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Characterization of an acid-resistant mutant of foot-and-mouth disease virus
T Twomey1, L L France, S Hassard
1Plum Island Animal Disease Center, USDA/ARS, Greenport, New York 11944-0848.
Abstract:
A foot-and-mouth disease virus mutant which is stable at pH 6.4 has been isolated from a virus of serotype A. In contrast to the parent (P) virus, which gave a mixture of large and small plaques in BHK21 cells and in a bovine kidney cell line, the acid-resistant (AR) virus gave small plaques which did not increase markedly in size after 24 hr. The infectivity titer of the acid-resistant virus was about 100-fold lower in suckling mice than in BHK21 cells, whether the inoculation was made intraperitoneally or intracerebrally, whereas the parent virus gave similar titers in both systems. Furthermore, in mice the AR virus reached its end point two to three times more slowly. The diameter of the AR virus was almost 20% less than that of the P virus and it had a more distinct topography, but the two viruses cosedimented in sucrose gradients. However, the buoyant density in CsCl of the AR virus was slightly lower (1.42 compared with 1.43 g/cc) in coruns. The RNAs and capsid proteins of the two viruses gave similar profiles in sucrose gradients and by SDS-PAGE, respectively. However, isoelectric focusing of the capsid proteins revealed considerable differences between the two viruses. Whereas the P virus gave four protein bands, corresponding to VP1-VP4, the AR virus gave one band for VP4, two for VP3, two for VP2, and four for VP1. Sequence analysis of the genes coding for the capsid protein regions of the two viruses showed four changes (one silent), resulting in an Ala-3-->Ser substitution in VP1 and Glu-131-->Lys and Asp-133-->Ser substitutions in VP2.
Insights
A new foot-and-mouth disease virus (FMDV) mutant, stable at pH 6.4, exhibits altered plaque formation and reduced virulence in mice. This acid-resistant FMDV shows significant capsid protein differences compared to the parent virus.
Area of Science:
- Virology
- Molecular Biology
- Animal Health
Background:
- Foot-and-mouth disease virus (FMDV) is a significant pathogen affecting livestock.
- Understanding FMDV stability and virulence is crucial for disease control.
- Previous studies have focused on FMDV serotypes and general characteristics.
Purpose of the Study:
- To isolate and characterize an acid-resistant mutant of FMDV serotype A.
- To investigate the biophysical and molecular differences between the parent and acid-resistant FMDV strains.
- To assess the virulence and infectivity of the acid-resistant mutant in cell culture and animal models.
Main Methods:
- Isolation of an acid-resistant (AR) FMDV mutant from a serotype A parent (P) virus.
- Plaque assays in BHK21 cells and bovine kidney cells.
- Infectivity titrations in suckling mice.
- Analysis of viral diameter, buoyant density, RNA, and capsid protein profiles (sucrose gradients, SDS-PAGE, isoelectric focusing, sequence analysis).
Main Results:
- The AR virus is stable at pH 6.4, unlike the parent virus.
- AR virus produced small plaques and had lower infectivity and slower endpoint in mice compared to the parent virus.
- Significant differences were observed in the isoelectric focusing profiles of capsid proteins, with four genetic changes identified, leading to specific amino acid substitutions in VP1 and VP2.
Conclusions:
- An acid-resistant FMDV mutant (serotype A) was successfully isolated and characterized.
- The AR mutant displays altered biological properties, including reduced virulence and distinct capsid protein composition.
- The identified genetic and protein alterations provide insights into FMDV acid resistance and virulence mechanisms.