  The role of thermal pressure fluctuation excited within tightly packaged DNA
prior to ejection from protein capsid shells is discussed in a model
calculation. At equilibrium before ejection we assume the DNA is folded many
times into a bundle of parallel segments that forms an equilibrium conformation
at minimum free energy, which presses tightly against internal capsid walls.
Using a canonical ensemble at temperature T we calculate internal pressure
fluctuations against a slowly moving or static capsid mantle for an elastic
continuum model of the folded DNA bundle. It is found that fluctuating pressure
on the capsid internal wall from thermal excitation of longitudinal acoustic
vibrations in the bundle may have root-mean-square values which are several
tens of atmospheres for typically small phage dimensions. Comparisons are given
with measured data on three mutants of lambda phage with different base pair
lengths and total genome ejection pressures.
