title: Initial fitness recovery of HIV-1 is associated with quasispecies heterogeneity and can occur without modifications in the consensus sequence.
abstract: BACKGROUND
  Fitness recovery of HIV-1 "in vitro" was studied using viral clones that had their fitness decreased as a result of plaque-to-plaque passages.
  
  
  RESULTS
  After ten large population passages, the viral populations showed an average increase of fitness, although with wide variations among clones. While 5 clones showed significant fitness increases, 3 clones showed increases that were only marginally significant (p<0.1), and 4 clones did not show any change. Fitness recovery was not accompanied by an increase in p24 production, but was associated with an increase in viral titer. Few mutations (an average of 2 mutations per genome) were detected in the consensus nucleotide sequence of the entire genome in all viral populations. Five of the populations did not fix any mutation, and three of them displayed marginally significant fitness increases, illustrating that fitness recovery can occur without detectable alterations of the consensus genomic sequence. The investigation of other possible viral factors associated with the initial steps of fitness recovery, showed that viral quasispecies heterogeneity increased between the initial clones and the passaged populations. A direct statistical correlation between viral heterogeneity and viral fitness was obtained.
  
  
  CONCLUSIONS
  Thus, the initial fitness recovery of debilitated HIV-1 clones was mediated by an increase in quasispecies heterogeneity. This observation, together with the invariance of the consensus sequence despite fitness increases demonstrates the relevance of quasispecies heterogeneity in the evolution of HIV-1 in cell culture.
authors.affiliation: Virologia Molecular, Centro Nacional de Microbiología (CNM), Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Antonio V
authors.initials: AV
authors.lastname: Bordería
authors.forename: Ramon
authors.initials: R
authors.lastname: Lorenzo-Redondo
authors.forename: Maria
authors.initials: M
authors.lastname: Pernas
authors.forename: Concepción
authors.initials: C
authors.lastname: Casado
authors.forename: Tamara
authors.initials: T
authors.lastname: Alvaro
authors.forename: Esteban
authors.initials: E
authors.lastname: Domingo
authors.forename: Cecilio
authors.initials: C
authors.lastname: Lopez-Galindez
mesh_terms: D016384:Consensus Sequence / Q000235:genetics*; D056084:Genetic Fitness; D018740:Genetic Heterogeneity; D016679:Genome, Viral / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics*; D009154:Mutation; D012641:Selection, Genetic; D012692:Serial Passage; D014773:Virology / Q000379:methods