Evidence of non-random mutation rates in Escherichia coli

A article in tomorrow’s edition of Nature caught my eye – Iñigo Martincorena and colleagues have sequenced a number of Escherichia coli genomes and compare the speed of genetic drift at different locations in the genome. They observe

that the neutral mutation rate varies by more than an order of magnitude across 2,659 genes, with mutational hot and cold spots spanning several kilobases.

More interestingly, however, those variations in mutation rate are not random. The study detects a

lower rate in highly expressed genes and in those undergoing stronger purifying selection. Our observations suggest that the mutation rate has been evolutionarily optimized to reduce the risk of deleterious mutations.

Left me wondering about the wider consequences for phylogenetic analysis if this phenomenon was widespread in nature. I suppose different, but constant mutation rates shouldn’t be a huge problem, but the story might be different if mutation rates have been under selection pressure over evolutionary time.

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