Effects of DDE on a soil natural microbial community in presence/absence of the Solanum lycopersicum plant

Although the use of DDTs has been banned in most Countries over 20 years ago, its residues (DTTr) still persist in the environment. DDE (1,1-dichloro-2,2-bis(4- chlorophenyl)ethylene) is the most toxic DDT metabolite and it is reported to be more persistent than its parental compound (Ortìz and Velasco, 2013). Plant-assisted bioremediation can be a promising and cost-effective clean-up technology to contaminated soil remediation. It relies on synergistic action between plant rhizosphere where microorganisms support toxic substance removal. Solanum lycopersicum is known to be able to accumulate DDTs in roots, owing to exudate production, which make these contaminants more bioavailable for soil microorganisms. Moreover, several natural bacterial strains have been shown to degrade organochlorine pesticide through their enzymes able to break-down complex molecules (Verma et al., 2014; Qu et al., 2015). In this context, a greenhouse experiment was performed to study the effects of tomato plant presence on DDE persistence in an agricultural soil. The experimental set up consisted of pots filled with contaminated soil (1ppm of DDE) in presence/absence of tomato plants and control soils (with/without plant and/or DDE). The plots were sampled 40 days from DDE exposure. The effects of DDE and/or plant presence on the natural microbial community were evaluated in terms of microbial abundance, viability, structure, dehydrogenase activity and DDE residual concentration. The overall results showed that although the plant presence stimulated the soil microbial community activity, it did not increase DDE degradation. On the other hand DDE presence not only did not negatively affect the natural microbial community, but the latter was able to degrade DDE independently from the plant presence, showing a preacquired capability presumably due to a soil previous contact with this pesticide.