Characterization of native strains of agricultural soils tolerant to imidacloprid

Abstract

Imidacloprid is a broad-spectrum insecticide frequently used in agricultural areas for the control of insect pests. The excessive use of this chemical has caused several ecological and health problems to mammals and humans. This insecticide can be degraded by soil microorganisms and transformed into by-products with a lower degree of toxicity. The objective of this study was to isolate bacteria from maize and sorghum soils contaminated with imidacloprid for several years. Bacteria were isolated with minimum salt medium supplemented with 100 mg/L of imidacloprid as the sole carbon source and energy. Isolated bacteria were subjected to in vitro growth tolerance tests and later 16S rDNA molecular characterization was conducted in isolates from different levels of tolerance. From both crops, we obtained 26 isolates with different morphological characteristics. The 63% of the isolates exhibited high tolerance to the insecticide, while 37% of the isolates showed medium, scarce or no tolerance. 16S rDNA molecular identification, grouped the isolates in Firmicutes and Actinomycetes, important phylum that include bacteria that participate in the degradation of imidacloprid in soil.