Characterization of a Multiple-Nucleocapsid Nucleopolyhedrovirus Isolated from Perina Nuda (Fabricius) (Lepidoptera: Lymantriidae) Larvae
Total Page：16
File Type：pdf, Size：1020Kb
Appl. Entomol. Zool. 39 (2): 283–292 (2004) Characterization of a multiple-nucleocapsid nucleopolyhedrovirus isolated from Perina nuda (Fabricius) (Lepidoptera: Lymantriidae) larvae Chih-Yu WU,1 Chu-Fang LO2 and Chung-Hsiung WANG1,* 1 Department of Entomology, and 2 Department of Zoology, National Taiwan University; Taipei, Taiwan, R.O.C. (Received 18 September 2003; Accepted 13 January 2004) Abstract A multiple-nucleocapsid nucleopolyhedrovirus (MNPV), named Perina nuda MNPV (or PenuNPV), isolated from P. nuda (Fabricius) (Lepidoptera: Lymantriidae)—a major banyan pest—was studied in terms of its main morphological, biochemical, and biological properties. The pleiomorphic occlusion bodies were 1.7–5.4 mm in diameter with a mean size of 2.2Ϯ0.52 (mmϮSE), and their most prominent protein had an apparent molecular mass of 32 kDa. The DNA genome size was estimated to be 120.38Ϯ0.38 (kbpϮSE) based on restriction endonuclease fragment sizes. The me- dian lethal dose response (LD50) for this virus in 2nd to 5th instar P. nuda larvae were estimated at 154, 1,431, 14,458, and 169,137 occluded bodies per larva, respectively. In host range tests, other nine lepidopteran species from five fam- ilies were not susceptible to PenuNPV. The high pathogenicity and specificity of this newly described MNPV indicate that it is indeed a good candidate for the biological control of this moth. Key words: Perina nuda; PenuNPV; restriction profiles; histopathology; biological activity uloviruses. Currently, more than 500 different in- INTRODUCTION sect species infected by baculoviruses have been Members of the family Baculoviridae are arthro- reported in the literature (Friesen and Miller, pod-specific pathogens and have been isolated pri- 2001). marily from lepidopteran (moth and butterfly) The transparent wing moth, Perina nuda (Fabri- species. The family is taxonomically characterized cius), is a serious pest of banyan (Ficus spp.) and is by their large and covalently closed genome of a major defoliator of forest and shade trees in double-stranded DNA (range from 80 to 180 kbp), Southeastern Asia (Su et al., 1983). To date, uti- which is packaged singly or multiply in an en- lization of broad-spectrum chemical insecticides is veloped, rod-shaped virion (Blissard et al., 1999; the only practical method of controlling this cater- Friesen and Miller, 2001). In addition, bac- pillar, but this method may cause safety issues in uloviruses are also distinguished by their two mor- the city, as well as it may cause the natural enemies phologically distinct forms of infectious particles: to delay or suppress field colonization. A safe alter- occlusion derived virions (ODVs), comprising en- native pest control method using their pathogens veloped virions embedded within a crystalline ma- was considered. Among pathogens, a nucleopoly- trix of protein (polyhedrin or granulin), and budded hedrovirus (PenuNPV) and an insect picorna-like virions (BVs), comprising a single virion en- virus (PnPV) were detected as the main mortality veloped by a plasma membrane. Baculoviruses in- factors (Su et al., 1983; Wang et al., 1998, 1999). volve two genera: the nucleopolyhedroviruses Nevertheless, PenuNPV could be more suitable (NPVs) and granuloviruses (GVs) (Blissard et al., than PnPV for inclusion in banyan pest biological 1999). The NPVs are characterized by the presence control because of its high virulence to the P. nuda of large occlusion bodies (OBs) in the nucleus of larvae (Lo et al., 1990; Wang and Tsai, 1995; the infected cells. Due to their economic impor- Wang et al., 1998). So far, both the success of in tance especially in pest control and in foreign gene vitro propagation of this NPV in its homogeneous expression, the NPVs have attracted the greatest cell line, NTU-PN-HH (Wang et al., 1996) and the attention and are the best characterized bac- analysis of the nucleotide sequence of polyhedrin *To whom correspondence should be addressed at: E-mail: [email protected] 283 284 C.-Y. WU et al. and p10 genes (Chou et al., 1996, 1997) facilitate propagation medium after a 3-day infection and further molecular biological studies of this virus. purified by sucrose gradient centrifugation as pre- However, former investigations were either di- viously described (Wang et al., 1996). The purified rected towards molecular level studies of this virus BVs were then prepared for negative staining. or toward evaluating its virulence, and none of the Transmission electron microscopy. The in- previous reports addresses its identification or fected and control larvae at 5-day postinoculation characterization. were dissected to small pieces, fixed with 2.5% In this paper we attempt to get a better overview glutaraldehyde in 0.1 M phosphate buffer (pH 7.2) of this virus, including its main morphological, for 3 h, postfixed with 1% osmium tetroxide for biochemical, and biological properties. The data 2 h, dehydrated through an alcoholic gradient se- presented here give further support to the argument ries, and then embedded in Epon-Araldite resin that PenuNPV is a distinct baculovirus species and (Luft, 1961). Thick and ultrathin sections were cut is a good candidate for the biological control of P. on a Reichert OMU3 Ultramicrotome. Thick sec- nuda moth outbreaks in the future. tions were stained with 0.05% toluidine blue (pre- pared in 1% borax solution), while ultrathin sec- tions were stained in 2% uranyl acetate and lead MATERIALS AND METHODS citrate. The micrographs were taken with a HI- Virus isolation and multiplication. A colony of TACHI H7100 electron microscope operated at an Perina nuda (Lepidoptera: Lymantriidae) caterpil- accelerating voltage of 75 kV. For negative staining, lars were obtained and reared in the laboratory a drop of either purified ODVs or BVs were placed with leaves of Banyan, Ficus spp. as in the previ- on a carbon coated grid for 3 min and excess virus ous paper (Wang and Tsai, 1995). The PenuNPV suspension was removed with filter paper. An addi- isolate used in this study originated from a single tional drop of 2% aqueous solution of phospho- infected larva of P. nuda, collected on the campus tungstic acid was placed on the grid, excess stain of Fu Jen Catholic University (Taipei, Taiwan). being removed from the grid with filter paper. The The genetic homogeneity of the isolate was further preparation was allowed to dry before examination. verified following plaque purification in P. nuda Protein profiles of occlusion body. The major culture cells (NTU-PN-HH; Wang et al., 1996). protein profiles of the OBs were carried out follow- Viral amplification was carried out, allowing 3rd- ing the method of Reinganum (1984) with slight instar larvae to feed on fresh Banyan leaves, super- modifications. Briefly, the purified OBs were pre- ficially contaminated with occlusion bodies (about treated with 1% SDS and 0.5% 2-mercaptoethanol 2.5ϫ103 OBs per larva). OBs were purified from (2-ME) for 30 min at pH 7.2 and 70°C, then homogenized larvae by centrifugation on continu- washed to remove soluble material. The washed ous 40 to 65% (wt/wt) sucrose gradients at OBs were then centrifuged at 7,650ϫg for 10 min. 100,000ϫg for 30 min as previously described The pellets were dissociated with 1ϫ SDS-PAGE (Chou et al., 1996). The purified OBs were exam- sample buffer (62.5 mM Tris-HCl, pH 6.8, 10% ined with an optic microscope (400ϫ) and fifty glycerol, 2% 2-ME, 0.1% bromophenol blue, and OBs were measured to determine their mean size. 2% SDS) at 100°C for 10 min. The soluble proteins ODVs were released by hydrolyzing OBs in diluted were electrophoresed in 12.5% sodium dodecyl alkaline solution (100 mM Na2CO3, 170 mM NaCl, sulfate (SDS)-polyacrylamide gels using the 10 mM EDTA, pH 10.5) at 37°C for 30 min. Fol- Laemmli (1970) buffer system. Proteins were visu- lowing the dissolution of the OBs, the suspension alized after staining with silver nitrate, and sizes was centrifuged on the same sucrose gradient at were estimated using molecular weight markers 100,000ϫg for 1 h. About five viral bands were (Amersham). The analysis was also performed on transferred to a new centrifuge tube, diluted with Autographa californica NPV (AcMNPV), kindly 3ϫvolume of 1ϫTE buffer (10 mM Tris-HCl, supplied by Dr. M. J. Fraser of the University of 1mM EDTA, pH 7.6), and then precipitated at Notre Dame. The other two viruses, Bombyx mori 100,000ϫg for 30 min. The purified ODVs were re- NPV Taiwan isolate (BmNPV-TWN) (unpub- suspended in 1ϫTE buffer and stored at Ϫ20°C. lished) and Spodoptera litura NPV Taiwan strain BVs of PenuNPV were collected from in vitro (SpltNPV-TWN) (Shih et al., 1995a), were isolated Characterization of PenuNPV 285 in our laboratory from NPV-infected larvae, B. Coomassie brilliant blue (Begon et al., 1993). The mori and S. litura, respectively. mean ingested volume per larvae was measured by Genome. ODV suspensions were adjusted to a feeding newly molted and 8-h (for 2nd- and 3rd- final concentration of 0.5% SDS and incubated instar) and 16-h (for 4th- and 5th-instar) starved with proteinase K (0.25 mg/ml at 37°C for 3 h), and larvae the standard PBS solution with 1% sucrose, the DNA was isolated by phenol extraction and mixed with a known concentration of fluoresbrite ethanol precipitation (Chou et al., 1996; Wang et carbosylate particles (FCP, Polysciences, Inc., al., 1996). The DNA fragments obtained after di- about 0.5 mm in diameter). The FCP suspensions gestion with EcoRI, EcoRV, HindIII, KpnI, and were offered in small droplets, applied in a circle SmaI endonucleases were separated by elec- on a layer of parafilm placed on the bottom of a trophoresis on 1% (wt/vol) agarose gels, stained petri dish.