The role of bacteria in the heavy metals removal and growth of Sedum alfredii Hance in an aqueous medium

This study was the first attempt to examine the possible role of the naturally occurring rhizospheric bacteria in heavy metal removal by Sedum alfredii Hance, a terrestrial Zn/Cd hyperaccumuluator, from Zn, Cd, Cu and Pb contaminated water using antibiotic ampicillin. Moreover, the toxicity symptom in plants under heavy metal stress expressed as total chlorophyll, chlorophyll a and b content, growth inhibition, root length, and N, P contents were studied, and the possible relationship among them were also discussed. These results indicate that rhizospheric bacteria may play an important role in the uptake of N and P by S. alfredii, and consequently result in the increase of Chlorophyll content in the leaves and plant biomass due to improved photosynthesis. At the same time, root length significantly decreased under the treatment with ampicillin, which suggested that rhizospheric bacteria appeared to protect the roots against heavy metal toxicity. The Pb, Zn, Cu and Cd concentrations in the roots, stems and leaves of S. alfredii were much higher than those exposed to ampicillin. Accordingly, metal concentrations in the contaminated water without ampicillin treatment were lower than those treated with ampicillin. These results suggest that the rhizospheric bacteria may be useful in plant tolerance to heavy metal toxicity, and also accelerate the metal removal from contaminated water.