Genetic diversity of bacterial communities of serpentine soil and of rhizosphere of the nickel-hyperaccumulator plant Alyssum bertolonii

Serpentine soils are characterized by high levels of heavy metals (Ni, Co, Cr), and low levels of important plant nutrients (P, Ca, N). Because of these inhospitable edaphic conditions, serpentine soils arc typically home to a very specialized flora including endemic species as the nickel hyperaccumulator Alyssum bertolonii. Although much is known about the serpentine flora, few researches have investigated the bacterial communities of serpentine areas. In the present study bacterial communities were sampled at various distances from A. bertolonii roots in three different serpentine areas and their genetic diversity was assessed by terminal restriction fragment length polymorphism (T-RFLP) analysis. The obtained results indicated the occurrence of a high genetic diversity and heterogeneity of the bacterial communities present in the different serpentine areas. Moreover, TRFs (terminal restriction fragments) common to all the investigated A. bertolonii rhizosphere samples were found. A new cloning strategy was applied to 27 TRFs that were sequenced and taxonomically interpreted as mainly belonging to Gram-positive and alpha-Proteobacteria representatives. In particular, cloned TRFs which discriminated between rhizosphere and soil samples were mainly interpreted as belonging to Proteobacteria representatives.