Mutagenesis is typically associated with DNA replication, a prominent source being the replicative polymerase itself that can make errors at some frequency. Additionally, upon encountering DNA lesions, the replicative polymerase is sometimes replaced by low fidelity translesion synthesis polymerases that can also be a source of stress-induced mutagenesis (PMID 32556198). 

 

We used microscopy to track DNA replication proteins in live Caulobacter cells. With this tool we asked whether mutagenenic mechanisms were always restricted to only actively replicating cells. We found that DNA lesion tolerance mechanisms were active in non-replicating cells, with replisome components associated with low-fidelity polymerases being loaded de-novo under DNA damage. This suggests that dormant or persistent cells that are metabolically active, have the potential for mutagenesis even though they are shut-down for replication (PMID 33856342).

 

The tools developed in this project enabled us to assess in single-cells the speed of replication and its impact on mutation rates. We found that replication rates vary based on nutrient availability, and surprisingly this does not trigger DNA stress or increased mutagenesis, as previously thought. We went on to provide mechanistic insights into how this variation occurs, that may enable bacterial adaptation to slow-growth or starvation conditions (PMID 38658616; 40168985). 

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Together these studies reveal context-dependent regulation of the DNA replication machinery and associated mutagenesis. We are now curious to understand how these dynamics affect/ are affected by extrachromosomal elements such as plasmids. ​​