Susceptibility of the Bombyx mori cardia cells to Nucleopolyhedrovirus, multiple subgroup, BmMNPV

Antioxidant Systems as a Response to Midgut Cellular of Bombyx mori Lineu, 1758 (Lepidoptera: Bombycidae) Infection for Baculoviruses

Bombyx mori nucleopolyhedrovirus (BmNPV) is a DNA virus that infects different tissues in Bombyx mori at immature stage. Caterpillars become infected after ingesting polyhedral occlusion bodies (POB) present in contaminated mulberry leaves and spread through the body after passing the epithelium of the midgut. As this organ is responsible for digestion, most absorption of nutrients requires an intact epithelium to maintain gastrointestinal physiology. Considering the importance of this organ in the feeding of caterpillars and in the production of quality silk threads, and because it is also the first barrier faced by the BmNPV, the study analyzed details of cytopathological events in the intestinal cells as well as evaluated the action of the antioxidant systems as a response to cellular infection. For this purpose, B. mori hybrid caterpillars of fifth instar were inoculated with a suspension of 7.8 × 107 POB ml-1 and, from the first to the eighth day post-inoculation (dpi), segments of the midgut were collected and processed for light and electronic microscopy. The nuclei of columnar cells showed polyhedric occlusion bodies in the seventh dpi and fragmentation of those cells, with peritrophic matrix disorganization. Analysis of antioxidant systems shows some moments of changes of the catalase enzymes and superoxide dismutase. Analysis of the cholinergic system revealed changes only at the beginning of the infection. Thus, the article acknowledges the antioxidant system as a barrier to stop viral infection, albeit it cannot stop infection from occurring, once a coevolutionary bond is maintained between virus and host.

The structure of viral cathepsin from Bombyx mori Nuclear Polyhedrosis Virus as a target against grasserie: docking and molecular dynamics simulations

The viral cathepsin from Bombyx mori Nuclear Polyhedrosis Virus (BmNPV-Cath) is a broad-spectrum protease that participates in the horizontal transmission of this virus in silkworm by facilitating solubilization of the integument of infected caterpillars. When a B. mori farm is attacked by BmNPV, there are significant sericultural losses because no drugs or therapies are available. In this work, the structure of viral cathepsin BmNPV-Cath was used as a target for virtual screening simulations, aiming to identify potential molecules that could be used to treat the infection. Virtual screening of the Natural Products library from the Zinc Database selected four molecules. Theoretical calculations of ΔG_binding by the molecular mechanics Poisson-Boltzmann surface analysis (MM-PBSA) method indicated that the molecule Zinc12888007 (Bm5) would have high affinity for the enzyme. The in vivo infection models of B. mori caterpillars with BmNPV showed that treatment with a dose of 100 μg Bm5 dissolved in Pluronic-F127 0.02% was able to reduce the mortality of caterpillars in 22.6%, however, it did not impede the liquefaction of dead bodies. Our results suggest a role of BmNPV-Cath in generating a pool of amino acids necessary for viral replication and indicate a mechanism to be exploited in the search for treatments for grasserie disease of the silkworm.

Complete genome sequence of the first non-Asian isolate of Bombyx mori nucleopolyhedrovirus

Brazil is one of the largest silk producers in the world. The domesticated silkworm (Bombyx mori) was formally introduced into the country in the twentieth century, and the state of Paraná is the main national producer. During larval stages, B. mori can be afflicted by many different infectious diseases, which lead to substantial losses in silk production. In this work, we describe the structure and complete genome sequence of the first non-Asian isolate of Bombyx mori nucleopolyhedrovirus (BmNPV), the most important silkworm pathogen. The BmNPV-Brazilian isolate is a nucleopolyhedrovirus with singly enveloped nucleocapsids within polyhedral occlusion bodies. Its genome has 126,861 bp with a G + C content of 40.4 %. Phylogenetic analysis clustered the virus with the Japanese strain (BmNPV-T3). As expected, we have detected intra-population variability in the virus sample. Variation along homologous regions (HRs) and bro genes was observed; there were seven HRs, deletion of bro-e, and division of bro-a into two ORFs. The study of baculoviruses allows for a better understanding of virus evolution providing insight for biological control of insect pests or protection against the pernicious disease caused by these viruses.

Physiological and metabolic consequences of viral infection in Drosophila melanogaster

An extensively used model system for investigating anti-pathogen defence and innate immunity involves Drosophila C virus (DCV) and Drosophila melanogaster. While there has been a significant effort to understand infection consequences at molecular and genetic levels, an understanding of fundamental higher-level physiology of this system is lacking. Here, we investigate the metabolic rate, locomotory activity, dry mass and water content of adult male flies injected with DCV, measured over the 4 days prior to virus-induced mortality. DCV infection resulted in multiple pathologies, notably the depression of metabolic rate beginning 2 days post-infection as a response to physiological stress. Even in this depressed metabolic state, infected flies did not decrease their activity until 1 day prior to mortality, which further suggests that cellular processes and synthesis are disrupted because of viral infection. Growth rate was also reduced, indicating that energy partitioning is altered as infection progresses. Microbial infection in insects typically results in an increase in excretion; however, water appeared to be retained in DCV-infected flies. We hypothesise that this is due to a fluid intake-output imbalance due to disrupted transport signalling and a reduced rate of metabolic processing. Furthermore, infected flies had a reduced rate of respiration as a consequence of metabolic depression, which minimised water loss, and the excess mass as a result of water retention is concurrent with impaired locomotory ability. These findings contribute to developing a mechanistic understanding of how pathologies accumulate and lead to mortality in infected flies.