In the surroundings of a former Pb/Zn smelter in Arnoldstein (Austria) heavy metal concentrations in
planted crops exceed thresholds for usage as food and feed. The aim was to study the effects of a plant
growth-promoting bacterial strain in combination with immobilizing soil amendments on plant growth,
heavy metal uptake and on microbial community structure. Pot experiments were performed whereby
two maize cultivars were grown in different contaminated soils and treatments consisted of Burkholderia
phytofirmans strain PsJN with and without addition of gravel sludge and siderite bearing material.
Inoculation with strain PsJN significantly improved root and shoot biomass of maize independent of
immobilizer addition. Analysis of heavy metal content of the rhizosphere and leaves indicated that
immobilizing amendments had significant reducing effects on NH4NO3 extractable Zn and Pb in soil and
in plants grown in treated soils. Microbiomes were analysed by cultivation-independent pyrosequencing
analysis of 16S rRNA genes. The results showed clear effects on community composition in response to
the immobilizer amendments, whereas inoculation with B. phytofirmans affected microbiome diversity
only to a minor extent.