BIODIVERSITY OF A BURKHOLDERIA-CEPACIA POPULATION ISOLATED FROM THE MAIZE RHIZOSPHERE AT DIFFERENT PLANT-GROWTH STAGES

A Burkholderia cepacia population naturally occurring in the rhizosphe re of Zea mays was investigated in order to assess the degree of root association and microbial biodiversity at five stages of plant growth. The bacterial strains isolated on semiselective PCAT medium were most ly assigned to the species B. cepacia by an analysis of the restrictio n patterns produced by amplified DNA coding for 16S rRNA (16S rDNA) (A RDRA) with the enzyme AluI. Partial 16S rDNA nucleotide sequences of s ome randomly chosen isolates confirmed the ARDRA results. Throughout t he study, B. cepacia aas strictly associated with maize roots, ranging from 0.6 to 3.6% of the total cultivable microflora. Biodiversity amo ng 83 B. cepacia isolates was analyzed by the random amplified polymor phic DNA (RAPD) technique with two 10-mer primers. An analysis of RAPD patterns by the analysis of molecular variance method revealed a high level of intraspecific genetic diversity in this B. cepacia populatio n. Moreover, the genetic diversity was related to divergences among ma ize root samplings, with microbial genetic variability markedly higher in the first stages of plant growth; in other words, the biodiversity of this rhizosphere bacterial population decreased over time.