Abstract
Mutational hotspots can determine evolutionary outcomes and make evolution repeatable. Hotspots are products of multiple evolutionary forces including mutation rate heterogeneity, but this variable is often hard to identify. In this work we reveal that a powerfully deterministic genetic hotspot can be built and broken by a handful of silent mutations. We observed this when studying homologous immotile variants of the bacteria Pseudomonas fluorescens, AR2 and Pf0-2x. AR2 resurrects motility through highly repeatable de novo mutation of the same nucleotide in >95% lines in minimal media (ntrB A289C). Pf0-2x, however, evolves via a number of mutations meaning the two strains diverge significantly during adaptation. We determined that this evolutionary disparity was owed to just 6 synonymous variations within the ntrB locus, which we demonstrated by swapping the sites and observing that we were able to both break (>95% to 0% in AR2) and build (0% to 80% in Pf0-2x) a powerfully deterministic mutational hotspot. Our work reveals a fundamental role for silent genetic variation in determining adaptive outcomes.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵a These authors share senior authorship
v2: The manuscript now includes figure 5; the abstract, results and discussion sections have been updated to incorporate this new data; the author list has been updated.
v3: The title, abstract and main manuscript text have been updated.
https://github.com/J-S-Horton/Syn-sequence-parallel-evolution.git