The incidence of Burkholderia in epiphytic and endophytic bacterial cenoses in hybrid aspen grown on sandy peat

Endophytic bacteria are not known from woody plant seedlings. Endophytic and epiphytic bacteria were isolated from leaves, stems and roots of hybrid aspen (Populus tremula x Populus tremuloides) seedlings. The uncultured 16S rRNA rhizospheric bacterial community was cloned from pristine and polyaromatic hydrocarbon polluted rhizosphere soil. The isolates were subjected to restriction fragment length polymorphism analysis and partial 16S rRNA of selected strains was sequenced for phylogenetic identification. The bacteria could be classified into 16 different genera, showing that epiphytes from plant surfaces were most often Gammaproteobacteria, which composed 47% of the isolates. Endophytes from plant tissue were most frequently Betaproteobacteria (45%). Polyaromatic hydrocarbons caused a shift in the cultured bacterial community in the rhizosphere soil to a Betaproteobacteria dominated one. The root bacterial community showed a strong association of Burkholderia bacteria with hybrid aspen. Over 50% of all isolated strains grew on benzoic acid, but only 16% of benzoic acid degraders grew on m-toluate.