Rapid evolution of diminished transformability in Acinetobacter baylyi.

The reason for genetic exchange remains a crucial question in evolutionary biology. Acinetobacter baylyi strain ADP1 is a highly competent and recombinogenic bacterium. We compared the parallel evolution of wild-type and engineered noncompetent lineages of A. baylyi in the laboratory. If transformability were to result in an evolutionary benefit, it was expected that competent lineages would adapt more rapidly than noncompetent lineages. Instead, regardless of competency, lineages adapted to the same extent under several laboratory conditions. Furthermore, competent lineages repeatedly evolved a much lower level of transformability. The loss of competency may be due to a selective advantage or the irreversible transfer of loss-of-function alleles of genes required for transformation within the competent population.