Use of plant growth-promoting bacteria in phytoremediation protocols for the reclamation of high level As polluted soils

In the present study, the effect of PGP (plant growth-promoting) bacterial inocula, resistant to arsenic, on the efficiency of Pteris vittata - grown on an arsenopyrite contaminated soil - in phytoextracting this metalloid was evaluated. The research was carried out on soil samples collected from an industrial site located in Tuscany (Italy), highly polluted with arsenic and heavy metals (Pb, Fe, Zn and Cd). At first, the characterization of the bacterial community acclimated to As was carried out starting from enrichment cultures in presence of either arsenite or arsenate. Several strains were isolated in pure culture and phylogenetically identified through 16S rRNA analysis. Afterwards, each strain was tested for its capability of growing in presence of high As levels and MIC (Minimum Inhibitory Concentration) values for both arsenite and arsenate were determined. Then, bacterial isolates were checked for the occurrence of As-resistance genotypes, namely ars and aox genes. Three strains - namely Ochrobactrum cytisi E, Pseudomonas putida O and Achromobacter marplatensis P - were chosen for bioaugmentation tests. Phytoremediation trials using Pteris vittata plants grown in As contaminated soil were performed under glasshouse conditions for six months. The persistence of bacterial inocula in soil was assessed through PCR-DGGE analysis.