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Plasmid segregation and stability in bacteria

Published on January 31, 2024   32 min

A selection of talks on Biochemistry

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0:00
My name is Barbara Funnell and I am from the Department of Molecular Genetics at the University of Toronto. My research interests are chromosome dynamics in bacteria and specifically the mechanisms of segregation of bacterial plasmids. In this talk, I will discuss plasmid segregation or as it is more commonly called in bacteria partition or partitioning. First, I will introduce and review general characteristics of plasmid partition systems and then I will discuss, in more detail the mechanisms of these events in bacteria. My research concerns the partition of a plasmid called P1 in the bacteria Escherichia coli. I will use examples from work on several different plasmids including P1 during this talk. This talk is an update from a previous version published in 2008 and there have been significant developments in the partition field since then. Particularly, in the structural biology, biochemistry, and mechanistic models, and in the variety of partition systems that have been identified in bacterial plasmids.
0:60
Plasmids as autonomous extrachromosomal elements must ensure their own replication and stable maintenance in bacterial populations, and they use several different types of processes. Without them, plasmids are lost from the population of bacterial cells and are thus unstable. First, plasmid replication systems control copy number to make sure that every cell has enough plasmid copies to segregate to daughter cells at the next cell division. Second, plasmids occasionally recombine with each other via homologous recombination to produce higher multimers, that is dimers or higher, which reduces the number of partitionable units. So, plasmids often contain specific recombination systems to resolve these back into monomers. Perhaps the most famous of these is the lox-cre recombinase pair from the P1 plasmid, which has been exploited very successfully for genetic engineering. Third, plasmids in code, what are often called addiction systems, these consist of a bacterial toxin and antitoxin which kill cells that lose the plasmid because the antitoxin is less stable than the toxin. Fourth, and the subject of this talk, the partition systems which make sure that enough plasmids are in the right place in the cell so that every daughter cell receives at least one copy. That is, the partition is a transport and positioning process where the cargo is plasmid DNA.
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Plasmid segregation and stability in bacteria

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