Mutators and sex in bacteria: Conflict between adaptive strategies

Bacterial mutation rates can increase and produce genetic novelty, as shown by in vitro and in silico experiments. Despite the cost due to a heavy del eterious mutation load, mutator alleles, which increase the mutation rare, can spread in asexual populations during adaptation because they remain ass ociated with the rare favorable mutations they generate. This indirect sele ction for a genetic system generating diversity (second-order selection) is expected to be highly sensitive to changes in the dynamics of adaptation. Here we show by a simulation approach that even rare genetic exchanges, suc h as bacterial conjugation or transformation, can dramatically reduce the s election of mutators. Moreover, drift or competition between the processes of mutation and recombination in the course of adaptation reveal how second -order selection is unable to optimize the rate of generation of novelty.