Internal DNA pressure modifies stability of WT phage

Research output: Contribution to journalArticle


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.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences


  • osmotic pressure, forces, DNA hydration, bacteriophage, atomic force microscopy, viral capsids
Original languageEnglish
Pages (from-to)9603-9608
JournalProceedings of the National Academy of Sciences
Issue number23
Publication statusPublished - 2007
Publication categoryResearch