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Evolution of a persistent aphthovirus in cytolytic infections: partial reversion of phenotypic traits accompanied by
1Centro de Biología Molecular "Severo Ochoa", Universidad Autonoma de Madrid, Spain.
Abstract:
Foot-and-mouth disease virus (FMDV) shows a dual potential to be cytolytic or to establish persistent infections in cell culture. FMDV R100, a virus rescued after 100 passages of carrier BHK-21 cells persistently infected with FMDV clone C-S8c1, showed multiple genetic and phenotypic alterations relative to the parental clone C-S8c1. Several FMDV R100 populations have been subjected to 100 serial cytolytic infections in BHK-21 cells, and the reversion of phenotypic and genetic alterations has been analyzed. An extreme temperature sensitivity of R100 reverted totally or partially in some passage series but not in others. The small-plaque morphology reverted to normal size in all cases. The hypervirulence for BHK-21 cells did not revert, and even showed an increase, upon cytolytic passage. Most of the mutations that had been fixed in the R100 genome during persistence did not revert in the course of cytolytic passages, but the extended polyribocytidylate tract of R100 (about 460 residues, versus 290 in C-S8c1) decreased dramatically in length, to the range of 220 to 260 residues in all passage series examined. In passages involving very large viral populations, a variant with two amino acid substitutions (L-144-->V and A-145-->P) next to the highly conserved Arg-Gly-Asp (RGD motif; positions 141 to 143) within the G-H loop of capsid protein VP1 became dominant. A clonal analysis allowed isolation of a mutant with the single replacement A-145-->P. Viral production and growth competition experiments showed the two variants to have a fitness very close to that of the parental virus. The results provide evidence that the repertoire of variants that could potentially become dominant in viral quasispecies may be influenced by the population size of the evolving virus. The net results of a series of persistent-infection passages followed by a series of cytolytic passages was progressive genomic diversification despite reversion or stasis of phenotypic traits. Implications for the evolution of RNA viruses are discussed.
Insights
Foot-and-mouth disease virus (FMDV) can cause cell death or persistent infections. After serial passages, FMDV R100 showed genomic diversification, with some traits reverting while others, like hypervirulence, persisted or increased, influenced by viral population size.
Area of Science:
- Virology
- Molecular Biology
- Evolutionary Biology
Background:
- Foot-and-mouth disease virus (FMDV) exhibits dual behavior: cytolytic or persistent infection in cell cultures.
- FMDV R100, derived from persistently infected cells, displayed genetic and phenotypic alterations compared to its parent clone.
Purpose of the Study:
- To analyze the reversion of genetic and phenotypic alterations in FMDV R100 after serial cytolytic infections.
- To investigate the influence of viral population size on the evolution of FMDV quasispecies.
Main Methods:
- Serial cytolytic infections of BHK-21 cells with FMDV R100 populations.
- Analysis of phenotypic traits including temperature sensitivity, plaque morphology, and virulence.
- Genomic sequencing to identify mutations and track changes in polyribocytidylate tract length and VP1 protein.
Main Results:
- Temperature sensitivity and plaque morphology showed variable reversion, while hypervirulence persisted or increased.
- Most mutations remained, but the polyribocytidylate tract significantly shortened; a variant with VP1 substitutions (L-144-->V, A-145-->P) became dominant in large populations.
- Isolated A-145-->P mutant and the double mutant exhibited fitness comparable to the parental virus.
Conclusions:
- Viral population size can influence the dominant variants within a viral quasispecies.
- Sequential persistent and cytolytic passages lead to progressive genomic diversification, irrespective of phenotypic trait reversion or stasis.
- Findings offer insights into the evolutionary dynamics of RNA viruses.