Single-cell study of the biophysics of bacteriophage infection

Abstract

Bacteriophages are the most populous organism on the planet and have huge potential as tools of research in micro- and synthetic biology. They have also more recently gained attention as powerful antimicrobial agents. Our understanding of the underlying processes by which phage infection occurs is in many areas still incomplete. By inspecting the biophysical effect of phage infection on bacteria it may be possible to shed light on some of the mechanisms that still elude us, and point towards areas of further research beneficial to a wide variety of phage scientist. I demonstrate in this thesis that Escherichia coli cells infected by T7 phage exhibit a drop of 5-10% cell volume at the point of infection. If developed further, this volume loss has the potential to be a truly label-free marker of phage infection of a single bacterial cell. This result accords with a mathematical model that predicts loss of volume and solutes by opening of a pore around the phage infection site. The process appears to be stochastic and dependent on the temperature history of the cells, with 36% of unperturbed cells showing measurable losses in volume compared to 58% of cells that have spent a short time at room temperature. Additionally, I present a mathematical model of a single E. coli cell during T4 phage infection wherein the transcription and replication of phage DNA is explicitly dependent on the expression of proteins controlling the processes temporally.