathways have been utilized to generate biosensors for the detection of bioavailable concentrations of environmentally relevant chemicals.     

Environmental genomics: exploring the unmined richness of microbes to degrade xenobiotics

Increasing pollution of water and soils by xenobiotic compounds has led in the last few decades to an acute need for understanding the impact of toxic compounds on microbial populations, the catabolic degradation pathways of xenobiotics and the set-up and improvement of bioremediation processes. Recent advances in molecular techniques, including high-throughput approaches such as microarrays and metagenomics, have opened up new perspectives and pointed towards new opportunities in pollution abatement and environmental management. Compared with traditional molecular techniques dependent on the isolation of pure cultures in the laboratory, microarrays and metagenomics allow specific environmental questions to be answered by exploring and using the phenomenal resources of uncultivable and uncharacterized micro-organisms. This paper reviews the current potential of microarrays and metagenomics to investigate the genetic diversity of environmentally relevant micro-organisms and identify new functional genes involved in the catabolism of xenobiotics.