Bottleneck Size-Dependent Changes in the Genetic Diversity and Specific Growth Rate of a Rotavirus A Strain

Abstract

ABSTRACTRNA viruses form a dynamic distribution of mutant swarm (termed “quasispecies”) due to the accumulation of mutations in the viral genome. The genetic diversity of a viral population is affected by several factors, including a bottleneck effect. Human-to-human transmission ex-emplifies a bottleneck effect in that only part of a viral population can reach the next susceptible hosts. In the present study, the rhesus rotavirus (RRV) strain of Rotavirus A was serially passaged five times at a multiplicity of infection (MOI) of 0.1 or 0.001 in duplicate (the 1st and 2nd lineages), and three phenotypes (infectious titer, cell binding ability and specific growth rate) were used to evaluate the impact of a bottleneck effect on the RRV population. The specific growth rate values of lineages passaged under the stronger bottleneck (MOI of 0.001) were higher after five passages. The nucleotide diversity also increased, which indicated that the mutant swarms of the lineages under the stronger bottleneck effect were expanded through the serial passages. The random distribution of synonymous and non-synonymous substitutions on rotaviral genome segments indicated that almost all mutations were selectively neutral. Simple simulations revealed that the presence of minor mutants could influence the specific growth rate of a population in a mutant frequency-dependent manner. These results indicate that a stronger bottleneck effect can create more sequence spaces for minor mutants originally existing in a hidden layer of mutant swarm.IMPORTANCEIn this study, we investigated a bottleneck effect on an RRV population, which may drastically impact a viral population structure. RRV populations were serially passaged under two levels of a bottleneck effect, which exemplified a human-to-human transmission. As a result, the genetic diversity and specific growth rate of RRV populations increased under the stronger bottleneck effect, which implied that a bottleneck could create a new sequence space in a population for minor mutants originally existing in a hidden layer of a mutant swarm of the double-stranded RNA virus. The results of this study suggest that the genetic drift caused by a bottleneck in a human-to-human transmission explains the random appearance of new genetic lineages causing viral outbreaks, which can be expected by the molecular epidemiology using next generation sequencing in which the viral genetic diversity within a viral population is investigated.