Figure 6

Evolutionary relationships of response regulator CtrA and QS genes in alpha-proteobacteria. (A) Neighbor-joining tree of CtrA homologs based on 179 amino acid positions excluding alignment gaps. Here shown are all 89 alphaproteobacterial strains for which complete genome information was available from IMG (http://img.jgi.doe.gov/) and that have both ctrA and an autoinducer synthase in their genome. Black, red, blue and green represent strains without, with one, with two and four putative CtrA binding sites in the promoters of either an autoinducer synthase or autoinducer –binding transcription factor gene, respectively. Numbers in front of the name are IMG unique identifiers. (B) Genetic organization of luxI/R or the homologs traI/R with putative CtrA binding sites indicated as red arrows in several selected strains from (A).