Complex dynamics of defective interfering baculoviruses during serial passage in insect cells

Abstract

Defective interfering (DI) viruses are thought to cause oscillations in virus levels, known as the 'Von Magnus effect'. Interference by DI viruses has been proposed to underlie these dynamics, although experimental tests of this idea have not been forthcoming. For the baculoviruses, insect viruses commonly used for the expression of heterologous proteins in insect cells, the molecular mechanisms underlying DI generation have been investigated. However, the dynamics of baculovirus populations harboring DIs have not been studied in detail. In order to address this issue, we used quantitative real-time PCR to determine the levels of helper and DI viruses during 50 serial passages of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) in Sf21 cells. Unexpectedly, the helper and DI viruses changed levels largely in phase, and oscillations were highly irregular, suggesting the presence of chaos. We therefore developed a simple mathematical model of baculovirus-DI dynamics. This theoretical model reproduced patterns qualitatively similar to the experimental data. Although we cannot exclude that experimental variation (noise) plays an important role in generating the observed patterns, the presence of chaos in the model dynamics was confirmed with the computation of the maximal Lyapunov exponent, and a Ruelle-Takens-Newhouse route to chaos was identified at decreasing production of DI viruses, using mutation as a control parameter. Our results contribute to a better understanding of the dynamics of DI baculoviruses, and suggest that changes in virus levels over passages may exhibit chaos.

Relocation of the attTn7 Transgene Insertion Site in Bacmid DNA Enhances Baculovirus Genome Stability and Recombinant Protein Expression in Insect Cells

“…The results show that viral titers fluctuated between 10 6 and 10 8 TCID 50 / mL during serial undiluted passages ( Figure 5 C). This is similar to what was seen in other studies [ 19 , 27 ]. Cell lysates of selected passages (P1, P4 and P10) were checked for GOI expression levels ( Figure 5 D).…”

Genetic Variation and Biological Activity of Two Closely Related Alphabaculoviruses during Serial Passage in Permissive and Semi-Permissive Heterologous Hosts

“…Natural baculovirus populations are characterized by high genetic variability that is likely to influence the host range and their ability to adapt to novel hosts [18]. Serial passage experiments have shown that baculoviruses can undergo genetic and phenotypic changes due to genetic bottlenecks and genetic drift when the inoculum is repeatedly used to infect semi-permissive insect hosts and cells [19,20,21,22]. During serial passage, adaptation to the semi-permissive host can involve complex genetic diversification, including alterations in the abundance of particular genotypic variants or the emergence of new genotypes due to recombination events [18,21].…”

Quantitative Characterization of Defective Virus Emergence by Deep Sequencing

“…Few studies have combined genome, particle, and activity measurements of mixed DIP and virus populations (21,22), though such measures can be useful for guiding computational models that aim to elucidate how such populations may grow, change, and be transmitted (23)(24)(25)(26). To advance models that not only elucidate but also enable forecasting of how virus populations grow and spread, new measures that facilitate the rapid quantitative characterization of viruses and their DIPs will need to be developed.…”