Bacterial adaptation to oxidative stress: implications for pathogenesis and interaction with phagocytic cells

During phagocytosis, phagocytic cells generate superoxide and other reactive oxygen species, which are involved in antibacterial activity. However, many bacteria possess antioxidant defenses that may explain their survival in inflammatory foci. These defenses include antioxidant enzymes such as superoxide dismutase and catalase, DNA repair systems, scavenging substrates, and competition with phagocytes for molecular oxygen. These defenses are probably coordinated, and different responses occur with different reactive oxygen species. Escherichia coli and Salmonella typhimurium mutants have allowed the demonstration of a variety of critical genes for enzymatic defense and DNA repair, as well as an oxyR regulon system. In more complex systems, the conditions found in inflammatory foci, such as decreasing glucose and the production of lactate, enhance bacterial catalase production and resistance to hydrogen peroxide. Resistance and adaptation to phagocyte-derived oxidant stress are critical aspects of bacterial pathogenesis.     

Oxidative Stress Resistance in Deinococcus radiodurans

Summary: Deinococcus radiodurans is a robust bacterium best known for its capacity to repair massive DNA damage efficiently and accurately. It is extremely resistant to many DNA-damaging agents, including ionizing radiation and UV radiation (100 to 295 nm), desiccation, and mitomycin C, which induce oxidative damage not only to DNA but also to all cellular macromolecules via the production of reactive oxygen species. The extreme resilience of D. radiodurans to oxidative stress is imparted synergistically by an efficient protection of proteins against oxidative stress and an efficient DNA repair mechanism, enhanced by functional redundancies in both systems. D. radiodurans assets for the prevention of and recovery from oxidative stress are extensively reviewed here. Radiation- and desiccation-resistant bacteria such as D. radiodurans have substantially lower protein oxidation levels than do sensitive bacteria but have similar yields of DNA double-strand breaks. These findings challenge the concept of DNA as the primary target of radiation toxicity while advancing protein damage, and the protection of proteins against oxidative damage, as a new paradigm of radiation toxicity and survival. The protection of DNA repair and other proteins against oxidative damage is imparted by enzymatic and nonenzymatic antioxidant defense systems dominated by divalent manganese complexes. Given that oxidative stress caused by the accumulation of reactive oxygen species is associated with aging and cancer, a comprehensive outlook on D. radiodurans strategies of combating oxidative stress may open new avenues for antiaging and anticancer treatments. The study of the antioxidation protection in D. radiodurans is therefore of considerable potential interest for medicine and public health.     

The 'strict' anaerobe Desulfovibrio gigas contains a membrane-bound oxygen-reducing respiratory chain

Sulfate-reducing bacteria are considered as strict anaerobic microorganisms, in spite of the fact that some strains have been shown to tolerate the transient presence of dioxygen. This report shows that membranes from Desulfovibrio gigas grown in fumarate/sulfate contain a respiratory chain fully competent to reduce dioxygen to water. In particular, a membrane-bound terminal oxygen reductase, of the cytochrome bd family, was isolated, characterized, and shown to completely reduce oxygen to water. This oxidase has two subunits with apparent molecular masses of 40 and 29 kDa. Using NADH or succinate as electron donors, the oxygen respiratory rates of D. gigas membranes are comparable to those of aerobic organisms (3.2 and 29 nmol O(2) min(-1) mg protein(-1), respectively). This 'strict anaerobic' bacterium contains all the necessary enzymatic complexes to live aerobically, showing that the relationships between oxygen and anaerobes are much more complex than originally thought.     

Defense strategy of old and modern spring wheat varieties during soil drying

Different defense mechanisms of three spring wheat ( Triticum aestivum L.) varieties were studied by withholding watering in well-watered pots to gradually increase water deficit of plants grown in containers. The strategies of plant adaptation were divided into three phases according to the severity of drought: first, a positive defense phase that started from commencement of non-hydraulic root-sourced signals (nHRS) and ended at onset of hydraulic root-sourced signals (HRS)—the plant responded to imminent drought by decreasing stomatal aperture to lessen water loss and no membrane injury occurred. The second defense phase occurred between the onset of HRS and temporary wilting (TW), characterized by enhancement of reactive oxygen species (ROS), marked enzyme activity and increased MDA content. Mild lipid membrane peroxidation came mainly from a dynamic imbalance between free radical production and enzymatic defense reaction, which indicated that injury by ROS had not been completely repaired by increasing enzymatic activity. The third defense phase was from TW to permanent wilting (PW), the synthesis of SOD and CAT during TW could not deal with the collapse of antioxidant enzymes, and SOD and CAT activities began to decrease, which caused the excessive ROS production and thus serious membrane lipid peroxidation. The defense strategies to drought are similar among the varieties, but modern varieties LC8275 and GY602 bred after 1975 had relatively higher defense levels at all three defense phases, which suggest that modern varieties are more resistant than old ones, and artificial selection would lead to a different direction in evolution from natural selection.     

NADPH oxidase-dependent oxidative stress in the failing heart: From pathogenic roles to therapeutic approach

Heart failure (HF) occurs when the adaptation mechanisms of the heart fail to compensate for stress factors, such as pressure overload, myocardial infarction, inflammation, diabetes, and cardiotoxic drugs, with subsequent ventricular hypertrophy, fibrosis, myocardial dysfunction, and chamber dilatation. Oxidative stress, defined as an imbalance between reactive oxygen species (ROS) generation and the capacity of antioxidant defense systems, has been authenticated as a pivotal player in the cardiopathogenesis of the various HF subtypes. The family of NADPH oxidases has been investigated as a key enzymatic source of ROS in the pathogenesis of HF. In this review, we discuss the importance of NADPH oxidase-dependent ROS generation in the various subtypes of HF and its implications. A better understanding of the pathogenic roles of NADPH oxidases in the failing heart is likely to provide novel therapeutic strategies for the prevention and treatment of HF.     

Iron metabolism at the host pathogen interface: lipocalin 2 and the pathogen-associated iroA gene cluster

The host innate immune defense protein lipocalin 2 binds bacterial enterobactin siderophores to limit bacterial iron acquisition. To counteract this host defense mechanism bacteria have acquired the iroA gene cluster, which encodes enzymatic machinery and transporters that revitalize enterobactin in the form of salmochelin. The iroB enzyme introduces glucosyl residues at the C5 site on 2,3-dihydroxybenzoylserine moieties of enterobactin and thereby prevents lipocalin 2 binding. Additional strategies to evade lipocalin 2 have evolved in other bacteria, such as Mycobacteria tuberculosis and Bacillus anthracis. Targeting these specialized bacterial evasion strategy may provide a mechanism to reinvigorate lipocalin 2 in defense against specific pathogens.     

Molecular genetics of superoxide dismutases

Molecular genetics of SOD has been recently developed primarily due to the new biotechnologies. Different types of isozymes have now been cloned and sequenced from several species ranging from bacteria to human and plants. Knowledge of the nucleotide sequences permitted refinement of structural models and provided information on subcellular locations. Cloned genes allowed the production of large amounts of SOD. They have been used for physiological and regulation studies, structural and enzymatic analyses, and are vital tools for the isolation of mutants. Isolation of mutants is generally essential to the understanding of the biological function of the gene in question. Indeed, SOD deficient mutants have now been isolated in bacteria and yeast. Their properties support, at numerous levels, a major role of SPD in cellular defense against oxygen toxicity. Few data are presently available on the molecular basis of mechanisms that regulate the expression of SOD.     

Roles of enzymatic and nonenzymatic antioxidants in plants during abiotic stress

Reactive oxygen species (ROS) are produced in plants as byproducts during many metabolic reactions, such as photosynthesis and respiration. Oxidative stress occurs when there is a serious imbalance between the production of ROS and antioxidant defense. Generation of ROS causes rapid cell damage by triggering a chain reaction. Cells have evolved an elaborate system of enzymatic and nonenzymatic antioxidants which help to scavenge these indigenously generated ROS. Various enzymes involved in ROS-scavenging have been manipulated, over expressed or downregulated to add to the present knowledge and understanding the role of the antioxidant systems. The present article reviews the manipulation of enzymatic and nonenzymatic antioxidants in plants to enhance the environmental stress tolerance and also throws light on ROS and redox signaling, calcium signaling, and ABA signaling.     

Microbial community of sulfate-reducing up-flow sludge bed in the SANI<Superscript>®</Superscript> process for saline sewage treatment

This study investigated the microbial community of the sulfate-reducing up-flow sludge bed (SRUSB) of a novel sulfate reduction, autotrophic denitrification, and nitrification integrated (SANI®) process for saline sewage treatment. The investigation involved a lab-scale SANI® system treating synthetic saline sewage and a pilot-scale SANI® plant treating 10 m³/day of screened saline sewage. Sulfate-reducing bacteria (SRB) were the dominant population, responsible for more than 80% of the chemical oxygen demand removal, and no methane-producing archaea were detected in both SRUSBs. Thermotogales-like bacteria were the dominant SRB in the pilot-scale SRUSB while Desulforhopalus-like bacteria were the major species in the lab-scale SRUSB.     

Sensitivity to oxidative damage of two Deinococcus radiodurans strains

The action of reactive oxygen species, i.e. hydrogen peroxide, cupric sulphate and ascorbic acid, added at different concentrations to culture media, has been studied in two strains of Deinococcus radiodurans (red-pigmented parental and colourless mutant strains) in relation to their defense antioxidant systems. While the pigmented bacteria were more resistant to elevated concentrations of the different oxidants, the colourless bacteria were more sensitive and their sensitivity was dose-dependent. Reactive oxygen species induced oxidative damage, particularly to the polyethylenic fatty acids, which were more abundant in the mutant strain. Similarly, a significant increase in lipid peroxide levels was observed, whatever the chemical added during the growth of the mutant bacteria. The parental strain required high concentrations of oxidants to shorten its survival. Vitamins A and E, carotenoids and enzymes, largely present in the parental strain, could be responsible for its higher resistance to the lethal effects of radicals generated within the cells.     

Strategies used by bacterial pathogens to suppress plant defenses

Plant immune systems effectively prevent infections caused by the majority of microbial pathogens that are encountered by plants. However, successful pathogens have evolved specialized strategies to suppress plant defense responses and induce disease susceptibility in otherwise resistant hosts. Recent advances reveal that phytopathogenic bacteria use type III effector proteins, toxins, and other factors to inhibit host defenses. Host processes that are targeted by bacteria include programmed cell death, cell wall-based defense, hormone signaling, the expression of defense genes, and other basal defenses. The discovery of plant defenses that are vulnerable to pathogen attack has provided new insights into mechanisms that are essential for both bacterial pathogenesis and plant disease resistance.     

Role of mitochondria in reactive oxygen species generation and removal; relevance to signaling and programmed cell death

Reactive oxygen species (ROS) are universal products of aerobic metabolism, which can be also produced in stress conditions. In eukaryotic cells, mitochondria are the main source of ROS. The main mitochondrial sites of ROS formation are electron carriers of respiratory chain. However, there are also other enzymatic sites capable of ROS generation in different mitochondrial compartments. Reactive oxygen species can cause serious damage to many biological macromolecules, such as proteins, lipids and nucleic acids, which oxidation leads to a lost of their biological properties and eventually to a cell death. Mitochondria, which are also exposed to harmful ROS action, have a defense system that decreases ROS production (first line of defense) or removes generated ROS (second line of defense). Mitochondrial antioxidant system involves proteins that decrease ROS formation, enzymes that directly react with ROS, and non-enzymatic antioxidants that also remove ROS and other oxygen derivatives. Mitochondrial ROS can also act as signal messengers and modify operation of many routes in different cell compartments. Mitochondrial ROS are also important in execution of programmed cell death.     

Oxidative burst in alfalfa-Sinorhizobium meliloti symbiotic interaction

Reactive oxygen species are produced as an early event in plant defense response against avirulent pathogens. We show here that alfalfa responds to infection with Sinorhizobium meliloti by production of superoxide and hydrogen peroxide. This similarity in the early response to infection by pathogenic and symbiotic bacteria addresses the question of which mechanism rhizobia use to counteract the plant defense response.     

Microbiological and Geochemical Characterization of Fluvially Deposited Sulfidic Mine Tailings

The fluvial deposition of mine tailings generated from historic mining operations near Butte, Montana, has resulted in substantial surface and shallow groundwater contamination along Silver Bow Creek. Biogeochemical processes in the sediment and underlying hyporheic zone were studied in an attempt to characterize interactions consequential to heavy-metal contamination of shallow groundwater. Sediment cores were extracted and fractionated based on sediment stratification. Subsamples of each fraction were assayed for culturable heterotrophic microbiota, specific microbial guilds involved in metal redox transformations, and both aqueous- and solid-phase geochemistry. Populations of cultivable Fe(III)-reducing bacteria were most prominent in the anoxic, circumneutral pH regions associated with a ferricrete layer or in an oxic zone high in organic carbon and soluble iron. Sulfur- and iron-oxidizing bacteria were distributed in discrete zones throughout the tailings and were often recovered from sections at and below the anoxic groundwater interface. Sulfate-reducing bacteria were also widely distributed in the cores and often occurred in zones overlapping iron and sulfur oxidizers. Sulfate-reducing bacteria were consistently recovered from oxic zones that contained high concentrations of metals in the oxidizable fraction. Altogether, these results suggest a highly varied and complex microbial ecology within a very heterogeneous geochemical environment. Such physical and biological heterogeneity has often been overlooked when remediation strategies for metal contaminated environments are formulated.     

Defense strategies used by two sympatric vineyard moth pests

Natural enemies including parasitoids are the major biological cause of mortality among phytophagous insects. In response to parasitism, these insects have evolved a set of defenses to protect themselves, including behavioral, morphological, physiological and immunological barriers. According to life history theory, resources are partitioned to various functions including defense, implying trade-offs among defense mechanisms. In this study we characterized the relative investment in behavioral, physical and immunological defense systems in two sympatric species of Tortricidae (Eupoecilia ambiguella, Lobesia botrana) which are important grapevine moth pests. We also estimated the parasitism by parasitoids in natural populations of both species, to infer the relative success of the investment strategies used by each moth. We demonstrated that larvae invest differently in defense systems according to the species. Relative to L. botrana, E. ambiguella larvae invested more into morphological defenses and less into behavioral defenses, and exhibited lower basal levels of immune defense but strongly responded to immune challenge. L. botrana larvae in a natural population were more heavily parasitized by various parasitoid species than E. ambiguella, suggesting that the efficacy of defense strategies against parasitoids is not equal among species. These results have implications for understanding of regulation in communities, and in the development of biological control strategies for these two grapevine pests.     

Growth, photosynthesis, active oxygen species and antioxidants responses of paddy field cyanobacterium Plectonema boryanum to endosulfan stress

The present paper deals with the insecticide endosulfan (5, 10 and 20 microg/ml)-induced changes in physiological and biochemical parameters related to photosynthesis and defense systems in paddy field cyanobacterium Plectonema boryanum grown under laboratory conditions. Growth and photosynthetic pigments, i.e., chlorophyll a, carotenoids and phycocyanin, were adversely affected by endosulfan treatment and the inhibition was found to be dose dependent. The toxic effect of endosulfan was more pronounced on phycocyanin; however, a considerable reduction in chlorophyll a and carotenoids was also noticed. 14C-fixation appeared to be more sensitive to insecticide than whole cell oxygen evolution. Spheroplasts treated with endosulfan exhibited a severe effect on PSII activity which was mainly due to blocking of the electron flow at the water oxidation side. In contrast to this, similar doses of endosulfan caused the least effect on PSI activity (DCPIP/ASC-->MV). Furthermore, endosulfan with increasing doses accelerated the formation of active oxygen species, i.e., O2- and H2O2, in cells progressively, whereby an enhanced peroxidation of lipid and leakage of cell membrane were noticed. As a consequence of active oxygen species (AOS) generation in endosulfan-treated cells, the activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was enhanced considerably. Besides the accelerated action of enzymatic defense systems, chemical antioxidant ascorbate showed a decreasing trend with the rising concentration of endosulfan (5, 10 and 20 microg/ml).     

Combining crystallography and molecular dynamics: The case of Schistosoma mansoni phospholipid glutathione peroxidase

Oxidative stress is a widespread challenge for living organisms, and especially so for parasitic ones, given the fact that their hosts can produce reactive oxygen species (ROS) as a mechanism of defense. Thus, long lived parasites, such as the flatworm Schistosomes, have evolved refined enzymatic systems capable of detoxifying ROS. Among these, glutathione peroxidases (Gpx) are a family of sulfur or selenium‐dependent isozymes sharing the ability to reduce peroxides using the reducing equivalents provided by glutathione or possibly small proteins such as thioredoxin. As for other frontline antioxidant enzymatic systems, Gpxs are localized in the tegument of the Schistosomes, the outermost defense layer. In this article, we present the first crystal structure at 1.0 and 1.7 Å resolution of two recombinant SmGpxs, carrying the active site mutations Sec43Cys and Sec43Ser, respectively. The structures confirm that this enzyme belongs to the monomeric class 4 (phospholipid hydroperoxide) Gpx. In the case of the Sec to Cys mutant, the catalytic Cys residue is oxidized to sulfonic acid. By combining static crystallography with molecular dynamics simulations, we obtained insight into the substrate binding sites and the conformational changes relevant to catalysis, proposing a role for the unusual reactivity of the catalytic residue. Proteins 2010. © 2009 Wiley‐Liss, Inc.     

植物病原细菌毒性调控网络的研究进展

植物病原细菌通过复杂和精细的全局性调控网络来协调多个层面的毒性决定因子。在不同的植物病原细菌中,这些全局性的毒性调控网络控制着细菌的侵染策略、存活以及在面临寄主植物防卫系统的互作环境中实现成功侵染的病程。本文详细分析了植物病原细菌4个重要属(假单胞菌属、果胶杆菌属、黄单胞菌属和雷尔氏菌属)的模式病原菌主要的毒性调控系统,包括群体感应系统、双组分调控系统、转录激活调控子以及转录后、翻译后的调控机制。在此基础上,重点评价了一些模式菌株全局性毒性调控机制的异同点,总结了一些最新的研究进展,并绘制了精细的网络调控图。这些分析表明,虽然一些相同的调控系统控制着病原菌的毒性,但是在不同种以及种下的亚种或者致病变种中这些调控机制功能各异,对于病原菌全毒性的贡献也存在着明显的差异。     

Dual Role of Plasma Membrane Electron Transport Systems in Defense

Bcause oxidative stress is one of the main sources of severe cellular damage, cells have different defense weapons against reactive oxygen species. Ubiquitous plasma membrane redox systems play a role in defense against oxidative stress damage. On the other hand, a tightly controlled and localized production of reactive oxygen species by a plasma membrane NADPH oxidase can be used as a potent microbicidal weapon. This dual, prooxidant and antioxidant role of plasma membrane electron transport systems in defense is studied and discussed.