土壤中高环多环芳烃微生物降解的研究进展

微生物修复是去除土壤中多环芳烃(PAHs)的主要措施。本文以微生物修复PAHs污染土壤的理论基础及其难点为主线,全面综述了土壤中高环PAHs的微生物降解机理。近年来,富集分离得到的以高环PAHs为唯一碳源和能源的优势降解菌逐渐增多,其中,主要是代谢降解四环PAHs的单株降解菌,一些降解菌还能以共代谢方式利用五环PAHs。高环PAHs污染土壤修复的一个难点是其低生物可利用性,微生物通过释放生物表面活性剂、形成生物膜以及分泌胞外多糖提高高环PAHs的生物可利用性,从而加速其降解。真菌和细菌联合作用能增强污染土壤实地修复的效果。因此,通过微生物修复技术来去除土壤中PAHs具有环境友好性、经济适用性以及可持续应用性。     

环境中污染物降解基因的水平转移(HGT)及其在生物修复中的作用

水平基因转移是不同于垂直基因转移的遗传物质的交流方式.在污染环境这一特异生态环境中,降解基因的水平转移有着独特的功能与作用.研究环境中污染物降解基因在微生物间的水平转移,更深入地了解微生物种群适应污染环境的机理,对于评价污染物的环境毒理、生物可降解性以及污染环境的可修复潜力具有重要参考价值.在污染物生物修复实践中,可以通过调控降解基因的水平转移,增强污染环境中微生物的降解能力,更有效地发挥生物修复作用.文章将对环境中细菌间基因交流的机制,污染物降解基因的水平转移对微生物适应污染环境的机理、水平基因转移对代谢途径的进化及其对污染物生物修复作用的影响等方面的研究进展做一综述.     

硝基苯类化合物微生物降解研究进展

硝基苯类化合物是一类具有稳定化学性质、高毒性和易在生物体内积累的优先污染物.微生物降解在硝基苯类化合物废水废气治理和污染环境修复方面具有明显优势.从降解菌的驯化筛选、降解途径、降解机理、共代谢、趋化性和分子遗传学角度,阐述了硝基苯类化合物微生物降解研究的最新进展,指出应进一步加强工程菌的构建及其应用开发研究.在硝基苯类化合物污染环境的微生物修复方面,共代谢和混合菌株的协同作用具有重要的应用前景.     

细菌吸附及转运芳香族化合物的研究进展

芳香族化合物是一类具有苯环结构的有机物,它们结构稳定,不易分解,并可通过食物链进行生物富集和生物放大,对生态环境及人类健康造成极大危害。细菌具有超强的分解代谢能力,能降解多环芳烃(polycyclic aromatic hydrocarbons, PAHs)等多种难降解芳香族污染物。吸附和转运是细菌进行芳香族化合物细胞内代谢的前提。虽然芳香族化合物的细菌降解已取得较为显著的研究进展,但吸附和转运机理仍不甚清楚。本文讨论了细菌对芳香族化合物的吸附有积极作用的细胞表面疏水性、生物被膜形成和细菌趋化性等影响因素,总结了FadL家族、TonB依赖性受体蛋白、OmpW家族等外膜转运系统和主要协同转运蛋白超家族(major facilitator superfamily, MFS)转运体、ATP结合盒(ATP-binding cassette, ABC)转运蛋白等内膜转运系统对该类化合物跨膜运输作用,并对跨膜转运机制进行了讨论和阐述,旨在为芳香族污染物的防控和治理提供一定理论参考。     

根际圈在污染土壤修复中的作用与机理分析

根际圈以植物根系为中心聚集了大量的生命物质及其分泌物,构成了极为独特的“生态修复单元”。本文叙述了根在根际圈污染土壤修复中的生理生态作用,富集、固定重金属,吸收、降解有机污染物等功能;菌根真菌对根际圈内重金属的吸收、屏障及螯合作用,对有机污染物的降解作用;根际圈内细菌对重金属的吸附与固定,对有机污染物的降解作用以及根际圈真菌和细菌的联合修复作用等,同时对可能存在的机理进行了分析,认为根际圈对污染土壤的修复作用是植物修复的重要组成部分和主要理论基础之一,并指出利用重金属超富集植物修复重金属污染土壤具有广阔的应用前景;筛选对水溶性有机污染物高吸收富集及其根 发泌能力强的特异植物,同时接种利于有机污染物降解的专性或非专性真菌和细菌可能会成为有机污染土壤植物修复研究的重要方向之一。     

利用生物基原料合成聚羟基脂肪酸酯

聚羟基脂肪酸脂(polyhydroxyalkanoates,PHA)是细菌胞内的一类具有相似结构的碳源和能源的储备物,由于它的力学性能与某些热塑性材料聚乙烯、聚丙烯类似,并且可以完全降解进入自然界的生态循环,因而被认为是一种"生物可降解塑料",有可能替代传统的、不可降解的、由石油产品合成的塑料,而受到世界各国的重视.     

微生物降解硝基苯废水的研究进展

硝基苯是一种淡黄色,苦杏仁味的高毒物质,且难生物降解,广泛应用于化工、染料、制药等工业,具有稳定化学性质、高毒性和易在生物体内积累的优先污染物.硝基苯的大量排放对环境构成了严重威胁,对该污染物的处理一直是研究焦点.对硝基苯的降解方法主要有物理法、化学法和生物法,生物法费用低、不易造成二次污染,可以最大程度的降解污染物.微生物降解在硝基苯类化合物废水治理和污染环境修复方面具有明显优势,近年来人们己筛选出许多硝基苯高效降解菌.从降解菌的种类,降解途径,共代谢,固定化,基因工程,高盐条件下的降解等方面阐述了硝基苯生物降解的最新研究进展.     

海洋石油污染物的微生物降解与生物修复

石油是海洋环境的主要污染物 ,已经对海洋及近岸环境造成了严重的危害。微生物降解是海洋石油污染去除的主要途径。海洋石油污染物的微生物降解受石油组分与理化性质、环境条件以及微生物群落组成等多方面因素的制约 ,N和P营养的缺乏是海洋石油污染物生物降解的主要限制因子。在生物降解研究基础上发展起来的生物修复技术在海洋石油污染治理中发展潜力巨大 ,并且取得了一系列成果。介绍了海洋中石油污染物的来源、转化过程、降解机理、影响生物降解因素及生物修复技术等方面内容 ,强调了生物修复技术在治理海洋石油污染环境中的优势和重要性 ,指出目前生物修复技术存在的问题。     

生物修复中细菌的遗传修饰

有机污染的土壤过去常用物理修复或化学修复 ,成本较高 ,易引起二次污染 ,还可能危害微生物区系和动物区系。生物修复技术以其独到的优势迅速兴起。土壤中“ＭａｇｉｃＳｉｘ”(水分、氧气、氧化还原电势、ｐＨ值、营养状态、温度 )对微生物降解的影响[1] 或者土著菌 (ｉｎｄｉｇｅｎｏｕｓｂａｃｔｅｒｉａ)缺少编码某一降解酶基因成为污染物生物降解的限制因子 ,土著菌常常难以适应处理环境 ,达不到环境治理工程的目的。细菌对有机污染物适应性的遗传机制研究表明 ,细菌为了在污染地区环境中生存 ,细菌之间可发生水平基因转移或细菌的染色…     

微生物降解石油污染物机制研究进展

石油污染是当前紧迫的水环境问题,研究石油污染物降解机制有助于探索石油污染修复技术路径。重点介绍了微生物降解石油污染物过程中的微生物种类、降解机制和反应机理,即具有代表性的细菌、真菌和藻类,石油烃的有氧降解(链烷烃、环烷烃和芳香烃)和厌氧降解(脱氢羟基化、延胡索酸盐加成)。并对微生物降解石油组分的影响因素进行了讨论,具体包括:烃类结构(支链多结构越复杂,越难降解)、微生物种类(混合菌的生化降解能力更强)、环境因子(pH、温度、盐度、含氧量和营养物质),进一步指出了生物修复技术应用于石油污染修复治理研究中的优缺点。此外,还对现有微生物降解技术的应用做了简要概述,归纳总结现有研究中存在的问题,尝试性的提出了今后生物降解石油污染物的研究重点,即生物降解石油的机制还需进一步明确,并重点分析了生物电化学方法在降解去除石油污染物方面可行性。综述石油烃生物降解机制和反应机理,以期为生物修复水体石油污染提供参考和借鉴作用。     

Revealing potential functions of VBNC bacteria in polycyclic aromatic hydrocarbons biodegradation

The bioremediation of polycyclic aromatic hydrocarbon (PAH)‐contaminated sites is not running smoothly, because of the lower activity of PAH‐degrading bacteria in actual bioremediation applications. The phenomenon of “viable but nonculturable” (VBNC) state may be a main limiting factor for their poor biodegradation capabilities of PAHs. Due to their abilities of entering into the VBNC state, most of bacterial populations with PAH‐degradation potential remain unculturable. Resuscitation of VBNC bacteria will enhance the degradation capability of indigenous bacteria which will eventually obtain their better capabilities in environmental bioremediation. Although evidences have been presented indicating that resuscitation of VBNC bacteria in polychlorinated biphenyl (PCB)‐contaminated environments not only significantly enhanced PCB degradation, but also obtained novel highly efficient PCB‐degrading bacteria, scanty information is available on the VBNC bacteria in PAH‐contaminated sites. VBNC bacteria, as a vast majority of potential microbial resource could be the repository of novel highly efficient PAH‐biodegraders. Therefore, studies need to be done on resuscitation of VBNC bacteria to overcome key bottlenecks in bioremediation of PAH‐contaminated sites. This mini‐review provides a new insight into the potential functions of VBNC bacteria in PAHs biodegradation.

Significance and Impact of the Study

As the vast majority microbial resource, viable but nonculturable (VBNC) bacteria, which showed their potential functions in polycyclic aromatic hydrocarbons (PAHs) biodegradation, can be of great significance in environmental bioremediation. It is therefore important to resuscitate VBNC bacteria for their better capabilities. Meanwhile, preventing the indigenous functional community from entering into the VBNC state will also maintain the high activity of PAH‐degrading bacteria in actual bioremediation applications. Undoubtedly, much more work needs to be done to reveal indigenous micro‐organisms in the VBNC state from the perspective of environmental functions.     

Bacterial chemotaxis to naphthalene desorbing from a nonaqueous liquid

Bacterial chemotaxis has the potential to increase the rate of degradation of chemoattractants, but its influence on degradation of hydrophobic attractants initially dissolved in a non-aqueous-phase liquid (NAPL) has not been examined. We studied the effect of chemotaxis by Pseudomonas putida G7 on naphthalene mass transfer and degradation in a system in which the naphthalene was dissolved in a model NAPL. Chemotaxis by wild-type P. putida G7 increased the rates of naphthalene desorption and degradation relative to rates observed with nonchemotactic and nonmotile mutant strains. While biodegradation alone influenced the rate of substrate desorption by increasing the concentration gradient against which desorption occurred, chemotaxis created an even steeper gradient as the cells accumulated near the NAPL source. The extent to which chemotaxis affected naphthalene desorption and degradation depended on the initial bacterial and naphthalene concentrations, reflecting the influences of these variables on concentration gradients and on the relative rates of mass transfer and biodegradation. The results of this study suggest that chemotaxis can substantially increase the rates of mass transfer and degradation of NAPL-associated hydrophobic pollutants.     

Biocatalytic degradation of pollutants

Microbial reactions play key roles in biocatalysis and biodegradation. The recent genome sequencing of environmentally relevant bacteria has revealed previously unsuspected metabolic potential that could be exploited for useful purposes. For example, oxygenases and other biodegradative enzymes are benign catalysts that can be used for the production of industrially useful compounds. In conjunction with their biodegradative capacities, bacterial chemotaxis towards pollutants might contribute to the ability of bacteria to compete with other organisms in the environment and to be efficient agents for bioremediation. In addition to the bacterial biomineralization of organic pollutants, certain bacteria are also capable of immobilizing toxic heavy metals in contaminated aquifers, further illustrating the potential of microorganisms for the removal of pollutants.     

Bacterial Chemotaxis to Naphthalene Desorbing from a Nonaqueous Liquid

Bacterial chemotaxis has the potential to increase the rate of degradation of chemoattractants, but its influence on degradation of hydrophobic attractants initially dissolved in a non-aqueous-phase liquid (NAPL) has not been examined. We studied the effect of chemotaxis by Pseudomonas putida G7 on naphthalene mass transfer and degradation in a system in which the naphthalene was dissolved in a model NAPL. Chemotaxis by wild-type P. putida G7 increased the rates of naphthalene desorption and degradation relative to rates observed with nonchemotactic and nonmotile mutant strains. While biodegradation alone influenced the rate of substrate desorption by increasing the concentration gradient against which desorption occurred, chemotaxis created an even steeper gradient as the cells accumulated near the NAPL source. The extent to which chemotaxis affected naphthalene desorption and degradation depended on the initial bacterial and naphthalene concentrations, reflecting the influences of these variables on concentration gradients and on the relative rates of mass transfer and biodegradation. The results of this study suggest that chemotaxis can substantially increase the rates of mass transfer and degradation of NAPL-associated hydrophobic pollutants.     

Bacterial biofilms and quorum sensing: fidelity in bioremediation technology

Increased contamination of the environment with toxic pollutants has paved the way for efficient strategies which can be implemented for environmental restoration. The major problem with conventional methods used for cleaning of pollutants is inefficiency and high economic costs. Bioremediation is a growing technology having advanced potential of cleaning pollutants. Biofilm formed by various micro-organisms potentially provide a suitable microenvironment for efficient bioremediation processes. High cell density and stress resistance properties of the biofilm environment provide opportunities for efficient metabolism of number of hydrophobic and toxic compounds. Bacterial biofilm formation is often regulated by quorum sensing (QS) which is a population density-based cell–cell communication process via signaling molecules. Numerous signaling molecules such as acyl homoserine lactones, peptides, autoinducer-2, diffusion signaling factors, and α-hydroxyketones have been studied in bacteria. Genetic alteration of QS machinery can be useful to modulate vital characters valuable for environmental applications such as biofilm formation, biosurfactant production, exopolysaccharide synthesis, horizontal gene transfer, catabolic gene expression, motility, and chemotaxis. These qualities are imperative for bacteria during degradation or detoxification of any pollutant. QS signals can be used for the fabrication of engineered biofilms with enhanced degradation kinetics. This review discusses the connection between QS and biofilm formation by bacteria in relation to bioremediation technology.     

Bacterial chemotaxis to pollutants and plant-derived aromatic molecules

There is accumulating evidence that motile bacteria are chemotactically attracted to environmental pollutants that they can degrade. Chemotaxis, the ability of motile bacteria to detect and respond to specific chemicals in the environment, can increase an organism's chances of locating useful sources of carbon, nitrogen and energy, and could thus play an important role in the biodegradation process. Recent evidence demonstrating that chemotaxis and biodegradation genes are coordinately regulated suggests that these processes are intimately linked in nature.     

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.     

Recent developments in microbial biotransformation and biodegradation of dioxins

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), commonly known as dioxins (PCDD/Fs), are toxic environmental pollutants formed from various sources. Elimination of these pollutants from the environment is a difficult task due to their persistent and ubiquitous nature. Removal of dioxins by biological degradation (biodegradation) is considered a feasible method as an alternative to other expensive physicochemical approaches. Biodegradation of dioxins has been extensively studied in several microorganisms, and details concerning biodiversity, biodegradation, biochemistry and molecular biology of this process have accumulated during the last three decades. There are several microbial mechanisms responsible for biodegradation of dioxins, including oxidative degradation by dioxygenase-containing aerobic bacteria, bacterial and fungal cytochrome P-450, fungal lignolytic enzymes, reductive dechlorination by anaerobic bacteria, and direct ether ring cleavage by fungi containing etherase-like enzymes. Many attempts have been made to bioremediate PCDD/Fs using this basic knowledge of microbial dioxin degradation. This review emphasizes the present knowledge and recent advancements in the microbial biotransformation, biodegradation and bioremediation of dioxins.     

Chemotaxis of Ralstonia sp. SJ98 towards p-nitrophenol in soil

Bioremediation of contaminated sites has been accepted as an efficient and cheaper alternative to physicochemical means of remediation in several cases. Although chemotactic behaviour of many bacteria has been studied earlier and assays have been developed to study bacterial chemotaxis in semi-solid media, this phenomenon has never been demonstrated in soil. For bioremediation application it is important to know whether bacteria actually migrate through the heterogenous soil medium towards a gradient of a particular chemoattractant. In the present study we have successfully demonstrated bacterial chemotaxis of a Ralstonia sp. SJ98 in soil microcosm using qualitative and quantitative plate and tray assays. The migration of bacteria has been established using several methods such as plate counting, vital staining and flow cytometry and slot blot hybridization. A non-chemotactic p-nitrophenol utilizing strain Burkholderia cepacia RKJ200 has been used as negative control. Our work clearly substantiates the hypothesis that chemotactic bacteria may enhance in situ bioremediation of toxic pollutants from soils and sediments.     

Enhancement of metal bioremediation by use of microbial surfactants

Metal pollution all around the globe, especially in the mining and plating areas of the world, has been found to have grave consequences. An excellent option for enhanced metal contaminated site bioremediation is the use of microbial products viz. microbial surfactants and extracellular polymers which would increase the efficiency of metal reducing/sequestering organisms for field bioremediation. Important here is the advantage of such compounds at metal and organic compound co-contaminated site since microorganisms have long been found to produce surface-active compounds when grown on hydrocarbons. Other options capable of proving efficient enhancers include exploiting the chemotactic potential and biofilm forming ability of the relevant microorganisms. Chemotaxis towards environmental pollutants has excellent potential to enhance the biodegradation of many contaminants and biofilm offers them a better survival niche even in the presence of high levels of toxic compounds.