title: Comparison of poliovirus recombinants: accumulation of point mutations provides further advantages.
abstract: The roles of recombination and accumulation of point mutations in the origin of new poliovirus (PV) characteristics have been hypothesized, but it is not known which are essential to evolution. We studied phenotypic differences between recombinant PV strains isolated from successive stool specimens of an oral PV vaccine recipient. The studied strains included three PV2/PV1 recombinants with increasing numbers of mutations in the VP1 gene, two of the three with an amino acid change I-->T in the DE-loop of VP1, their putative PV1 parent and strains Sabin 1 and 2. Growth of these viruses was examined in three cell lines: colorectal adenocarcinoma, neuroblastoma and HeLa. The main observation was a higher growth rate between 4 and 6 h post-infection of the two recombinants with the I-->T substitution. All recombinants grew at a higher rate than parental strains in the exponential phase of the replication cycle. In a temperature sensitivity test, the I-->T-substituted recombinants replicated equally well at an elevated temperature. Complete genome sequencing of the three recombinants revealed 12 (3), 19 (3) and 27 (3) nucleotide (amino acid) differences from Sabin. Mutations were located in regions defining attenuation, temperature sensitivity, antigenicity and the cis-acting replicating element. The recombination site was in the 5' end of 3D. In a competition assay, the most mutated recombinant beat parental Sabin in all three cell lines, strongly suggesting that this virus has an advantage. Two independent intertypic recombinants, PV3/PV1 and PV3/PV2, also showed similar growth advantages, but they also contained several point mutations. Thus, our data defend the hypothesis that accumulation of certain advantageous mutations plays a key role in gaining increased fitness.
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Carita
authors.initials: C
authors.lastname: Savolainen-Kopra
authors.affiliation: Immunoprofylaxis Laboratory, Research Institute of Epidemiology and Microbiology, Minsk, Belarus.
authors.forename: Elena
authors.initials: E
authors.lastname: Samoilovich
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Heidi
authors.initials: H
authors.lastname: Kahelin
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Anna-Kaisa
authors.initials: AK
authors.lastname: Hiekka
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Tapani
authors.initials: T
authors.lastname: Hovi
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Merja
authors.initials: M
authors.lastname: Roivainen
mesh_terms: D000220:Adaptation, Biological; D019943:Amino Acid Substitution / Q000235:genetics; D036022:Capsid Proteins / Q000235:genetics; D002460:Cell Line; D002648:Child; D016679:Genome, Viral; D006801:Humans; D008969:Molecular Sequence Data; D017354:Point Mutation; D017955:Poliovirus / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity*; D011055:Poliovirus Vaccine, Oral / Q000008:administration & dosage; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D010948:Viral Plaque Assay / Q000379:methods; D014774:Virulence
chemical_list: D036022:Capsid Proteins; D011055:Poliovirus Vaccine, Oral; C442540:VP1 protein, Poliovirus