Study of the biodegradation of the insecticide thiamethoxam by streptomyces strains isolated from wastewater treatment plants in Algeria

Thiamethoxam is a neonicotinoid insecticide used to control a wide range of pests in a broad variety of agricultural fields. Thiamethoxam may pose some risk to the environment and the health of living organisms. The objective of this study is to isolate actinomycetes strains able to degrade thiamethoxam. In the present study, three thiamethoxam-degrading actinomycetes, were isolated from the activated sludge of Oued El Athmania wastewater treatment plant (Algeria). On the basis of morphological, physiological and biochemical characteristics, combined with phylogenetic analysis of the 16S rRNA gene, these actinomycetes were affiliated to the genus Streptomyces. Evaluation of the degradation of 35 mg/L of thiamethoxam was accomplished in liquid medium. The monitoring of the biodegradation was done by HPLC. The results show that Streptomyces sp. OV was able to degrade 84% of thiamethoxam in the presence of 10 mM glucose, while the strains Streptomyces sp. OB and Streptomyces sp. OH could degrade 78% and 69% of thiamethoxam, respectively, in the presence of 5.9 mM sodium acetate, during 18 days of incubation. Experiments were performed at 30°C, pH 7 and under agitation of 130 rpm. The isolated Streptomyces strains are potential candidates to be used for the developed of biotechnological solutions to eliminate this insecticide from contaminated sites.