Effect of microalgae on viability of microorganisms in the natural and artificial environment

The data of literature on complicated relationships between microorganisms and microalgae in algobacterial associations with microalgae often playing the leading role are analyzed. Under these conditions inhibiting and stimulating substances synthesized by microalgae, as well as their nutritional value, may have an essential impact on the state of the bacterial population. Apparently that microalgae may become the main substrate in the development of new culture media (ecologically pure culture media, media for the reversion of the noncultured forms of bacteria into the vegetative state, media for the prolonged preservation of microbes in the noncultured form).     

Anaerobic methyl tert-butyl ether-degrading microorganisms identified in wastewater treatment plant samples by stable isotope probing

Anaerobic methyl tert-butyl ether (MTBE) degradation potential was investigated in samples from a range of sources. From these 22 experimental variations, only one source (from wastewater treatment plant samples) exhibited MTBE degradation. These microcosms were methanogenic and were subjected to DNA-based stable isotope probing (SIP) targeted to both bacteria and archaea to identify the putative MTBE degraders. For this purpose, DNA was extracted at two time points, subjected to ultracentrifugation, fractioning, and terminal restriction fragment length polymorphism (TRFLP). In addition, bacterial and archaeal 16S rRNA gene clone libraries were constructed. The SIP experiments indicated bacteria in the phyla Firmicutes (family Ruminococcaceae) and Alphaproteobacteria (genus Sphingopyxis) were the dominant MTBE degraders. Previous studies have suggested a role for Firmicutes in anaerobic MTBE degradation; however, the putative MTBE-degrading microorganism in the current study is a novel MTBE-degrading phylotype within this phylum. Two archaeal phylotypes (genera Methanosarcina and Methanocorpusculum) were also enriched in the heavy fractions, and these organisms may be responsible for minor amounts of MTBE degradation or for the uptake of metabolites released from the primary MTBE degraders. Currently, limited information exists on the microorganisms able to degrade MTBE under anaerobic conditions. This work represents the first application of DNA-based SIP to identify anaerobic MTBE-degrading microorganisms in laboratory microcosms and therefore provides a valuable set of data to definitively link identity with anaerobic MTBE degradation.     

Antagonistic activity of Lactobacillus bacteria strains against anaerobic gastrointestinal tract pathogens (Helicobacter pylori, Campylobacter coli, Campylobacter jejuni, Clostridium difficile)]

Antagonistic activity of Lactobacillus strains has been known for some time. This property is connected with production of many active substances by lactobacilli e.g., organic acids and bacteriocin-like substances which interfere with other indigenous microorganisms inhabiting the same ecological niche, including also anaerobic gastrointestinal tract pathogens. Growing interest of clinical medicine in finding new approaches to treatment and prevention of common inflammatory infections of the digestive tract resulted in studies on a possible usage of lactic acid bacteria. Last years, several in vitro and in vivo experiments on antagonism of different Lactobacillus strains against Helicobacter pylori and Clostridium difficile were performed. These observations had been done on already established, well known probiotic Lactobacillus strains. We tested antibacterial activities of Lactobacillus strains isolated from human digestive tract. As indicator bacteria, four species known as anaerobic bacterial etiologic agents of gastroenteric infections: Helicobacter pylori, Campylobacter jejuni, C. coli and Clostridium difficile were used. Some of them were obtained from international collections, others were clinical isolates from specimens taken from patients with different defined gastrointestinal infections. We used a slab method of testing inhibitory activity described in details previously. Following conclusions were drawn from our study: All tested human Lactobacillus strains were able to inhibit the growth of all strains of anaerobic human gastrointestinal pathogens used in this study. Inhibitory activities of tested Lactobacillus strains against Helicobacter pylori, Campylobacter spp., and Clostridium difficile as measured by comparing mean diameters of the inhibition zones were similar. Differences in susceptibility of individual indicator strains of Campylobacter spp. and Clostridium difficile to inhibitory activity of Lactobacillus strains were small. A similar mechanism of inhibition of anaerobic bacteria by lactobacilli is postulated.     

Are the Soft,Liquid-Like Structures Detected around Bacteria by Ambient Dynamic Atomic Force Microscopy Capsules?

High-resolution imaging of bacterial capsules by microscopy is of paramount importance in microbiology due to their role in pathogenesis. This is, however, quite a challenging task due to their delicate nature. In this context, recent reports have claimed successful exploitation of the capacity of atomic force microscopy (AFM) for imaging of extremely deformable (even liquid) surfaces under ambient conditions to detect bacterial capsules in the form of tiny amounts of liquid-like substances around bacteria. In order to further explore this supposed capacity of AFM, in this work, three staphylococcal strains have been scrutinized for the presence of capsules using such an AFM-based approach with a phosphate buffer and water as the suspending liquids. Similar results were obtained with the three strains. AFM showed the presence of liquid-like substances identical to those attributed to bacterial capsules in the previous literature. Extensive imaging and chemical analysis point out the central role of the suspending liquid (buffer) in the formation of these substances. The phenomenon has been reproduced even by using nonliving particles, a finding that refutes the biological origin of the liquid-like substances visualized around the cells. Deliquescence of major components of biological buffers, such as K(2)HPO(4), CaCl(2), or HEPES, is proposed as the fundamental mechanism of the formation of these ultrasmall liquid-like structures. Such an origin could explain the high similarity of our results obtained with three very different strains and also the high similarity of these results to others reported in the literature based on other bacteria and suspending liquids. Finally, possible biological/biomedical implications of the presence of these ultrasmall amounts of liquids wrapping microorganisms are discussed.     

Microbial transformation of chlorinated benzoates

Chlorinated benzoates enter the environment through their use as herbicides or as metabolites of other halogenated compounds. Ample evidence is available indicating biodegradation of chlorinated benzoates to CO₂ and chloride in the environment under aerobic as well as anaerobic conditions. Under aerobic conditions, lower chlorinated benzoates can serve as sole electron and carbon sources supporting growth of a large list of taxonomically diverse bacterial strains. These bacteria utilize a variety of pathways ranging from those involving an initial degradative attack by dioxygenases to those initiated by hydrolytic dehalogenases. In addition to monochlorinated benzoates, several bacterial strains have been isolated that can grow on dichloro-, and trichloro- isomers of chlorobenzoates. Some aerobic bacteria are capable of cometabolizing chlorinated benzoates with simple primary substrates such as benzoate. Under anaerobic conditions, chlorinated benzoates are subject to reductive dechlorination when suitable electron-donating substrates are available. Several halorespiring bacteria are known which can use chlorobenzoates as electron acceptors to support growth. For example, Desulfomonile tiedjei catalyzes the reductive dechlorination of 3-chlorobenzoate to benzoate. The benzoate skeleton is mineralized by other microorganisms in the anaerobic environment. Various dichloro- and trichlorobenzoates are also known to be dechlorinated in anaerobic sediments.     

Exocellular electron transfer in anaerobic microbial communities

Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory syntrophic consortia of proton-reducing acetogenic bacteria and hydrogen-consuming methanogenic archaea. Anaerobic microorganisms that use insoluble electron acceptors for growth, such as iron- and manganese-oxide as well as inert graphite electrodes in microbial fuel cells, also transfer electrons exocellularly. Soluble compounds, like humic substances, quinones, phenazines and riboflavin, can function as exocellular electron mediators enhancing this type of anaerobic respiration. However, direct electron transfer by cell-cell contact is important as well. This review addresses the mechanisms of exocellular electron transfer in anaerobic microbial communities. There are fundamental differences but also similarities between electron transfer to another microorganism or to an insoluble electron acceptor. The physical separation of the electron donor and electron acceptor metabolism allows energy conservation in compounds as methane and hydrogen or as electricity. Furthermore, this separation is essential in the donation or acceptance of electrons in some environmental technological processes, e.g. soil remediation, wastewater purification and corrosion.     

Bacterial anaerobic respiration and electron transfer relevant to the biotransformation of pollutants

Bacterial anaerobic respiration is one of the most ancient and essential metabolism processes, possessing the characteristics of both flexibility and high diversity, and a very close relationship with the physiological function in the ecological environment. Under anaerobic conditions, bacteria and anthropogenic substances can form coupling process facilitating terminal electron transfer. Several forms of bacterial anaerobic respiration and electron transfer related to the biotransformation of pollutants, including respiration with humics, sulfonates, halogenated chemicals, azo compounds, TNTs, metallic and non-metallic elements, are reviewed in this paper. These respirations and electron transfers on diverse electron acceptors in the environment have important biotechnological implications because these biochemical reactions have their roles on the transformation/degradation of toxic substances and the cycling of organic carbon as well as many inorganic elements. Furthermore, remediation of sites contaminated with toxic pollutants based on bacterial anaerobic respirations is being recognized widely.     

Effect of the medium redox potential on the growth and metabolism of anaerobic bacteria

Based on the available literature data on a decrease in the redox potential of medium to low negative values and a decrease in pH during the growth of sugar-fermenting anaerobic bacteria, it was concluded that these processes cannot be described by the theory of redox potential. A theory was developed according to which the regulation of bacterial metabolism is accomplished through changes in the redox potential. The theory considers the redox potential as a factor determining the growth of anaerobic bacteria, which is regulated by oxidizers and reducers. The assumption is put forward that, under anaerobic conditions, bacteria are sensitive to changes in the redox potential and have a redox taxis. The effect of the redox potential on the transport of protons and other substances through membranes and the activity of membrane-bound enzymes, including the proton F1-F0-ATPase, whose mechanisms of action involve changes in the proton conductance of the membrane, the generation of proton-driving force, and dithiol-disulfide transitions in proteins was studied.     

THE USE OF MICROBIAL MEMBRANES TO ACHIEVE ANAEROBIOSIS

Several years ago, it was observed that sterile microbial membrane preparations stimulated recovery of certain radiation-injured bacteria. Later it was noted that these same preparations reduce dissolved oxygen to water in a variety of environments, including bacteriological media. This reduction of oxygen is an enzymatic process and is influenced by parameters such as temperature, pH, and the availability of specific oxidizable substrates. Oxygenreducing membrane preparations can be made from several different bacterial species. When added to liquid or solid bacteriological media, membrane preparations rapidly produce and maintain anaerobic conditions favorable for the growth of a wide variety of oxygen-sensitive microorganisms. When used with a specifically designed disposable dish, membrane preparations allow the development of colonies of many anaerobic microorganisms on the surface of agar without the use of anaerobic hoods or other devices. In addition to providing conditions suitable for the growth of anaerobes, membrane preparations stimulate recovery of heat and cold injured bacteria of several different genera including facultative organisms. These results are reminiscent of the early observations regarding the recovery of radiation-injured bacteria. In addition to their usefulness in microbiology, oxygen-reducing membrane preparations have the potential for protecting a wide variety of oxygen-sensitive organic compounds.     

羧酶体的组成、结构、功能和检测及其在脱氮细菌中的意义

羧酶体(Carboxysome)是一种具有CO2浓缩功能的"类细胞器",它存在于自养型脱氮细菌中,可增强细菌的自养生长能力。硝化细菌、厌氧氨氧化细菌和部分反硝化细菌都是重要的自养型脱氮细菌,探明其羧酶体的组成、结构和功能,将有助于揭示自养型脱氮菌的生长规律,进而强化生物脱氮过程。基于文献阅读和相关研究,本文对自养型细菌中羧酶体在组成、结构、功能和检测等方面的研究进展进行综述,以期为自养生物脱氮过程的深入理解和优化改进提供参考。     

Bacterial Activity and Preservation of Sedimentary Organic Matter: The Role of Exopolymeric Substances

Although exopolymeric substances (EPS) are associated with the microorganisms contributing to the production/degradation of sedimentary organic matter, their role in theses processes have so far never been mentioned. Using high-resolution microscopical tools (scanning and transmission electron microscopy, atomic force microscopy), fossil organic matter in the Miocene Monterey Formation (California) and Kimmeridgian laminites (France) has been compared with its present-day analogs, i.e., respectively sulphuroxidizing bacteria and cyanobacterial biofilms. This comparison shows that, particularly in the case of Kimmeridgian cyanobacterial mats deposited in a shallow back-reef environment, organic matter preservation is conditioned by exopolymeric substances secreted by bacteria. A model is proposed for the evolution through time of exopolymeric substances in relation to the mechanical constrains they have been exposed to, during lithification and diagenesis. This model is based on the microscopical observation of sulphuroxidizing bacteria and could explain the morphology of fossil organic matter usually referred to as “amorphous” in standard light microscopy. The highly hydrated nature of exopolymeric substances helps to protect organic matter from degradation and remineralization. These substances can be observed only in microscopy and are undetectable through organic geochemical methods, hence the need to combine these two methods in organic matter studies. Consequently, exopolymeric substances must be considered as an important contributing agent to organic matter preservation. These results confirm the complexity of the bacterial role in geoenvironments and add a new parameter in the productivity-vs-preservation debate.     

Aerotolerance of strictly anaerobic microorganisms and factors of defense against oxidative stress: A review

Effects of aerobic conditions on strictly anaerobic microorganisms belonging to diverse taxa (clostridia, acetogenic bacteria, lactic acid bacteria, bacteroids, sulfate-reducing bacteria, and methanogenic archaea) and differing considerably in their oxygen resistance have been reviewed, with emphasis on the role of aerotolerance in the ecology of anaerobes. Consideration is given to components of nutritive media for anaerobe culturing, which decrease the toxic effects of oxygen and there by contribute significantly to maintenance and storage of industrial cultures of strictly anaerobic microorganisms. Physiological and biochemical factors are described, accounting for the relative resistance of many strict anaerobes to oxygen and products of incomplete reduction thereof. Specific attention is given to regulation of enzymes of antioxidative defense, operating in the cells of strict anaerobes under the conditions of oxidative stress caused by oxygen, superoxide anion, or hydrogen peroxide.     

Responses of the anaerobic bacterial community to addition of organic C in chromium(VI)- and iron(III)-amended microcosms

Chromium (VI) is toxic to microorganisms and can inhibit the biodegradation of organic pollutants in contaminated soils. We used microcosms amended with either glucose or protein (to drive bacterial community change) and Fe(III) (to stimulate iron-reducing bacteria) to study the effect of various concentrations of Cr(VI) on anaerobic bacterial communities. Microcosms were destructively sampled based on microbial activity (measured as evolution of CO2) and analyzed for the following: (i) dominant bacterial community by PCR-denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA gene; (ii) culturable Cr-resistant bacteria; and (iii) enrichment of iron-reducing bacteria of the Geobacteraceae family by real-time PCR. The addition of organic C stimulated the activities of anaerobic communities. Cr(VI) amendment resulted in lower rates of CO2 production in glucose microcosms and a slow mineralization phase in protein-amended microcosms. Glucose and protein amendments selected for different bacterial communities. This selection was modified by the addition of Cr(VI), since some DGGE bands were intensified and new bands appeared in Cr(VI)-amended microcosms. A second dose of Cr(VI), added after the onset of activity, had a strong inhibitory effect when higher levels of Cr were added, indicating that the developing Cr-resistant communities had a relatively low tolerance threshold. Most of the isolated Cr-resistant bacteria were closely related to previously studied Cr-resistant anaerobes, such as Pantoea, Pseudomonas, and Enterobacter species. Geobacteraceae were not enriched during the incubation. The studied Cr(VI)-contaminated soil contained a viable anaerobic bacterial community; however, Cr(VI) altered its composition, which could affect the soil biodegradation potential.     

Aerotolerance of strictly anaerobic microorganisms and factors of defense against oxidative stress: a review

Effects of aerobic conditions on strictly anaerobic microorganisms belonging to diverse taxa (clostridia, acetogenic bacteria, lactic acid bacteria, bacteroids, sulfate-reducing bacteria, and methanogenic archaea) and differing considerably in their oxygen resistance have been reviewed, with emphasis on the role of aerotolerance in the ecology of anaerobes. Consideration is given to components of nutritive media for anaerobe culturing, which decrease the toxic effects of oxygen and there by contribute significantly to maintenance and storage of industrial cultures of strictly anaerobic microorganisms. Physiological and biochemical factors are described, accounting for the relative resistance of many strict anaerobes to oxygen and products of incomplete reduction thereof. Specific attention is given to regulation of enzymes of antioxidative defense, operating in the cells of strict anaerobes under the conditions of oxidative stress caused by oxygen, superoxide anion, or hydrogen peroxide.     

厌氧甲烷氧化微生物物质代谢与能量代谢研究进展

甲烷既是一种温室气体,也是一种潜在的能源物质,其源与汇的平衡对地球化学循环及工程应用均有重要意义。厌氧甲烷氧化(anaerobic oxidation of methane,AOM)过程是深海、湿地和农田等自然生境中重要的甲烷汇,在缓解温室气体排放方面发挥了巨大作用。AOM微生物的中枢代谢机制及其能量转化途径则是介导厌氧甲烷氧化耦合其他物质还原的关键所在。因此,本文从电子受体多样性的视角,主要分析了硫酸盐型,硝酸盐/亚硝酸盐型,金属还原型厌氧甲烷氧化微生物的生理生化过程及环境分布,并对近些年发现的新型厌氧甲烷氧化进行了梳理;重点总结了厌氧甲烷氧化微生物细胞内电子传递路径以及胞外电子传递方式;根据厌氧甲烷氧化微生物环境分布及反应特征,就其生态学意义及在污染治理与能源回收方面的潜在应用价值进行了展望。本综述以期深化对厌氧甲烷氧化过程的微生物学认知,并为其潜在的工程应用方向提供新的思路。     

河流沉积物氮循环主要微生物的生态特征

微生物驱动的氮循环过程是全球生物地球化学循环的重要组成部分,由于人类活动的影响,氮循环负荷加剧,氮素的生态平衡和微生物的功能特征也相应地受到干扰。河流生态系统是陆地与海洋联系的纽带,因人类活动过量活性氮的输入导致水体富营养化,明显影响着河流的生态功能以及河口沿岸海洋生态系统的平衡。富含微生物的沉积物对氮素的转化和去除起着至关重要的作用。本文主要介绍河流沉积物氮循环主要功能微生物,包括氨氧化细菌、氨氧化古菌、亚硝酸盐氧化菌、反硝化细菌和厌氧氨氧化细菌的群落特征和生态功能,总结氮相关营养盐、溶氧和季节变化等环境因子,以及河道控制管理措施和污水处理厂扰动等条件下氮循环过程主要功能类群的生态特征和响应关系。指出还需深入全面地研究河流沉积物生态系统氮循环过程的驱动机制和微生物的贡献效率,加强城市河流沉积物微生物功能作用的研究及河道生物修复技术的开发。     

Identification of crude-oil components and microorganisms that cause souring under anaerobic conditions

Oil souring has important implications with respect to energy resources. Understanding the physiology of the microorganisms that play a role and the biological mechanisms are both important for the maintenance of infrastructure and mitigation of corrosion processes. The objective of this study was to identify crude-oil components and microorganisms in oil-field water that contribute to crude-oil souring. To identify the crude-oil components and microorganisms that are responsible for anaerobic souring in oil reservoirs, biological conversion of crude-oil components under anaerobic conditions was investigated. Microorganisms in oil field water in Akita, Japan degraded alkanes and aromatics to volatile fatty acids (VFAs) under anaerobic conditions, and fermenting bacteria such as Fusibacter sp. were involved in VFA production. Aromatics such as toluene and ethylbenzene were degraded by sulfate-reducing bacteria (Desulfotignum sp.) via the fumarate-addition pathway and not only degradation of VFA but also degradation of aromatics by sulfate-reducing bacteria was the cause of souring. Naphthenic acid and 2,4-xylenol were not converted.     

Anaerobic free-living protozoa: growth efficiencies and the structure of anaeorobic communities

Abstract Most anoxic environments host populations of phagotrophic, eukaryote microorganisms. Many physiological properties of these anaerobic eukaryotes are still incompletely understood and their role in communities of anaerobic microorganisms has so far drawn little attention. Here we present theoretical considerations and experimental evidence to show that the net growth efficiency ([assimilated C]/[assimilated C + dissimilated C]) and gross growth efficiency (yield = [assimilated C]/[consumed C]) of anaerobic protozoa are about 20% and about 25%, respectively of those of their aerobic counterparts. This accords with the observation that the biomass ratios of predators and their prey is about one fourth of that foundin oxic environments. These fiedl data also suggest that bacterial numbers are controlled by protozoa grazing in at least some anoxic environments. Finally, the results explain whe phagotrophic food chains are short and eukaryote diversity is low in anaerobic habitats.     

Nitrogen removal and microbial communities in a three-stage system simulating a riparian environment

The riparian zone is an active interface for nitrogen removal, in which nitrogen transformations by microorganisms have not been valued. In this study, a three-stage system was constructed to simulate the riparian zone environments, and nitrogen removal as well as the microbial community was investigated in this ‘engineered riparian system’. The results demonstrated that stage 1 of this system accounted for 41–51 % of total nitrogen removal. Initial ammonium loading and redox potential significantly impacted the nitrogen removal performances. Stages 1 and 2 were both composed of an anoxic/oxic (A/O) zone and an anaerobic column. The A/O zone removed most of the ammonium load (6.8 g/m²/day), while the anaerobic column showed a significant nitrate removal rate (11.1 g/m²/day). Molecular biological analysis demonstrated that bacterial diversity was high in the A/O zones, where ammonium-oxidizing bacteria and nitrite-oxidizing bacteria accounted for 8.42 and 3.32 % of the bacterial population, respectively. The denitrifying bacteria Acidovorax sp. and the nitrifying bacteria Nitrosospira/Nitrosomonas were the predominant microorganisms in this engineered riparian system. This three-stage system was established to achieve favorable nitrogen removal and the microbial community in the system was also retained. This investigation should deepen our understanding of biological nitrogen removal in engineered riparian zones.     

The use of fatty acid methyl esters as biomarkers to determine aerobic, facultatively aerobic and anaerobic communities in wastewater treatment systems

The use of fatty acid methyl esters (FAME) as biomarkers to identify groups of microorganisms was studied. A database was constructed using previously published results that identify FAME biomarkers for aerobic, anaerobic and facultatively aerobic bacteria. FAME profiles obtained from pure cultures were utilized to confirm the predicted presence of biomarkers. Principal component analysis demonstrated that the FAME profiles can be used to determine the incidence of these bacterial groups. The presence of aerobic, anaerobic and facultatively aerobic bacteria in the communities, in four bioreactors being used to treat different wastewaters, was investigated by applying FAME biomarkers.