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

Abstract

Large-scale commercialization of baculovirus biopesticides for the control of insect pests requires a cell culture production process, and knowledge of the infection kinetics is a vital prerequisite for process optimization. Well-characterized kinetic parameters have so far only been reported for the commercially established recombinant Autographa californica nucleopolyhedrovirus (AcMNPV), a Group I NPV. In this work, key infection kinetic parameters of the Group II NPV Helicoverpa armigera nucleopolyhedrovirus (HaSNPV), and its Few Polyhedra (FP) mutant, were well characterized for the first time, in suspension HzAM1 insect cell cultures, to facilitate the scale-up of an HaSNPV-based biopesticide. The FP mutant had a selective advantage over wild-type HaSNPV in cell cultures, and the kinetic analysis showed that this was due to a superior budding rate, rather than a faster binding rate (BR) or longer budding duration. Another finding was that wild-type HaSNPV had very poor infection kinetics when compared with AcMNPV, exhibiting an 18-fold lower BR, a more than 50-fold lower budding rate, and a 60-fold lower extracellular/total progeny virus ratio. Such poor infection kinetics have serious implications during scale-up of an HaSNPV biopesticide production process, including the requirement for large volumes of virus inocula and the difficulty of achieving synchronous infections. Groups I and II NPVs may have very different infection kinetics because of their different envelope fusion proteins. This study is the first to compare the two groups of NPVs in terms of well-characterized cell-specific infection kinetics, and the findings may indicate a phylogenetic basis for kinetic differences.