The genotypic diversity of Pseudomonas brassicacearum populations isolated from roots of Arabidopsis thaliana: influence of plant genotype

Pseudomonas brassicacearum is a newly described bacterial species isolated from the rhizosphere of Arabidopsis thaliana. The P. brassicacearum populations were isolated from the rhizosphere of two ecotypes of A. thaliana (Wassilewskija (WS) and Columbia (COL)), a mutant of Columbia impaired in starch metabolism (pgm mutant), and a genetically distant plant (wheat), grown in a French eutric cambisol (Méréville). The strains were isolated on semi-selective media. Their diversity was assessed using repetitive extragenic palindromic (REP)-PCR profiling and their affiliation to the P. brassicacearum species using ARDRA and siderotyping. A total of 379 strains isolated in two experiments were clustered into 68 REP-genotypes. Statistical analysis showed that the genetic structure of the P. brassicacearum populations was homogeneous for strains isolated from different plants of the same genotype within the same experiment, but significantly differed across the four tested plant genotypes. Comparison of the REP-genotype distributions showed that some bacterial genotypes were poorly represented, whereas others were strongly stimulated by plant roots.