Neighbor-Joining phylogenic tree of ECF σ 70 factors. The sequences were retrieved from sequenced Burkholderia genomes or the GenBank database. Within one species, when sequences were orthologs, only one sequence per sigma factor was kept. A total of 746 sites were analyzed (with pairwise deletion of gap-containing sites). Distances are proportional to evolutionary divergences expressed in substitutions per 100 sites. Bootstrap values higher than 85% are given. Distribution among other proteobacterial groups is indicated. Likely role of the identified ECF factors is indicated.