1
|
Molina-Ruiz CS, Zamora-Briseño JA, Simón O, Lasa R, Williams T. A qPCR Assay for the Quantification of Selected Genotypic Variants of Spodoptera frugiperda Multiple Nucleopolyhedrovirus ( Baculoviridae). Viruses 2024; 16:881. [PMID: 38932173 PMCID: PMC11209410 DOI: 10.3390/v16060881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2024] [Revised: 05/26/2024] [Accepted: 05/29/2024] [Indexed: 06/28/2024] Open
Abstract
Alphabaculoviruses are lethal dsDNA viruses of Lepidoptera that have high genetic diversity and are transmitted in aggregates within proteinaceous occlusion bodies. This mode of transmission has implications for their efficacy as biological insecticides. A Nicaraguan isolate of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV-NIC) comprising nine genotypic variants has been the subject of considerable study due to the influence of variant interactions on the insecticidal properties of mixed-variant occlusion bodies. As part of a systematic study on the replication and transmission of variant mixtures, a tool for the accurate quantification of a selection of genotypic variants was developed based on the quantitative PCR technique (qPCR). First, primer pairs were designed around a region of high variability in four variants named SfNic-A, SfNic-B, SfNic-C and SfNic-E to produce amplicons of 103-150 bp. Then, using cloned purified amplicons as standards, amplification was demonstrated over a dynamic range of 108-101 copies of each target. The assay was efficient (mean ± SD: 98.5 ± 0.8%), reproducible, as shown by low inter- and intra-assay coefficients of variation (<5%), and specific to the target variants (99.7-100% specificity across variants). The quantification method was validated on mixtures of genotype-specific amplicons and demonstrated accurate quantification. Finally, mixtures of the four variants were quantified based on mixtures of budded virions and mixtures of DNA extracted from occlusion-derived virions. In both cases, mixed-variant preparations compared favorably to total viral genome numbers by quantification of the polyhedrin (polh) gene that is present in all variants. This technique should prove invaluable in elucidating the influence of variant diversity on the transmission and insecticidal characteristics of this pathogen.
Collapse
Affiliation(s)
- Cindy S. Molina-Ruiz
- Instituto de Ecología AC (INECOL), Xalapa, Veracruz 91073, Mexico; (C.S.M.-R.); (J.A.Z.-B.); (R.L.)
| | | | - Oihane Simón
- Institute for Multidisciplinary Research in Applied Biology, Universidad Pública de Navarra, 31006 Pamplona, Spain;
| | - Rodrigo Lasa
- Instituto de Ecología AC (INECOL), Xalapa, Veracruz 91073, Mexico; (C.S.M.-R.); (J.A.Z.-B.); (R.L.)
| | - Trevor Williams
- Instituto de Ecología AC (INECOL), Xalapa, Veracruz 91073, Mexico; (C.S.M.-R.); (J.A.Z.-B.); (R.L.)
| |
Collapse
|
2
|
Pazmiño-Ibarra V, Herrero S, Sanjuan R. Spatially Segregated Transmission of Co-Occluded Baculoviruses Limits Virus-Virus Interactions Mediated by Cellular Coinfection during Primary Infection. Viruses 2022; 14:1697. [PMID: 36016318 PMCID: PMC9413315 DOI: 10.3390/v14081697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 07/26/2022] [Accepted: 07/27/2022] [Indexed: 11/16/2022] Open
Abstract
The occlusion bodies (OBs) of certain alphabaculoviruses are polyhedrin-rich structures that mediate the collective transmission of tens of viral particles to the same insect host. In addition, in multiple nucleopolyhedroviruses, occlusion-derived virions (ODVs) form nucleocapsid aggregates that are delivered to the same host cell. It has been suggested that, by favoring coinfection, this transmission mode promotes evolutionarily stable interactions between different baculovirus variants. To quantify the joint transmission of different variants, we obtained OBs from cells coinfected with two viral constructs, each encoding a different fluorescent reporter, and used them for inoculating Spodoptera exigua larvae. The microscopy analysis of midguts revealed that the two reporter genes were typically segregated into different infection foci, suggesting that ODVs show limited ability to promote the co-transmission of different virus variants to the same host cell. However, a polyhedrin-deficient mutant underwent inter-host transmission by exploiting the OBs of a fully functional virus and re-acquired the lost gene through recombination, demonstrating cellular coinfection. Our results suggest that viral spatial segregation during transmission and primary infection limits interactions between different baculovirus variants, but that these interactions still occur within the cells of infected insects later in infection.
Collapse
Affiliation(s)
- Verónica Pazmiño-Ibarra
- Institute for Integrative Systems Biology (I2SysBio), Consejo Superior de Investigaciones Científicas-Universitat de València, C/Catedrático Agustín Escardino 9, 46980 Paterna, Spain;
| | - Salvador Herrero
- Department of Genetics and Institute BIOTECMED, Universitat de València, 46100 Burjassot, Spain;
| | - Rafael Sanjuan
- Institute for Integrative Systems Biology (I2SysBio), Consejo Superior de Investigaciones Científicas-Universitat de València, C/Catedrático Agustín Escardino 9, 46980 Paterna, Spain;
| |
Collapse
|
3
|
Boezen D, Ali G, Wang M, Wang X, van der Werf W, Vlak JM, Zwart MP. Empirical estimates of the mutation rate for an alphabaculovirus. PLoS Genet 2022; 18:e1009806. [PMID: 35666722 PMCID: PMC9203023 DOI: 10.1371/journal.pgen.1009806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 06/16/2022] [Accepted: 04/27/2022] [Indexed: 01/02/2023] Open
Abstract
Mutation rates are of key importance for understanding evolutionary processes and predicting their outcomes. Empirical mutation rate estimates are available for a number of RNA viruses, but few are available for DNA viruses, which tend to have larger genomes. Whilst some viruses have very high mutation rates, lower mutation rates are expected for viruses with large genomes to ensure genome integrity. Alphabaculoviruses are insect viruses with large genomes and often have high levels of polymorphism, suggesting high mutation rates despite evidence of proofreading activity by the replication machinery. Here, we report an empirical estimate of the mutation rate per base per strand copying (s/n/r) of Autographa californica multiple nucleopolyhedrovirus (AcMNPV). To avoid biases due to selection, we analyzed mutations that occurred in a stable, non-functional genomic insert after five serial passages in Spodoptera exigua larvae. Our results highlight that viral demography and the stringency of mutation calling affect mutation rate estimates, and that using a population genetic simulation model to make inferences can mitigate the impact of these processes on estimates of mutation rate. We estimated a mutation rate of μ = 1×10−7 s/n/r when applying the most stringent criteria for mutation calling, and estimates of up to μ = 5×10−7 s/n/r when relaxing these criteria. The rates at which different classes of mutations accumulate provide good evidence for neutrality of mutations occurring within the inserted region. We therefore present a robust approach for mutation rate estimation for viruses with stable genomes, and strong evidence of a much lower alphabaculovirus mutation rate than supposed based on the high levels of polymorphism observed. Virus populations can evolve rapidly, driven by the large number of mutations that occur during virus replication. It is challenging to measure mutation rates because selection will affect which mutations are observed: beneficial mutations are overrepresented in virus populations, while deleterious mutations are selected against and therefore underrepresented. Few mutation rates have been estimated for viruses with large DNA genomes, and there are no estimates for any insect virus. Here, we estimate the mutation rate for an alphabaculovirus, a virus that infects caterpillars and has a large, 134 kilobase pair DNA genome. To ensure that selection did not bias our estimate of mutation rate, we studied which mutations occurred in a large artificial region inserted into the virus genome, where mutations did not affect viral fitness. We deep sequenced evolved virus populations, and compared the distribution of observed mutants to predictions from a simulation model to estimate mutation rate. We found evidence for a relatively low mutation rate, of one mutation in every 10 million bases replicated. This estimate is in line with expectations for a DNA virus with self-correcting replication machinery and a large genome.
Collapse
Affiliation(s)
- Dieke Boezen
- Department of Microbial Ecology, The Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
| | - Ghulam Ali
- Laboratory of Virology, Wageningen University and Research, Wageningen, The Netherlands
| | - Manli Wang
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, PR China
| | - Xi Wang
- Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, PR China
| | - Wopke van der Werf
- Centre for Crop Systems Analysis, Wageningen University and Research, Wageningen, The Netherlands
| | - Just M. Vlak
- Laboratory of Virology, Wageningen University and Research, Wageningen, The Netherlands
| | - Mark P. Zwart
- Department of Microbial Ecology, The Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
- * E-mail:
| |
Collapse
|
4
|
Thézé J, Cabodevilla O, Palma L, Williams T, Caballero P, Herniou EA. Genomic diversity in European Spodoptera exigua multiple nucleopolyhedrovirus isolates. J Gen Virol 2014; 95:2297-2309. [PMID: 24854001 DOI: 10.1099/vir.0.064766-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Key virus traits such as virulence and transmission strategies rely on genetic variation that results in functional changes in the interactions between hosts and viruses. Here, comparative genomic analyses of seven isolates of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) with differing phenotypes were employed to pinpoint candidate genes that may be involved in host-virus interactions. These isolates obtained after vertical or horizontal transmission of infection in insects differed in virulence. Apart from one genome containing a piggyBac transposon, all European SeMNPV isolates had a similar genome size and content. Complete genome analyses of single nucleotide polymorphisms and insertions/deletions identified mutations in 48 ORFs that could result in functional changes. Among these, 13 ORFs could be correlated with particular phenotypic characteristics of SeMNPV isolates. Mutations were found in all gene functional classes and most of the changes we highlighted could potentially be associated with differences in transmission. The regulation of DNA replication (helicase, lef-7) and transcription (lef-9, p47) might be important for the establishment of sublethal infection prior to and following vertical transmission. Virus-host cell interactions also appear instrumental in the modulation of viral transmission as significant mutations were detected in virion proteins involved in primary (AC150) or secondary infections (ME35) and in apoptosis inhibition (IAP2, AC134). Baculovirus populations naturally harbour high genomic variation located in genes involved at different levels of the complex interactions between virus and host during the course of an infection. The comparative analyses performed here suggest that the differences in baculovirus virulence and transmission phenotypes involve multiple molecular pathways.
Collapse
Affiliation(s)
- Julien Thézé
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université François-Rabelais de Tours, UFR Sciences et Techniques, 37200 Tours, France
| | - Oihana Cabodevilla
- Instituto de Agrobiotecnología, CSIC-Gobierno de Navarra, 31192 Mutilva Baja, Navarra, Spain
| | - Leopoldo Palma
- Instituto de Agrobiotecnología, CSIC-Gobierno de Navarra, 31192 Mutilva Baja, Navarra, Spain
| | | | - Primitivo Caballero
- Departamento de Producción Agraria, Universidad Pública de Navarra, 31006 Pamplona, Navarra, Spain.,Instituto de Agrobiotecnología, CSIC-Gobierno de Navarra, 31192 Mutilva Baja, Navarra, Spain
| | - Elisabeth A Herniou
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université François-Rabelais de Tours, UFR Sciences et Techniques, 37200 Tours, France
| |
Collapse
|
5
|
Complex dynamics of defective interfering baculoviruses during serial passage in insect cells. J Biol Phys 2013; 39:327-42. [DOI: 10.1007/s10867-013-9317-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 03/28/2013] [Indexed: 11/26/2022] Open
|
6
|
Rapid and cost-effective baculovirus sample preparation method as a viable alternative to conventional preparation for quantitative real-time PCR. J Virol Methods 2012; 182:27-36. [PMID: 22406450 DOI: 10.1016/j.jviromet.2012.03.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Revised: 02/21/2012] [Accepted: 03/01/2012] [Indexed: 01/14/2023]
Abstract
The increasing use of the baculovirus expression vector system (BEVS) has generated significant interest into techniques for quantifying baculovirus stocks. One method involves the use of quantitative real-time polymerase chain reaction (PCR). This study investigated simplifying baculovirus sample preparation for quantitative Real Time PCR to provide an alternative to current kit-based preparation methods. To achieve this goal, combinations of freeze/thaw cycles and Triton X-100 treatment were investigated. A treatment with only Triton X-100 was found to be sufficient to provide a simple, rapid and cheap alternative to kit-based preparation methods. This study also examined other factors such as primer choice to further examine the process of baculovirus quantitation by qPCR.
Collapse
|
7
|
Kamen AA, Aucoin MG, Merten OW, Alves P, Hashimoto Y, Airenne K, Hu YC, Mezzina M, van Oers MM. An initiative to manufacture and characterize baculovirus reference material. J Invertebr Pathol 2011; 107 Suppl:S113-7. [PMID: 21784226 DOI: 10.1016/j.jip.2011.02.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Accepted: 02/07/2011] [Indexed: 01/25/2023]
Abstract
This letter to the editor brings to the attention of researchers an initiative to develop a baculovirus reference material repository. To be successful this initiative needs the support of a broad panel of researchers working with baculovirus vectors for recombinant protein production and gene delivery for either therapy or vaccination. First there is a need to reach a consensus on the nature of the reference material, the production protocols and the baculovirus characterization methods. It will also be important to define repository and distribution procedures so that the reference material is available to any researcher for calibrating experimental data and to compare experiments performed in the various laboratories. As more and more baculovirus-based products are licensed or in the final stages of development, the development of a repository of baculovirus reference material is timely. This letter describes the requirements for the reference material and for the project as a whole to be successful and calls for a partnership that would involve academic, industrial laboratories and governmental organizations to support this international initiative.
Collapse
|
8
|
van der Werf W, Hemerik L, Vlak JM, Zwart MP. Heterogeneous host susceptibility enhances prevalence of mixed-genotype micro-parasite infections. PLoS Comput Biol 2011; 7:e1002097. [PMID: 21738463 PMCID: PMC3127814 DOI: 10.1371/journal.pcbi.1002097] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2010] [Accepted: 05/05/2011] [Indexed: 11/19/2022] Open
Abstract
Dose response in micro-parasite infections is usually shallower than predicted by the independent action model, which assumes that each infectious unit has a probability of infection that is independent of the presence of other infectious units. Moreover, the prevalence of mixed-genotype infections was greater than predicted by this model. No probabilistic infection model has been proposed to account for the higher prevalence of mixed-genotype infections. We use model selection within a set of four alternative models to explain high prevalence of mixed-genotype infections in combination with a shallow dose response. These models contrast dependent versus independent action of micro-parasite infectious units, and homogeneous versus heterogeneous host susceptibility. We specifically consider a situation in which genome differences between genotypes are minimal, and highly unlikely to result in genotype-genotype interactions. Data on dose response and mixed-genotype infection prevalence were collected by challenging fifth instar Spodoptera exigua larvae with two genotypes of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), differing only in a 100 bp PCR marker sequence. We show that an independent action model that includes heterogeneity in host susceptibility can explain both the shallow dose response and the high prevalence of mixed-genotype infections. Theoretical results indicate that variation in host susceptibility is inextricably linked to increased prevalence of mixed-genotype infections. We have shown, to our knowledge for the first time, how heterogeneity in host susceptibility affects mixed-genotype infection prevalence. No evidence was found that virions operate dependently. While it has been recognized that heterogeneity in host susceptibility must be included in models of micro-parasite transmission and epidemiology to account for dose response, here we show that heterogeneity in susceptibility is also a fundamental principle explaining patterns of pathogen genetic diversity among hosts in a population. This principle has potentially wide implications for the monitoring, modeling and management of infectious diseases. What elements are indispensable in the description of the most basic host-pathogen interactions? The simplest models of infection generally fail to predict how many host plants or animals will become infected, and which virus genotypes will be present in these infected hosts. These simple models of infection are the building blocks for more complicated models of epidemiology and disease dynamics and diversity, making it important to identify the reasons for failure. We developed four probabilistic models of infection incorporating different mechanisms that could potentially explain and overcome this failure. We obtained experimental data to test these models by exposing Lepidopteran larvae to different genotypes of an insect DNA virus, and determining which virus genotypes had infected them. The model which best described the data added only one element: variation in the susceptibility of individual caterpillars to the virus. Host variation in susceptibility is known to affect transmission of viruses between hosts, but here we show it is inextricably linked to infection biology and indispensable for understanding pathogen diversity in host populations.
Collapse
Affiliation(s)
- Wopke van der Werf
- Centre for Crop Systems Analysis, Wageningen University, Wageningen, The Netherlands
| | - Lia Hemerik
- Biometris, Wageningen University, Wageningen, The Netherlands
| | - Just M. Vlak
- Laboratory of Virology, Wageningen University, Wageningen, The Netherlands
| | - Mark P. Zwart
- Laboratory of Virology, Wageningen University, Wageningen, The Netherlands
- Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-UPV, Valencia, Spain
- Quantitative Veterinary Epidemiology Group, Wageningen University, Wageningen, The Netherlands
- * E-mail:
| |
Collapse
|
9
|
Rodríguez VA, Belaich MN, Gómez DLM, Sciocco-Cap A, Ghiringhelli PD. Identification of nucleopolyhedrovirus that infect Nymphalid butterflies Agraulis vanillae and Dione juno. J Invertebr Pathol 2010; 106:255-62. [PMID: 21047512 DOI: 10.1016/j.jip.2010.10.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Revised: 10/11/2010] [Accepted: 10/22/2010] [Indexed: 11/17/2022]
Abstract
Dione juno and Agraulis vanillae are very common butterflies in natural gardens in South America, and also bred worldwide. In addition, larvae of these butterflies are considered as pests in crops of Passiflora spp. For these reasons, it is important to identify and describe pathogens of these species, both for preservation purposes and for use in pest control. Baculoviridae is a family of insect viruses that predominantly infect species of Lepidoptera and are used as bioinsecticides. Larvae of D. juno and A. vanillae exhibiting symptoms of baculovirus infection were examined for the presence of baculoviruses by PCR and transmission electron microscopy. Degenerate primers were designed and used to amplify partial sequences from the baculovirus p74, cathepsin, and chitinase genes, along with previously designed primers for amplification of lef-8, lef-9, and polh. Sequence data from these six loci, along with ultrastructural observations on occlusion bodies isolated from the larvae, confirmed that the larvae were infected with nucleopolyhedroviruses from genus Alphabaculovirus. The NPVs from the two different larval hosts appear to be variants of the same, previously undescribed baculovirus species. Phylogenetic analysis of the sequence data placed these NPVs in Alphabaculovirus group I/clade 1b.
Collapse
Affiliation(s)
- Vanina Andrea Rodríguez
- LIGBCM, Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Roque Saenz Peña 352, Bernal, Argentina
| | | | | | | | | |
Collapse
|
10
|
Base-pairing promotes leader selection to prime in vitro influenza genome transcription. Virology 2010; 409:17-26. [PMID: 21051068 DOI: 10.1016/j.virol.2010.09.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Revised: 07/21/2010] [Accepted: 09/07/2010] [Indexed: 11/21/2022]
Abstract
The requirements for alignment of capped leader sequences along the viral genome during influenza transcription initiation (cap-snatching) have long been an enigma. In this study, competition experiments using an in vitro transcription assay revealed that influenza virus transcriptase prefers leader sequences with base complementarity to the 3'-ultimate residues of the viral template, 10 or 11 nt from the 5' cap. Internal priming at the 3'-penultimate residue, as well as prime-and-realign was observed. The nucleotide identity immediately 5' of the base-pairing residues also affected cap donor usage. Application to the in vitro system of RNA molecules with increased base complementarity to the viral RNA template showed stronger reduction of globin RNA leader initiated influenza transcription compared to those with a single base-pairing possibility. Altogether the results indicated an optimal cap donor consensus sequence of (7m)G-(N)(7-8)-(A/U/G)-(A/U)-AGC-3'.
Collapse
|
11
|
Georgievska L, De Vries RSM, Gao P, Sun X, Cory JS, Vlak JM, van der Werf W. Transmission of wild-type and recombinant HaSNPV among larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) on cotton. ENVIRONMENTAL ENTOMOLOGY 2010; 39:459-467. [PMID: 20388275 DOI: 10.1603/en09183] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Horizontal transmission of insect viruses is a key factor in their cycling in agro-ecosystems. Here we study the transmission of the baculovirus HaSNPV among larvae of Helicoverpa armigera (Hübner) in cotton. Transmission of three HaSNPV genotypes was studied from larvae infected with a single virus genotype and from larvae infected with two different genotypes. Genotypes included a wild-type virus, an ecdysteroid UDP-glucosyltransferase (egt) deletion mutant (HaSNPV-LM2) with slightly enhanced speed of kill, and an egt-negative genotype that expresses a neurotoxin gene derived from the scorpion Androctonus australis Hector (HaSNPV-4A). The latter genotype has a substantially increased speed of kill. In three field experiments, the wild-type and egt deletion virus variants and a mixture of the two had similar rates of transmission. Transmission increased with density of infector insects and decreased with time lapsed since the inoculation of the infector larvae. Transmission of the neurotoxin expressing virus was lower than that of the other two genotypes in a glasshouse experiment. The studied genotypes of HaSNPV have significant differences in time to kill and virus yield, but we found no significant differences in rates of virus transmission at the crop level in the case of the egt deletion variant HaSNPV-LM2. Transmission of the transgenic virus genotype HaSNPV-4A was significantly reduced. Overall, differences in transmission between virus genotypes were subtler, and more difficult to detect with statistical significance, than effects of other factors, such as density of infectors and time delay between release of infectors and recipient caterpillars on the plant.
Collapse
Affiliation(s)
- Liljana Georgievska
- Wageningen University, Laboratory of Virology, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands
| | | | | | | | | | | | | |
Collapse
|
12
|
Zwart MP, Hemerik L, Cory JS, de Visser JAGM, Bianchi FJJA, Van Oers MM, Vlak JM, Hoekstra RF, Van der Werf W. An experimental test of the independent action hypothesis in virus-insect pathosystems. Proc Biol Sci 2009; 276:2233-42. [PMID: 19324752 DOI: 10.1098/rspb.2009.0064] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The 'independent action hypothesis' (IAH) states that each pathogen individual has a non-zero probability of causing host death and that pathogen individuals act independently. IAH has not been rigorously tested. In this paper, we (i) develop a probabilistic framework for testing IAH and (ii) demonstrate that, in two out of the six virus-insect pathosystems tested, IAH is supported by the data. We first show that IAH inextricably links host survivorship to the number of infecting pathogen individuals, and develop a model to predict the frequency of single- and dual-genotype infections when a host is challenged with a mixture of two genotypes. Model predictions were tested using genetically marked, near-identical baculovirus genotypes, and insect larvae from three host species differing in susceptibility. Observations in early-instar larvae of two susceptible host species support IAH, but observations in late-instar larvae of susceptible host species and larvae of a less susceptible host species were not in agreement with IAH. Hence the model is experimentally supported only in pathosystems in which the host is highly susceptible. We provide, to our knowledge, the first qualitative experimental evidence that, in such pathosystems, the action of a single virion is sufficient to cause disease.
Collapse
Affiliation(s)
- Mark P Zwart
- Laboratory of Virology, Wageningen University, 6709 PD Wageningen, The Netherlands
| | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Mixtures of complete and pif1- and pif2-deficient genotypes are required for increased potency of an insect nucleopolyhedrovirus. J Virol 2009; 83:5127-36. [PMID: 19264787 DOI: 10.1128/jvi.02020-08] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The insecticidal potency of a nucleopolyhedrovirus population (SfNIC) that infects Spodoptera frugiperda (Lepidoptera) is greater than the potency of any of the component genotypes alone. Occlusion bodies (OBs) produced in mixed infections comprising the complete genotype and a deletion genotype are as pathogenic as the natural population of genotypes from the field. To test whether this increased potency was due to the deletion or to some other characteristic of the deletion variant genome, we used the SfNIC-B genome to construct a recombinant virus (SfNIC-B Delta 16K) with the same 16.4-kb deletion as that observed in SfNIC-C and another recombinant (SfNIC-B Delta pifs) with a deletion encompassing two adjacent genes (pif1 and pif2) that are essential for transmission per os. Mixtures comprising SfNIC-B and SfNIC-B Delta 16K in OB ratios that varied between 10:90 and 90:10 were injected into insects, and the progeny OBs were fed to larvae in an insecticidal potency assay. A densitometric analysis of PCR products indicated that SfNIC-B was generally more abundant than expected in mixtures based on the proportions of OBs used to produce the inocula. Mixtures derived from OB ratios of 10, 25, or 50% of SfNIC-B Delta 16K and the corresponding SfNIC-B proportions showed a significant increase in potency compared to SfNIC-B alone. The results of potency assays with mixtures comprising various proportions of SfNIC-B plus SfNIC-B Delta pifs were almost identical to the results observed with SfNIC-B Delta 16K, indicating that deletion of the pif gene region was responsible for the increased potency observed in mixtures of SfNIC-B and each deletion recombinant virus. Subsequently, mixtures produced from OB ratios involving 10 or 90% of SfNIC-B Delta 16K with the corresponding proportions of SfNIC-B were subjected to four rounds of per os transmission in larvae. The composition of each experimental mixture rapidly converged to a common equilibrium with a genotypic composition of approximately 85% SfNIC-B plus approximately 15% SfNIC-B Delta 16K. Nearly identical results were observed in peroral-passage experiments involving mixtures of SfNIC-B plus SfNIC-B Delta pifs. We conclude that (i) the deletion of the pif1 and pif2 region is necessary and sufficient to explain the increased potency observed in mixtures of complete and deletion genotypes and (ii) viral populations with decreased ratios of pif1- and pif2-deficient genotypes in the virus population increase the potency of genotypic mixtures and are likely to positively influence the transmission of this pathogen.
Collapse
|
14
|
Zwart MP, Van Der Werf W, Van Oers MM, Hemerik L, Van Lent JMV, De Visser JAGM, Vlak JM, Cory JS. Mixed infections and the competitive fitness of faster-acting genetically modified viruses. Evol Appl 2009; 2:209-21. [PMID: 25567862 PMCID: PMC3352374 DOI: 10.1111/j.1752-4571.2008.00058.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2008] [Accepted: 11/28/2008] [Indexed: 11/28/2022] Open
Abstract
Faster-acting recombinant baculoviruses have shown potential for improved suppression of insect pests, but their ecological impact on target and nontarget hosts and naturally occurring pathogens needs to be assessed. Previous studies have focused on the fitness of recombinants at the between-hosts level. However, the population structure of the transmission stages will also be decided by within-host selection. Here we have experimentally quantified the within-host competitive fitness of a fast-acting recombinant Autographa californica multicapsid nucleopolyhedrovirus missing the endogenous egt gene (vEGTDEL), by means of direct competition in single- and serial-passage experiments with its parental virus. Quantitative real-time PCR was employed to determine the ratio of these two viruses in passaged mixtures. We found that vEGTDEL had reduced within-host fitness: per passage the ratio of wild type to vEGTDEL was on average enhanced by a factor of 1.53 (single passage) and 1.68 (serial passage). There is also frequency-dependence: the higher the frequency of vEGTDEL, the stronger the selection against it is. Additionally, the virus ratio is a predictor of time to host death and virus yield. Our results show that egt is important to within-host fitness and allow for a more complete assessment of the ecological impact of recombinant baculovirus release.
Collapse
Affiliation(s)
- Mark P Zwart
- Laboratory of Virology, Wageningen University Wageningen, The Netherlands ; Laboratory of Genetics, Wageningen University Wageningen, The Netherlands
| | - Wopke Van Der Werf
- Crop and Weed Ecology Group, Wageningen University Wageningen, The Netherlands
| | - Monique M Van Oers
- Laboratory of Virology, Wageningen University Wageningen, The Netherlands
| | - Lia Hemerik
- Biometris, Wageningen University Wageningen, The Netherlands
| | - Jan M V Van Lent
- Laboratory of Virology, Wageningen University Wageningen, The Netherlands
| | | | - Just M Vlak
- Laboratory of Virology, Wageningen University Wageningen, The Netherlands
| | - Jenny S Cory
- Department of Biology, Algoma University Sault Ste. Marie, Ontario, Canada ; Department of Biological Sciences, Simon Fraser University Burnaby, British Columbia, Canada
| |
Collapse
|
15
|
Zwart MP, Erro E, van Oers MM, de Visser JAGM, Vlak JM. Low multiplicity of infection in vivo results in purifying selection against baculovirus deletion mutants. J Gen Virol 2008; 89:1220-1224. [PMID: 18420800 DOI: 10.1099/vir.0.83645-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The in vivo fate of Autographa californica multiple nucleopolyhedrovirus deletion mutants originating from serial passage in cell culture was investigated by passaging a population enriched in these mutants in insect larvae. The infectivity of polyhedra and occlusion-derived virion content per polyhedron were restored within two passages in vivo. The frequency of occurrence of deletion mutants was determined by real-time PCR. The frequency of the non-homologous region origin (non-HR ori) of DNA replication was reduced to wild-type levels within two passages. The frequency of the polyhedrin gene did not increase and remained below wild-type levels. A low m.o.i. during the initial infection in insect larvae, causing strong purifying selection for autonomously replicating viruses, could explain these observations. The same virus population used in vivo was also passaged once at a different m.o.i. in cell culture. A similar effect (i.e. lower non-HR ori frequency) was observed at low m.o.i. only, indicating that m.o.i. was the key selective condition.
Collapse
Affiliation(s)
- Mark P Zwart
- Laboratory of Genetics, Wageningen University, The Netherlands.,Laboratory of Virology, Wageningen University, The Netherlands
| | - Eloy Erro
- Laboratory of Virology, Wageningen University, The Netherlands
| | | | | | - Just M Vlak
- Laboratory of Virology, Wageningen University, The Netherlands
| |
Collapse
|