Résumé:
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.
