Internal DNA pressure modifies stability of WT phage

Irena Ivanovska, Gijs Wuite, Bengt Jönsson, Alex Evilevitch

Research output: Contribution to journalArticlepeer-review


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 A 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.

Original languageEnglish (US)
Pages (from-to)9603-9608
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number23
StatePublished - Jun 5 2007
Externally publishedYes


  • Atomic force microscopy
  • Bacteriophage
  • DNA hydration forces
  • Osmotic pressure
  • Viral capsids

ASJC Scopus subject areas

  • General


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