Phage-host interactions and the dynamic nature of tRNA modification during the infection cycle of a tailed bacteriophage and cold-active bacterium from Baltic Sea ice

• Main Author: Ahlblad, Niklas
• Other Authors: Helsingin yliopisto, Bio- ja ympäristötieteellinen tiedekunta, University of Helsinki, Faculty of Biological and Environmental Sciences, Helsingfors universitet, Bio- och miljövetenskapliga fakulteten
• Format: Master Thesis
• Language: English
• Published: Helsingin yliopisto 2021
• Subjects: Baltic Sea; Shewanella; Phage 1/4; tRNA modifications; Genetiikan ja molekulaaristen biotieteiden maisteriohjelma; Master's Programme in Genetics and Molecular Biosciences; Magisterprogrammet i genetik och molekylära biovetenskaper; Biokemia ja rakennebiologia; Biochemistry and Structural biology; Biokemi och strukturbiologi; Sea ice
• Online Access: http://hdl.handle.net/10138/334688

The infection mechanisms between cold-active bacteria and their respective bacteriophages are currently relatively unknown and undocumented. Shewanella sp. 4 is a cold-active bacterium that was recently isolated from Baltic Sea ice along with bacteriophage isolate 1/4. Little is known about this particular isolate, although many Shewanella species have important environmental roles incl. carbon cycling, and they have also been associated with the spoilage of fishery products and bioremediation. Previous studies have shown that an infection caused by bacteriophages may lead to significant changes in transfer RNA (tRNA) modifications in the host cell. Commonly, tRNA modification levels may be altered as a response to different stressors, to which viral infections belong as well. Bacteriophages may take advantage of tRNA modifications during the infection of their host, as changes in tRNA modifications lead to much faster response than affecting only the transcription and translation machineries. Here, the infection cycle and changes in tRNA modifications in Shewanella sp. 4 were investigated, along with using a more defined growth media and comparing it to previously conducted characterization. A multitude of methods were applied, such as transmission electron microscopy and mass spectrometry, to observe both the infection mechanisms and changes in tRNA modifications over the course of the infection. I found that the infection cycle of the phage-host pair is predictable and consistent with previously conducted research, lasting 3 hours until cell lysis. Plaque assay and SDS-PAGE showed the release of virions 2-3 h post-infection (p.i.), and the production of viral proteins within cells starting from 100 min p.i. An intriguing periodic change in cell turbidity was also observed already before cell lysis. Furthermore, the tRNA modifications m1A, m5U, m6t6A, and Cm undergo statistically significant changes or display high variance during the course of the infection when comparing infected and uninfected cells. These ...