Baculoviruses-- re-emerging biopesticides

Innovative applications for insect viruses: towards insecticide sensitization

The effective management of emerging insect-borne disease is dependent on the use of safe and efficacious chemical insecticides. Given the inherent ability of insects to develop resistance, it is essential to propose innovative strategies because insecticides remain the most important element of integrated approaches to vector control. Recently, intracellular phosphorylation and dephosphorylation of membrane receptors and ion channels targeted by insecticides have been described as new processes for increasing the sensitivity of insecticides. An efficient method might be to infect host insects with recombinant viruses overexpressing specific protein phosphatases/kinases known to regulate specific insecticide-sensitive targets. This attractive strategy could lead to sensitization of the insects, thus reducing the doses of insecticides and increasing the efficacy of treatments.

Genomic sequence, organization and characteristics of a new nucleopolyhedrovirus isolated from Clanis bilineata larva

Background

Baculoviruses are well known for their potential as biological agents for controlling agricultural and forest pests. They are also widely used as expression vectors in molecular cloning studies. The genome sequences of 48 baculoviruses are currently available in NCBI databases. As the number of sequenced viral genomes increases, it is important for the authors to present sufficiently detailed analyses and annotations to advance understanding of them. In this study, the complete genome of Clanis bilineata nucleopolyhedrovirus (ClbiNPV) has been sequenced and analyzed in order to understand this virus better.

Results

The genome of ClbiNPV contains 135,454 base pairs (bp) with a G+C content of 37%, and 139 putative open reading frames (ORFs) of at least 150 nucleotides. One hundred and twenty-six of these ORFs have homologues with other baculovirus genes while the other 13 are unique to ClbiNPV. The 30 baculovirus core genes are all present in ClbiNPV. Phylogenetic analysis based on the combined pif-2 and lef-8 sequences places ClbiNPV in the Group II Alphabaculoviruses. This result is consistent with the absence of gp64 from the ClbiNPV genome and the presence instead of a fusion protein gene, characteristic of Group II. Blast searches revealed that ClbiNPV encodes a photolyase-like gene sequence, which has a 1-bp deletion when compared with photolyases of other baculoviruses. This deletion disrupts the sequence into two small photolyase ORFs, designated Clbiphr-1 and Clbiphr-2, which correspond to the CPD-DNA photolyase and FAD-binding domains of photolyases, respectively.

Conclusion

ClbiNPV belongs to the Group II Alphabaculoviruses and is most closely related to OrleNPV, LdMNPV, TnSNPV, EcobNPV and ChchNPV. It contains a variant DNA photolyase gene, which only exists in ChchNPV, TnSNPV and SpltGV among the baculoviruses.

Real-time PCR assay for detection of a new simulant for poxvirus biothreat agents

Research and financial efforts spent on biodefense technologies highlight the current concern for biothreat event preparedness. Nonhazardous but relevant "simulant" microorganisms are typically used to simplify technological developments, testing, and staff training. The bacteriophage MS2, a small RNA virus, is classically used as the reference simulant for biothreat viruses within the biodefense community. However, variola virus, considered a major threat, displays very different features (size, envelope, and double-stranded DNA genome). The size parameter is critical for aerosol sampling, detection, and protection/filtration technologies. Therefore, a panel of relevant simulants should be used to cover the diversity of biothreat agents. Thus, we investigated a new virus model, the Cydia pomonella granulovirus (baculovirus), which is currently used as a biopesticide. It displays a size similar to that of poxviruses, is enveloped, and contains double-stranded DNA. To provide a molecular tool to detect and quantify this model virus, we developed an assay based on real-time PCR, with a limit of detection ranging from roughly 10 to a few tens of target copies per microl according to the sample matrix. The specificity of the assay against a large panel of potential cross-reactive microorganisms was checked, and the suitability of the assay for environmental samples, especially aerosol studies, was determined. In conclusion, we suggest that our PCR assay allows Cydia pomonella granulovirus to be used as a simulant for poxviruses. This assay may also be useful for environmental or crop treatment studies.

Plant-mediated alteration of the peritrophic matrix and baculovirus infection in lepidopteran larvae

The peritrophic matrix (PM) lines the midgut of most insects, providing protection to the midgut epithelial cells while permitting passage of nutrients and water. Herein, we provide evidence that plant-mediated alteration of the PM contributes to the well-documented inhibition of fatal infection by Autographa californica multiple nucleopolyhedrovirus (AcMNPV) of Heliothis virescens F. larvae fed cotton foliage. We examined the impact of the PM on pathogenesis using a viral construct expressing a reporter gene (AcMNPV-hsp70/lacZ) orally inoculated into larvae with either intact PMs or PMs disrupted by Trichoplusia ni granulovirus occlusion bodies containing enhancin, known to degrade insect intestinal mucin. Larvae possessing disrupted PMs displayed infection foci (lacZ signaling) earlier than those with intact PMs. We then examined PMs from larvae fed artificial diet or plant foliage using electron microscopy; foliage-fed larvae had significantly thicker PMs than diet-fed larvae. Moreover, mean PM width was inversely related to both the proportion of larvae with lacZ signaling at 18h post-inoculation and the final percentage mortality from virus. Thus, feeding on foliage altered PM structure, and these foliage-mediated changes reduced baculoviral efficacy. These data indicate that the PM is an important factor determining the success of an ingested pathogen in foliage-fed lepidopteran larvae.

Characterization of an early gene orf122 from Bombyx mori nucleopolyhedrovirus

The open reading frame 122 of Bombyx mori nucleopolyhedrovirus (BmNPV) (Bm122) has been observed to be a conserved gene in the lepidopteran baculoviruses that have been completely sequenced so far. Its transcript was detected at 3 h post infection (h p.i.) and remained detectable at up to 96 h p.i. Temporal transcription analysis indicated that Bm122 is transcribed by host RNA polymerase. The size of the translational product of the Bm122 gene in Tn5B-1-4 cells was approximately 23 kDa, which is in agreement with the predicted value of 22.9 kDa, suggesting that no major posttranslational modification occurred in the primary protein product. The subcellular localization of Bm122 was studied using EGFP-Bm122, which revealed that Bm122 protein was accumulated within the nuclear region of virus-infected BmN cells. All these results suggest that Bm122 is an early gene encoding a protein that functions in the nucleus.

Mechanisms of pathogenesis and the evolution of parasite virulence

When studying how much a parasite harms its host, evolutionary biologists turn to the evolutionary theory of virulence. That theory has been successful in predicting how parasite virulence evolves in response to changes in epidemiological conditions of parasite transmission or to perturbations induced by drug treatments. The evolutionary theory of virulence is, however, nearly silent about the expected differences in virulence between different species of parasite. Why, for example, is anthrax so virulent, whereas closely related bacterial species cause little harm? The evolutionary theory might address such comparisons by analysing differences in tradeoffs between parasite fitness components: transmission as a measure of parasite fecundity, clearance as a measure of parasite lifespan and virulence as another measure that delimits parasite survival within a host. However, even crude quantitative estimates of such tradeoffs remain beyond reach in all but the most controlled of experimental conditions. Here, we argue that the great recent advances in the molecular study of pathogenesis provide a way forward. In light of those mechanistic studies, we analyse the relative sensitivity of tradeoffs between components of parasite fitness. We argue that pathogenic mechanisms that manipulate host immunity or escape from host defences have particularly high sensitivity to parasite fitness and thus dominate as causes of parasite virulence. The high sensitivity of immunomodulation and immune escape arise because those mechanisms affect parasite survival within the host, the most sensitive of fitness components. In our view, relating the sensitivity of pathogenic mechanisms to fitness components will provide a way to build a much richer and more general theory of parasite virulence.

A silkworm–baculovirus model for assessing the therapeutic effects of antiviral compounds: characterization and application to the isolation of antivirals from traditional medicines

Ganciclovir, foscarnet, vidarabine and ribavirin, which are used to treat viral infections in humans, inhibited the proliferation of a baculovirus (Bombyx mori nucleopolyhedrovirus) in BmN4 cells, a cultured silkworm cell line. These antiviral agents inhibited the proliferation of baculovirus in silkworm body fluid and had therapeutic effects. Using the silkworm infection model, the antiviral activity of Kampo medicines was screened and it was found that cinnamon bark, a component of the traditional Japanese medicine Mao-to, had a therapeutic effect. Based on the therapeutic activity, the antiviral substance was purified. Nuclear magnetic resonance analysis of the purified fraction revealed that the antiviral activity was due to cinnzeylanine, which has previously been isolated from Cinnamomum zeylanicum. Cinnzeylanine inhibits the proliferation of herpes simplex virus type 1 in Vero cells. These results suggest that the silkworm–baculovirus infection model is useful for screening antiviral agents that are effective for treating humans infected with DNA viruses.

Induction of Systemic Acquired Resistance in Cotton Foliage Does Not Adversely Affect the Performance of an Entomopathogen

Baculoviral efficacy against lepidopteran larvae is substantially impacted by the host plant. Here, we characterized how baculoviral pathogenicity to cotton-fed Heliothis virescens larvae is affected by induction of systemic acquired resistance (SAR). Numerous studies have shown that SAR induced by the plant elicitor benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) can protect against plant pathogens, but reports on the impacts of SAR on chewing herbivores or on natural enemies of herbivores are few. We found that BTH application significantly increased foliar peroxidase activity, condensed tannin levels, and total phenolic levels but did not alter dihydroxyphenolic levels. Consumption of BTH-treated foliage did not influence H. virescens pupal weight or larval mortality by the microbial control agent Autographa californica multiple nucleopolyhedrovirus any more than did consumption of untreated foliage. Thus, activation of SAR, although it did not protect the plant against a chewing herbivore, also did not reduce the effect of a natural enemy on a herbivore, indicating that SAR and microbial control agents may be compatible components of integrated pest management.

The promise of insect genomics

Insects are the largest animal group in the world and are ecologically and economically extremely important. This importance of insects is reflected by the existence of currently 24 insect genome projects. Our perspective discusses the state-of-the-art of these genome projects and the impacts that they have on basic insect science and pest control.

Infection, transfection, and co-transfection of baculoviruses by microprojectile bombardment of larvae

The use of baculoviruses as expression vectors for heterologous proteins has been practically limited to the use of the Autographa californica multiple nucleopolyhedrovirus (AcMNPV). In this work, infection, transfection and co-transfection events with the baculoviruses AcMNPV and Trichoplusia ni granulovirus (TnGV) were accomplished by bombardment of T. ni first-instar larvae with microprojectiles coated with virions, viral DNA, and viral DNA and a transfer vector, respectively. A series of shooting conditions were tested until positive results were obtained. The use of 1.6 microm gold particles at 900 psi shooting pressure, 400 Torr vacuum, 7 cm distance to target, on sets of 20 first-instar larvae held in a 16 mm diameter container, proved to be the best shooting conditions. Typical infection symptoms were shown by larvae when shot with viruses or viral DNA from AcMNPV or TnGV. Co-transfected recombinant AcMNPV and TnGV were identified by the formation of occlusion bodies and GFP, respectively, in bombarded larvae. This technique opens a wide range of possibilities, not only to use an extensive number of baculoviruses as expression vectors for heterologous proteins, but also be used to infect, transfect or co-transfect a wide variety of viruses into animal cells.

The insecticidal potential of scorpion β-toxins

Voltage-gated sodium channels are a major target for toxins and insecticides due to their central role in excitability, but due to the conservation of these channels in Animalia most insecticides do not distinguish between those of insects and mammals, thereby imposing risks to humans and livestock. Evidently, as long as modern agriculture depends heavily on the use of insecticides there is a great need for new substances capable of differentiating between sodium channel subtypes. Such substances exist in venomous animals, but ways for their exploitation have not yet been developed due to problems associated with manufacturing, degradation, and delivery to the target channels. Engineering of plants for expression of anti-insect toxins or use of natural vectors that express toxins near their target site (e.g. baculoviruses) are still problematic and raise public concern. In this problematic reality a rational approach might be to learn from nature how to design highly selective anti-insect compounds preferably in the form of peptidomimetics. This is a complex task that requires the elucidation of the face of interaction between insect-selective toxins and their sodium channel receptor sites. This review delineates current progress in: (i) elucidation of the bioactive surfaces of scorpion beta-toxins, especially the excitatory and depressant groups, which show high preference for insects and bind insect sodium channels with high affinity; (ii) studies of the mode of interaction of scorpion beta-toxins with receptor site-4 on voltage-gated sodium channels; and (iii) clarification of channel elements that constitute receptor site-4. This information may be useful in future attempts to mimic the bioactive surface of the toxins for the design of anti-insect selective peptidomimetics.

New measures of insecticidal efficacy and safety obtained with the 39K promoter of a recombinant baculovirus

Baculoviruses are orally infectious to insects and considered to be natural insecticides. To enhance their speed-of-kill these viruses were engineered to express arthropod neurotoxins under the control of various strong promoters. Although this strategy proved to be efficient, it raised recently concerns about safety. We analyzed the speed-of-kill and safety of Autographa californica multiple nucleopolyhedrovirus expressing the insecticidal scorpion neurotoxin AaIT and found that the mortality of Helicoverpa armigera larvae was enhanced significantly when the expression was controlled by the baculovirus delayed-early promoter 39K rather than the very late promoter p10. This improvement was also reflected in better protection of cotton leaves on which these insects were fed. Using lacZ as a sensitive reporter we also found that expression driven by the 39K promoter was detected in insect but not in mammalian cells. These results imply that by selection of an appropriate viral promoter, engineered baculoviruses may comply with the high standard biosafety requirements from a genetically modified organism (GMO). Our results provide further support for the potential use of engineered baculoviruses in insect pest control in a safely manner.

Temporal transcription program of recombinant Autographa californica multiple nucleopolyhedrosis virus

Baculoviruses, a family of large, rod-shaped viruses that mainly infect lepidopteran insects, have been widely used to transduce various cells for exogenous gene expression. Nonetheless, how a virus controls its transcription program in cells is poorly understood. With a custom-made baculovirus DNA microarray, we investigated the recombinant Autographa californica multiple nucleopolyhedrosis virus (AcMNPV) gene expression program in lepidopteran Sf21 cells over the time course of infection. Our analysis of transcription kinetics in the cells uncovered sequential viral gene expression patterns possibly regulated by different mechanisms during different phases of infection. To gain further insight into the regulatory network, we investigated the transcription program of a mutant virus deficient in an early transactivator (pe38) and uncovered several pe38-dependent and pe38-independent genes. This study of baculovirus dynamic transcription programs in different virus genetic backgrounds provides new molecular insights into how gene expression in viruses is regulated.

Applied microbiology and biotechnology in the conservation of stone cultural heritage materials

The contribution of applied microbiology and biotechnology for the preservation and restoration of culturally relevant stoneworks has been used only to a minor extent. Until recently it only involved the identification of the living organisms accountable for the deterioration of those materials by classic phenotypic identification methods. This seems to be changing, given the amount of work recently published that focuses in the introduction of molecular-based techniques for the detection of microorganisms in historic stone. Such techniques complement and expand the information up till now gathered by conventional identification methods. Along with this, efforts are being made to develop and implement bio-based methodologies that may actively contribute to the bioremediation of weathered historic stoneworks. The present mini-review aims to provide an overview of recent findings on these matters.