Search for a command to run...
Fluorescent pseudomonads protecting plant roots from phytopathogens by producing 2,4-diacetylphloroglucinol (DAPG) are considered to form a monophyletic lineage comprised of DAPG<sup>+</sup><i>Pseudomonas</i> strains in the "<i>P. corrugata</i>" and "<i>P. protegens</i>" subgroups of the "<i>Pseudomonas fluorescens</i>" group. However, DAPG production ability has not been investigated for many species of these two subgroups, and whether or not the DAPG<sup>+</sup><i>Pseudomonas</i> are truly monophyletic remained to be verified. Thus, the distribution of the DAPG biosynthetic operon (<i>phlACBD</i> genes) in the <i>Pseudomonas</i> spp. was investigated in sequenced genomes and type strains. Results showed that the DAPG<sup>+</sup><i>Pseudomonas</i> include species of the "<i>P. fluorescens</i>" group, i.e., <i>P. protegens, P. brassicacearum, P. kilonensis</i>, and <i>P. thivervalensis</i>, as expected, as well as <i>P. gingeri</i> in which it had not been documented. Surprisingly, they also include bacteria outside the "<i>P. fluorescens"</i> group, as exemplified by <i>Pseudomonas</i> sp. OT69, and even two Betaproteobacteria genera. The <i>phl</i> operon-based phylogenetic tree was substantially congruent with the one inferred from concatenated housekeeping genes <i>rpoB, gyrB</i>, and <i>rrs</i>. Contrariwise to current supposition, ancestral character reconstructions favored multiple independent acquisitions rather that one ancestral event followed by vertical inheritance. Indeed, based on synteny analyses, these acquisitions appeared to vary according to the <i>Pseudomonas</i> subgroup and even the phylogenetic groups within the subgroups. In conclusion, our study shows that the <i>phl</i><sup>+</sup><i>Pseudomonas</i> populations form a polyphyletic group and suggests that DAPG biosynthesis might not be restricted to this genus. This is important to consider when assessing the ecological significance of <i>phl</i><sup>+</sup> bacterial populations in rhizosphere ecosystems.