Electrochemically active biofilms: facts and fiction. A review

This review examines the electrochemical techniques used to study extracellular electron transfer in the electrochemically active biofilms that are used in microbial fuel cells and other bioelectrochemical systems. Electrochemically active biofilms are defined as biofilms that exchange electrons with conductive surfaces: electrodes. Following the electrochemical conventions, and recognizing that electrodes can be considered reactants in these bioelectrochemical processes, biofilms that deliver electrons to the biofilm electrode are called anodic, ie electrode-reducing, biofilms, while biofilms that accept electrons from the biofilm electrode are called cathodic, ie electrode-oxidizing, biofilms. How to grow these electrochemically active biofilms in bioelectrochemical systems is discussed and also the critical choices made in the experimental setup that affect the experimental results. The reactor configurations used in bioelectrochemical systems research are also described and the authors demonstrate how to use selected voltammetric techniques to study extracellular electron transfer in bioelectrochemical systems. Finally, some critical concerns with the proposed electron transfer mechanisms in bioelectrochemical systems are addressed together with the prospects of bioelectrochemical systems as energy-converting and energy-harvesting devices.     

Nutraceuticals: facts and fiction

Epidemiological studies show a link between the consumption of plant-derived foods and a range of health benefits. These benefits have been associated, at least partially, to some of the phytochemical constituents, and, in particular, to polyphenols. In the last few years, nutraceuticals have appeared in the market. These are pharmaceutical forms (pills, powders, capsules, vials, etc.) containing food bioactive compounds as active principles. The bioactive phytochemicals have become a very significant source for nutraceutical ingredients. Scientific research supports the biological activity of many of these food phytochemicals, but the health claims attributed to the final marketed nutraceutical products have often little or doubtful scientific foundation. This is due to the fact that a lot of the scientific evidence is derived from animal testing and in vitro assays, whereas human clinical trials are scarce and inconclusive. Some key issues such as bioavailability, metabolism, dose/response and toxicity of these food bioactive compounds or the nutraceuticals themselves have not been well established yet. Amongst the phytochemicals, several groups of polyphenols (anthocyanins, proanthocyanidins, flavanones, isoflavones, resveratrol and ellagic acid) are currently used in the nutraceutical industry. In this report, we have reviewed the most recent scientific knowledge on the bioavailability and biological activity of these polyphenols ('fact'), as well as the health claims (which are not always supported by scientific studies) ascribed to the polyphenols-containing nutraceuticals ('fiction'). The in vitro antioxidant capacity, often used as a claim, can be irrelevant in terms of in vivo antioxidant effects. Bioavailability, metabolism, and tissue distribution of these polyphenols in humans are key factors that need to be clearly established in association to the biological effects of these polyphenols-containing nutraceuticals. The future trends of phytochemistry research regarding nutraceuticals are discussed.     

Nucleosome sliding: facts and fiction

Nucleosome sliding is a frequent result of energy-dependent nucleosome remodelling in vitro. This review discusses the possible roles for nucleosome sliding in the assembly and maintenance of dynamic chromatin and for the regulation of diverse functions in eukaryotic nuclei.     

Quantifying biofilm structure: facts and fiction

There is no doubt among biofilm researchers that biofilm structure is important to many biofilm processes, such as the transport of nutrients to deeper layers of the biofilm. However, biofilm structure is an elusive term understood only qualitatively, and as such it cannot be directly correlated with any measurable parameters characterizing biofilm performance. To correlate biofilm structure with the parameters characterizing biofilm performance, such as the rate of nutrient transport within the space occupied by the biofilms, biofilm structure must first be quantified and expressed numerically on an appropriate scale. The task of extracting numerical parameters quantifying biofilm structure relies on using biofilm imaging and image analysis. Although defining parameters characterizing biofilm structure is relatively straightforward, and multiple parameters have been described in the computer science literature, interpreting the results of such analyses is not trivial. Existing computer software developed by several research groups, including ours, for the sole purpose of analyzing biofilm images helps quantify parameters from biofilm images but does nothing to help interpret the results of such analyses. Although computing structural parameters from biofilm images permits correlating biofilm structure with other biofilm processes, the meaning of the results is not obvious. The first step to understanding the quantification of biofilm structure, developing image analysis, methods to quantify information from biofilm images, has been made by several research groups. The next step is to explain the meaning of these analyses. This presentation explains the meaning of several parameters commonly used to characterize biofilm structure. It also reviews the authors' research and experience in quantifying biofilm structure and their attempts to quantitatively relate biofilm structure to fundamental biofilm processes.     

Antioxidants and vision health: facts and fiction

A number of nutritional supplements containing antioxidants are advertised for better vision health. Do they benefit the average consumer? The literature was examined for the effectiveness of antioxidants for human eye health, and for the intricacies in collection of such evidence. The following diseases were considered: cataract, glaucoma, age-related macular degeneration (AMD), retinopathy, retinitis pigmentosa, eye infections, and uveitis. The literature indicates that antioxidant supplements plus lutein have a reasonable probability of retarding AMD. For glaucoma, such supplements were ineffectual in some studies but useful in others. In some studies, antioxidant rich fruits and vegetables were also useful for protection against glaucoma. For diabetic retinopathy, antioxidant supplements may have a small benefit, if any, but only as an adjunct to glycemic control. In very high-risk premature retinopathy and retinitis pigmentosa, antioxidant supplements may be beneficial but those with excess Vitamin E should be avoided. For cataract, there is no evidence for an advantage of such nutritional supplements. However, lubricant drops containing N-acetylcarnosine may be helpful in initial stages of the disease. For eye infections and other causes of uveitis, antioxidants have not been found useful. We recommend that a diet high in antioxidant rich foods should be developed as a habit from an early age. However, when initial signs of vision health deterioration are observed, the appropriate nutritional supplement products may be recommended but only to augment the primary medical treatments.     

利用电化学活跃微生物协助电解发酵产氢

摘要：电解协助发酵产氢是在外源电解协助下,利用电化学活跃微生物在石墨阳极上生长达到彻底氧化因发酵产氢残存的有机酸,产生CO2、电子与质子,电子进入石墨阳极经导线传到铂阴极,而质子则穿过阳离子膜进入阴极池,在无氧环境下,通过外加电压和铂的催化下,电子与质子结合为氢。此过程电子回收率可达90%以上,产氢效率可达8-9mol H2/mol Glucose。这一战略从根本上克服发酵产氢的发酵障碍和代谢产物的反馈抑制,极大地提高了氢转化率,极有可能率先应用于能源作物原料的氢能转化、以及有机污水和有机废弃物处理。     

Polyhydroxybutyrate particles in Synechocystis sp. PCC 6803: facts and fiction

Transmission electron microscopy has been used to identify poly-3-hydroxybutyrate (PHB) granules in cyanobacteria for over 40 years. Spherical inclusions inside the cell that are electron-transparent and/or slightly electron-dense and that are found in transmission electron micrographs of cyanobacteria are generally assumed to be PHB granules. The aim of this study was to test this assumption in different strains of the cyanobacterium Synechocystis sp. PCC 6803. Inclusions that resemble PHB granules were present in strains lacking a pair of genes essential for PHB synthesis and in wild-type cells under conditions that no PHB granules could be detected by fluorescence staining of PHB. Indeed, in these cells PHB could not be demonstrated chemically by GC/MS either. Based on the results gathered, it is concluded that not all the slightly electron-dense spherical inclusions are PHB granules in Synechocystis sp. PCC 6803. This result is potentially applicable to other cyanobacteria. Alternate assignments for these inclusions are discussed.     

Cancer metabolism: facts, fantasy, and fiction

The concept of a glycolytic cancer cell was introduced by Warburg over 70 years ago. This perception has since become the rationale that drives a considerable proportion of basic research on cancer, and it influences the current strategies for the diagnosis, monitoring, and treatment of cancer. Here we review the data from the last 40 years on this issue. We conclude that there is no evidence that cancer cells are inherently glycolytic, but that some tumours might indeed be glycolytic in vivo as a result of their hypoxic environment.     

Insect diversity: facts,fiction and speculation*

Biologists are still trying to grasp the global dimensions of the phylum Arthropoda and its major class the Insecta, in spite of the fact that over a million species of arthropods have been described. The canopy of rain forest trees is believed by many to hold the key to the immense diversity of insects. In recent years the use of knock-down insecticides to sample insects from rain forest canopy has revealed information on the canopy's arthropod inhabitants and community structure. The sampling techniques involved are outlined and data reviewed on taxonomic and guild structure, species abundance, body size and biomass of insects, and the faunal similarity of trees. Calculations by Erwin (1982), based on knock-down insecticide studies of the beetle fauna of one species of Central American tree, suggest there may be 30 million species of tropical forest arthropods. Reanalysis of these calculations, using additional data, produces a range of possible estimates from about 10 to 80 million. The unknown range of plant host-specificities of tropical insects is the main weakness of this method of calculation. Assessment of the faunal importance of the canopy in relation to that of other rain forest biotopes requires comparative quantitative studies. The preliminary results of one such simple study suggest that over 42 million arthropods may be found in a hectare of Seram rain forest (at the time of study), and that 70% occur in the soil and leaf litter and 14% in the canopy. They also suggest that Collembola and Acarina are the dominant groups in this hectare, and that there are as many ants as all the other insects (excluding Collembola).     

Medicinal plants for helminth parasite control: facts and fiction

The use of medicinal plants for the prevention and treatment of gastro-intestinal parasitism has its origin in ethnoveterinary medicine. Although until recently the majority of the evidence on the antiparasitic activity of medicinal plants was anecdotal and lacked scientific validity, there is currently an increasing number of controlled experimental studies that aim to verify and quantify such plant activity. There are indeed a large number of plants whose anthelmintic activity has been demonstrated under controlled experimentation, either through feeding the whole plant or administering plant extracts to parasitised hosts. However, contrary to traditional expectation, there are also a great number of plants with purported antiparasitic properties, which have not been reproduced under experimental conditions. In this paper, we discuss the source of such inconsistencies between ethnoveterinary wisdom and scientific experimentation. We focus on the strengths and weaknesses of the existing methodologies used in the controlled studies to determine the activity of antiparasitic plants. We discuss issues like the seasonal and environmental variability of the plant composition, and how this can affect their antiparasitic properties and highlight the importance of identifying the mechanisms of action of such plants and the target parasite species. In addition to their antiparasitic properties, medicinal plants may also have anti-nutritional properties, which can affect animal performance and behaviour. For this reason, we emphasise the need for considering additional dimensions when evaluating medicinal plants. We also question whether using similar criteria as those used for the evaluation of anthelmintics is the way forward. We propose that a holistic approach is required to evaluate the potential of medicinal plants in parasite control and maximise their benefits on parasitised hosts.     

Sulfur metabolism in Escherichia coli and related bacteria: facts and fiction

Living organisms are composed of macromolecules made of hydrogen, carbon, nitrogen, oxygen, phosphorus and sulfur. Much work has been devoted to the metabolism of the first five elements, but much remains to be understood about sulfur metabolism. We review here the situation in Escherichia coli and related bacteria, where more than one hundred genes involved in sulfur metabolism have already been discovered in this organism. Examination of the genome suggests that many more will be found, especially genes involved in regulation, scavenging of sulfur containing molecules and synthesis of coenzymes or prosthetic groups. Furthermore, the involvement of methionine as the universal start of proteins as well as that of its derivative S-adenosylmethionine in a vast variety of cell processes argue in favour of a major importance of sulfur metabolism in all organisms.     

Anabolic steroid usage in athletics: facts, fiction, and public relations

Anecdotal evidence suggests the widespread usage of anabolic steroids among athletes (20-90%), particularly at the professional and elite amateur levels. In contrast, scientific studies indicate that usage is rare and no higher than 6%. Conclusions from scientific studies suggest that anabolic steroid usage declines progressively from high school to college and beyond; however, anecdotal evidence claims the opposite trend. In this clash between "hard" scientific data vs. "soft" anecdotal information, it is natural that professionals would gravitate toward scientifically based conclusions. However, in the case of anabolic steroids (a stigmatized and illegal substance), should word-of-mouth testimony from individuals closest to the issues--those who have participated in and coached sports, those who have served as drug-testing overseers, and journalists who relentlessly track leads and verify sources--be set aside as irrelevant? Not if a complete picture is to emerge. In this review, hard scientific evidence is placed on the table side-by-side with soft anecdotal evidence, without weighting or bias. The purpose is to allow the opportunity for each to illuminate the other and, in so doing, potentially bring us a step closer to determining the true extent of anabolic steroid usage in athletics.     

土壤微生物膜生理生态功能研究进展

土壤微生物膜是由土壤细菌及其分泌物积聚形成的生物群落,是生物土壤结皮的初始形态和重要组成部分。作为土壤细菌生命过程中最典型的生存形式,土壤微生物膜不仅能保护基质内细胞生存,还可黏附于土壤颗粒和植物根系表面,发挥重要的生态功能。本文在解析土壤微生物膜结构与组成的基础上,从土壤质量与植物健康两个方面总结分析了土壤微生物膜生理生态功能:土壤微生物膜代谢活性高于游离细胞,可高效分泌胞外聚合物并且具有更强的有机物质转化速率,在提升土壤肥力,吸附、固持和降解土壤污染物和促进土壤团聚体形成方面具有重要意义;土壤微生物膜可通过多种微生物间协同作用、促进分泌多种促生物质与胞外聚合物以发挥固持作用等改善植物养分利用状况,增强植物抗逆性。揭示土壤微生物膜生态功能的微观机制、筛选和应用功能性土壤微生物膜是未来重要的发展方向。     

Continuous nondestructive monitoring of microbial biofilms: A review of analytical techniques

A fundamental requirement for the understanding and control of biofilms is the continuous nondestructive monitoring of biofilm processes. This paper reviews research analytical techniques that monitor biofilm processes in a continuous nondestructive manner and that could also be modified for industrial applications. To be considered continuous and nondestructive for the purpose of this review a technique must: (a) function in an aqueous system; (b) not require sample removal; (c) minimize signal from organisms or contaminants in the bulk phase; and (d) provide real-time data. Various microscopic, spectrochemical, electrochemical, and piezoelectrical analysis methods fulfill these criteria. These techniques monitor the formation of biofilms, the physiology of the microorganisms within biofilms, and/or the interaction of the biofilms with their environment. It is hoped that this review will stimulate development and use of biofilm monitoring techniques in industrial and environmental settings.     

沉水植物化感作用控藻能力评述

沉水植物所释放的化学物质对藻类的抑制作用是浅水湖泊维持清水状态的机制之一.本文从具有化感活性的沉水植物在湖泊中出现的频度、盖度、化感物质的种类、抑藻效应等方面对化感控藻进行了评述.已有研究结果表明：穗花狐尾藻、金鱼藻、伊乐藻等是具有很高活性的沉水植物,尤其是在其生物量达到一定程度,且湖泊中的优势藻为较敏感的种类时,沉水植物分泌的化感物质对浮游藻类的抑制作用更强;沉水植物释放的多酚类等化感物质具有控藻能力;化感物质对于不同种类藻的抑制作用具有选择性,蓝藻和硅藻比绿藻更为敏感,附生藻类通常比浮游藻类具有更高的耐受性;环境因素如光照、营养限制、温度等会显著影响沉水植物化感作用效果.沉水植物的化感控藻研究尚处于初始阶段,关于环境因素对化感作用的影响、化感物质的分离鉴定、选择性抑藻机理以及化感物质代谢途径等方面还有待深入、全面的研究.     

Resistance of bacterial biofilms to disinfectants: a review

A biofilm can be defined as a community of microorganisms adhering to a surface and surrounded by a complex matrix of extrapolymeric substances. It is now generally accepted that the biofilm growth mode induces microbial resistance to disinfection that can lead to substantial economic and health concerns. Although the precise origin of such resistance remains unclear, different studies have shown that it is a multifactorial process involving the spatial organization of the biofilm. This review will discuss the mechanisms identified as playing a role in biofilm resistance to disinfectants, as well as novel anti-biofilm strategies that have recently been explored.     

Resistance of bacterial biofilms to disinfectants: a review

A biofilm can be defined as a community of microorganisms adhering to a surface and surrounded by a complex matrix of extrapolymeric substances. It is now generally accepted that the biofilm growth mode induces microbial resistance to disinfection that can lead to substantial economic and health concerns. Although the precise origin of such resistance remains unclear, different studies have shown that it is a multifactorial process involving the spatial organization of the biofilm. This review will discuss the mechanisms identified as playing a role in biofilm resistance to disinfectants, as well as novel anti-biofilm strategies that have recently been explored.