Mechanical characterization of P2 bacteriophage by using Young’s modulus measurements

The bacteriophage P2 capsids have been characterized by transmission electron microscopy and atomic force microscopy (AFM). Studies have been carried out on fully filled and 2/3 filled capsids containing dsDNA genomes. In order to get the quantitative information of the capsid, a nanoindentation technique depending on the tip-shape and an effective spring constant technique with a homogeneous capsid shell model were adopted. The contact region of the AFM contact force curve in an approach mode has been used for the calculation of Young’s moduli as well as the internal pressures of the capsids. By using the continuum theory of elasticity of thin homogeneous capsid shells, Young’s moduli of fully filled and 2/3 filled phage capsids are measured to be 1.17 ± 0.10 GPa and 0.87 ± 0.10 GPa, respectively. These values are close to other reported results. Analysis of the force curves also presented that a fully filled capsid reveals a higher internal pressure than that of a 2/3 filled capsid.