沙蚕耐污染的特征及机理研究进展

沙蚕（Nereis diversicolor）是一种栖息于海陆交错带、具有重要生态学意义的无脊椎动物.近年来发现,沙蚕体内能够蓄积大量的重金属等有毒有害污染物,且表现出较强的污染耐性.文中就沙蚕对重金属和有机污染物具有的污染耐性特征和最新国内外研究进展进行了概述,并就其污染耐性形成的机理进行了分析.沙蚕的污染耐性机制可能是通过多种生态化学过程实现的,包括通过大量粘液的分泌,在沙蚕体表形成一层保护膜;与有效态以及溶解于水中的污染物离子结合,从而降低污染物的生物可利用性;加快排泄速率等.更多的研究认为,沙蚕将吸收进入体内的重金属等有毒有害污染物以无毒的形式存贮,达到解毒的目的.这些无毒形式主要包括:与金属结合蛋白MTs和MTLP的结合物,热稳定硫醇化合物（CHSTC）,或者与重金属相互结合形成不溶性的溶酶体/微粒和结石等颗粒物或沉淀物.最后,对沙蚕生态毒理学研究以及耐性机制研究的工作重点进行了展望.     

铜和营养缺失对海州香薷两个种群生长、耐性及矿质营养吸收的差异影响

以来自铜矿区(CS)和非矿区(UCS)两个海州香薷种群为对象,通过室内水培实验,分析了两种群幼苗在铜及营养缺失胁迫下植物生长、铜富集及矿质营养含量的差异.结果显示,铜、低营养胁迫及其相互作用对非矿区种群生长具有明显的抑制作用,而对矿区种群的影响则远比非矿区种群小,且较低铜浓度(25μmol/L Cu)明显促进了矿区种群的生长;从耐性指数结果看,矿区种群铜耐性指数和营养胁迫耐性指数均高于非矿区种群.这表明矿区种群不仅进化为铜耐受种群,同时也进化成营养胁迫耐受种群.低营养胁迫明显促进了植物对铜的吸收和运转,如在低营养胁迫和25 μmol/L Cu复合处理下,矿区种群根铜含量约为单一铜处理的25倍,非矿区种群是单一铜处理5倍多.低营养胁迫和过量铜显著减少了非矿区种群矿质营养元素如P,Mg,K和Mn的吸收积累,而矿区种群则仍然能保持相对稳定;在铜和营养缺失复合作用下,两个种群矿质营养除Ca和部分Fe外,均显著减少,但矿区种群减少程度明显比非矿区种群小.这些结果表明,矿区种群在胁迫条件下具有保持营养相对稳定和平衡的能力,这种能力使其能在高铜污染和营养缺乏的土壤中正常生长和定居.     

酿酒酵母乙醇耐性的分子机制及基因工程改造

提高工业微生物对毒性代谢产物及高温等环境胁迫因素的耐受性对工业生产具有重要的意义。发酵过程中产生的乙醇对酵母细胞的生长和代谢都具有较强的抑制作用,是酿酒酵母的重要环境胁迫因素之一。对酿酒酵母乙醇耐性的分子机制的研究可为选育具有较强乙醇耐受性的酵母菌种提供理论基础。近年来,通过细胞全局基因转录分析和基因功能分析,对酿酒酵母乙醇耐性的分子机制有了更多新的认识,揭示了很多新的与乙醇耐性相关的基因,并在此基础上,通过对相关基因进行过量表达或敲除,成功提高了酵母菌的乙醇耐性。以下综述了近年来酵母菌乙醇耐性的生物化学与分子生物学机制的研究进展,以及构建具有较高乙醇耐性的酵母菌的基因工程操作。这些研究不仅加深了对酿酒酵母乙醇耐性的机理认识,也可为高效进行生物转化生产生物质能源奠定理论基础。     

铁氧化菌耐砷机制及其砷污染修复应用的研究进展

砷污染作为全球性环境问题已经引起了人们的高度重视。无机砷化合物可与铁氢氧化物络合通过共沉淀作用去除。因此,利用具有砷耐性的铁氧化菌氧化环境中的铁元素去除砷化合物具有潜在的应用前景。目前已有利用铁氧化菌去除环境中砷污染物的报道。用于砷污染修复的铁氧化菌必须有一定的砷耐性才能在含砷环境中行使功能。微生物是否具有砷耐性往往取决于基因,并且不同的菌株具有不同的生理特征,适宜不同砷污染环境的修复。本文通过对8株代表性的铁氧化菌砷耐性基因的总结,阐述其耐砷机制、研究概况及应用前景,以期为铁氧化菌用于除砷新技术的开发提供参考。     

细菌持留与抗生素表型耐药机制

持留菌是细菌群体中一小部分具有表型耐药的细菌。自1944年被发现后,近几十年来因其在慢性持续性感染和生物膜感染中的重要作用而得到越来越多的重视。已有的研究结果表明,细菌持留的机理复杂,涉及的相关信号通路有毒素-抗毒素系统、细胞能量代谢及蛋白核酸合成等生理状态的降低、DNA保护修复系统、蛋白酶系统、反式翻译、外排泵系统等。虽然不同细菌的持留机理有一定的相似性和保守性,但不同细菌的持留机制也存在差异,如毒素-抗毒素系统在大肠埃希菌(Escherichia coli)中的过度激活可导致持留菌增加,但在金黄色葡萄球菌(Staphylococcus aureus)中却并无相同作用。本文从持留菌的研究历史出发,综述了当前对革兰氏阴性菌和阳性菌的持留机制方面的研究进展,同时探讨了在持留菌相关感染疾病方面的治疗策略,以期为更好地解决持留菌带来的问题,缩短治疗时间提供新的思路。     

金黄色葡萄球菌sdhCAB操纵子影响持留菌形成机制的研究

持留菌是细菌群体中的一小部分细菌,可耐受致死浓度抗生素的处理,是引起慢性感染的重要原因。金黄色葡萄球菌(Staphylococcus aureus,S. aureus)作为常见致病菌,有重要临床意义。分别敲除sdhA和sdhB后,金黄色葡萄球菌持留菌形成水平下降,但sdhCAB操纵子对持留菌形成的作用及机制尚不明确。本研究敲除sdh操纵子,通过酸压力、氧化压力、热压力及抗生素压力实验检测敲除株的持留菌水平,转录组测序检测敲除株的代谢通路变化,高通量微生物细胞表型检测评估敲除株的代谢水平变化。结果显示,敲除sdhCAB或sdhAB后,金黄色葡萄球菌对酸压力、氧化压力的耐受能力均下降;而在抗生素压力、热压力条件下,分别仅sdhCAB敲除株、sdhAB敲除株耐受能力下降。转录组测序发现,sdhCAB敲除后三羧酸循环、甲烷代谢通路及聚合酶Ⅳ等基因表达上调,耐药相关基因、氨基酸代谢基因、糖类代谢基因、卟啉代谢基因及一些转运体基因等表达下调,提示这些通路的基因参与sdhCAB影响持留菌形成的过程。此外,高通量微生物细胞表型检测发现,敲除sdhCAB可降低金黄色葡萄球菌对琥珀酸、柠檬酸、糖原、L-天冬氨酸等64种碳源的代谢。结果提示,sdhCAB操纵子对金黄色葡萄球菌持留菌形成水平有重要影响。本研究初步阐明了sdhCAB操纵子影响持留菌形成的可能机制,为研究和治疗金黄色葡萄球菌慢性感染提供了新的思路。     

持留菌的控制研究进展

持留菌是高度耐受抗生素的细菌亚群。持留菌的出现加剧了抗生素治疗感染性疾病的难度,对人类的生命健康造成不可忽视的威胁。因此,如何控制与去除持留菌成为目前的一个研究热点。本文主要综述了持留菌的基本特性与危害,分析了持留菌形成的机制,并系统地总结了目前持留菌控制与去除的方法。本文对研究控制持留菌及改善持续性感染的治疗具有一定的指导意义和参考价值。     

金黄色葡萄球菌持留菌形成机制的研究进展

金黄色葡萄球菌(Staphylococcus aureus)是一种重要的院内感染致病菌,是导致人类各类感染最重要的病原体之一。金黄色葡萄球菌耐药问题一直是临床慢性感染治疗的最大障碍。随着细菌耐药机制研究的不断深入,研究者发现持留菌可能是导致疾病的持续性和复发性感染的真正原因。近年来持留菌的存在引起的耐药问题被高度重视,金黄色葡萄球菌持留菌的基本特征和形成机制的研究对临床上更好地控制耐药及感染问题具有重要的意义。为此,本文将从金黄色葡萄球菌持留菌的特性、生物膜、能量代谢、基因调控等多方面对金黄色葡萄球菌持留菌进行系统全面的综述。     

土壤微生物生物地理学研究进展

生物地理学是研究生物（包括种群、群落等不同层次）地理分布格局及成因的一门交叉学科。微生物生物地理学的研究长期滞后于宏生物地理学。鉴于土壤微生物在调控生物地球化学过程和维持生态系统功能方面的重要作用,对其空间分布格局及形成机制的认识具有十分重要的理论和实际意义。随着分子生物学技术的发展,对微生物多样性的认知日益深入。越来越多的证据表明,土壤微生物群落结构和多样性具有一定的时空分布格局,从而对微生物全球性随机分布的传统观点提出了挑战。对当前土壤微生物生物地理学研究中的一些概念性问题,如微生物物种的定义、微生物多样性的定量测度、对微生物全球性随机分布的争论等,进行了系统评述;以微生物种-面积关系和距离-衰减关系为例对当前最新的土壤微生物生物地理学研究成果进行总结,并初步探讨了土壤微生物群落的地带性分布问题;在传统生物地理学理论的指导下,提出了一个可用于验证土壤微生物空间分布格局形成和机制维持的简单研究框架。这些对今后土壤微生物生物地理学的研究有一定借鉴和指导意义。     

微生物相互作用中的空间自组织

微生物在全球生态系统中占据着重要地位, 其中一个重要的研究领域是微生物与环境(包括无机环境与生物环境)之间的相互作用。在生态相互作用过程中, 微生物常常通过自组织形成特定的空间模式。微生物的空间模式在种群稳定性、群落动态变化以及维持合作行为方面具有重要作用。本文中, 我们梳理了当下对微生物空间自组织及其所形成的空间模式的研究内容, 首先介绍什么是空间自组织, 再根据生态相互作用类型对自组织的空间模式进行描述, 其中重点讨论合作与竞争中的空间模式, 接着关注微生物空间自组织的过程, 最后我们指出空间自组织对整个群体的结构和功能稳定具有重要意义。研究微生物种群间相互作用中的空间模式, 有助于探索维持合作行为的新机制, 进而为微生物共生系统的构建提供新的理解。     

Persister cells and tolerance to antimicrobials

Bacterial populations produce persister cells that neither grow nor die in the presence of microbicidal antibiotics. Persisters are largely responsible for high levels of biofilm tolerance to antimicrobials, but virtually nothing was known about their biology. Tolerance of Escherichia coli to ampicillin and ofloxacin was tested at different growth stages to gain insight into the nature of persisters. The number of persisters did not change in lag or early exponential phase, and increased dramatically in mid-exponential phase. Similar dynamics were observed with Pseudomonas aeruginosa (ofloxacin) and Staphylococcus aureus (ciprofloxacin and penicillin). This shows that production of persisters depends on growth stage. Maintaining a culture of E. coli at early exponential phase by reinoculation eliminated persisters. This suggests that persisters are not at a particular stage in the cell cycle, neither are they defective cells nor cells created in response to antibiotics. Our data indicate that persisters are specialized survivor cells.     

Specialized persister cells and the mechanism of multidrug tolerance in Escherichia coli

Bacterial populations produce persisters, cells that neither grow nor die in the presence of bactericidal agents, and thus exhibit multidrug tolerance (MDT). The mechanisms of MDT and the nature of persisters have remained elusive. Our previous research has shown that persisters are largely responsible for the recalcitrance of biofilm infections. A general method for isolating persisters was developed, based on lysis of regular cells by ampicillin. A gene expression profile of persisters contained toxin-antitoxin (TA) modules and other genes that can block important cellular functions such as translation. Bactericidal antibiotics kill cells by corrupting the target function (for example, aminoglycosides interrupt translation, producing toxic peptides). We reasoned that inhibition of translation will lead to a shutdown of cellular functions, preventing antibiotics from corrupting their targets, giving rise to MDT persister cells. Overproduction of the RelE toxin, an inhibitor of translation, caused a sharp increase in persisters. Functional expression of a putative HipA toxin also increased persisters, while deletion of the hipBA module caused a sharp decrease in persisters in both stationary and biofilm populations. HipA is thus the first validated persister-MDT gene. We suggest that random fluctuation in the levels of MDT proteins leads to the formation of rare persister cells. The function of these specialized dormant cells is to ensure the survival of the population in the presence of lethal factors.     

Starvation,Together with the SOS Response,Mediates High Biofilm-Specific Tolerance to the Fluoroquinolone Ofloxacin

High levels of antibiotic tolerance are a hallmark of bacterial biofilms. In contrast to well-characterized inherited antibiotic resistance, molecular mechanisms leading to reversible and transient antibiotic tolerance displayed by biofilm bacteria are still poorly understood. The physiological heterogeneity of biofilms influences the formation of transient specialized subpopulations that may be more tolerant to antibiotics. In this study, we used random transposon mutagenesis to identify biofilm-specific tolerant mutants normally exhibited by subpopulations located in specialized niches of heterogeneous biofilms. Using Escherichia coli as a model organism, we demonstrated, through identification of amino acid auxotroph mutants, that starved biofilms exhibited significantly greater tolerance towards fluoroquinolone ofloxacin than their planktonic counterparts. We demonstrated that the biofilm-associated tolerance to ofloxacin was fully dependent on a functional SOS response upon starvation to both amino acids and carbon source and partially dependent on the stringent response upon leucine starvation. However, the biofilm-specific ofloxacin increased tolerance did not involve any of the SOS-induced toxin–antitoxin systems previously associated with formation of highly tolerant persisters. We further demonstrated that ofloxacin tolerance was induced as a function of biofilm age, which was dependent on the SOS response. Our results therefore show that the SOS stress response induced in heterogeneous and nutrient-deprived biofilm microenvironments is a molecular mechanism leading to biofilm-specific high tolerance to the fluoroquinolone ofloxacin.     

Persisters: a distinct physiological state of E. coli

Background  

Bacterial populations contain persisters, phenotypic variants that constitute approximately 1% of cells in stationary phase and biofilm cultures. Multidrug tolerance of persisters is largely responsible for the inability of antibiotics to completely eradicate infections. Recent progress in understanding persisters is encouraging, but the main obstacle in understanding their nature was our inability to isolate these elusive cells from a wild-type population since their discovery in 1944.     

Bacterial persistence: some new insights into an old phenomenon

Bigger discovered more than 60 years ago, at the very beginning of the antibiotic era, that populations of antibiotic-sensitive bacteria contained a very small fraction (approximately 10⁻⁶) of antibiotic-tolerant cells (persisters). Persisters are different from antibiotic-resistant mutants in that their antibiotic tolerance is non-heritable and reversible. In spite of its importance as an interesting biological phenomenon and in the treatment of infectious diseases, persistence did not attract the attention of the scientific community for more than four decades since its discovery. The main reason for this lack of interest was the difficulty in isolating sufficient numbers of persister cells for experimentation, since the proportion of persisters in a population of wild-type cells is extremely small. However, with the discovery of high-persister (hip) mutants of Escherichia coli by Moyed and his group in the early 1980s, the phenomenon attracted the attention of many groups and significant progress has occurred since then. It is now believed that persistence is the end result of a stochastic switch in the expression of some toxin-antitoxin (TA) modules (of which the hipA and hipB genes could be examples), creating an imbalance in their intracellular levels. There are also models invoking the involvement of the alarmone (p) ppGpp in the generation of persisters. However, the precise mechanisms are still unknown. Bacterial persistence is part of a wider gamut of phenomena variously called as bistability, multistability, phenotypic heterogeneity, stochastic switching processes, etc. It has attracted the attention of not only microbiologists but also a diverse band of researchers such as biofilm researchers, evolutionary biologists, sociobiologists, etc. In this article, I attempt to present a broad overview of bacterial persistence to illustrate its significance and the need for further exploration.     

Medical significance and new therapeutical strategies for biofilm associated infections

Recent public announcements stated that 60% to 85% of all microbial infections involve biofilms developed on natural tissues (skin, mucosa, endothelial epithelia, teeth, bones) or artificial devices (central venous, peritoneal and urinary catheters, dental materials, cardiac valves, intrauterine contraceptive devices, contact lenses, different types of implants). Prosthetic medical devices are risk factors of chronic infections in developed countries and these infections are characterized by slow onset, middle intensity symptoms, chronic evolution and resistance to antibiotic treatment. In case of biofilm development, a series of genes (40-60% of the prokaryotic genome) are modulated (activated/inhibited) by complex cell to cell signalling mechanisms and the biofilm cells become phenotypically distinct from their counterpart--free cells, being more resistant to stress conditions (including all types of antimicrobial substances); this resistance is phenotypical, behavioural and, more recently, called TOLERANCE. Four major mechanisms can account for biofilm antibiotic tolerance: (1) the failure of antibiotic penetration into the depth of a mature biofilm due to the biofilm matrix; (2) the accumulation of high levels of antibiotic degrading enzymes; (3) in the depth of biofilm, cells are experiencing nutrient limitation entering in a slow-growing or starved state; slow-growing or non-growing cells being not highly susceptible to antimicrobial agents, this phenomenon could be amplified by the presence of phenotypic variants or "persisters" and (4) biofilm's bacteria can turn on stress-response genes and switch to more tolerant phenotypes on exposure to environmental stresses; (5) genetic changes, probably selected by different stress conditions, such as mutations and gene transfer could occur inside the biofilm. In these conditions, biofilm associated infections require a different approach, both clinically and paraclinically.     

Persister cells and the riddle of biofilm survival

This review addresses a long standing puzzle in the life and death of bacterial populations—the existence of a small fraction of essentially invulnerable cells. Bacterial populations produce persisters, cells that neither grow nor die in the presence of bactericidal agents, and thus exhibit multidrug tolerance (MDT). The mechanism of MDT and the nature of persisters, which were discovered in 1944, have remained elusive. Our research has shown that persisters are largely responsible for the recalcitrance of infections caused by bacterial biofilms. The majority of infections in the developed world are caused by biofilms, which sparked a renewed interest in persisters. We developed a method to isolate persister cells, and obtained a gene expression profile of Escherichia coli persisters. The profile indicated an elevated expression of toxin-antitoxin modules and other genes that can block important cellular functions such as translation. Bactericidal antibiotics kill cells by corrupting the target function, such as translation. For example, aminoglycosides interrupt translation, producing toxic peptides. Inhibition of translation leads to a shutdown of other cellular functions as well, preventing antibiotics from corrupting their targets, which will give rise to tolerant persister cells. Overproduction of chromosomally-encoded toxins such as RelE, an inhibitor of translation, or HipA, causes a sharp increase in persisters. Deletion of the hipBA module produces a sharp decrease in persisters in both stationary and biofilm cells. HipA is thus the first validated persister/MDT gene. We conclude that the function of toxins is the exact opposite of the term, namely, to protect the cell from lethal damage. It appears that stochastic fluctuations in the levels of MDT proteins lead to formation of rare persister cells. Persisters are essentially altruistic cells that forfeit propagation in order to ensure survival of kin cells in the presence of lethal factors.Translated from Biokhimiya, Vol. 70, No. 2, 2005, pp. 327–336.Original Russian Text Copyright © 2005 by Lewis.This revised version was published online in April 2005 with corrections to the post codes.     

细菌生物被膜基质的研究进展

细菌生物被膜(biofilm)附着在生物或者非生物表面,由细菌及其分泌的糖、蛋白质和核酸等多种基质组成的细菌群落,是造成病原细菌持续性感染、毒力和耐药性的重要原因之一.细菌的生物被膜基质由复杂的胞外聚合物(extracellular polymeric substances,EPS)构成,影响生物被膜的结构和功能.本文...     

酶标仪分光光度法在微生物耐性研究上的应用

微生物在环境中的耐性是该微生物在相应环境发挥作用的重要基础。为了获得一种用于微生物耐性分析的快速简便方法,传统平板分离法和酶标仪分光光度法被用于评估其在细菌和链霉菌紫外耐受水平检测中的差异,并分析了酶标仪分光光度法在微生物其他耐性水平检测中的适用性。结果显示,两种检测方法均能体现细菌和链霉菌对紫外线的耐受水平,前者经过稀释、涂布、培养、菌落计数,获得的是菌株在紫外线照射后的存活浓度,而后者经过接种96孔培养板、培养、吸光度检测,获得的是菌株经紫外线照射后的生长曲线,并从生长曲线获知菌株的生长速率、增殖能力等信息。此外,酶标仪分光光度法同样适用于细菌对pH和盐的耐受水平分析,对于链霉菌耐受性分析有一定的适用性。酶标仪法除了能获得与平板分离法相似的耐性水平检测外,还能获得菌株在不同耐性水平上的增殖潜力,且在操作上比平板分离法省时、省力,可用于微生物耐性分析、高通量筛选等研究工作。