The Bacterial Flora of the Nickel-Hyperaccumulator Plant Alyssum bertolonii

Recent years have witnessed a considerable growth of microbiological researches in serpentine soils in relation to the presence of hyperaccumulating plants. Nickel-hyperaccumulating plants accumulate huge amounts of heavy metals in shoots, and therefore, provide a specific environment for bacterial populations and in particular for endophytic bacteria. Bacterial endophytes have been studied in many different plant species and in some cases they have been found to promote plant growth or to confer the plant higher tolerance to biotic and abiotic stress. Here, we report the data on presence, composition and possible roles of bacteria associated with Alyssum bertolonii Desv. (Brassicaceae), the first nickel-hyperaccumulator plant discovered endemic to serpentine outcrops of Central Italy. The analysis of both cultivable and total fraction of the soil bacterial community showed a very strong effect of the plant in shaping the community composition. Moreover, the plant harbors a complex and highly variable endophytic bacterial flora with many Ni-resistant strains. Endophytic bacteria were isolated from roots, stems, and leaves of several A. bertolonii plants and populations allowing providing a model of correlation between taxonomic compositions of bacterial communities from different organs, plants, populations, and surrounding soils. Some of the endophytic bacteria tested for plant tissue colonization ability, and for their influence on plant growth and nickel-hyperaccumulation, resulted in increased biomass production and metal accumulation. Ecological and evolutionary implications of such findings are also discussed.