Arsenic hyperaccumulator Pteris vittata L (Chinese Brake fern) may accumulate up to 2.3% As in its biomass, making it a viable candidate for phytoremediation of arsenic contaminated sites. Rhizosphere soils from naturally growing P. vittata and bulk soils from 10 feet away were collected from four sites in Florida: Archer Feed Store (AF), Archer Ministorage (AM), Rainbow Springs (RS) and Crystal Quarry site (CQ). When incubated in nutrient medium containing 1 mM of arsenate (AsV), >80% of the AsV in the soils was reduced to arsenite (AsIII). When incubated in nutrient medium containing 1 mM AsIII, significantly more AsIII oxidation occurred in the bulk soils than rhizosphere soils while AsV reduction was equally high in both soils. To test the role of rhizosphere bacteria in arsenic transformation in soils, we isolated and characterized seven arsenic-resistant bacteria at 10 mM AsV, which were all fluorescent indicating the presence of siderophores. We tested the individual rates of AsIII oxidation and AsVreduction in modified Luria Bertani medium containing 1 mM AsV or AsIII. All bacteria were capable of both AsIII oxidation and AsV reduction though their rates were different.  Our results showed that rhizosphere bacteria are important in arsenic transformation in soils.

Keywords: arsenic-resistant bacteria, fluorescence, rhizosphere, hyperaccumulator, Chinese brake fern.