人工碳纳米材料在环境中的降解与转化研究进展

随着人工碳纳米材料的大量生产和使用,其潜在的生态风险已引起学术界的广泛关注.碳纳米材料在环境中的转化和降解直接影响它们在环境中的归趋及生态毒性,对该过程的研究是确定其环境可容纳量及进行生命周期评价的重要环节.本文概述了主要人工碳纳米材料(碳纳米管、富勒烯)在环境中的化学转化、微生物降解及光降解过程,总结了影响人工碳纳米材料降解的环境与结构因素及降解的机理,指出了现有研究的不足和未来研究的方向.     

天然水环境中纳米银的来源、分析与转化

纳米银(AgNPs)作为当前应用最广的金属纳米材料之一,可通过各种途径进入水土环境,对水生生物产生毒性,从而破坏水体生态环境.天然水体成分复杂,纳米银具有纳米材料特殊的理化性质,使得其在水体中的转化过程变得尤为复杂,因此理解纳米银在水环境中的转化与归趋,对于水质管理与生态环境保护极其重要.现代科技的发展为更好地研究纳米银在进入环境中后的溶解、聚凝等一系列转化过程提供了可能.本文概述了环境中纳米银的来源和环境风险,分析了pH、溶解氧、离子强度等环境因素及粒径、涂层等自身因素对其在水体环境中转化的影响,并归纳了对纳米银的粒径、电位及形貌等分析的主要技术手段.最后指出了当前研究中存在的主要不足,并对今后的研究方向进行了展望.     

黄土高原植被建设与土壤干燥化:问题与展望

黄土高原大规模植被建设有效减少了水土流失、改善了区域生态环境,大规模人工植被种植也造成了土壤水分的过度消耗,导致了土壤干燥化,成为当前黄土高原生态恢复的重要制约因素,威胁区域生态系统健康与稳定。系统综述了黄土高原地区人工植被恢复对土壤干燥化的作用机制,植被群落特征与土壤干燥化的耦合关系,多尺度土壤干燥化时空分异规律及其影响因素,明确了当前大规模人工植被恢复过程中土壤水分持续利用面临的问题与挑战。建议今后加强植被动态对水文过程影响的研究,明确多尺度植被格局与土壤干燥化时空分异的耦合关系,系统开展变化环境下不同尺度植被与土壤水分相互作用的模拟研究,探讨基于植被格局优化的土壤水分调控机制,维护黄土高原地区土壤安全,提升区域生态系统服务功能。     

细菌的群体性行为与耐药

随着抗生素的广泛使用,细菌耐药已经成为一个严重的问题。细菌耐药是一个复杂的过程,涉及宿主、细菌与环境等几个既相互独立又相互作用的因素。很久以来,人们认为细菌以个体为单位进行各种活动,直到发现细菌相互之间也存在联系,才意识到细菌群体对其个体生存的重要性。目前将细菌作为一个群体来研究其耐药行为与机制的研究越来越多,特别是细菌生物膜与细菌程序性死亡两方面受到极大重视。本文综述了细菌生物膜、细菌程序性死亡与耐药相关机制的研究进展。     

氧化石墨烯对红细胞功能的影响

纳米材料的生物相容性是人们关注的热点。氧化石墨烯是一种被广泛应用于生物医学的纳米材料,但其毒性不容忽视。本文从溶血率、红细胞脆性、乙酰胆碱酯酶活性三方面研究了氧化石墨烯对血液系统的毒性。结果表明,红细胞的溶血率在氧化石墨烯浓度低于100 μg/mL时均低于8% (P<0.01);低浓度氧化石墨烯 (<5 μg/mL) 对红细胞的脆性没有显著影响,高浓度氧化石墨烯 (如10 μg/mL) 会提高红细胞的脆性 (P=0.01);氧化石墨烯能增加红细胞上乙酰胆碱酯酶的活性,浓度为20 μg/mL的直径>5 μm的氧化石墨烯 (LGO) 可将乙酰胆碱酯酶的活性提高42.67% (P<0.05)。之后利用分子动力学模拟研究氧化石墨烯与乙酰胆碱酯酶相互作用并提高其活性的机理,推测氧化石墨烯会附着在细胞膜上并提供一个电负性环境,帮助水解产物更快地从活性位点脱离,从而提高乙酰胆碱酯酶的活性。     

纳米银对污水生物处理系统的影响

纳米银(silver nanoparticles,Ag-NPs)是目前商业化应用最多的纳米材料,因其优越的抗菌性能,广泛使用于纳米技术强化的消费品。释放到环境中的Ag-NPs随污水收集系统进入市政污水处理厂。市场上Ag-NPs产品日益增多,Ag-NPs与污水处理系统中微生物相互作用,可能影响污水处理厂的运行,引起人们广泛关注。污水中Ag-NPs去向和形态变化具有很大的不确定性。本文总结了Ag-NPs抗菌机制以及污水中Ag-NPs暴露对污水生物处理系统去除有机物、氮、磷等微生物的影响。为了降低Ag-NPs在水环境中的风险,今后需要关注的研究方向,包括:研究不同暴露时长下,Ag-NPs在污水中的形态转变,确定各种形态银的数量,寻求控制或消除Ag-NPs对污水处理系统微生物毒性作用的有效措施,为全面评估水体中Ag-NPs的环境风险提供依据。     

环境中生物膜的菌群结构与污染物降解特性

生物膜是细菌最常见的生长方式。结构有序、功能分化的生物膜群落为内部细菌提供在不利环境中生存的庇护,其环境功效也日益受到关注。本文综述了多种环境中微生物与不同材料表面相互作用、进而发展为生物膜的机制;介绍了环境工程领域中生物膜的先锋菌种和菌群结构动态变化;介绍了生物膜在污染环境中的抗逆与降解特性。     

纳米氧化铜对生物体的毒害作用及机理

随着纳米技术的飞速发展,人工纳米材料被广泛应用到能源、医药、军事、环保等各个领域。人工纳米氧化铜(Cu O NPs)由于其独特的物化性质和广泛的用途备受人们关注,其在生产及使用过程中形成的颗粒物有意无意地会进入土壤和水体中,进而对生物体造成潜在危害。现就近几年来Cu O NPs对不同生物体,包括动物、植物、细菌等以及细胞和基因方面的纳米效应及致毒机制进行了分析和综述。对Cu O NPs毒性的全面认识将为减轻人工纳米颗粒物的环境毒性研究提供参考,并提出了今后相关研究的重要方向。     

高脱氮活性海洋着色菌YL28生物膜特性

【背景】细菌生物膜在废水处理领域显示出良好的前景,但目前应用于海水养殖水体处理的菌株主要源自淡水菌株,存在难以适应海水高盐环境的问题。源自红树林的海洋着色菌(Marichromatiumgracile)YL28应用于海水养殖水体处理,不仅具有高效除氮能力,而且趋光贴壁能力很强。【目的】阐明海洋着色菌(Marichromatium gracile) YL28的生物膜形成特性和规律,以期为海水养殖水体生物膜反应系统的开发和应用提供参考。【方法】以生物膜和游离菌体生物量、脱氢酶活性、生物膜多糖含量和蛋白含量、无机三态氮去除活性为测定指标,在光照厌氧环境中研究海洋着色菌YL28菌株的生物膜形成规律、生物活性和脱氮效果。【结果】随着时间延长,4 000 lx光照时游离菌体生物量逐渐升高,但在稳定期前快速降低,而成膜生物量经过延滞期后逐渐升高并趋于稳定,表明培养过程中游离菌体能趋光贴壁生长并形成生物膜。在0-5 000 lx光照范围内培养4 d,低光照强度(500 lx)时成膜率(71.21%)最高,1 000-4 000 lx光照强度下成膜率虽然不是最高(54.64%-68.66%),但适宜菌体成膜,膜生物量干重达到0.60-0.80 mg/cm2。除了5 000 lx光照对成膜菌体脱氢酶活性有不利影响外,成膜菌体和游离菌体脱氢酶活性随光照强度升高而升高,而且没有明显差异。生物膜的形成会导致光反应器内部光照受限,但反应器内部游离菌体的脱氢酶活性并没有降低,由此表明,培养液中的菌体主要在生物膜及其界面生长并游离扩散至培养液中。随光照强度(1 000-5 000 lx)和培养时间(4-10 d)的变化,胞外复合物(Extracellularpolymericsubstances,EPS)中蛋白含量变异较大,多糖含量变化较小;随时间延长,蛋白含量升高,其中3 000 lx时蛋白含量最高;4 000 lx时生物膜菌体与游离菌体脱氮活性相比,单位质量菌体的氨氮和亚硝氮去除活性未受到明显影响,而硝氮去除活性有所降低。【结论】海洋着色菌YL28具有良好的生物膜形成能力,其成膜过程主要是菌体趋光贴壁生长成膜,成膜菌体具有良好的脱氮活性,这为利用生物膜系统消除海水养殖水体氮污染奠定了基础。     

碳纳米材料的环境行为及其对环境中污染物迁移归趋的影响

碳纳米材料具有广阔的应用前景,近年来已成为一大研究热点.工程碳纳米材料的大量生产和使用将不可避免地造成这些材料向环境中的释放,可能带来环境和生态风险.一方面,碳纳米材料本身具有环境毒性,另一方面碳纳米材料对环境中有毒有害污染物有较强的吸附性能,因此会影响污染物迁移转化等环境行为.目前,对碳纳米材料生态风险的研究主要集中于碳纳米材料对生物体可能的毒性,而对其自身环境行为以及影响污染物迁移归趋等方面的研究较少.本文简要概述了碳纳米材料的来源、暴露途径、环境行为以及对污染物迁移归趋的影响,阐述了这些研究对于评估碳纳米材料的环境和生态风险所具有的重要意义.     

Bacterial biofilms as a natural form of existence of bacteria in the environment and host organism

Advances in microscopic analysis and molecular genetics research methods promoted the acquisition of evidence that natural bacteria populations exist predominately as substrate attached biofilms. Bacteria in biofilms are able to exchange signals and display coordinated activity that is inherent to multicellular organisms. Formation of biofilm communities turned out to be one of the main survival strategies of bacteria in their ecological niche. Bacteria in attached condition in biofilm are protected from the environmental damaging factors and effects of antibacterial substances in the environment and host organism during infection. According to contemporary conception, biofilm is a continuous layer of bacterial cells that are attached to a surface and each other, and contained in a biopolymer matrix. Such bacterial communities may be composed of bacteria of one or several species, and composed of actively functioning cells as well as latent and uncultured forms. Particular attention has recently been paid to the role of biofilms in the environment and host organism. Microorganisms form biofilm on any biotic and abiotic surfaces which creates serious problems in medicine and various areas of economic activity. Currently, it is established that biofilms are one of the pathogenetic factors of chronic inflection process formation. The review presents data on ubiquity of bacteria existence as biofilms, contemporary methods of microbial community analysis, structural-functional features of bacterial biofilms. Particular attention is paid to the role of biofilm in chronic infection process formation, heightened resistance to antibiotics of bacteria in biofilms and possible mechanisms of resistance. Screening approaches for agents against biofilms in chronic infections are discussed.     

Environmental factors that shape biofilm formation

Cells respond to the environment and alter gene expression. Recent studies have revealed the social aspects of bacterial life, such as biofilm formation. Biofilm formation is largely affected by the environment, and the mechanisms by which the gene expression of individual cells affects biofilm development have attracted interest. Environmental factors determine the cell’s decision to form or leave a biofilm. In addition, the biofilm structure largely depends on the environment, implying that biofilms are shaped to adapt to local conditions. Second messengers such as cAMP and c-di-GMP are key factors that link environmental factors with gene regulation. Cell-to-cell communication is also an important factor in shaping the biofilm. In this short review, we will introduce the basics of biofilm formation and further discuss environmental factors that shape biofilm formation. Finally, the state-of-the-art tools that allow us investigate biofilms under various conditions are discussed.     

Escherichia coli biofilm: development and therapeutic strategies

Escherichia coli biofilm consists of a bacterial colony embedded in a matrix of extracellular polymeric substances (EPS) which protects the microbes from adverse environmental conditions and results in infection. Besides being the major causative agent for recurrent urinary tract infections, E. coli biofilm is also responsible for indwelling medical device‐related infectivity. The cell‐to‐cell communication within the biofilm occurs due to quorum sensors that can modulate the key biochemical players enabling the bacteria to proliferate and intensify the resultant infections. The diversity in structural components of biofilm gets compounded due to the development of antibiotic resistance, hampering its eradication. Conventionally used antimicrobial agents have a restricted range of cellular targets and limited efficacy on biofilms. This emphasizes the need to explore the alternate therapeuticals like anti‐adhesion compounds, phytochemicals, nanomaterials for effective drug delivery to restrict the growth of biofilm. The current review focuses on various aspects of E. coli biofilm development and the possible therapeutic approaches for prevention and treatment of biofilm‐related infections.     

Biofilm formation and persistence on abiotic surfaces in the context of food and medical environments

The biofilm formation on abiotic surfaces in food and medical sectors constitutes a great public health concerns. In fact, biofilms present a persistent source for pathogens, such as Pseudomonas aeruginosa and Staphylococcus aureus, which lead to severe infections such as foodborne and nosocomial infections. Such biofilms are also a source of material deterioration and failure. The environmental conditions, commonly met in food and medical area, seem also to enhance the biofilm formation and their resistance to disinfectant agents. In this regard, this review highlights the effect of environmental conditions on bacterial adhesion and biofilm formation on abiotic surfaces in the context of food and medical environment. It also describes the current and emergent strategies used to study the biofilm formation and its eradication. The mechanisms of biofilm resistance to commercialized disinfectants are also discussed, since this phenomenon remains unclear to date.     

Influence of Small RNAs on Biofilm Formation Process in Bacteria

Small non-coding RNAs (sRNAs) play a significant role in regulation of bacterial physiological behaviors. After sensing any environmental cue such as fluctuation of nutrient concentration, temperature, pH, and osmolarity, these sRNAs interfere to transmit these signals to target regulators and genes. sRNAs have key role in biofilm formation process by base pairing with target mRNAs or interaction with modulating proteins to both positive and negative regulation mechanisms. There are various regulatory systems to characterize the initiation and formation of special bacterial biofilms that are mostly described as two component systems based on sRNAs functions. In this study, regulatory pathways that are important for biofilm formation and genetic responses to environmental stimuli in mature biofilms were evaluated. Some of the regulatory systems that produce common types of biofilms such as curli, PGA, cellulose and polysaccharides such as alginate, colonic acid, Psl and their involved sRNAs functions were also discussed.     

Management of biofilm-associated infections: what can we expect from recent research on biofilm lifestyles?

Biofilms are surface-associated microbial communities present in all environments. Although biofilms play important ecological roles, they also lead to negative or deleterious effects in industrial and medical settings. In the latter, high levels of antibiotic tolerance of bacterial biofilms developing on medical devices and during chronic infections determine the physiopathology of many healthcare-associated infections. Original approaches have been developed to avoid bacterial adhesion or biofilm development targetting specific mechanisms or pathways. We herein review recent data about biofilm lifestyle understanding and ways to fight against related infections.     

A Comparison of Effects of Broad-Spectrum Antibiotics and Biosurfactants on Established Bacterial Biofilms

Current antibiofilm solutions based on planktonic bacterial physiology have limited efficacy in clinical and occasionally environmental settings. This has prompted a search for suitable alternatives to conventional therapies. This study compares the inhibitory properties of two biological surfactants (rhamnolipids and a plant-derived surfactant) against a selection of broad-spectrum antibiotics (ampicillin, chloramphenicol and kanamycin). Testing was carried out on a range of bacterial physiologies from planktonic and mixed bacterial biofilms. Rhamnolipids (Rhs) have been extensively characterised for their role in the development of biofilms and inhibition of planktonic bacteria. However, there are limited direct comparisons with antimicrobial substances on established biofilms comprising single or mixed bacterial strains. Baseline measurements of inhibitory activity using planktonic bacterial assays established that broad-spectrum antibiotics were 500 times more effective at inhibiting bacterial growth than either Rhs or plant surfactants. Conversely, Rhs and plant biosurfactants reduced biofilm biomass of established single bacterial biofilms by 74–88 and 74–98 %, respectively. Only kanamycin showed activity against biofilms of Bacillus subtilis and Staphylococcus aureus. Broad-spectrum antibiotics were also ineffective against a complex biofilm of marine bacteria; however, Rhs and plant biosurfactants reduced biofilm biomass by 69 and 42 %, respectively. These data suggest that Rhs and plant-derived surfactants may have an important role in the inhibition of complex biofilms.     

Aggregation of ammonia-oxidizing bacteria in microbial biofilm on oyster shell surface

Summary Formation and activity of bacterial nitrifying biofilms play an important role in the closed seawater systems for shrimp cultivation. The structure of microbial biofilm on empty oyster shells, used as a biofilm carrier in biofiltration of aquacultural water, was studied using fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy. FISH was performed with specific oligonucleotide probes for Bacteria and ammonia-oxidizing Nitrosomonas spp. The bacterial cells were arranged within the biofilm as a layer of vertically elongated aggregates. Aggregates of ammonia-oxidizing bacteria were embedded within the matrix formed by other bacteria. Vertically elongated cell aggregates may be ecologically important in bacterial biofilms because they have a higher surface-to-volume ratio than that of laminated biofilms.     

Nanocarriers for combating biofilms: Advantages and challenges

Bacterial biofilms are highly resistant to antibiotics and pose a great threat to human and animal health. The control and removal of bacterial biofilms have become an important topic in the field of bacterial infectious diseases. Nanocarriers show great anti-biofilm potential because of their small particle size and strong permeability. In this review, the advantages of nanocarriers for combating biofilms are analysed. Nanocarriers can act on all stages of bacterial biofilm formation and diffusion. They can improve the scavenging effect of biofilm by targeting biofilm, destroying extracellular polymeric substances and enhancing the biofilm permeability of antimicrobial substances. Nanocarriers can also improve the antibacterial ability of antimicrobial drugs against bacteria in biofilm by protecting the loaded drugs and controlling the release of antimicrobial substances. Additionally, we emphasize the challenges faced in using nanocarrier formulations and translating them from a preclinical level to a clinical setting.     

In vitro Biofilm Formation in an 8-well Chamber Slide

The chronic nature of many diseases is attributed to the formation of bacterial biofilms which are recalcitrant to traditional antibiotic therapy. Biofilms are community-associated bacteria attached to a surface and encased in a matrix. The role of the extracellular matrix is multifaceted, including facilitating nutrient acquisition, and offers significant protection against environmental stresses (e.g. host immune responses). In an effort to acquire a better understanding as to how the bacteria within a biofilm respond to environmental stresses we have used a protocol wherein we visualize bacterial biofilms which have formed in an 8-well chamber slide. The biofilms were stained with the BacLight Live/Dead stain and examined using a confocal microscope to characterize the relative biofilm size, and structure under varying incubation conditions. Z-stack images were collected via confocal microscopy and analyzed by COMSTAT. This protocol can be used to help elucidate the mechanism and kinetics by which biofilms form, as well as identify components that are important to biofilm structure and stability.