Diversity of Paenibacillus polymyxa strains isolated from the rhizosphere of maize planted in Cerrado soil

Paenibacillus polymyxa populations present in the rhizosphere of maize (cul tivar BR-201) planted in Cerrado soil were investigated in order to assess their diversity at four stages of plant growth. A total of 67 strains were isolated and all strains were identified as P. polymyxa by classical bioche mical tests, API50CH tests and a set of species-specific primers based on t he 23S rDNA sequence. To compare the isolated strains, phenotypic character istics (utilization of different carbohydrates, resistance to antibiotics a nd production of antimicrobial substances) and genetic approaches (hybridiz ation with a Klebsiella pneumoniae nifKDH probe and BOX-PCR) were used. Fer mentation of glycerol, arabinose, xylose and rhamnose varied among the isol ates and these data divided the strains into five groups. Fifty strains (75 %) showed homology to plasmid pSA30 (containing the nifKDH genes) resulting in five different hybridization patterns. Using BOX-PCR 18 groups were obs erved. Phenetic analyses were applied based on the unweighted pair group me thod with arithmetic means using the phenotypic and genetic data, separatel y All P. polymyxa isolates could be divided into two main clusters at appro ximately 52% and into 18 groups at approximately 89% of similarity, when ph enotypic data were used. Also, two main clusters were formed at 65% of simi larity when genetic data were used. In this dendrogram, clusters were furth er split into 10 and 22 groups, at about 88 and 97% of similarity, respecti vely. Finally, all phenotypic and genetic data, or just the genetic data, w ere used in a multivariate analysis of variance (MANOVA) in order to addres s the heterogeneity among P. polymyxa populations during the different stag es of maize growth. The resulting data showed that strains isolated 10, 30, 60 and 90 days after maize sowing were statistically different. (C) 2000 E ditions scientifiques et medicales Elsevier SAS.