Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed and relocated in the environment as a result of the incomplete combustion of organic matter. Many PAHs and their epoxides are highly toxic, mutagenic and/or carcinogenic to microorganisms as well as to higher systems including humans. Although various physicochemical methods have been used to remove these compounds from our environment, they have many limitations. Xenobiotic-degrading microorganisms have tremendous potential for bioremediation but new modifications are required to make such microorganisms effective and efficient in removing these compounds, which were once thought to be recalcitrant. Metabolic engineering might help to improve the efficiency of degradation of toxic compounds by microorganisms. However, efficiency of naturally occurring microorganisms for field bioremediation could be significantly improved by optimizing certain factors such as bioavailability, adsorption and mass transfer. Chemotaxis could also have an important role in enhancing biodegradation of pollutants. Here, we discuss the problems of PAH pollution and PAH degradation, and relevant bioremediation efforts.     

Mass transfer limitation of microbial growth and pollutant degradation

Organic pollutants in soil can be removed by biotechnological treatment. A limitation of this technology is the efficiency of biodegradation. In many cases, the bulk of the pollution can be removed but residual pollutants remain and biodegradation rates are slower than expected from laboratory trials. Low biodegradation rates are often a result of limited accessibility of the pollutants. Major reasons for the reduced bioavailability are the unequal spatial distribution of microorganisms and pollutants and the retardation of substrate diffusion by the soil matrix. Mechanical mixing and the addition of surfactants are possible approaches to improve the bioavailability of pollutants during bioremediation. The application of flow-stop-flow techniques may be of help to overcome the limitations resulting from advective-diffusive transport mechanisms during pump-and-treat remediation of contaminant plumes. Received 31 October 1995/ Accepted in revised form 31 March 1996     

Microbial reporters of metal bioavailability

When attempting to assess the extent and the implications of environmental pollution, it is often essential to quantify not only the total concentration of the studied contaminant but also its bioavailable fraction: higher bioavailability, often correlated with increased mobility, signifies enhanced risk but may also facilitate bioremediation. Genetically engineered microorganisms, tailored to respond by a quantifiable signal to the presence of the target chemical(s), may serve as powerful tools for bioavailability assessment. This review summarizes the current knowledge on such microbial bioreporters designed to assay metal bioavailability. Numerous bacterial metal‐sensor strains have been developed over the past 15 years, displaying very high detection sensitivities for a broad spectrum of environmentally significant metal targets. These constructs are based on the use of a relatively small number of gene promoters as the sensing elements, and an even smaller selection of molecular reporter systems; they comprise a potentially useful panel of tools for simple and cost‐effective determination of the bioavailability of heavy metals in the environment, and for the quantification of the non‐bioavailable fraction of the pollutant. In spite of their inherent advantages, however, these tools have not yet been put to actual use in the evaluation of metal bioavailability in a real environmental remediation scheme. For this to happen, acceptance by regulatory authorities is essential, as is a standardization of assay conditions.     

土壤重金属生物毒性研究进展

世界范围内土壤重金属污染不断加重,由污染所带来的问题以及如何治理污染已经受到人们越来越多的关注.土壤重金属将对土壤生物产生影响,而土壤生物在重金属的胁迫下也会产生不同的响应.综述了国内外近年来土壤重金属生物毒性的研究进展,介绍了土壤重金属污染对陆地生态系统中植物、动物和微生物生长的影响;土壤重金属生物毒性的影响因素;土壤重金属生物毒性的研究方法;土壤重金属生物毒性的预测模型,最后提出了问题和展望.     

The Probiotic Bacterial Strain Lactobacillus fermentum D3 Increases In Vitro the Bioavailability of Ca, P, and Zn in Fermented Goat Milk

We determined calcium, magnesium, phosphorus and zinc levels in a total of 27 samples of commercial goat- and cow-milk fermented products and 9 samples of a goat-milk fermented product with addition of a probiotic bacterial strain, Lactobacillus fermentum D3, manufactured experimentally by our research group. Atomic absorption spectroscopy with flame atomization and UV/VIS spectrophotometry were used as analytic techniques. The results of an in vitro digestion process showed that the bioavailability of calcium, phosphorus, and zinc was significantly higher in our fermented milk containing the probiotic bacterial strain than it was in commercial goat-milk fermented products. Furthermore, our product showed a significantly higher bioavailability of calcium and zinc compared to goat- and cow-milk fermented products made with other microorganisms. We conclude that, in in vitro assays, strain D3 seems to increase the bioavailability of these minerals and that this new product may constitute a better source of bioavailable minerals compared to other products already on the market.     

The Role of Respiratory Microbiota in Lung Cancer

Recently, the impact of microorganisms on tumor growth and metastasis has attracted great attention. The pathogenesis and progression of lung cancer are related to an increase in respiratory bacterial load as well as changes in the bacterial community because the microbiota affects tumors in many ways, including canceration, metastasis, angiogenesis, and treatment. The microbiota may increase tumor susceptibility by altering metabolism and immune responses, promoting inflammation, and increasing toxic effects. The microbiota can regulate tumor metastasis by altering multiple cell signaling pathways and participate in tumor angiogenesis through vascular endothelial growth factors (VEGF), endothelial cells (ECs), inflammatory factors and inflammatory cells. Tumor angiogenesis not only maintains tumor growth at the primary site but also promotes tumor metastasis and invasion. Therefore, angiogenesis is an important mediator of the interaction between microorganisms and tumors. The microbiota also plays a part in antitumor therapy. Alteration of the microbiota caused by antibiotics can regulate tumor growth and metastasis. Moreover, the microbiota also influences the efficacy and toxicity of tumor immunotherapy and chemotherapy. Finally, the effects of air pollution, a risk factor for lung cancer, on microorganisms and the possible role of respiratory microorganisms in the effects of air pollution on lung cancer are discussed.     

Quantifying the biodegradation of phenanthrene by Pseudomonas stutzeri P16 in the presence of a nonionic surfactant.

The low water solubility of polycyclic aromatic hydrocarbons is believed to limit their availability to microorganisms, which is a potential problem for bioremediation of polycyclic aromatic hydrocarbon-contaminated sites. Surfactants have been suggested to enhance the bioavailability of hydrophobic compounds, but both negative and positive effects of surfactants on biodegradation have been reported in the literature. Earlier, we presented mechanistic models of the effects of surfactants on phenanthrene dissolution and on the biodegradation kinetics of phenanthrene solubilized in surfactant micelles. In this study, we combined the biodegradation and dissolution models to quantify the influence of the surfactant Tergitol NP-10 on biodegradation of solid-phase phenanthrene by Pseudomonas stutzeri P16. Although micellized phenanthrene does not appear to be available directly to the bacterium, the ability of the surfactant to increase the phenanthrene dissolution rate resulted in an overall increase in bacterial growth rate in the presence of the surfactant. Experimental observations could be predicted well by the derived model with measured biokinetic and dissolution parameters. The proposed model therefore can serve as a base case for understanding the physical-chemical effects of surfactants on nonaqueous hydrocarbon bioavailability.     

水产品病原菌及其检测与控制技术研究进展

病原微生物一直以来是影响水产品质量安全的重要因素, 本文阐述了当前水产品中存在的主要病原微生物及其污染现状, 介绍了病原微生物快速检测新技术的研究进展, 并就如何控制水产品中病原微生物的污染, 提出预防措施和建议。     

Inorganic nitrite therapy: historical perspective and future directions

Over the past several years, investigators studying nitric oxide (NO) biology and metabolism have come to learn that the one-electron oxidation product of NO, nitrite anion, serves as a unique player in modulating tissue NO bioavailability. Numerous studies have examined how this oxidized metabolite of NO can act as a salvage pathway for maintaining NO equivalents through multiple reduction mechanisms in permissive tissue environments. Moreover, it is now clear that nitrite anion production and distribution throughout the body can act in an endocrine manner to augment NO bioavailability, which is important for physiological and pathological processes. These discoveries have led to renewed hope and efforts for an effective NO-based therapeutic agent through the unique action of sodium nitrite as an NO prodrug. More recent studies also indicate that sodium nitrate may also increase plasma nitrite levels via the enterosalivary circulatory system resulting in nitrate reduction to nitrite by microorganisms found within the oral cavity. In this review, we discuss the importance of nitrite anion in several disease models along with an appraisal of sodium nitrite therapy in the clinic, potential caveats of such clinical uses, and future possibilities for nitrite-based therapies.     

Pollution and Its Impact on Wild Animals: A Meta-Analysis on Oxidative Stress

Oxidative stress is the unifying feature underlying the toxicity of anthropogenic pollution (e.g., heavy metals, polycyclic aromatic hydrocarbons, and nitrogen-oxides) and the ultimate culprit in the development of many diseases. Yet, there has been no attempt to summarize the published data on wild terrestrial animals to reveal general trends regarding the effects of pollution on oxidative stress. The main findings of this meta-analysis reveal that, as predicted, there is an overall increase in oxidative stress when exposed to pollution. This is mainly due to a weak overall increase of oxidative damages, although there is some variation across taxa. The reduced form of glutathione (GSH) and its associated enzymes are the most reliable biomarkers. This result is important when choosing biomarkers and when using less-invasive sampling of endangered species, or for longitudinal approaches. To be able to predict future population outcomes, possible treatments, but also evolutionary responses to a changing environment, a greater integration of biotic factors such as temperature, bioavailability of toxic elements, and species-specific responses are needed.     

微生物胞外多糖的合成及其在重金属修复中的作用机制与应用

重金属的生物不可降解性使其在环境中长期存在,导致严重的环境污染,对人类健康和生态系统构成威胁。与传统的物化修复技术相比,微生物修复具有成本低廉、环境友好和高效等特点。在面对重金属胁迫或营养不均衡时,微生物会被激发以分泌合成胞外多糖(exopolysaccharides, EPS)。由此可见,EPS的产生是微生物对抗重金属胁迫的重要策略之一。EPS不仅能保护微生物在低温、高温、高盐等极端环境或受毒性化合物胁迫的条件下存活,并且在细胞内外进行信息和物质的交流与传递,既作为保护屏障限制重金属离子进入细胞,又作为介质进行交流。EPS结构中含有多个带负电荷的官能团,能够与重金属离子发生络合、离子交换、氧化还原等反应,从而降低重金属的生物有效性并减轻其毒性。微生物EPS在重金属胁迫环境中的修复具有重要意义。然而,目前缺乏关于微生物EPS合成过程、与重金属互作机制及其在重金属胁迫环境中应用现状的系统综述。本文概述了微生物EPS及其分类,详细阐述了细菌EPS胞内及胞外的生物合成机制,并探讨了微生物EPS与重金属互作机制,以及微生物EPS修复水、土环境中重金属污染方面的研究进展。最后,展望了EPS合成及其在重金属修复中的作用机制研究,可为微生物EPS进一步应用于环境重金属污染修复提供支持。     

内生菌协同宿主植物修复土壤复合污染的研究进展

土壤复合污染日益严重,危及植物生长及人类发展,寻找修复土壤复合污染的有效方法已经成为环境领域的优先事项。复合污染指同一环境中存在两种或两种以上的污染物,分为复合重金属污染、复合有机污染物污染及重金属-有机污染物复合污染。近些年发现内生菌能定殖在植物中,并且被感染的植物不会引起任何外在病症,其主要通过促进宿主植物生长,改变植物摄取污染物能力和酶促降解污染物等方法增强植物修复能力。本文综述了具有复合重金属和复合有机污染抗性的内生菌种类及其作用机制,并展望了内生菌协同宿主植物修复环境中复合污染物的研究方向。     

Hydrocarbon degradation by a soil microbial population with beta-cyclodextrin as surfactant to enhance bioavailability

In general the biodegradation of nonchlorinated aliphatic and aromatic hydrocarbons is influenced by their bioavailability. Hydrocarbons are very poorly soluble in water. They are easily adsorbed to clay or humus fractions in the soil, and pass very slowly to the aqueous phase, where they are metabolised by microorganisms. Surfactants that increase their solubility and improve their bioavailability can thereby accelerate degradation. Cyclodextrins are natural compounds that form soluble complexes with hydrophobic molecules. They are widely used in medicine and harmless to microorganisms and enzymes. This paper describes their in vitro effect on the biodegradative activity of a microbial population isolated from a petroleum-polluted soil, as shown by the decrease of dodecane (C12), tetracosane (C24) anthracene and naphthalene added individually as the sole carbon source to mineral medium liquid cultures. beta-cyclodextrin accelerated the degradation of all four hydrocarbons, particularly naphthalene, and influenced the growth kinetics as shown by a higher biomass yield and better utilization of hydrocarbon as a carbon and energy source. Its low cost, biocompatibility and effective acceleration of degradation make beta-cyclodextrin an attractive option for bioremediation.     

Recent advances in biodegradation in China: New microorganisms and pathways,biodegradation engineering,and bioenergy from pollutant biodegradation

We are facing serious environmental challenges, and environmental biotechnology is an enabling technology to reduce or eliminate pollution. In recent years, environmental pollution in China has been receiving great attention, and this paper provides an up-to-date review on progress in biodegradation research in China. This progress includes the isolation of extremophilic microorganisms for pollutant degradation in extreme conditions and the study of genes and enzymes related to biodegradation pathways. Biodegradation engineering has potential as an interesting and powerful platform, where genetic engineering, process engineering, and signal transduction engineering are applied together. In addition, pollutant treatment combined with the production of renewable sources of bioenergy by microorganisms is attractive.     

The Structural and Functional State of Soil Microbiota in a Chemically Polluted Environment

The structural and functional diversity of the main ecological trophic groups of soil microorganisms in meadow soils of the Central Urals anthropogenically contaminated with heavy metals was studied. The increase in the total numbers of these microorganisms in technozems, in comparison with those in agrozems, is due to the higher abundance of iron-reducing, denitrifying, nitrogen-fixing, and sulfate-reducing bacteria, an increase in cellulolytic activity, and the dependence of these characteristics on the toxic load of the soil. A reductive structure of the microbial community with the predominance of r-strategists, which reflects earlier stages of microbiocenoses succession under soil contamination, is formed under soil pollution with heavy metals.     

Interactions of microorganisms with rare earth ions and their utilization for separation and environmental technology

In recent years, rare earth elements (REEs) have been widely used in various modern technological devices and the global demand for REE has been increasing. The increased demand for REEs has led to environmental exposure or water pollution from rare earth metal mines and various commercial products. Therefore, the development of a safe technology for the separation and adsorption of REEs is very important from the perspective of green chemistry and environmental pollution. In this review, the application and mechanisms of microorganisms for the removal and extraction of REEs from aqueous solutions are described. In addition, the advantages in using microorganisms for REE adsorption and future studies on this topic are discussed.     

生态修复过程中的若干问题——以POPs污染土壤为例

生态修复是在受污染土壤所在的区域环境条件下,以土壤生态系统自净能力为基础耦合其它修复技术,达到修复高效、安全和可靠的目的。以POPs污染土壤为例,总结了污染土壤生态修复的4个原则,分析了生态修复过程,对修复目标确立,修复过程控制,修复结果评估做了探讨。在分析耦合概念和生态修复过程的基础上,认为修复技术的耦合过程是生态修复的关键,总结了生态修复中的耦合原则、耦合策略和耦合方式。展望了生态修复的发展趋势和研究方向。     

微生物对偶氮染料的脱色及其基因工程研究进展

偶氮染料广泛应用在纺织印染、造纸印刷等行业中。染料废水的排放将会导致严重的环境污染,使用微生物处理染料废水是解决此问题的有效方法。该文概述了微生物对偶氮染料的脱色的研究,包括细菌对偶氮染料的脱色,真菌对偶氮染料的脱色,脱色产生的芳香胺并进一步被降解,以及基因工程技术在微生物对偶氮染料脱色的研究进展。     

Characterization of the iron-regulated <Emphasis Type="Italic">desA</Emphasis> promoter of <Emphasis Type="Italic">Streptomyces pilosus</Emphasis> as a system for controlled gene expression in actinomycetes

Background  

The bioavailability of iron is quite low since it is usually present as insoluble complexes. To solve the bioavailability problem microorganisms have developed highly efficient iron-scavenging systems based on the synthesis of siderophores that have high iron affinity. The systems of iron assimilation in microorganisms are strictly regulated to control the intracellular iron levels since at high concentrations iron is toxic for cells. Streptomyces pilosus synthesizes the siderofore desferrioxamine B. The first step in desferrioxamine biosynthesis is decarboxylation of L-lysine to form cadaverine, a desferrioxamine B precursor. This reaction is catalyzed by the lysine decarboxylase, an enzyme encoded by the desA gene that is repressed by iron.     

Synergistic plant-microbes interactions in the rhizosphere: a potential headway for the remediation of hydrocarbon polluted soils

Soil pollution is an unavoidable evil; many crude-oil exploring communities have been identified to be the most ecologically impacted regions around the world due to hydrocarbon pollution and their concurrent health risks. Several clean-up technologies have been reported on the removal of hydrocarbons in polluted soils but most of them are either very expensive, require the integration of advanced mechanization and/or cannot be implemented in small scale. However, “Bioremediation” has been reported as an efficient, cost-effective and environment-friendly technology for clean-up of hydrocarbon”s contaminated soils. Here, we suggest the implementation of synergistic mechanism of bioremediation such as the use of rhizosphere mechanism which involves the actions of plant and microorganisms, which involves the exploitation of plant and microorganisms for effective and speedy remediation of hydrocarbon”s contaminated soils. In this mechanism, plant”s action is synergized with the soil microorganisms through the root rhizosphere to promote soil remediation. The microorganisms benefit from the root metabolites (exudates) and the plant in turn benefits from the microbial recycling/solubilizing of mineral nutrients. Harnessing the abilities of plants and microorganisms is a potential headway for cost-effective clean-up of hydrocarbon”s polluted sites; such technology could be very important in countries with great oil producing activities/records over many years but still developing.