title: Internal DNA pressure modifies stability of WT phage.
abstract: dsDNA in bacteriophages is highly stressed and exerts internal pressures of many atmospheres (1 atm = 101.3 kPa) on the capsid walls. We investigate the correlation between packaged DNA length in lambda phage (78-100% of WT DNA) and capsid strength by using an atomic force microscope indentation technique. We show that phages with WT DNA are twice as strong as shorter genome mutants, which behave like empty capsids, regardless of high internal pressure. Our analytical model of DNA-filled capsid deformation shows that, because of DNA-hydrating water molecules, an osmotic pressure exists inside capsids that increases exponentially when the packaged DNA density is close to WT phage. This osmotic pressure raises the WT capsid strength and is approximately equal to the maximum breaking force of empty shells. This result suggests that the strength of the shells limits the maximal packaged genome length. Moreover, it implies an evolutionary optimization of WT phages allowing them to survive greater external mechanical stresses in nature.
authors.affiliation: Physics of Complex Systems, Division of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Irena
authors.initials: I
authors.lastname: Ivanovska
authors.forename: Gijs
authors.initials: G
authors.lastname: Wuite
authors.forename: Bengt
authors.initials: B
authors.lastname: Jönsson
authors.forename: Alex
authors.initials: A
authors.lastname: Evilevitch
mesh_terms: D010582:Bacteriophage lambda / Q000737:chemistry* / Q000235:genetics; D055592:Biophysical Phenomena; D001703:Biophysics; D002213:Capsid / Q000737:chemistry* / Q000648:ultrastructure; D004279:DNA, Viral / Q000737:chemistry*; D016679:Genome, Viral; D018625:Microscopy, Atomic Force; D008954:Models, Biological; D009997:Osmotic Pressure; D019065:Virus Assembly / Q000502:physiology
chemical_list: D004279:DNA, Viral