Extensive variation in natural competence in Haemophilus influenzae

The ability of some bacteria to take up and recombine DNA from the environment is an important evolutionary problem because its function is controversial; although populations may benefit in the long-term from the introduction of new alleles, cells also reap immediate benefits from the contribution of DNA to metabolism. To clarify how selection has acted, we have characterized competence in natural isolates of H. influenzae by measuring DNA uptake and transformation. Most of the 34 strains we tested became competent, but the amounts of DNA they took up and recombined varied more than 1000-fold. Differences in recombination were not due to sequence divergence and were only partly explained by differences in the amounts of DNA taken up. One strain was highly competent during log phase growth, unlike the reference strain Rd, but several strains did not develop competence under any of the tested conditions. Analysis of competence genes identified genetic defects in two poorly transformable strains. These results show that strains can differ considerably in the amount of DNA they take up and recombine, indicating that the benefit associated with competence is likely to vary in space and/or time.