The Virus Resistance Mechanism of Abortive Infection K in Lactococcus lactis
Date
2023-07
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Abstract
In nature, there is a constant battle between viruses and their hosts known as the evolutionary arms race, where they both continuously evolve to attempt to gain an advantage over the other. This evolutionary arms race has resulted in many mechanistic inventions, such as abortive infection (Abi) mechanisms in bacteria. In Abi mechanisms, viruses inject their genetic material into cells, but bacteria block phage replication by preventing one of the steps of phage maturation, typically resulting in cell death. This study looks at the Abi mechanism called AbiK, which is controlled by a protein of the same name that was discovered on a plasmid in Lactococcus lactis. A large portion of the study focuses on what happens in vivo during the AbiK mechanism. The normal wild-type infection, the abortive infection mediated by the AbiK protein, and the escape of the AbiK mechanism by a mutant phage are all studied for comparative analyses. Observations have shown that phage DNA replication is inhibited, and that transcription of the phage genes is delayed during the AbiK mechanism. The mutant phage can bypass these inhibitions, and successfully replicate its DNA and complete the phage lytic cycle. RNA-Sequencing experiments were conducted to narrow down the mechanism behind AbiK, and preliminary results indicate that AbiK depletes the nucleotide resources available in the cell, eventually resulting in cell death and inhibition of the phage replication cycle. A second part of this study focuses on the biochemistry of the AbiK protein. The AbiK protein has a polymerase activity that polymerizes an untemplated long single-stranded DNA that is covalently attached to the AbiK protein. This study identified which amino acid is used as a primer, which is tyrosine 44 on the AbiK protein. The release of protein structure prediction databases allowed for the analysis of a generated model of the AbiK protein, allowing for the elucidation of other biochemical functions the AbiK protein has. In addition to the polymerization activity, AbiK is hypothesized to bind to nucleotides or other proteins. The culmination of these studies allowed for insight on the AbiK mechanism, generating a hypothesis for future studies.
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Keywords
Bacteriophage, Defense Mechanism, Abortive Infection, Lactococcus lactis
Citation
Du, A. (2023). The virus resistance mechanism of abortive infection K in Lactococcus lactis (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.