Optimization of DDE-phytoremediation by exploiting plant-associated bacteria and nanoparticles

Abstract

Researchers at The Connecticut Agricultural Experiment Station observed a remarkable difference in the accumulation of 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE) at the subspecies level of Cucurbita pepo. C. pepo ssp pepo (zucchini Raven) accumulates DDE, while C. pepo ssp ovifera (squash Zephyr) did not possess this capacity. In a first part, this study investigates whether the differences in DDE-accumulation can be related to differences in the plant-associated bacterial populations. Bacteria associated with DDE-exposed (100 µg L-1 DDE ) plants of the accumulating and non-accumulating subspecies were isolated and characterized. The results revealed that bacteria associated with the DDE-accumulator zucchini Raven were more numerous and diverse and show more plant growth promoting capacity and potential DDE-degradation capacity than bacteria associated with the non-DDE-accumulating squash Zephyr. The second part of this project concentrates on carbon nanoparticles (CNPs) and their capability to increase the DDE-uptake by plants. Here, the possibility to optimize DDE-phytoremediation by exploiting both plant-associated bacteria and CNPs was investigated. Plants will be exposed to 100 µg L-1 DDE, 500 mg L-1 CNPs or both. The effects of DDE and CNPs on plant growth and on the plant-associated bacterial populations were investigated. DDE proved to have a toxic effect on plant growth, while AgNPs did not cause a decrease in biomass. On the contrary, DDE increased the number of endophytes in zucchini Raven, while exposure to AgNPs caused a severe decrease. Bacteria that were isolated from plants that were exposed to DDE or AgNPs experienced less toxic effects when again exposed to these products. Although AgNPs can be used to increase the DDE-uptake of Cucurbita pepo, it also has severe toxic effects on the plant-associated bacteria. Therefore, a good balance has to be discovered between the advantages and disadvantages of AgNPs for bacteria-enhanced phytoremediation of DDE using Cucurbita pepo ssp. pepo.