McMaster University MASTER OF SCIENCE (2020) Hamilton, Ontario
(Department of Biochemistry and Biomedical Sciences)
TITLE: Identifying new compounds capable of inducing model phages
AUTHOR: Anisha Nandy
SUPERVISOR: Dr. Alexander P. Hynes
NUMBER OF PAGES: xi, 80 / Prophages are the genomes of bacteriophages (phages, bacterial
viruses) that integrate into the chromosome of their host upon infection, lying dormant until conditions favour their reactivation. A cell harbouring a
prophage is called a lysogen, as, upon exposure to certain signals, the
prophage will initiate a replicative cycle ending in lysis of the host bacterium
and release of phages. This process is known as induction. Canonically,
induction occurs through activation of the bacterial SOS-response, a DNA repair cascade initiated by detection of DNA damage. Studies of prophage
induction have almost exclusively relied on challenges with compounds that
result in the initiation of the host SOS response.
Recent studies have identified some signals that affect prophage
induction independently of the SOS response, but these approaches have not
been systematic. To identify non-canonical triggers of prophage induction, I
screened 3,936 compounds against two model lysogens. The first, carrying
phage HK97, is a model for induction. The second, carrying phage Mu—a
prophage thought to be uninducible—serves as a control. Any compound
which inhibited bacterial growth in only our HK97 lysogen was considered to
have resulted in a phage-mediated response. The 171 compounds identified in this screen were then used to re-challenge the lysogen at a range of
concentrations and monitor the resulting release of free phages associated
with induction. Increases in phage counts were seen for 86 compounds. While 38 of these were known SOS activators, 49 were novel, ‘non-canonical’ inducers. Unexpectedly, the screening also revealed seven unique chemical inducers for the supposedly un-inducible model prophage, Mu.
The 56 new phage-inducers identified by this work include compounds
likely to be driving phage induction through non-canonical pathways. As
prophages are thought to respond to bacterial stress, these may reflect stressors acting through new mechanisms. Using these compounds as tools opens up an avenue to probe other stress pathways in bacteria, and, as evidenced by induction of Mu, potentially help discover new phages that don’t respond to canonical inducers. / Thesis / Master of Science (MSc) / Bacterial viruses (phages) can lie dormant as prophages in their host
bacterium until a signal triggers their activation, production of viruses, and
rapid killing of the host. This switch from dormant prophage to active phage called induction. Almost all molecules that result in prophage inductions
belong to a limited set of compounds which elicit a specific stress response in
bacteria.
Screening 3936 compounds for their ability to inhibit the growth of
bacteria carrying known prophages resulted in the identification of a small
subset associated with increased phage production. For one Escherichia coli
prophage—HK97, a model of induction—we found 49 compounds not
previously known as inducers. For another model prophage—Mu, a prophage
thought to be chemically uninducible—we identified seven such compounds.
These compounds will serve as tools to determine what signals prophages can respond to, and potentially identify new stress pathways of
interest in bacteria.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/25466 |
| Date | January 2020 |
| Creators | Nandy, Anisha |
| Contributors | Hynes, Alexander, Biochemistry and Biomedical Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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