Robert, L. et al. Science 359, 1283–1286 (2018).

Mutations in DNA are crucial for adaptation and evolution. However, mutations and their effects are challenging to study directly, especially at the single-cell level. To address this challenge, Robert et al. developed an approach to study the effects of mutations as they arise in Escherichia coli. Their approach involves the use of a microfluidic device known as a 'mother machine' that enables imaging of single cells over multiple generations. In this device, they carried out time-lapse imaging of E. coli harboring a mismatch repair protein fused to a fluorescent protein reporter. This reporter formed fluorescent foci whenever a mutation occurred in a strain of E. coli that could not repair mutations. The researchers monitored ∼20,000 mutation events in single cells over hundreds of generations, and found that 1% of mutations were lethal, whereas the vast majority were relatively neutral.