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Comparative Study
. 2017 Dec 20;12(12):e0189992.
doi: 10.1371/journal.pone.0189992. eCollection 2017.

Comparison of Tolerance to Sunlight Between Spatially Distant and Genetically Different Strains of Lymantria Dispar Nucleopolyhedrovirus

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Free PMC article
Comparative Study

Comparison of Tolerance to Sunlight Between Spatially Distant and Genetically Different Strains of Lymantria Dispar Nucleopolyhedrovirus

Yuriy B Akhanaev et al. PLoS One. .
Free PMC article

Abstract

Baculoviruses are a family of insect-specific pathogenic viruses can persist outside for long periods through the formation of occlusion bodies. In spite of this ability, the UV of sunlight is an essential factor that limits the survival of baculoviruses outside the host. In the current study, we compared the UV tolerance of two strains of Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV), which were isolated in spatially different regions (LdMNPV-27/0 in Western Siberia (Russia) and LdMNPV-45/0 in North America (USA)) and dramatically differ in their potency. We exposed the studied strains to sunlight in an open area for 0.25, 0.5, 1, and 2 hours and later perorally inoculated host larvae with the same doses of virus (5x105) and with doses leading to same effect (LD90). We observed that strain LdMNPV-45/0, which previously showed high virulence against L. dispar larvae, was more sensitive to UV irradiation (estimated as the relative rate of inactivation (r, h -1) and as the half-life of the virus (τ1/2, h)) compared to LdMNPV-27/0. Exposure to sunlight induced a significant delay of LdMNPV-45/0-induced pathogenesis already after 0.25 h of sunlight exposure, while for LdMNPV-27/0 this delay was occurred only after 2 h exposure in spite of used concentrations. We also compared the sequences of the main structural proteins of the studied strains as UV light contributes not only to genome damage in viruses but also to structural protein damage. The most prominent genetic difference between the structural proteins of the strains was related to the loss of the virus enhancin factor-1 (vef-1) gene in the LdMNPV-27/0 strain. Thus initially highly potent viral strain (such as LdMNPV-45/0) is not recommend to use in the regions (or forest stand density) with high UV load. The role of virus enhancin factor-1 in baculovirus tolerance to UV needs for following studies.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Scheme for UV treatments of LdMNPV.
Fig 2
Fig 2. Inhibition of viral potency by sunlight treatment.
Percentage of original activity remaining (%OAR) of LdMNPV-45/0 (dose 5x105 OBs/larvae, a), LdMNPV-27/0 (dose 5x106 OBs/larvae, b) and LdMNPV-27/0 (dose 5x105 OBs/larvae, c) strains exposed to sunlight UV.
Fig 3
Fig 3. Effect of sunlight treatment on LdMNPV productivity.
Productivity of LdMNPV strains after challenging of Lymantria dispar larvae with same dose (5x105 OBs/larvae, a) or a dose leading to the same effect (LD90, b) of LdMNPV strains. The productivity was calculated using a light microscope with the help of hemocytometer.
Fig 4
Fig 4. Frameshift in LdMNPV-45/0 DNA sequence.
A two-nucleotide deletion in the vef-2 gene of the LdMNPV-45/0 strain resulted in a frameshift (FS) at the 309 amino-acid position, which led to a shortened protein with a partially affected peptidase domain (Peptidase_M60), lost mucin-binding (Mucin_bdg) and transmembrane (TMM) domains, and a disordered C-terminal structure.

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Grant support

This work was supported by the Russian science foundation (15-14-10014) to VVG. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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