Superoxide dismutases: ancient enzymes and new insights

Copper/Zinc Superoxide Dismutase from the Crocodile Icefish Chionodraco hamatus: Antioxidant Defense at Constant Sub-Zero Temperature

In the present study, we describe the purification and molecular characterization of Cu,Zn superoxide dismutase (SOD) from Chionodraco hamatus, an Antarctic teleost widely distributed in many areas of the Ross Sea that plays a pivotal role in the Antarctic food chain. The primary sequence was obtained using biochemical and molecular biology approaches and compared with Cu,Zn SODs from other organisms. Multiple sequence alignment using the amino acid sequence revealed that Cu,Zn SOD showed considerable sequence similarity with its orthologues from various vertebrate species, but also some specific substitutions directly linked to cold adaptation. Phylogenetic analyses presented the monophyletic status of Antartic Teleostei among the Perciformes, confirming the erratic differentiation of these proteins and concurring with the theory of the "unclock-like" behavior of Cu,Zn SOD evolution. Expression of C. hamatus Cu,Zn SOD at both the mRNA and protein levels were analyzed in various tissues, highlighting the regulation of gene expression related to environmental stress conditions and also animal physiology. The data presented are the first on the antioxidant enzymes of a fish belonging to the Channichthyidae family and represent an important starting point in understanding the antioxidant systems of these organisms that are subject to constant risk of oxidative stress.

The S. mutans mntE gene encodes a manganese efflux transporter

Streptococcus mutans is a colonizer of the human dentition, and under conditions of dysbiosis is the primary causative agent of dental caries. The pathogenic potential of S. mutans depends, in part, on its ability to regulate the transport of metal ions across the plasma membrane to maintain intracellular metal ion homeostasis. Research in our laboratory has focused on the Mn²⁺ -specific SloC lipoprotein importer and its regulator encoded by the S. mutans sloR gene. Herein, we used a bioinformatics approach to identify a gene on the S. mutans UA159 chromosome, SMU_1176, as a metal ion efflux transporter that contributes to S. mutans manganese ion homeostasis. Metal ion sensitivity assays performed with the wild-type S. mutans UA159 strain and an isogenic SMU_1176 insertion-deletion mutant, called GMS3000, revealed significantly heightened sensitivity of GMS3000 to MnSO₄ challenge. ⁵⁴ Mn uptake experiments support the accumulation of ⁵⁴ Mn in GMS3000 cell pellets when compared to ⁵⁴ Mn concentrations in UA159 or in a complemented strain of GMS3000, called GMS3001. Inductively coupled plasma mass spectrometry (ICP-MS) studies were performed in parallel to quantify intracellular manganese concentrations in these strains, the results of which corroborate the ⁵⁴ Mn uptake studies, and support the SMU_1176 gene product as a Mn²⁺ efflux protein. Expression profiling experiments revealed de-repression of SMU_1176 gene transcription in the SloR-deficient GMS584 strain of S. mutans, especially under high manganese conditions. In conclusion, the S. mutans SMU_1176 gene, which we renamed mntE, is a manganese efflux transporter that contributes to essential metal ion homeostasis as part of the SloR regulon.

Clethodim (herbicide) alters the growth and toxins content of Microcystis aeruginosa and Raphidiopsis raciborskii

Increased agricultural intensification goes with the widespread use of herbicides that adversely affect aquatic biodiversity. The effects of herbicides on toxin-producing cyanobacteria have been poorly studied. The present study aimed to investigate the toxicological and physiological effects of the herbicide clethodim on Raphidiopsis raciborskii (a.k.a. Cylindrospermopsis raciborskii) ITEPA1 and Microcystis aeruginosa BCCUSP232. On day four of the experiment, the exposure to 25 mg/L clethodim resulted in the highest cell density of R. raciborskii. Similarly, exposure to the 1, 5, 20, and 50 mg/L clethodim treatments resulted in the highest cell densities of M. aeruginosa on day 4 of the experiment. Medium effect concentrations (EC₅₀) after 96 h of exposure of both strains to clethodim were 192.98 mg/L and 168.73 mg/L for R. raciborskii and M. aeruginosa, respectively. The presence of clethodim significantly increased the total microcystin content of M. aeruginosa compared to the control cultures. At 400 mg/L, total saxitoxins content of R. raciborskii was 27% higher than that of the control cultures on day 4. In contrast, cultures exposed to 100 mg/L clethodim had the lowest saxitoxins levels per cell quota. There was an increase in the levels of intracellular hydrogen peroxide in both species during exposure to clethodim, which was followed by significant changes (p < 0.05) in the activity of antioxidant enzymes such as peroxidase and superoxide dismutase. These results revealed that the presence of low levels of clethodim in the aquatic environment might lead to the excessive proliferation of cyanobacteria and alteration of their cyanotoxins content.

Reactive oxygen species or reactive sulfur species: why we should consider the latter

The biological effects of oxidants, especially reactive oxygen species (ROS), include signaling functions (oxidative eustress), initiation of measures to reduce elevated ROS (oxidative stress), and a cascade of pathophysiological events that accompany excessive ROS (oxidative distress). Although these effects have long been studied in animal models with perturbed ROS, their actions under physiological conditions are less clear. I propose that some of the apparent uncertainty may be due to confusion of ROS with endogenously generated reactive sulfur species (RSS). ROS and RSS are chemically similar, but RSS are more reactive and versatile, and can be stored and reused. Both ROS and RSS signal via oxidation reactions with protein cysteine sulfur and they produce identical effector responses, but RSS appear to be more effective. RSS in the form of persulfidated cysteines (Cys-S-S) are produced endogenously and co-translationally introduced into proteins, and there is increasing evidence that many cellular proteins are persulfidated. A number of practical factors have contributed to confusion between ROS and RSS, and these are discussed herein. Furthermore, essentially all endogenous antioxidant enzymes appeared shortly after life began, some 3.8 billion years ago, when RSS metabolism dominated evolution. This was long before the rise in ROS, 600 million years ago, and I propose that these same enzymes, with only minor modifications, still effectively metabolize RSS in extant organisms. I am not suggesting that all ROS are RSS; however, I believe that the relative importance of ROS and RSS in biological systems needs further consideration.

The Role of Natural Antioxidants Against Reactive Oxygen Species Produced by Cadmium Toxicity: A Review

Cadmium (Cd) is a significant ecotoxic heavy metal that adversely affects all biological processes of humans, animals and plants. Exposure to acute and chronic Cd damages many organs in humans and animals (e.g. lung, liver, brain, kidney, and testes). In humans, the Cd concentration at birth is zero, but because the biological half-life is long (about 30 years in humans), the concentration increases with age. The industrial developments of the last century have significantly increased the use of this metal. Especially in developing countries, this consumption is higher. Oxidative stress is the imbalance between antioxidants and oxidants. Cd increases reactive oxygen species (ROS) production and causes oxidative stress. Excess cellular levels of ROS cause damage to proteins, nucleic acids, lipids, membranes and organelles. This damage has been associated with various diseases. These include cancer, hypertension, ischemia/perfusion, cardiovascular diseases, chronic obstructive pulmonary disease, diabetes, insulin resistance, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, asthma, skin diseases, chronic kidney disease, eye diseases, neurodegenerative diseases (amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, and Huntington disease). Natural antioxidants are popular drugs that are used by the majority of people and have few side effects. Natural antioxidants play an important role in reducing free radicals caused by Cd toxicity. Our goal in this review is to establish the relationship between Cd and oxidative stress and to discuss the role of natural antioxidants in reducing Cd toxicity.

Measurements of Hydrogen Peroxide and Oxidative DNA Damage in a Cell Model of Premature Aging

Reactive oxygen species (ROS) represent a number of highly reactive oxygen-derived by-products generated by the normal mitochondrial respiration and other cellular metabolic reactions. ROS can oxidize macromolecules including lipids, proteins, and nucleic acids. Under physiological condition, the cellular levels of ROS are controlled by several antioxidant enzymes. However, an imbalance between ROS production and detoxification results in oxidative stress, which leads to the accumulation of macromolecular damage and progressive decline in normal physiological functions.Oxidative deterioration of DNA can result in lesion that are mutagenic and contribute to aging and age-related diseases. Therefore, methods for the detection of ROS and oxidative deterioration of macromolecules such as DNA in cells provide important tool in aging research. Here, we described protocols for the detection of cytoplasmic and mitochondria pools of hydrogen peroxide, and the DNA modification 8-oxoguanine, a biomarker of oxidative damage, that are applicable to cell-based studies on aging and other related areas.

Whole-transcriptome sequencing (RNA-seq) analyses of the zebrafish liver cell line, ZFL, after acute exposure to Cu2+ ions

All cells require Cu as a cofactor, but Cu²⁺ induces toxicity and oxidative damage. A strict system is thus needed to maintain Cu homeostasis.

Mechanistic dichotomies in redox reactions of mononuclear metal–oxygen intermediates

This review article focuses on various mechanistic dichotomies in redox reactions of metal–oxygen intermediates with the emphasis on understanding and controlling their redox reactivity from experimental and theoretical points of view.

Oxidative stress induced by cadmium in lettuce (Lactuca sativa Linn.): Oxidative stress indicators and prediction of their genes

Environmental contamination with heavy metals is of concern as plants have the ability to absorb chemical toxicants facilitating the entry of toxic metals into the food chain. Lettuce (Lactuca sativa Linn.) was cultured in four nutrient solutions containing different concentrations of cadmium (0, 3, 6, and 9 mmol). The impact of heavy metal on the morphological features, antioxidant properties and antioxidant enzymes activity were investigated with primary focus on superoxide dismutase, ascorbate peroxidase, peroxidase and catalase enzymes. In silico methods were utilized in the study of the genes of these enzymes. Significant changes were observed in the morphological features of the plant with plants appearing stunted, more spherical and yellow in colour. A decrease in the dry mass of the plant was also detected. The Translocation factor (TF) for cadmium was significantly high in lettuce. Enhanced antioxidant enzymatic activity suggests that these enzymes are integrally involved in the defense mechanism of the plant to heavy metal stress. Also observed was an increase in total soluble protein, and total phenolic content. Total flavonoid content was not significantly affected. Fourteen genes encoding for ascorbate peroxidase and nineteen genes for superoxide dismutase were identified in lettuce. These enzymes varied from each other with regards to the number of exons and amino acids present, as well as their location within the cell. Plants exhibit various response mechanisms to combat heavy metal contamination.

Metagenomics and metatranscriptomics analyses reveal oxygen detoxification and mixotrophic potentials of an enriched anammox culture in a continuous stirred-tank reactor

The metabolisms of anaerobic ammonium oxidation (anammox) bacteria related to ammonia oxidation with nitrite reduction and autotrophic carbon fixation have been extensively observed. However, little is known about the specific metabolic pathways associated with oxygen detoxification and organic carbon utilization. To this end, we obtained high abundance of anammox species (∼50%) in a lab-scale continuous stirred-tank reactor (CSTR) at room temperature without strict anaerobic condition. The draft genome of the dominant anammox bacteria affiliated to Ca. Brocadia sp. was recovered. Its metabolic pathways and genes expression were reconstructed and examined through metagenomic and metatranscriptomic analyses. Interestingly, the results suggested that this anammox lineage likely performs oxygen detoxification with genes encoding superoxide dismutase (SOD) and cytochrome c peroxidase (Ccp). Moreover, the Ccp-activated hydrogen peroxide (intermediate of oxygen detoxification) reduction might be energetically beneficial for the observed acetate conversion related to cell synthesis of Ca. Brocadia sp. This study offers a comprehensive understanding on the diverse metabolic activities in anammox species affiliated to Ca. Brocadia sp., and expanded the applicability of anammox process.

Beyond N and P: The impact of Ni on crude oil biodegradation

N and P are the key limiting nutrients considered most important for the stimulation of crude oil degradation but other trace nutrients may also be important. Experimental soil microcosms were setup to investigate crude oil degradation in the context of Ni amendments. Amended Nickel as NiO, NiCl₂, or, a porphyrin complex either inhibited, had no effect, or, enhanced aerobic hydrocarbon degradation in an oil-contaminated soil. Biodegradation was significantly (95% confidence) enhanced (70%) with low levels of Ni-Porph (12 mg/kg) relative to an oil-only control; whereas, NiO (200 and 350 mg/kg) significantly inhibited (36 and 87%) biodegradation consistent with oxide particle induced reactive oxygen stress. Microbial community compositions were also significantly affected by Ni. In 16S rRNA sequence libraries, the enriched hydrocarbon degrading genus, Rhodococcus, was partially replaced by a Nocardia sp. in the presence of low levels of NiO (12 and 50 mg/kg). In contrast, the highest relative and absolute Rhodococcus abundances were coincident with the maximal rates of oil degradation observed in the Ni-Porph-amended soils. Growth dependent constitutive requirements for Ni-dependent urease or perhaps Ni-dependent superoxide dismutase enzymes (found in Rhodococcus genomes) provided a mechanistic explanation for stimulation. These results suggest biostimulation technologies, in addition to N and P, should also consider trace nutrients such as Ni tacitly considered adequately supplied and available in a typical soil.

A review of cinnamaldehyde and its derivatives as antibacterial agents

There is a continuing rise in the occurrence of multidrug-resistant bacterial infections. Antibiotic resistance to currently available antibiotics has become a global health issue leading to an urgent need for alternative antibacterial strategies. There has been a renewed interest in the development of antibacterial agents from natural sources, and trans-cinnamaldehyde is an example of a naturally occurring compound that has received significant attention in recent years. Trans-Cinnamaldehyde has been shown to possess substantial antimicrobial activity, as well as an array of other medicinal properties, and represents an intriguing hit compound from which a number of derivatives have been developed. In some cases, these derivatives have been shown to possess improved activity, not only compared to trans-cinnamaldehyde but also to commonly used antibiotics. Therefore, understanding the antibacterial mechanisms of action that these compounds elicit is imperative in order to facilitate their development and the development of new antibacterial agents that could exploit similar mechanistic approaches. The purpose of this review is to provide an overview of current knowledge on the antibacterial activity and mechanisms of action of cinnamaldehyde and its derivatives, and to highlight significant contributions made in this research area. It is hoped that the findings presented in this work will aid the future development of new antibacterial agents.

Analysis of Arabidopsis thaliana Redox Gene Network Indicates Evolutionary Expansion of Class III Peroxidase in Plants

Reactive oxygen species (ROS) are byproducts of aerobic metabolism and may cause oxidative damage to biomolecules. Plants have a complex redox system, involving enzymatic and non-enzymatic compounds. The evolutionary origin of enzymatic antioxidant defense in plants is yet unclear. Here, we describe the redox gene network for A. thaliana and investigate the evolutionary origin of this network. We gathered from public repositories 246 A. thaliana genes directly involved with ROS metabolism and proposed an A. thaliana redox gene network. Using orthology information of 238 Eukaryotes from STRINGdb, we inferred the evolutionary root of each gene to reconstruct the evolutionary history of A. thaliana antioxidant gene network. We found two interconnected clusters: one formed by SOD-related, Thiol-redox, peroxidases, and other oxido-reductase; and the other formed entirely by class III peroxidases. Each cluster emerged in different periods of evolution: the cluster formed by SOD-related, Thiol-redox, peroxidases, and other oxido-reductase emerged before opisthokonta-plant divergence; the cluster composed by class III peroxidases emerged after opisthokonta-plant divergence and therefore contained the most recent network components. According to our results, class III peroxidases are in expansion throughout plant evolution, with new orthologs emerging in each evaluated plant clade divergence.

The Biochemical Properties of Manganese in Plants

Manganese (Mn) is an essential micronutrient with many functional roles in plant metabolism. Manganese acts as an activator and co-factor of hundreds of metalloenzymes in plants. Because of its ability to readily change oxidation state in biological systems, Mn plays and important role in a broad range of enzyme-catalyzed reactions, including redox reactions, phosphorylation, decarboxylation, and hydrolysis. Manganese(II) is the prevalent oxidation state of Mn in plants and exhibits fast ligand exchange kinetics, which means that Mn can often be substituted by other metal ions, such as Mg(II), which has similar ion characteristics and requirements to the ligand environment of the metal binding sites. Knowledge of the molecular mechanisms catalyzed by Mn and regulation of Mn insertion into the active site of Mn-dependent enzymes, in the presence of other metals, is gradually evolving. This review presents an overview of the chemistry and biochemistry of Mn in plants, including an updated list of known Mn-dependent enzymes, together with enzymes where Mn has been shown to exchange with other metal ions. Furthermore, the current knowledge of the structure and functional role of the three most well characterized Mn-containing metalloenzymes in plants; the oxygen evolving complex of photosystem II, Mn superoxide dismutase, and oxalate oxidase is summarized.

Identification and Molecular Characterization of Superoxide Dismutases Isolated From A Scuticociliate Parasite: Physiological Role in Oxidative Stress

Philasterides dicentrarchi is a free-living microaerophilic scuticociliate that can become a facultative parasite and cause a serious parasitic disease in farmed fish. Both the free-living and parasitic forms of this scuticociliate are exposed to oxidative stress associated with environmental factors and the host immune system. The reactive oxygen species (ROS) generated by the host are neutralized by the ciliate by means of antioxidant defences. In this study we aimed to identify metalloenzymes with superoxide dismutase (SOD) activity capable of inactivating the superoxide anion (•O2-) generated during induction of oxidative stress. P. dicentrarchi possesses the three characteristic types of SOD isoenzymes in eukaryotes: copper/zinc-SOD, manganese-SOD and iron-SOD. The Cu/Zn-SOD isoenzymes comprise three types of homodimeric proteins (CSD1-3) of molecular weight (MW) 34-44 kDa and with very different AA sequences. All Cu/Zn-SODs are sensitive to NaCN, located in the cytosol and in the alveolar sacs, and one of them (CSD2) is extracellular. Mn- and Fe-SOD transcripts encode homodimeric proteins (MSD and FSD, respectively) in their native state: a) MSD (MW 50 kDa) is insensitive to H2O2 and NaN3 and is located in the mitochondria; and b) FSD (MW 60 kDa) is sensitive to H2O2, NaN3 and the polyphenol trans-resveratrol and is located extracellularly. Expression of SOD isoenzymes increases when •O2- is induced by ultraviolet (UV) irradiation, and the increase is proportional to the dose of energy applied, indicating that these enzymes are actively involved in cellular protection against oxidative stress.

Highlight on the expression and the function of a novel MnSOD from diploid wheat (T. monococcum) in response to abiotic stress and heavy metal toxicity

Superoxide dismutases (SODs) play a pivotal role in improving abiotic stress tolerance in plant cells. A novel manganese superoxide dismutase gene, denoted as TmMnSOD, was identified from Triticum monococcum. The encoded protein displayed high sequence identity with MnSOD family members and was highly homologous to TdMnSOD from durum wheat. Furthermore, the 3D structure analysis revealed that TmMnSOD displayed homotetramer subunit organization, incorporating four Mn²⁺ ions. Notably, TmMnSOD structure contains predominantly alpha helices with three beta sheets. On the other hand, under stress conditions, TmMnSOD transcript level was significantly up-regulated by salt, oxidative and heavy metal stresses. At the functional level, TmMnSOD imparts tolerance of yeast and E. coli cells under diverse stresses. Promoter analysis of TmMnSOD gene showed the presence of a great number of salt and pathogen-responsive cis-regulatory elements, highlighting the interest of this gene in breeding programs towards improved tolerance to salt stress in wheat.

Oxidative stress links response to lead and Acyrthosiphon pisum in Pisum sativum L

This study demonstrates the impact of lead at hormetic (0.075 mM Pb(NO3)2) and sublethal (0.5 mM Pb(NO3)2) doses on the intensity of oxidative stress in pea seedlings (Pisum sativum L. cv. 'Cysterski'). Our first objective was to determine how exposure of pea seedlings to Pb alters the plant defence responses to pea aphid (Acyrthosiphon pisum Harris), and whether these responses could indirectly affect A. pisum. The second objective was to investigate the effects of various Pb concentrations in the medium on demographic parameters of pea aphid population and the process of its feeding on edible pea. We found that the dose of Pb sublethal for pea seedlings strongly reduced net reproductive rate and limited the number of A. pisum individuals reaching the phloem. An important defence line of pea seedlings growing on Pb-supplemented medium and next during combinatory effect of the two stressors Pb and A. pisum was a high generation of superoxide anion (O2-). This was accompanied by a considerable reduction in superoxide dismutase (SOD) activity, and a decrease in the level of Mn2+ ions. A the same time, weak activity of Mn-SOD was detected in the roots of the seedlings exposed to the sublethal dose of Pb and during Pb and aphid interaction. Apart from the marked increase in O2-, an increase in semiquinone radicals occurred, especially in the roots of the seedlings treated with the sublethal dose of Pb and both infested and non-infested with aphids. Also, hydrogen peroxide (H2O2) generation markedly intensified in aphid-infested leaves. It reached the highest level 24 h post infestation (hpi), mainly in the cell wall of leaf epidermis. This may be related to the function of H2O2 as a signalling molecule that triggers defence mechanisms. The activity of peroxidase (POX), an important enzyme involved in scavenging H2O2, was also high at 24 hpi and at subsequent time points. Moreover, the contents of thiobarbituric acid reactive substances (TBARS), products of lipid peroxidation, rose but to a small degree thanks to an efficient antioxidant system. Total antioxidant capacity (TAC) dependent on the pool of fast antioxidants, both in infested and non-infested and leaves was higher than in the control. In conclusion, the reaction of pea seedlings to low and sublethal doses of Pb and then A. pisum infestation differed substantially and depended on a direct contact of the stress factor with the organ (Pb with roots and A. pisum with leaves). The probing behavior of A. pisum also depended on Pb concentration in the plant tissues.

How to define obligatory anaerobiosis? An evolutionary view on the antioxidant response system and the early stages of the evolution of life on Earth

One of the former definitions of "obligate anaerobiosis" was based on three main criteria: 1) it occurs in organisms, so-called obligate anaerobes, which live in environments without oxygen (O₂), 2) O₂-dependent (aerobic) respiration, and 3) antioxidant enzymes are absent in obligate anaerobes. In contrast, aerobes need O₂ in order to grow and develop properly. Obligate (or strict) anaerobes belong to prokaryotic microorganisms from two domains, Bacteria and Archaea. A closer look at anaerobiosis covers a wide range of microorganisms that permanently or in a time-dependent manner tolerate different concentrations of O₂ in their habitats. On this basis they can be classified as obligate/facultative anaerobes, microaerophiles and nanaerobes. Paradoxically, O₂ tolerance in strict anaerobes is usually, as in aerobes, associated with the activity of the antioxidant response system, which involves different antioxidant enzymes responsible for removing excess reactive oxygen species (ROS). In our opinion, the traditional definition of "obligate anaerobiosis" loses its original sense. Strict anaerobiosis should only be restricted to the occurrence of O₂-independent pathways involved in energy generation. For that reason, a term better than "obligate anaerobes" would be O₂/ROS tolerant anaerobes, where the role of the O₂/ROS detoxification system is separated from O₂-independent metabolic pathways that supply energy. Ubiquitous key antioxidant enzymes like superoxide dismutase (SOD) and superoxide reductase (SOR) in contemporary obligate anaerobes might suggest that their origin is ancient, maybe even the beginning of the evolution of life on Earth. It cannot be ruled out that c. 3.5 Gyr ago, local microquantities of O₂/ROS played a role in the evolution of the last universal common ancestor (LUCA) of all modern organisms. On the basis of data in the literature, the hypothesis that LUCA could be an O₂/ROS tolerant anaerobe is discussed together with the question of the abiotic sources of O₂/ROS and/or the early evolution of cyanobacteria that perform oxygenic photosynthesis.

Hydrogen sulfide, reactive sulfur species and coping with reactive oxygen species

Life began in a ferruginous (anoxic and Fe²⁺ dominated) world around 3.8 billion years ago (bya). Hydrogen sulfide (H₂S) and other sulfur molecules from hydrothermal vents and other fissures provided many key necessities for life's origin including catalytic platforms (primordial enzymes) that also served as primitive boundaries (cell walls), substrates for organic synthesis and a continuous source of energy in the form of reducing equivalents. Anoxigenic photosynthesis oxidizing H₂S followed within a few hundred million years and laid the metabolic groundwork for oxidative photosynthesis some half-billion years later that slightly and episodically increased atmospheric oxygen around 2.3 bya. This oxidized terrestrial sulfur to sulfate which was washed to the sea where it was reduced creating vast euxinic (anoxic and sulfidic) areas. It was in this environment that eukaryotic cells appeared around 1.5 bya and where they evolved for nearly 1 billion additional years. Oxidative photosynthesis finally oxidized the oceans and around 0.6 bya oxygen levels in the atmosphere and oceans began to rise toward present day levels. This is purported to have been a life-threatening event due to the prevalence of reactive oxygen species (ROS) and thus necessitated the elaboration of chemical and enzymatic antioxidant mechanisms. However, these antioxidants initially appeared around the time of anoxigenic photosynthesis suggesting a commitment to metabolism of reactive sulfur species (RSS). This review examines these events and suggests that many of the biological attributes assigned to ROS may, in fact, be due to RSS. This is underscored by observations that ROS and RSS are chemically similar, often indistinguishable by analytical methods and the fact that the bulk of biochemical and physiological experiments are performed in unphysiologically oxic environments where ROS are artifactually favored over RSS.

The molecular pathogenesis of superoxide dismutase 1-linked ALS is promoted by low oxygen tension

Mutations in superoxide dismutase 1 (SOD1) cause amyotrophic lateral sclerosis (ALS). Disease pathogenesis is linked to destabilization, disorder and aggregation of the SOD1 protein. However, the non-genetic factors that promote disorder and the subsequent aggregation of SOD1 have not been studied. Mainly located to the reducing cytosol, mature SOD1 contains an oxidized disulfide bond that is important for its stability. Since O₂ is required for formation of the bond, we reasoned that low O₂ tension might be a risk factor for the pathological changes associated with ALS development. By combining biochemical approaches in an extensive range of genetically distinct patient-derived cell lines, we show that the disulfide bond is an Achilles heel of the SOD1 protein. Culture of patient-derived fibroblasts, astrocytes, and induced pluripotent stem cell-derived mixed motor neuron and astrocyte cultures (MNACs) under low O₂ tensions caused reductive bond cleavage and increases in disordered SOD1. The effects were greatest in cells derived from patients carrying ALS-linked mutations in SOD1. However, significant increases also occurred in wild-type SOD1 in cultures derived from non-disease controls, and patients carrying mutations in other common ALS-linked genes. Compared to fibroblasts, MNACs showed far greater increases in SOD1 disorder and even aggregation of mutant SOD1s, in line with the vulnerability of the motor system to SOD1-mediated neurotoxicity. Our results show for the first time that O₂ tension is a principal determinant of SOD1 stability in human patient-derived cells. Furthermore, we provide a mechanism by which non-genetic risk factors for ALS, such as aging and other conditions causing reduced vascular perfusion, could promote disease initiation and progression.

Role of Nickel in Microbial Pathogenesis

Nickel is an essential cofactor for some pathogen virulence factors. Due to its low availability in hosts, pathogens must efficiently transport the metal and then balance its ready intracellular availability for enzyme maturation with metal toxicity concerns. The most notable virulence-associated components are the Ni-enzymes hydrogenase and urease. Both enzymes, along with their associated nickel transporters, storage reservoirs, and maturation enzymes have been best-studied in the gastric pathogen Helicobacter pylori, a bacterium which depends heavily on nickel. Molecular hydrogen utilization is associated with efficient host colonization by the Helicobacters, which include both gastric and liver pathogens. Translocation of a H. pylori carcinogenic toxin into host epithelial cells is powered by H2 use. The multiple [NiFe] hydrogenases of Salmonella enterica Typhimurium are important in host colonization, while ureases play important roles in both prokaryotic (Proteus mirabilis and Staphylococcus spp.) and eukaryotic (Cryptoccoccus genus) pathogens associated with urinary tract infections. Other Ni-requiring enzymes, such as Ni-acireductone dioxygenase (ARD), Ni-superoxide dismutase (SOD), and Ni-glyoxalase I (GloI) play important metabolic or detoxifying roles in other pathogens. Nickel-requiring enzymes are likely important for virulence of at least 40 prokaryotic and nine eukaryotic pathogenic species, as described herein. The potential for pathogenic roles of many new Ni-binding components exists, based on recent experimental data and on the key roles that Ni enzymes play in a diverse array of pathogens.

Genome-Wide Analysis of ROS Antioxidant Genes in Resurrection Species Suggest an Involvement of Distinct ROS Detoxification Systems during Desiccation

Abiotic stress is one of the major threats to plant crop yield and productivity. When plants are exposed to stress, production of reactive oxygen species (ROS) increases, which could lead to extensive cellular damage and hence crop loss. During evolution, plants have acquired antioxidant defense systems which can not only detoxify ROS but also adjust ROS levels required for proper cell signaling. Ascorbate peroxidase (APX), glutathione peroxidase (GPX), catalase (CAT) and superoxide dismutase (SOD) are crucial enzymes involved in ROS detoxification. In this study, 40 putative APX, 28 GPX, 16 CAT, and 41 SOD genes were identified from genomes of the resurrection species Boea hygrometrica, Selaginella lepidophylla, Xerophyta viscosa, and Oropetium thomaeum, and the mesophile Selaginellamoellendorffii. Phylogenetic analyses classified the APX, GPX, and SOD proteins into five clades each, and CAT proteins into three clades. Using co-expression network analysis, various regulatory modules were discovered, mainly involving glutathione, that likely work together to maintain ROS homeostasis upon desiccation stress in resurrection species. These regulatory modules also support the existence of species-specific ROS detoxification systems. The results suggest molecular pathways that regulate ROS in resurrection species and the role of APX, GPX, CAT and SOD genes in resurrection species during stress.

The Redox architecture of physiological function

The ability of organisms to accommodate variations in metabolic need and environmental conditions is essential for their survival. However, an explanation is lacking as to how the necessary accommodations in response to these challenges are organized and coordinated from (sub)cellular to higher-level physiological functions, especially in mammals. We propose that the chemistry that enables coordination and synchronization of these processes dates to the origins of Life. We offer a conceptual framework based upon the nature of electron exchange (Redox) processes that co-evolved with biological complexification, giving rise to a multi-layered system in which intra/intercellular and inter-organ exchange processes essential to sensing and adaptation stay fully synchronized. Our analysis explains why Redox is both the lingua franca and the mechanism that enable integration by connecting the various elements of regulatory processes. We here define these interactions across levels of organization as the 'Redox Interactome'. This framework provides novel insight into the chemical and biological basis of Redox signalling and may explain the recent convergence of metabolism, bioenergetics, and inflammation as well as the relationship between Redox stress and human disease.

Effect of flavonoids isolated from Tridax procumbens on the growth and toxin production of Microcystis aeruginos

The excessive proliferation of toxin producing cyanobacteria constitutes a significant health risk to the environment and humans. This is due to the contamination of potable water and accumulation of cyanotoxins in plant and animal tissues. As a means of controlling bloom forming cyanobacteria, secondary metabolites with pro-oxidative activities from plants are used to treat water bodies contaminated with cyanobacterial blooms and their associated toxins. The objective of the present study was to evaluate the mechanism of action of extract, fractions and isolated flavonoids of Tridax procumbens L. on Microcystis aeruginosa (Kützing) Kützing. by monitoring changes in growth, oxidative stress, antioxidant response, and cyanatoxin microcystins (MCs) production. The extract, fraction 3 and the isolated flavonoids significantly reduced the cell density of the cyanobacterium. Furthermore, the extract and fraction 3 increased the production of reactive oxygen species, induced lipid peroxidation, and altered antioxidant enzyme activities of M. aeruginosa. The total MCs content of the cyanobacterium was negatively affected by the presence of the extract, fractions and isolated flavonoids. The present study show that T. procumbens has secondary metabolites that are capable of interfering with the physiology and microcystins production of M. aeruginosa. These characteristics are promising for the control of this noxious cyanobacterium in aquatic ecosystems.

Effects of inhibiting antioxidant pathways on cellular hydrogen sulfide and polysulfide metabolism

Elaborate antioxidant pathways have evolved to minimize the threat of excessive reactive oxygen species (ROS) and to regulate ROS as signaling entities. ROS are chemically and functionally similar to reactive sulfur species (RSS) and both ROS and RSS have been shown to be metabolized by the antioxidant enzymes, superoxide dismutase and catalase. Here we use fluorophores to examine the effects of a variety of inhibitors of antioxidant pathways on metabolism of two important RSS, hydrogen sulfide (H₂S with AzMC) and polysulfides (H₂S_n, where n = 2-7, with SSP4) in HEK293 cells. Cells were exposed to inhibitors for up to 5 days in normoxia (21% O₂) and hypoxia (5% O₂), conditions also known to affect ROS production. Decreasing intracellular glutathione (GSH) with l-buthionine-sulfoximine (BSO) or diethyl maleate (DEM) decreased H₂S production for 5 days but did not affect H₂S_n. The glutathione reductase inhibitor, auranofin, initially decreased H₂S and H₂S_n but after two days H₂S_n increased over controls. Inhibition of peroxiredoxins with conoidin A decreased H₂S and increased H₂S_n, whereas the glutathione peroxidase inhibitor, tiopronin, increased H₂S. Aminoadipic acid, an inhibitor of cystine uptake did not affect either H₂S or H₂S_n. In buffer, the glutathione reductase and thioredoxin reductase inhibitor, 2-AAPA, the glutathione peroxidase mimetic, ebselen, and tiopronin variously reacted directly with AzMC and SSP4, reacted with H₂S and H₂S₂, or optically interfered with AzMC or SSP4 fluorescence. Collectively these results show that antioxidant inhibitors, generally known for their ability to increase cellular ROS, have various effects on cellular RSS. These findings suggest that the inhibitors may affect cellular sulfur metabolism pathways that are not related to ROS production and in some instances they may directly affect RSS or the methods used to measure them. They also illustrate the importance of carefully evaluating RSS metabolism when biologically or pharmacologically attempting to manipulate ROS.

Roles of the Two-MnSOD System of Stenotrophomonas maltophilia in the Alleviation of Superoxide Stress

Manganese-dependent superoxide dismutase (MnSOD, SodA) and iron-dependent SOD (FeSOD, SodB) are critical cytosolic enzymes for alleviating superoxide stress. Distinct from the singular sodA gene in most bacteria, Stenotrophomonas maltophilia harbors two sodA genes, sodA1 and sodA2. The roles of SodA1, SodA2, and SodB of S. maltophilia in alleviating superoxide stress were investigated. The expression of sod genes was determined by promoter–xylE transcriptional fusion assay and qRT–PCR. SodA2 and sodB expressions were proportional to the bacterial logarithmic growth, but unaffected by menadione (MD), iron, or manganese challenges. SodA1 was intrinsically unexpressed and inducibly expressed by MD. Complementary expression of sodA1 was observed when sodA2 was inactivated. The individual or combined sod deletion mutants were constructed using the gene replacement strategy. The functions of SODs were assessed by evaluating cell viabilities of different sod mutants in MD, low iron-stressed, and/or low manganese-stressed conditions. Inactivation of SodA1 or SodA2 alone did not affect bacterial viability; however, simultaneously inactivating sodA1 and sodA2 significantly compromised bacterial viability in both aerobic growth and stressed conditions. SodA1 can either rescue or support SodA2 when SodA2 is defective or insufficiently potent. The presence of two MnSODs gives S. maltophilia an advantage against superoxide stress.

Astaxanthin Prevents Decreases in Superoxide Dismutase 2 Level and Superoxide Dismutase Activity in Helicobacter pylori-infected Gastric Epithelial Cells

Background

Helicobacter pylori increases production of reactive oxygen species (ROS), which activates inflammatory and carcinogenesis-related signaling pathways in gastric epithelial cells. Therefore, reducing ROS, by upregulating antioxidant enzyme, such as superoxide dismutase (SOD), may be a novel strategy to prevent H. pylori-associated gastric diseases. Astaxanthin is an antioxidant carotenoid that prevents oxidative stress-induced cell injury. The present study was aimed to determine whether H. pylori decreases SOD activity by changing the levels of SOD1/SOD2 and whether astaxanthin prevents changes in SOD levels and activity in H. pylori-infected gastric epithelial AGS cells.

Methods

AGS cells were pre-treated with astaxanthin for 3 hours prior to H. pylori infection and cultured for 1 hour in the presence of H. pylori. SOD levels and activity were assessed by Western blot analysis and a commercial assay kit, respectively. Mitochondrial ROS was determined using MitoSOX fluorescence.

Results

H. pylori decreased SOD activity and the SOD2 level, but increased mitochondrial ROS in AGS cells. The SOD1 level was not changed by H. pylori infection. Astaxanthin prevented H. pylori-induced decreases in the SOD2 level and SOD activity and reduced mitochondrial ROS in AGS cells.

Conclusions

Consumption of astaxanthin-rich food may prevent the development of H. pylori-associated gastric disorders by suppressing mitochondrial oxidative stress.

Plasma-sensitive Escherichia coli mutants reveal plasma resistance mechanisms

Non-thermal atmospheric pressure plasmas are investigated as augmenting therapy to combat bacterial infections. The strong antibacterial effects of plasmas are attributed to the complex mixture of reactive species, (V)UV radiation and electric fields. The experience with antibiotics is that upon their introduction as medicines, resistance occurs in pathogens and spreads. To assess the possibility of bacterial resistance developing against plasma, we investigated intrinsic protective mechanisms that allow Escherichia coli to survive plasma stress. We performed a genome-wide screening of single-gene knockout mutants of E. coli and identified 87 mutants that are hypersensitive to the effluent of a microscale atmospheric pressure plasma jet. For selected genes ( cysB, mntH, rep and iscS) we showed in complementation studies that plasma resistance can be restored and increased above wild-type levels upon over-expression. To identify plasma-derived components that the 87 genes confer resistance against, mutants were tested for hypersensitivity against individual stressors (hydrogen peroxide, superoxide, hydroxyl radicals, ozone, HOCl, peroxynitrite, NO•, nitrite, nitrate, HNO3, acid stress, diamide, heat stress and detergents). k-means++ clustering revealed that most genes protect from hydrogen peroxide, superoxide and/or nitric oxide. In conclusion, individual bacterial genes confer resistance against plasma providing insights into the antibacterial mechanisms of plasma.

Genome-wide identification and characterization of abiotic-stress responsive SOD (superoxide dismutase) gene family in Brassica juncea and B. rapa

Background

Abiotic stresses like drought, heat, cold and salinity cause major productivity loss in the rapeseed-mustard crops (Brassica). Major efforts have been made in the past to identify genes that provide resistance against such stresses. Superoxide dismutase (SOD) proteins, member of the metallo-enzyme family play vital role in protecting plants against abiotic stresses. In the present study, genome-wide analysis of abiotic stress responsive SOD gene family has been done in B. juncea and B. rapa.

Results

A total of 29 and 18 SOD genes were identified in B. juncea and B. rapa respectively and chromosome location mapping indicated their wide distribution across genome. On the basis of domain composition, the SODs were phylogenetically classified into sub-groups which was also substantiated by the gene structure and sub-cellular locations of SOD proteins. Functional annotation of SODs was also done by Gene Ontology (GO) mapping and the result was corroborated by the identified cis-regulatory elements in the promoter region of SOD genes. Based on FPKM analysis of SRA data available for drought, heat and salt stress, we identified 14 and 10 abiotic stress responsive SOD genes in B. rapa and B. juncea respectively. The differential expression analysis under drought and heat stress of identified abiotic-stress responsive SOD genes was done through quantitative Real Time PCR.

Conclusion

We identified abiotic-stress responsive genes that could help in improving the plant tolerance against abiotic stresses. This was the first study to describe the genome-wide analysis of SOD gene family in B. rapa and B. juncea, and the results will help in laying basic ground for future work of cloning and functional validation of SOD genes during abiotic stresses leading to Brassica crop improvement.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5593-5) contains supplementary material, which is available to authorized users.

Hydroalcoholic extract of Tagetes erecta L. flowers, rich in the carotenoid lutein, attenuates inflammatory cytokine secretion and improves the oxidative stress in an animal model of ulcerative colitis

Given the role of oxidative stress in ulcerative colitis (UC) etiology, and the amount of lutein (a carotenoid with antioxidant properties) in the dry hydroalcoholic extract of Tagetes erecta flowers (DHETE), this study investigated the intestinal anti-inflammatory properties of DHETE in an animal model of UC. The amount of lutein in the extract was determined by ¹H-nuclear magnetic resonance spectroscopy, and total phenols, radical scavenger capability, cytotoxicity, and effects on reactive oxygen species and nitric oxide production were evaluated in vitro. Experimental UC was established by adding 5% dextran sulfate sodium (DSS) to drinking water, with the effects of DHETE (30-300 mg/kg, once a day for 7 days) on the morphological (colon length and weight), clinical (disease activity index and body weight loss), microscopic (histological score and mucin levels), and biochemical parameters analyzed. The lutein concentration found in DHETE was 8.2%, and DHETE scavenged 2,2-diphenyl-1-picrylhydrazyl radicals at 1000 μg/mL The exposure of intestinal epithelial cells to DHETE did not change its viability but reduced reactive oxygen species and nitric oxide production after lipopolysaccharide stimulation. In vivo, DHETE (300 mg/kg) attenuated weight loss, disease activity index, colon shortening, and histopathological changes promoted by DSS intake. Moreover, DHETE increased mucin colonic staining. The treatment with DHETE decreased myeloperoxidase activity as well as tumor necrosis factor and interleukin-6 levels. The extract also increased reduced glutathione levels and catalase activity and normalized superoxide dismutase and glutathione-S-transferase activities. In conclusion, DHETE reduced colitis severity by attenuating inflammatory cytokine secretion and improved the endogenous antioxidant defense in DSS-induced UC in mice.

Evaluation of trace elements associated with antioxidant enzymes in blood of primary epithelial ovarian cancer patients

Epithelial ovarian cancer (EOC) has been associated with oxidative stress (OS) due to epithelial inflammation which makes ovaries more vulnerable to the deleterious effects of reactive oxygen species (ROS). However, antioxidant enzymes (AOEs) such as manganese-superoxide dismutase (Mn-SOD), copper,zinc-superoxide dismutase (Cu,Zn-SOD) and glutathione peroxidase (GPx1) protect cells against the biological damage of ROS-induced OS and support cancer prevention by maintaining normal cell cycle progression, inhibiting proliferation, tumor invasion, angiogenesis, inflammation or inducing apoptosis. In the present study, we aimed to measure the levels of trace elements [manganese (Mn), copper (Cu), zinc (Zn) and selenium (Se)] which are structurally and/or functionally associated with the AOEs by inductively coupled plasma/mass-spectrometry (ICP/MS) in blood samples of patients with EOC (M, n = 26) and compare the data with healthy subjects (C, n = 46). Serous EOC (M1, n = 18) data were also evaluated according to the tumor grading [well or moderately well differentiated (G 1-2) vs. poorly differentiated or undifferentiated (G3)] and staging of disease [stage I-II (SI-II) vs. stage III (SIII)]. We obtained; i) The Mn and Se levels of M were significantly lower than C, ii) only Mn levels were changed [(G3_(Mn) < G 1-2 _(Mn)] in M1, iii) significant correlations were observed between [Cu and Zn levels (r = 0.701, p = 0.036) in G 1-2 and (r = 0.686, p = 0.041) in G3; Cu and Se levels (r = 0.960, p = 0.000) in G3; Mn levels and Mn-SOD expression (r = 0.551, p = 0.006) in M, (r = 0.857, p = 0.007) in G 1-2 and (r = 0.690, p = 0.056) in G3; Se levels and erythrocyte GPx1 activity (r = 0.660, p = 0.053) in G 1-2 ; Se levels and erythrocyte Cu,Zn-SOD activity (r = 0.693, p = 0.038) in G3]. The study revealed that trace elements, particularly low Mn and Se levels along with high Cu/Se ratios might be of value in all histologic subtypes of EOC. Although Mn level was important in terms of discriminating tumor grades, positive correlation between Cu-Se levels was also remarkable in patients with G 1-2 tumors of M1. Moreover, high erythrocyte Cu/Se ratios might be a favourable marker for EOC.

Direct and Indirect Inhibition Effects of Resveratrol against Toxoplasma gondii Tachyzoites In Vitro

Toxoplasma gondii is one of the most widespread obligatory parasitic protozoa and infects nearly all warm-blooded animals, leading to toxoplasmosis. The therapeutic drugs currently administered, like the combination of pyrimethamine and sulfadiazine, show high rates of toxic side effects, and drug resistance is encountered in some cases. Resveratrol is a natural plant extract with multiple functions, such as antibacterial, anticancer, and antiparasite activities. In this study, we evaluated the inhibitory effects of resveratrol on tachyzoites of the Toxoplasma gondii RH strain extracellularly and intracellularly. We demonstrate that resveratrol possesses direct antitoxoplasma activity by reducing the population of extracellularly grown tachyzoites, probably by disturbing the redox homeostasis of the parasites. Moreover, resveratrol was also able to release the burden of cellular stress, promote apoptosis, and maintain the autophagic status of macrophages, which turned out to be regulated by intracellular parasites, thereby functioning indirectly in eliminating T. gondii In conclusion, resveratrol has both direct and indirect antitoxoplasma effects against RH tachyzoites and may possess the potential to be further evaluated and employed for toxoplasmosis treatment.

Cellular Response of Escherichia coli to Photocatalysis: Flagellar Assembly Variation and Beyond

Bacterial cells can be inactivated by external reactive oxygen species (ROS) produced by semiconductor photocatalysis. However, little is known about cellular responses to photocatalysis. For a better understanding of this issue, one strain of Escherichia coli ( E. coli, hereafter named as MT), which has an increased ability to metabolize carbon sources, was screened out from the wild-type (WT) E. coli K12 by repeated exposure to photocatalysis with palladium oxide modified nitrogen-doped titanium dioxide. In this study, transcriptome sequencing of the WT and MT strains that were exposed or unexposed to photocatalysis were carried out. Cellular responses to photocatalysis were inferred from the functions of genes whose transcripts were either increased or decreased. Upregulation of expression of bacterial flagellar assembly genes used for chemotaxis was detected in cells exposed to semilethal photocatalytic conditions of the WT E. coli. Increased capability to degrade superoxide radicals and decreased bacterial flagellar assembly and chemotaxis were observed in MT E. coli compared to WT cells. We conclude that the differences in motility and intracellular ROS between MT and WT are directly related to survivability of E. coli during exposure to photodisinfection.

Comparative analysis of seven types of superoxide dismutases for their ability to respond to oxidative stress in Bombyx mori

Insects are well adapted to changing environmental conditions. They have unique systems for eliminating reactive oxygen species (ROS). Superoxide dismutase (SOD) is a key enzyme that plays a primary role in removing ROS. Bombyx mori is a lepidopteran insect, whose body size is larger than the model insect Drosophila melanogaster, which enabled us to more easily examine gene expression at the tissue level. We searched B. mori SOD (BmSOD) genes using genome database, and we analyzed their function under different type of oxidative stress. Consequently, we identified four new types of BmSODs in addition to the three types already known. Two of the seven types had a unique domain architecture that has not been discovered previously in the SOD family, and they were expressed in different tissues and developmental stages. Furthermore, these BmSODs responded differently to several kinds of stressors. Our results showed that the seven types of BmSODs are likely to play different roles in B. mori; therefore, B. mori could be used to distinguish the functions of each SOD for resistance to oxidative stress that changes with the environmental conditions.

Group A Streptococcus co-ordinates manganese import and iron efflux in response to hydrogen peroxide stress

Bacterial pathogens encounter a variety of adverse physiological conditions during infection, including metal starvation, metal overload and oxidative stress. Here, we demonstrate that group A Streptococcus (GAS) utilises Mn(II) import via MtsABC during conditions of hydrogen peroxide stress to optimally metallate the superoxide dismutase, SodA, with Mn. MtsABC expression is controlled by the DtxR family metalloregulator MtsR, which also regulates the expression of Fe uptake systems in GAS. Our results indicate that the SodA in GAS requires Mn for full activity and has lower activity when it contains Fe. As a consequence, under conditions of hydrogen peroxide stress where Fe is elevated, we observed that the PerR-regulated Fe(II) efflux system PmtA was required to reduce intracellular Fe, thus protecting SodA from becoming mismetallated. Our findings demonstrate the co-ordinate action of MtsR-regulated Mn(II) import by MtsABC and PerR-regulated Fe(II) efflux by PmtA to ensure appropriate Mn(II) metallation of SodA for optimal superoxide dismutase function.

Inhibition of Aflatoxin Production by Paraquat and External Superoxide Dismutase in Aspergillus flavus

Aflatoxin contamination of crops is a worldwide problem, and elucidation of the regulatory mechanism of aflatoxin production, for example relative to the oxidative–antioxidative system, is needed. Studies have shown that oxidative stress induced by reactive oxygen species promotes aflatoxin production. However, superoxide has been suggested to have the opposite effect. Here, we investigated the effects of the superoxide generator, paraquat, and externally added superoxide dismutase (SOD) on aflatoxin production in Aspergillus flavus. Paraquat with an IC₅₀ value of 54.9 µM inhibited aflatoxin production without affecting fungal growth. It increased cytosolic and mitochondrial superoxide levels and downregulated the transcription of aflatoxin biosynthetic cluster genes, including aflR, a key regulatory protein. The addition of bovine Cu/ZnSOD to the culture medium suppressed the paraquat-induced increase in superoxide levels, but it did not fully restore paraquat-inhibited aflatoxin production because bovine Cu/ZnSOD with an IC₅₀ value of 17.9 µg/mL itself inhibited aflatoxin production. Externally added bovine Cu/ZnSOD increased the SOD activity in fungal cell extracts and upregulated the transcription of genes encoding Cu/ZnSOD and alcohol dehydrogenase. These results suggest that intracellular accumulation of superoxide impairs aflatoxin production by downregulating aflR expression, and that externally added Cu/ZnSOD also suppresses aflatoxin production by a mechanism other than canonical superoxide elimination activity.

The Individual and Combined Effects of the Cyanotoxins, Anatoxin-a and Microcystin-LR, on the Growth, Toxin Production, and Nitrogen Fixation of Prokaryotic and Eukaryotic Algae

Globally, eutrophication and warming of aquatic ecosystems has increased the frequency and intensity of cyanobacterial blooms and their associated toxins, with the simultaneous detection of multiple cyanotoxins often occurring. Despite the co-occurrence of cyanotoxins such as microcystins and anatoxin-a (ATX) in water bodies, their effects on phytoplankton communities are poorly understood. The individual and combined effects of microcystin-LR (MC-LR) and ATX on the cyanobacteria Microcystis spp., and Anabaena variabilis (a.k.a. Trichormus variabilis), and the chlorophyte, Selenastrum capricornutum were investigated in the present study. Cell density, chlorophyll-a content, and the maximum quantum efficiency of photosystem II (Fv/Fm) of Microcystis cells were generally lowered after exposure to ATX or MC-LR, while the combined treatment with MC-LR and ATX synergistically reduced the chlorophyll-a concentration of Microcystis strain LE-3. Intracellular levels of microcystin in Microcystis LE-3 significantly increased following exposure to MC-LR + ATX. The maximum quantum efficiency of photosystem II of Anabaena strain UTEX B377 declined during exposure to the cyanotoxins. Nitrogen fixation by Anabaena UTEX B377 was significantly inhibited by exposure to ATX, but was unaffected by MC-LR. In contrast, the combination of both cyanotoxins (MC-LR + ATX) caused a synergistic increase in the growth of S. capricornutum. While the toxins caused an increase in the activity of enzymes that scavenge reactive oxygen species in cyanobacteria, enzyme activity was unchanged or decreased in S. capricornutum. Collectively this study demonstrates that MC-LR and ATX can selectively promote and inhibit the growth and performance of green algae and cyanobacteria, respectively, and that the combined effect of these cyanotoxins was often more intense than their individual effects on some strains. This suggests that the release of multiple cyanotoxins in aquatic ecosystems, following the collapse of blooms, may influence the succession of plankton communities.

Molecular characterization and expression analysis of iron superoxide dismutase gene from Pseudochlorella pringsheimii (Trebouxiophyceae, Chlorophyta)

The FeSOD isoforms of Pseudochlorella pringsheimii were identified, a preliminary characterization of the enzyme was conducted, and the relationship among the FeSOD gene from P. pringsheimii and that of other organisms was examined. The FeSOD has an open reading frame of 612 bp that encodes 203 deduced amino acids with a molecular mass of 23 kDa. Expression of the recombinant FeSOD gene was done successfully in Escherichia coli. The purified FeSOD has a specific enzyme activity that reached 688 U mg^-1 protein (in vitro assay). Alkaline conditions showed the highest activity for the recombinant FeSOD. Moreover, it showed a relative thermostability up to 50 °C, while at 50 and 70 °C, the activity was reduced by 32 and 68%, respectively, after 1 h as compared to the maximum. Phylogenetic analysis revealed three main clusters i.e., the prokaryotic Cyanophyta, bacteria, and the eukaryotic Chlorophyta intermingled with plant species and a dinoflagellate. P. pringsheimii was closely grouped with Chlorella pyrenoidosa, however, other species showed a relative disparity. Alignment of FeSOD gene sequences of the different species showed many conserved regions which could be used for FeSOD sequences among unexplored species and may be useful for the taxonomy of the revised coccoid Chlorella species.

Metal tolerance protein MTP6 affects mitochondrial iron and manganese homeostasis in cucumber

Members of the cation diffusion facilitator (CDF) family have been identified in all kingdoms of life. They have been divided into three subgroups, namely Zn-CDF, Fe/Zn-CDF, and Mn-CDF, based on their putative specificity to transported metal ions. The plant metal tolerance protein 6 (MTP6) proteins fall into the Fe/Zn-CDF subgroup; however, their function in iron/zinc transport has not yet been confirmed. Here, we characterized the MTP6 protein from cucumber, Cucumis sativus. When expressed in yeast and in protoplasts isolated from Arabidopsis cells, CsMTP6 localized in mitochondria and contributed to the efflux of Fe and Mn from these organelles. Immunolocalization of CsMTP6 in cucumber membranes confirmed this association with mitochondria. Root expression and protein levels of CsMTP6 were significantly up-regulated in conditions of Fe deficiency and excess, but were not affected by Mn availability. These results indicate that MTP6 proteins contribute to the distribution of Fe and Mn between the cytosol and mitochondria of plant cells, and are regulated by Fe to maintain mitochondrial and cytosolic iron homeostasis under varying conditions of Fe availability.

Health Characteristics and Blood Bacterial Assemblages of Healthy Captive Red Drum: Implications for Aquaculture and Fish Health Management

The newly emerging tissue microbiota hypothesis suggests that bacteria found in blood and tissues play a role in host health, as these bacterial communities have been associated with various noncommunicable diseases such as obesity, liver disease, and cardiovascular disease. Numerous reports have identified bacteria in the blood of healthy finfish, indicating bacteremia may not always indicate disease. Current research priorities in aquaculture include the development of technologies and practices that will allow for an effective reduction in antibiotic use for the prevention and treatment of disease. Overall, a better understanding of fish health is needed, particularly among species selected for commercial-scale production. This study investigated blood characteristics of cultured Red Drum Sciaenops ocellatus with the tissue microbiota hypothesis in mind. Bacterial assemblages within the blood were characterized using next-generation sequencing and compared with other various blood characteristics, including innate immune function enzymes, between two fish cohorts reared in aquaculture. A total of 137 prokaryotic operational taxonomic units (OTUs) were identified from the blood of Red Drum. Microbiota diversity and structure varied greatly among individuals, for which the number of OTUs ranged from 4 to 58; however, predicted metagenomic function was highly similar between individuals and was dominated by the metabolism of carbohydrates and amino acids and membrane transport. Communities were dominated by Proteobacteria, followed by Bacteroidetes, Firmicutes, and Actinobacteria. The most commonly identified genera included Acinetobacter, Bacillus, Corynebacterium, and Pseudomonas. Three genera previously identified as containing marine fish pathogens were detected: Corynebacterium, Pantoea, and Chryseobacterium. A subset of bacterial OTUs were positively correlated with superoxide dismutase activity and negatively correlated with lysozyme activity, indicating a relationship between blood microbiota and the innate immune system. The results of this study provide further evidence for the tissue microbiota hypothesis and demonstrate the potential for these bacterial communities to be linked to immunological characteristics often used as biomarkers for fish health.

Genome-wide analysis of superoxide dismutase genes in Larix kaempferi

Superoxide dismutase is a key enzyme that scavenges superoxide anion and plays vital roles in plant antioxidant system. This study identified six SOD genes from the deciduous conifer Larix kaempferi, which is widely distributed across the cooler regions of the northern hemisphere. These six SOD genes were classified into three types: Cu/Zn-SOD (LkSOD1, 2, 3 and 4), Fe-SOD (LkSOD5) and Mn-SODs (LkSOD6). Three Cu/Zn-SOD proteins (LkSOD1, 3 and 4) were cytosolic-localized, while the other three proteins (LkSOD2, 5 and 6) were chloroplast-localized. Larix SOD proteins displayed catalytic activities toward superoxide anion, and retained >55% of its maximum enzymatic activity between 10 °C and 40 °C. Over expressions of three Larix SOD genes (LkSOD2, 4 and 6) in Arabidopsis thaliana, respectively, showed increased germination rates and root lengths during salt stress. LkSOD5 gene could rescue pale green and dwarf phenotype of Arabidopsis atfsd2-2 mutant. Taken together, this study provided comprehensive insight into the gymnosperm SOD gene family.

Genome Structure of the Opportunistic Pathogen Paracoccus yeei (Alphaproteobacteria) and Identification of Putative Virulence Factors

Bacteria of the genus Paracoccus are common components of the microbiomes of many naturally- and anthropogenically shaped environments. One species, Paracoccus yeei, is unique within the genus because it is associated with opportunistic human infections. Therefore, strains of P. yeei may serve as an interesting model to study the transition from a saprophytic to a pathogenic lifestyle in environmental bacteria. Unfortunately, knowledge concerning the biology, genetics and genomic content of P. yeei is fragmentary; also the mechanisms of pathogenicity of this bacterium remain unclear. In this study we provide the first insight into the genome composition and metabolic potential of a clinical isolate, P. yeei CCUG 32053. This strain has a multipartite genome (4,632,079 bp) composed of a circular chromosome plus eight extrachromosomal replicons pYEE1–8: 3 chromids and 5 plasmids, with a total size of 1,247,173 bp. The genome has been significantly shaped by the acquisition of genomic islands, prophages (Myoviridae and Siphoviridae phage families) and numerous insertion sequences (ISs) representing seven IS families. Detailed comparative analysis with other complete genomic sequences of Paracoccus spp. (including P. yeei FDAARGOS_252 and TT13, as well as non-pathogenic strains of other species in this genus) enabled us to identify P. yeei species-specific genes and to predict putative determinants of virulence. This is the first attempt to identify pathoadaptive genetic information of P. yeei and to estimate the role of the mobilome in the evolution of pathogenicity in this species.

The Role of Hydrogen Peroxide in Redox-Dependent Signaling: Homeostatic and Pathological Responses in Mammalian Cells

Hydrogen peroxide (H₂O₂) is an important metabolite involved in most of the redox metabolism reactions and processes of the cells. H₂O₂ is recognized as one of the main molecules in the sensing, modulation and signaling of redox metabolism, and it is acting as a second messenger together with hydrogen sulfide (H₂S) and nitric oxide (NO). These second messengers activate in turn a cascade of downstream proteins via specific oxidations leading to a metabolic response of the cell. This metabolic response can determine proliferation, survival or death of the cell depending on which downstream pathways (homeostatic, pathological, or protective) have been activated. The cells have several sources of H₂O₂ and cellular systems strictly control its concentration in different subcellular compartments. This review summarizes research on the role played by H₂O₂ in signaling pathways of eukaryotic cells and how this signaling leads to homeostatic or pathological responses.