Figure 3

Thermal inactivation of MVM virions. (a) Thermal inactivation kinetics of wt virion (black squares) and representative mutant virions T257K (red circles) and Q137K (blue triangles) in a representative experiment at 70 °C.Virus inactivation curves were fitted to exponential decays. Because initial absolute virus titers are very high (in the order of 10⁷ plaque-forming units/ml), virus titers can be determined with similar accuracy over a range of 4-5 orders of magnitude at least. Even at the longest times tested, absolute titers were above 10³ plaque-forming units/ml. Thus, titers obtained at every time point were equally accurate and significant in the fitting process to determine the inactivation rate constant, which yielded reasonably low fitting errors and high correlation coefficients (Table 1). (b) Relative thermal inactivation rate constants for every tested mutant virion, normalized with respect to the wt rate constant (green bar). Average values obtained for mutants of Groups 1, 2, or 3 are respectively indicated by blue, red or yellow bars. For each mutant, the average inactivation rate was determined from values obtained in two or three experiments. Error bars indicate standard deviations (SD). Differences in average values relative to wt that correspond to ≥1 standard deviation were taken as statistically significant (with a 66% confidence; Table 1).