Genes for breakfast: the have-your-cake-and-eat-it-too of bacterial transformation

Bacterial transformation, in which cells take up and recombine free strands of DNA, is the simplest process thought to have evolved for genetic exchange, i.e., because of the potential benefits of producing progeny with recombinant genotypes. However, two other functions are equally plausible: acquisition of intact DNA strands to use for recombinational repair of DNA damage, and acquisition of the nutrients contained in DNA molecules. Although the recombinant progeny produced by transformation can be beneficial, the success of genes causing transformation is limited by other factors, especially by the genetic quality of DNA derived from dead cells. Our recent experiments in the naturally transformable bacteria Haemophilus influenzae and Bacillus subtilis suggest that the DNA-repair hypothesis is unlikely to be correct. In H. influenzae, transformation does not detectably increase the cells' ability to survive DNA damage. More importantly, we have found that, although competence (the ability to take up DNA) is induced by nutritional limitation in both H. influenzae and B. subtilis, it is not induced by DNA damage in either. Thus we favor the hypothesis that transformation evolved as a nutrient-uptake system, especially because unrelated DNA is abundant in the environments of many naturally transformable bacteria.