Virus particle packaging in baculovirus and cytoplasmic polyhedrosis virus inclusion bodies

Abstract

The structure of the inclusion bodies (IBs) of three multiply enveloped nuclear polyhedrosis viruses (MNPVs), one singly enveloped NPV (SNPV), two granulosis viruses (GVs) and one cytoplasmic polyhedrosis virus (CPV) were compared. A method was devised to calculate the numbers of virus particles and nucleocapsids in IBs using data from light microscopy and thin sections. The three MNPVs, from Agrotis segetum (English and Polish virus isolates) and Mamestra brassicae had similar concentrations of virus particles ranging from 17.3 to 19.6 per μm 3 of IB. Plusia gamma SNPV had a higher density of 59.6 virus particles per μm 3 of IB, which partly compensated for its having smaller IBs (mean volume 0.65 μm 3) than the MNPVs (2.60–9.71 μm 3). The English A. segetum MNPV isolate had the most nucleocapsids in each virus particle (mean, 4.04) and the largest IBs (mean volume, 9.71 μm 3), giving 674 nucleocapsids per IB on average. The GVs, from A. segetum and Pieris brassicae, mainly contained one nucleocapsid per IB. P. gamma CPV IBs had a much higher density of virus particles than the baculoviruses (260 per μm 3 compared with 17–60 per μm 3). These data are discussed in relation to the biological properties of these viruses, and possible adaptational advantages of alternative IB designs are considered.