Daily variations of antioxidant enzyme and luciferase activities in the luminescent click-beetle Pyrearinus termitilluminans: cooperation against oxygen toxicity

Physiological Responses of the Firefly Pyrocoelia analis (Coleoptera: Lampyridae) to an Environmental Residue From Chemical Pesticide Imidacloprid

Imidacloprid, a neonicotinoid insecticide, is widely applied to control insect pests across a broad spectrum. Though the impact of residues from this chemical pesticide on non-target organisms in the field has been reported, it was not well characterized across a wide range of ecosystems, especially for some species considered as environmental indicators that live in forests. The effects of sublethal dose of imidacloprid on firefly, Pyrocoelia analis, were analyzed physiologically and biochemically in this study to better understand the impact of chemical pesticide application on environmental indicators such as fireflies. After imidacloprid treatment, the midgut tissues of the larva presented an abnormal morphology featured as atrophy of fat body cells, shrinking cells, and the destruction of a midgut structure. The activities of antioxidant enzymes, superoxide dismutase, catalase, and peroxidase were noticeably increased during early exposure to sublethal imidacloprid and then decreased at later stages. The malondialdehyde content significantly increased after 12 h of exposure to imidacloprid compared with the control. Similarly, the enzyme activities of polyphenol oxidase and acetylcholinesterase were increased after the imidacloprid treatment and then decreased at the later stage. In summary, a sublethal dose of imidacloprid caused destructive change in the tissue structure, and this damage was followed by an excessive reactive oxygen species that could not be eliminated by antioxidant enzymes. Our results indicated that the residues of imidacloprid might cause severe toxicity to non-target insects in the environment even far away from the agro-ecosystem where the chemicals were applied.

Molecular analysis of the Mycobacterium tuberculosis lux-like mel2 operon

Using a high throughput genetic strategy, designated Random Inducible Controlled Expression (RICE), we identified the six gene mel2 locus in Mtb and M. marinum. Interestingly, three of the genes present in mel2 have similarities to bioluminescence genes. Similar to other bacterial bioluminescence systems, mel2 facilitates detoxification of reactive oxygen species (ROS). Through the use of thin layer chromatography (TLC) we demonstrate enhanced production of the cell wall virulence lipid, pthiocerol dimycoserosate (PDIM), in a Mtb mel2 mutant relative to the wild type strain in the presence of both H2O2 and diamide oxidative stresses. Furthermore, propionate toxicity assays revealed increased accumulation of triacylglycerol (TAG) in the mel2 mutant relative to wild type. These observations provide the first evidence that mel2 plays a critical role in Mtb lipid biosynthesis.

Disentangling detoxification: gene expression analysis of feeding mountain pine beetle illuminates molecular-level host chemical defense detoxification mechanisms

The mountain pine beetle, Dendroctonus ponderosae, is a native species of bark beetle (Coleoptera: Curculionidae) that caused unprecedented damage to the pine forests of British Columbia and other parts of western North America and is currently expanding its range into the boreal forests of central and eastern Canada and the USA. We conducted a large-scale gene expression analysis (RNA-seq) of mountain pine beetle male and female adults either starved or fed in male-female pairs for 24 hours on lodgepole pine host tree tissues. Our aim was to uncover transcripts involved in coniferophagous mountain pine beetle detoxification systems during early host colonization. Transcripts of members from several gene families significantly increased in insects fed on host tissue including: cytochromes P450, glucosyl transferases and glutathione S-transferases, esterases, and one ABC transporter. Other significantly increasing transcripts with potential roles in detoxification of host defenses included alcohol dehydrogenases and a group of unexpected transcripts whose products may play an, as yet, undiscovered role in host colonization by mountain pine beetle.

RNAi-mediated knockdown of catalase causes cell cycle arrest in SL-1 cells and results in low survival rate of Spodoptera litura (Fabricius)

Deregulated reactive oxygen species (ROS) production can lead to the disruption of structural and functional integrity of cells as a consequence of reactive interaction between ROS and various biological components. Catalase (CAT) is a common enzyme existing in nearly all organisms exposed to oxygen, which decomposes harmful hydrogen peroxide, into water and oxygen. In this study, the full length sequence that encodes CAT-like protein from Spodoptera litura named siltCAT (GenBank accession number: JQ_663444) was cloned and characterized. Amino acid sequence alignment showed siltCAT shared relatively high conservation with other insect, especially the conserved residues which defined heme and NADPH orientation. Expression pattern analysis showed that siltCAT mRNA was mainly expressed in the fat body, midgut, cuticle and malpighian tube, and as well as over last instar larvae, pupa and adult stages. RNA interference was used to silence CAT gene in SL-1 cells and the fourth-instar stage of S. litura larvae respectively. Our results provided evidence that CAT knockdown induced ROS generation, cell cycle arrest and apoptosis in SL-1 cells. It also confirmed the decrease in survival rate because of increased ROS production in experimental groups injected with double-stranded RNA of CAT (dsCAT). This study implied that ROS scavenging by CAT is important for S. litura survival.

Random inducible controlled expression (RICE) for identification of mycobacterial virulence genes

We have developed Random Inducible Controlled Expression (RICE), a high throughput genetic approach to identify regulated virulence pathways in pathogenic mycobacteria. RICE allows expression of bacterial genes under conditions where they are normally off, e.g. under laboratory growth conditions, via the use of an inducible or constitutive promoter as well as gene dosage effects due to the presence of the gene on a plasmid. Mycobacterial genomic DNA can be digested to yield random fragments for cloning into a suicide expression vector downstream of a mycobacterial promoter or with their own promoter on a replicating plasmid increasing expression by gene dosage effects. The plasmid DNA is normally amplified in Escherichia coli and delivered into mycobacteria to select for recombinants or plasmid transformants. The resulting library is then directly screened for enhanced host cell interactions in functional assays that evaluate the efficiency of adherence, entry and replication inside host cells. This approach has resulted in identification of several virulence factors from pathogenic mycobacteria. Our analysis of one such locus identified by RICE, the mycobacterial enhanced entry locus (mel2), found that the genes present facilitate bacterial persistence inside the host by protecting the pathogen against oxidative damage. Thus, we have developed a genetic strategy that offers several advantages: (i) it allows identification of bacterial genetic elements that have a direct role during host-pathogen interactions (ii) it can be used to identify virulence factors in a broad range of pathogens and (iii) it can reveal genes that are only induced at specific stages of infection.

Protection of Mycobacterium tuberculosis from reactive oxygen species conferred by the mel2 locus impacts persistence and dissemination

Persistence of Mycobacterium tuberculosis in humans represents a major roadblock to elimination of tuberculosis. We describe identification of a locus in M. tuberculosis, mel2, that displays similarity to bacterial bioluminescent loci and plays an important role during persistence in mice. We constructed a deletion of the mel2 locus and found that the mutant displays increased susceptibility to reactive oxygen species (ROS). Upon infection of mice by aerosol the mutant grows normally until the persistent stage, where it does not persist as well as wild type. Histopathological analyses show that infection with the mel2 mutant results in reduced pathology and both CFU and histopathology indicate that dissemination of the mel2 mutant to the spleen is delayed. These data along with growth in activated macrophages and infection of Phox(-/-) and iNOS(-/-) mice and bone marrow-derived macrophages suggest that the primary mechanism by which mel2 affects pathogenesis is through its ability to confer resistance to ROS. These studies provide the first insight into the mechanism of action for this novel class of genes that are related to bioluminescence genes. The role of mel2 in resistance to ROS is important for persistence and dissemination of M. tuberculosis and suggests that homologues in other bacterial species are likely to play a role in pathogenesis.

The Mycobacterium marinum mel2 locus displays similarity to bacterial bioluminescence systems and plays a role in defense against reactive oxygen and nitrogen species

BACKGROUND

Mycobacteria have developed a number of pathways that provide partial protection against both reactive oxygen species (ROS) and reactive nitrogen species (RNS). We recently identified a locus in Mycobacterium marinum, mel2, that plays a role during infection of macrophages. The molecular mechanism of mel2 action is not well understood.

RESULTS

To better understand the role of the M. marinum mel2 locus, we examined these genes for conserved motifs in silico. Striking similarities were observed between the mel2 locus and loci that encode bioluminescence in other bacterial species. Since bioluminescence systems can play a role in resistance to oxidative stress, we postulated that the mel2 locus might be important for mycobacterial resistance to ROS and RNS. We found that an M. marinum mutant in the first gene in this putative operon, melF, confers increased susceptibility to both ROS and RNS. This mutant is more susceptible to ROS and RNS together than either reactive species alone.

CONCLUSION

These observations support a role for the M. marinum mel2 locus in resistance to oxidative stress and provide additional evidence that bioluminescence systems may have evolved from oxidative defense mechanisms.

Catalase from the silkworm, Bombyx mori: gene sequence, distribution, and overexpression

Living organisms require mechanisms regulating reactive oxygen species (ROS) such as hydrogen peroxide and superoxide anion. Catalase is one of the regulatory enzymes and facilitates the degradation of hydrogen peroxide to oxygen and water. Biochemical information on an insect catalase is, however, insufficient. Using mRNA from fat body of the silkworm, Bombyx mori, a cDNA encoding a putative catalase was amplified by reverse transcriptase-polymerase chain reaction and sequenced. The deduced amino acid sequence comprised 507 residues with more than seventy residues forming a scaffold for a heme cofactor conserved. The sequence showed 71% and 66% identities to those of the Drosophila melanogaster and Apis mellifera catalases, respectively; the catalase from B. mori was estimated to be phylogenetically close to that from A. mellifera. The transcripts of the gene and the catalase activity were distributed in diverse tissues of B. mori, suggesting its ubiquitous nature. Using the gene, a recombinant catalase (rCAT) was functionally overexpressed in a soluble form using Escherichia coli, purified to homogeneity, and characterized. The pH-optimum of rCAT was broad around pH 8.0. More than 80% of the original rCAT activity was retained after incubation in the following conditions: at pH 8-11 and 4 degrees C for 24 h; at pH 7 and temperatures below 50 degrees C for 30 min. The Michaelis constant for hydrogen peroxide was evaluated to be 28 mM at pH 6.5 and 30 degrees C. rCAT was suggested to be a member of the typical catalase family.

Circadian rhythms, oxidative stress, and antioxidative defense mechanisms

Endogenous circadian and exogenously driven daily rhythms of antioxidative enzyme activities and of low molecular weight antioxidants (LMWAs) are described in various phylogenetically distant organisms. Substantial amplitudes are detected in several cases, suggesting the significance of rhythmicity in avoiding excessive oxidative stress. Mammalian and/or avian glutathione peroxidase and, as a consequence, glutathione reductase activities follow the rhythm of melatonin. Another hint for an involvement of melatonin in the control of redox processes is seen in its high-affinity binding to cytosolic quinone reductase 2, previously believed to be a melatonin receptor. Although antioxidative protection by pharmacological doses of melatonin is repeatedly reported, explanations of these findings are still insufficient and their physiological and chronobiological relevance is not yet settled. Recent data indicate a role of melatonin in the avoidance of mitochondrial radical formation, a function which may prevail over direct scavenging. Rhythmic changes in oxidative damage of protein and lipid molecules are also reported. Enhanced oxidative protein modification accompanied by a marked increase in the circadian amplitude of this parameter is detected in the Drosophila mutant rosy, which is deficient in the LMWA urate. Preliminary evidence for the significance of circadian rhythmicity in diminishing oxidative stress comes from clock mutants. In Drosophila, moderately enhanced protein damage is described for the arrhythmic and melatonin null mutant per0, but even more elevated, periodic damage is found in the short-period mutant per(s), synchronized to LD 12:12. Remarkably large increases in oxidative protein damage, along with impairment of tissue integrity and--obviously insufficient--compensatory elevations in protective enzymes are observed in a particularly vulnerable organ, the Harderian gland, of another short-period mutant tau, in the Syrian hamster. Mice deficient in the per2 gene homolog are reported to be cancer-prone, a finding which might also relate to oxidative stress. In the dinoflagellate Lingulodinium polyedrum [Gonyaulax polyedra], various treatments that cause oxidative stress result in strong suppressions of melatonin and its metabolite 5-methoxytryptamine (5-MT) and to secondary effects on overt rhythmicity. The glow maximum, depending on the presence of elevated 5-MT at the end of subjective night, decreases in a dose-dependent manner already under moderate, non-lethal oxidative stress, but is restored by replenishing melatonin. Therefore, a general effect of oxidative stress may consist in declines of easily oxidizable signaling molecules such as melatonin, and this can have consequences on the circadian intraorganismal organization and expression of overt rhythms. Recent findings on a redox-sensitive input into the core oscillator via modulation of NPAS2/BMAL1 or CLK/BMAL1 heterodimer binding to DNA indicate a direct influence of cellular redox balance, including oxidative stress, on the circadian clock.

Fire?y luciferin as antioxidant and light emitter: the evolution of insect bioluminescence

Insects are the main group with luminescent species among terrestrial animals. In this paper, we report that fire fly luciferin is endowed with antioxidant properties against oxidative and nitrosative stress. The luciferin reduces linoleate peroxidation in acellular tests and increases the viability of mammalian cells exposed to the oxidant tert-butyl hydroperoxide. Dehydrorhodamine-based tests indicate that fire fly luciferin also scavenges peroxynitrite, whereas parallel tests on cells showed a marked protection of cells subjected to the peroxynitrite generator SIN-1. Together, these results suggest that fire fly luciferin's antioxidant properties could help photocytes coping with the hyperoxidant conditions to which they are submitted during luminous emissions. These data could also suggest that the evolutionary foundation of the bioluminescent system could have been the luciferin, and not the luciferase, first serving as a scavenger of oxidants toxic to the cells, then as a light emitting substrate for luciferase precursors. Similarities with the evolutionary scenario proposed for marine bioluminescent organisms relying on coelenterazine suggest that the surprisingly high success rate observed in the independent emergence of bioluminescent animals could reflect the ease of transformation of antioxidant mechanisms into light-producing systems.