EVERYDAY SCIENCE

Detailed explanation-1: -Bacterial mutation rates typically range from 1 in 10 million to 1 in a billion base substitutions per nucleotide per generation (reviewed in [54]), but bacteria with approximately 100-fold higher mutation frequencies are frequently found in both natural and clinical environments [55–57].

Detailed explanation-2: -Above all, mutation rates in bacteria are remarkably low, even dropping below 10−3/genome/generation (1, 19). Such low rates mean that MA experiments using wild-type strains with intact mismatch repair (MMR) fail to capture enough mutations to detect long-range mutation rate variation (19–21).

Detailed explanation-3: -Before the bacterium can divide, it needs to make two identical copies of the DNA in its chromosome; one for each cell. Every time the bacterium goes through this process there is a chance (or risk, depending on the end result) that errors occur; so-called mutations.

Detailed explanation-4: -For instance, Paramecium tetraurelia has a base-substitution mutation rate of  2 × 10−11 per site per cell division. This is the lowest mutation rate observed in nature so far, being about 75× lower than in other eukaryotes with a similar genome size, and even 10× lower than in most prokaryotes.