Importance of virus–medium interactions on the biological activity of wild-type Heliothine nucleopolyhedroviruses propagated via suspension insect cell cultures

Abstract

In vitro serial passaging of nucleopolyhedroviruses often results in virus instability, leading to reduction of both yield and biological activity of polyhedra (virus occlusion bodies). In this study, uncloned Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus (HaSNPV) and cloned Helicoverpa zea single-nucleocapsid nucleopolyhedrovirus (HzSNPV) were each serially passaged five times in both low cost (VPM) and commercial (Excell 401) media using H. zea cell cultures. When the experimental data was analysed as a 2 3 full factorial design (testing two levels of virus, medium and passage number), the passage number was shown to have the most significant effect on polyhedra yield, while the virus-medium interaction had the most important effect on polyhedra biological activity. This interaction was most pronounced for HzSNPV, which experienced a dramatic decline in biological activity when switched from its original Excell 401 medium to the in-house VPM medium. This suggests that genetically homogeneous viruses are less able to adapt to perturbations in the nutrient environment, hence medium changes should be avoided. Therefore, it is important to standardise the scale-up process of nucleopolyhedrovirus biopesticides at the earliest stage of development, especially when it requires both a low cost medium and a plaque purified virus.

Kinetic characterization of the group II helicoverpa armigera nucleopolyhedrovirus propagated in suspension cell cultures: Implications for development of a biopesticides production process

“…Studies on Group I CfMNPV in CF‐2C1 cells57 and BmNPV in Bm5 cells55 did not follow BV production, but the modest cell growth reported after application of a low MOI (0.1 PFU per cell) was similar to that reported for AcMNPV at the same MOI,5 which suggested similarly fast infection kinetics. Studies on Group II SfMNPV in Sf9 cells58 also did not monitor BV production, but the infection kinetics appeared to be poor because the application of high MOIs (by adding 10% v/v of virus inoculum) still resulted in a doubling in cell density postinfection, similar to the experience with HaSNPV 20, 48…”

“…In this study, key cell‐specific infection kinetics were determined for suspension‐cultured wild‐type Helicoverpa armigera single‐capsid nucleopolyhedrovirus (HaSNPV) and its Few Polyhedra (FP) mutant, the first time for a Group II NPV. HaSNPV is a promising baculovirus biopesticide against the highly destructive and increasingly insecticide‐resistant Heliothine caterpillar pest complex1, 17 and is the subject of a decade‐long in vitro research program in this group 18–20…”

Comparative Analysis of HaSNPV-AC53 and Derived Strains

“…HaSNPV isolate AC53, also known as A44WT [10,16], was obtained from AgBiTech and isolate H25EA1 was selected in vitro by CSIRO from P9/H25WT [15,32,33,34,35], and obtained from the University of Queensland [17]. Both were originally isolated from cadavers of an unspecified Helicoverpa species in Queensland, Australia in 1973 and 1974, respectively, and passaged once through H. punctigera before repeated passage through H. armigera .…”

Production of Insecticidal Baculoviruses in Insect Cell Cultures: Potential and Limitations

“…This protease, which is not present in the occlusion bodies produced in cell cultures, could be an additional factor of virulence, accelerating the dissolution of occlusion bodies in the insect midgut and thus contributing to increase its biological activity (Rohrmann, 2011). Finally, it has been also reported that the composition of the culture medium could affect the activity of occlusion bodies, but the causes are unknown (Pedrini et al, 2006).…”