Measuring Genetic Robustness in Vesicular Stomatitis Virus

Abstract

Genetic robustness is the ability of a genome to incorporate mutations with the result of no fitness changes. Thus, more robust viruses have an increased neutral mutation rate. This property is particularly important in RNA viruses due to their high mutation rates. The most direct way of measuring robustness in vesicular stomatitis virus (VSV) is to carry out clonal analysis of populations: randomly isolating individual VSV strains (plaques), measuring the fitness of each one and generating fitness distributions (Novella et al., 2010). A second possibility is to carry out multiple replicates of repeated plaque-to-plaque passages, determining fitness in progeny populations and generating fitness distributions (Novella et al., 2010). Depending on the expected differences, the former may require hundreds of determinations, while the latter may require tens of determinations. A third approach consists of increasing the mutation rate of populations under analysis to magnify any differences that may exist and, instead of measuring fitness, measuring survival (Novella et al., 2013). One caveat of this method is that changes in survival can also be explained by changes in polymerase fidelity. For that reason, it is important to perform complementary experiments, in this case quantifying mutant frequency.