Abstract
The bacteriophage infection cycle has been extensively studied, yet little is known about the nanostructure and mechanical changes that lead to bacterial lysis. Here, atomic force microscopy was used to study in real time and in situ the impact of the canonical phage T4 on the nanotopography and biomechanics of irreversibly attached, biofilm-forming E. coli cells. The results show that in contrast to the lytic cycle in planktonic cells, which ends explosively, anchored cells that are in the process of forming a biofilm undergo a more gradual lysis, developing distinct nanoscale lesions (~300 nm in diameter) within the cell envelope. Furthermore, it is shown that the envelope rigidity and cell elasticity decrease (>50% and >40%, respectively) following T4 infection, a process likely linked to changes in the nanostructure of infected cells. These insights show that the well-established lytic pathway of planktonic cells may be significantly different from that of biofilm-forming cells. Elucidating the lysis paradigm of these cells may advance biofilm removal and phage therapeutics.
Highlights
Caudovirales, the dsDNA tailed phages that dominate the virosphere, are being developed as alternative therapeutics against multi-drug-resistant bacterial infections[1]
E. coli culture was grown on a glass atomic force microscopy (AFM) coupon that was precoated with an ~5-nm thin, rigid[17], and positively charged lipid bilayer (LBL) (Fig. 1)
Over a few hours (8 h), E. coli cells were irreversibly anchored to the AFM coupon (~1 × 106 cells cm−2), with some developed into monolayer clusters, which are early stages in biofilm formation[18]
Summary
Caudovirales, the dsDNA tailed phages that dominate the virosphere, are being developed as alternative therapeutics against multi-drug-resistant bacterial infections[1]. AFM imaging of infected and dehydrated E. coli revealed that by ~30 min after T4-phage infection, the cell envelope has undergone various topographical changes[13]. RESULTS Changes in nanotopography of biofilm-forming E. coli cells during T4-phage infection
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