Bioluminescence as a possible auxiliary oxygen detoxifying mechanism in elaterid larvae

Genome analysis of Phrixothrix hirtus (Phengodidae) railroad worm shows the expansion of odorant-binding gene families and positive selection on morphogenesis and sex determination genes

Among bioluminescent beetles of the Elateroidea superfamily, Phengodidae is the third largest family, with 244 bioluminescent species distributed only in the Americas, but is still the least studied from the phylogenetic and evolutionary points of view. The railroad worm Phrixothrix hirtus is an essential biological model and symbolic species due to its bicolor bioluminescence, being the only organism that produces true red light among bioluminescent terrestrial species. Here, we performed partial genome assembly of P. hirtus, combining short and long reads generated with Illumina sequencing, providing the first source of genomic information and a framework for comparative analyses of the bioluminescent system in Elateroidea. This is the largest genome described in the Elateroidea superfamily, with an estimated size of ∼3.4 Gb, displaying 32 % GC content, and 67 % transposable elements. Comparative genomic analyses showed a positive selection of genes and gene family expansion events of growths and morphogenesis gene products, which could be associated with the atypical anatomical development and morphogenesis found in paedomorphic females and underdeveloped males. We also observed gene family expansion among distinct odorant-binding receptors, which could be associated with the pheromone communication system typical of these beetles, and retrotransposable elements. Common genes putatively regulating bioluminescence production and control, including two luciferase genes corresponding to lateral lanterns green-emitting and head lanterns red-emitting luciferases with 7 exons and 6 introns, and genes potentially involved in luciferin biosynthesis were found, indicating that there are no clear differences about the presence or absence of gene families associated with bioluminescence in Elateroidea.

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.

Evaluation of Phenolic Compound Toxicity Using a Bioluminescent Assay with the Fungus Gerronema viridilucens

Basidiomycetes (phylum Basidiomycota) are filamentous fungi characterized by the exogenous formation of spores on a club-shaped cell called a basidium that are often formed on complex fruiting bodies (mushrooms). Many basidiomycetes serve an important role in recycling lignocellulosic material to higher trophic levels, and some show symbiotic relationships with plants. All known bioluminescent fungi are mushroom-forming basidiomycetes in the order Agaricales. Hence, the disruption of the basidiomycete community can entirely compromise the carbon cycle in nature from fungi to higher trophic levels. The fungus Gerronema viridilucens was used in the present study to investigate the toxicity of a phenolic compound series based on the inhibition of its bioluminescence. The median effect concentration (EC50) obtained from curves of bioluminescence inhibition versus log [phenolic compound] showed that 2,4,6-trichlorophenol was the most toxic compound in the series. The log EC50 values of all phenolic compounds were then used for the prediction of their toxicity. The univariate correlation of log EC50 values obtained from 6 different phenolic compounds was stronger with the dissociation constant (pK_a ) than with 1-octanol/water partition coefficient (K_OW ). Nevertheless, the toxicity can be better predicted by using both parameters, suggesting that the phenol-driven uncoupling of fungus mitochondrial adenosine triphosphate synthesis is the origin of phenolic compound toxicity to the test fungus. Environ Toxicol Chem 2020;39:1558-1565. © 2020 SETAC.

Exposure to static magnetic field stimulates quorum sensing circuit in luminescent Vibrio strains of the Harveyi clade

In this study, the evidence of electron-dense magnetic inclusions with polyhedral shape in the cytoplasm of Harveyi clade Vibrio strain PS1, a bioluminescent bacterium living in symbiosis with marine organisms, led us to investigate the behavior of this bacterium under exposure to static magnetic fields ranging between 20 and 2000 Gauss. When compared to sham-exposed, the light emission of magnetic field-exposed bacteria growing on solid medium at 18°C ±0.1°C was increased up to two-fold as a function of dose and growth phase. Stimulation of bioluminescence by magnetic field was more pronounced during the post-exponential growth and stationary phase, and was lost when bacteria were grown in the presence of the iron chelator deferoxamine, which caused disassembly of the magnetic inclusions suggesting their involvement in magnetic response. As in luminescent Vibrio spp. bioluminescence is regulated by quorum sensing, possible effects of magnetic field exposure on quorum sensing were investigated. Measurement of mRNA levels by reverse transcriptase real time-PCR demonstrated that luxR regulatory gene and luxCDABE operon coding for luciferase and fatty acid reductase complex were significantly up-regulated in magnetic field-exposed bacteria. In contrast, genes coding for a type III secretion system, whose expression was negatively affected by LuxR, were down-regulated. Up-regulation of luxR paralleled with down-regulation of small RNAs that mediate destabilization of luxR mRNA in quorum sensing signaling pathways. The results of experiments with the well-studied Vibrio campbellii strain BB120 (originally classified as Vibrio harveyi) and derivative mutants unable to synthesize autoinducers suggest that the effects of magnetic fields on quorum sensing may be mediated by AI-2, the interspecies quorum sensing signal molecule.

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.

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.

Cell-free expression of soluble and membrane proteins in an array device for drug screening

Enzymes and membrane protein receptors represent almost three-quarters of all current drug targets. As a result, it would be beneficial to have a platform to produce them in a high-throughput format for drug screening. We have developed a miniaturized fluid array device for cell-free protein synthesis, and the device was exploited to produce both soluble and membrane proteins. Two membrane-associated proteins, bacteriorhodopsin and ApoA lipoprotein, were coexpressed in an expression medium in the presence of lipids. Simultaneous expression of ApoA lipoprotein enhanced the solubility of bacteriorhodopsin and would facilitate functional studies. In addition, the device was employed to produce two enzymes, luciferase and beta-lactamase, both of which were demonstrated to be compatible with enzyme inhibition assays. Beta-lactamase, a drug target associated with antibiotic resistance, was further used to show the capability of the device for drug screening. Beta-lactamase was synthesized in the 96 units of the device and then assayed by a range of concentrations of four mock drug compounds without harvesting and purification. The inhibitory effects of these compounds on beta-lactamase were measured in a parallel format, and the degree in their drug effectiveness agreed well with the data in the literature. This work demonstrated the feasibility of the use of the fluid array device and cell-free protein expression for drug screening, with advantages in less reagent consumption, shorter analysis time, and higher throughput.

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.

Synthesis of 7′-[ 123 I]iodo- d -luciferin for in vivo studies of firefly luciferase gene expression

D-(-)-2-(6'-hydroxy-7'-[(123)I]iodobenzothiazolyl)-delta(2)-thiazoline-4-caroxylic acid (7'-[(123)I]iodo-D-luciferin) was synthesized as a novel reporter probe for in vivo studies of firefly luciferase gene expression. 7'-Iodo-D-luciferin, a nonradioactive standard, was synthesized and showed the binding property (K(M)=4.28 microM) similar to that of D-luciferin (2.53 microM) for firefly luciferase in luminescence assay.

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.

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

Several lines of investigation have suggested an interplay between bioluminescence (BL) and oxyradical metabolism, mainly in bacteria and beetles. Although not yet confirmed, luminescent beetles seem to be challenged daily by oxidative conditions imposed by higher oxygen absorption necessary to enhance light emission for courtship (adult lampyrids and elaterids) and prey attraction (e.g. Pyrearinus termitilluminans larvae). This work reports the activities of luciferase, superoxide dismutase (SOD), catalase and dehydroascorbate reductase (DHAR) and total glutathione content at different times of the day in the bright prothorax and dim abdomen of larval Pyrearinus termitilluminans (Coleoptera: Elateridae), investigating a possible adjuvant role for luciferase in oxygen detoxification. Luciferase activity in the prothorax was shown to peak at 7 p.m., which is the time when P. termitilluminans larvae light up for prey attraction. In their habitat, P. termitilluminans larvae emit light until 8.30 p.m. However, at 8 p.m., prothorax luciferase activity achieved basal levels and total glutathione content declined to the daily lowest value, possibly resulting from hyperoxidative conditions during this time. Significant increases in the activities of total SOD (28%) and catalase (37%) were observed in the prothorax at 9 p.m., which should minimize the extent of damage from this potentially hazardous period. Prothorax total SOD (42% higher than daily average) and abdomen CuZnSOD (41%) and catalase (95%) activities showed extra peaks at 7-10 a.m., and abdomen DHAR activity was maximal (37%) earlier (4-7 a.m.). These morning increases in antioxidant enzyme activities may be associated with biological events other than bioluminescence, e.g. intense physical activity for digging tunnels and/or digestion of captured preys. These data suggest that oxyradical pathway and bioluminescence are coordinated, especially in the prothorax, to minimize the oxidative stress imposed by higher irrigation of the photocytes with O(2) when P. termitilluminans larvae emit light.

Luciferase and urate may act as antioxidant defenses in larval Pyrearinus termitilluminans (Elateridae: Coleoptera) during natural development and upon 20-hydroxyecdysone treatment

Insects show unique adaptations to cope with oxidative challenges during larval development, metamorphosis and adulthood. Our previous findings suggested that bioluminescence may act as an auxiliary oxygen-detoxifying mechanism in larvae of Pyrearinus termitilluminans (Elateridae: Coleoptera). We now study the antioxidant status in larval P. termitilluminans, evaluated in terms of levels of chemical and enzymatic antioxidant defenses, as compared to luciferase activity in the prothorax (intensely bright) and abdomen (dim) of the larvae, during natural- and 20-hydroxyecdysone (20-HE)-induced development. In the prothorax, relative total SOD activities in small (< 1 cm), medium (1-2 cm) and large (> 2 cm) larvae were 1.00:0.53:0.32. Catalase activity also decreased with development (1.00:0.69:0.55). In contrast, prothorax luciferase activities and urate content increased with ratios of 1.0:2.2:2.5 and 1:15:97, respectively. No increases were found in the level of prothorax lipid and protein oxidation. In the abdomen, luciferase activity decreased markedly with development (1.00:0.33:0.17), as did other antioxidant enzymes, including dehydroascorbate reductase (1.00:0.59:0.17) and levels of lipid peroxidation products and protein carbonyls. Similar variations were observed in antioxidant enzyme activities when the larvae were treated with 20-HE, except for prothorax catalase. As observed in natural larval growth, luciferase activity was augmented (two-fold in prothorax) upon steroid treatment, and the levels of thiobarbituric acid-reactive substances were magnified in both segments. The increase of luciferase activity and a higher urate content in the prothorax during larval development may reflect metabolic adaptations to keep levels of oxyradicals low in order to compensate for decreased antioxidant enzyme activities.

Bioluminescence

Bioluminescence has evolved independently many times; thus the responsible genes are unrelated in bacteria, unicellular algae, coelenterates, beetles, fishes, and others. Chemically, all involve exergonic reactions of molecular oxygen with different substrates (luciferins) and enzymes (luciferases), resulting in photons of visible light (approximately 50 kcal). In addition to the structure of luciferan, several factors determine the color of the emissions, such as the amino acid sequence of the luciferase (as in beetles, for example) or the presence of accessory proteins, notably GFP, discovered in coelenterates and now used as a reporter of gene expression and a cellular marker. The mechanisms used to control the intensity and kinetics of luminescence, often emitted as flashes, also vary. Bioluminescence is credited with the discovery of how some bacteria, luminous or not, sense their density and regulate specific genes by chemical communication, as in the fascinating example of symbiosis between luminous bacteria and squid.