Capacité des actinobactéries isolées à partir des stations d’épuration des eaux usées ainsi que Labrys portucalensis F11 à dégrader certains pesticides.

Abstract

In this study, physico-chemical analysis was conducted to evaluate the functionality and quality of effluent from the wastewater treatment plant (WWTP) of Ibn Ziad, Oued El Athmania and Sidi Merouane. The physico-chemical results revealed that the effluents of wastewater at the outlet of the three WWTPs were loading with lower organic matter than the inlet. From the samples of raw, treated wastewater and from the aeration basins of these WWTPs, 15 strains of actinobacteria were isolated and purified. On the basis of morphological, physiological and biochemical characteristics, combined with phylogenetic analysis of the 16S RNAr gene; 13 isolates were affiliated to the genus Streptomyces sp., one to the genus Actinomadura sp. and another isolate to Micrococcus sp. Preliminary screening of these strains on minimum agar media separately supplemented with 17 different pesticides resulted in the selection of 13 strains capable of degrading 9 different pesticides as the sole carbon source. Secondary screening on minimum liquid medium allowed us to evaluate the degradation kinetics of the pesticides 2,4-dichlorophenol (2,4-DCP) and thiamethoxam by the selected actinobacteria strains. Streptomyces sp. ML and OV were considered as the most efficient strains for the degradation of these two pesticides. In this work we also studied the biodegradation of thiamethoxam by the bacterial strain Labrys portucalensis F11. The results show that this strain can degrade 41%, 35% and 100% of thiamethoxam (10,84 mg/L) as sole source of carbon-nitrogen, carbon-sulfur and carbon, respectively after 30 days of incubation. Periodic feeding with sodium acetate resulted in faster degradation of thiamethoxam. Detection and identification of biodegradation intermediates were performed by UPLCQTOF/MS/MS and the chemical structure of 12 metabolites was proposed. Degradation of thiamethoxam by strain F11 is achieved mainly by dechlorination reactions, nitrate reduction and oxadiazine ring cleavage. The impact of thiamethoxam and its degradation intermediates on the germination of Lactuca sativa, the bioluminescence of Vibrio fescheri as well as on the Toxi-Chromo assay showed that L .portucalensis F11 efficiently degrades thiamethoxam to non-toxic metabolites. The present work demonstrates that actinobacteria and L .portucalensis F11 can be used effectively for the detoxification of such sites contaminated by these pesticides.