- Institution
- BRAC University
- Period
- 2020
- Supervisors
- Dr. Iftekhar Bin Naser
Overview
This master’s thesis, submitted to BRAC University in 2020 and published in the BRAC University Institutional Repository in 2021, asked whether bacteriophages can be “cheated” into propagating when their host bacteria are scarce.
Scientific background
Bacteriophages are reported to need a minimum density of host cells to propagate in laboratory cultures, yet phage infection is observed in natural environments, particularly water bodies, where host densities can be lower. The thesis examined which factors might allow propagation under those conditions, using phage–host systems of Vibrio spp. and Shiga toxin-producing Escherichia coli (STEC).
Research question
Can molecules produced by host bacteria or by phages influence bacteriophage propagation at low host cell densities?
Research objectives
To determine the threshold host cell densities for bacteriophage propagation in Vibrio spp. and STEC phage-host systems, and to test whether molecules produced by the host and/or phage can influence propagation at low host cell densities.
Methodology
Threshold host cell densities for phage propagation were determined for each phage-host system. Cultures at low host cell densities were then supplemented with spent media taken from phage and host cultures at the logarithmic phase of infection, and phage propagation was compared with and without supplementation.
Findings
Phage propagation stopped at the threshold host cell densities determined for each system and began again when cultures were supplemented with spent media from phage and host cultures taken at the logarithmic phase of infection. The thesis therefore hypothesises that molecules produced by the host and/or the phage can influence how a bacteriophage decides to infect its host, especially in the environment. The effect of these molecules was investigated in the Vibrio spp. system only.
Research significance
Understanding the signals that govern phage infection when hosts are scarce is relevant to phage ecology in natural environments and to the propagation of phages for research and phage-based applications.