Bacteria from the rhizosphere and tissues of As-hyperaccumulator Pteris vittata and their role in arsenic transformation.

Arsenic (As)-resistant bacteria are abundant in the rhizosphere and tissues of As-hyperaccumulator Pteris vittata. However, little is known about their roles in As transformation and As uptake in P. vittata. In this study, the impacts of P. vittata tissue extracts with or without surface sterilization on As transformation in solutions containing 100 μg L-1 AsIII or AsV were investigated. After 48 h incubation, the sterilized and unsterilized root extracts resulted in 45% and 73% oxidation of AsIII, indicating a role of both rhizobacteria and endobacteria. In contrast, AsV reduction was only found in rhizome and frond extracts at 3.7-24% of AsV. A total of 37 strains were isolated from the tissue extracts, which are classified into 18 species based on morphology and 16S rRNA. Phylogenic analysis showed that ∼44% isolates were Firmicutes and others were Proteobacteria except for one strain belonging to Bacteroidetes. While most endobacteria were Firmicutes, most rhizobacteria were Proteobacteria. All isolated bacteria belonged to AsV reducers except for an As-sensitive strain and one AsIII- oxidizer PVR-YHB6-1. Since As transformation was not observed in solutions after filtrating or boiling, we concluded that both rhizobacteria and endobacteria were involved in As transformation in the rhizosphere and tissues of P. vittata.