Degradação de fipronil por bactérias bioprospectadas de solo

Abstract

Fipronil is a phenylpyrazole insecticide that has a broad-spectrum action, since it has a direct action on gamma-aminobutyric acid receptors (GABA). It is widely used nowadays, mainly due to agricultural expansion, in soybean, sugarcane, corn and other crops. However, this agrotoxic shows toxicity to non-target insects such as pollinators and to other animals along the trophic chains. Thus, the present study had the objective of bioprospecting bacteria with the potential to growth and degradation of fipronil as the only sources of carbon and nitrogen. In this way, soil samples were collected under maize cultivation with a history of application of fipronil aiming the isolation of bacteria in microcosm enrichments. Isolation resulted in strains of Gram- positive, sporulated, catalase positive bacteria and possibly belonging to the genus Bacillus. The medium used for isolation was ATZ-R (adapted), using a fipronil concentration of 600 mg.L-1 , as the sole source of carbon and nitrogen. From the aerobic growth kinetics, the isolates that showed the best growth were selected. The E1 isolate was selected as the best isolate and from the sequencing of the 16S RNAr gene it was verified that it possibly belongs to the species Bacillus megaterium. A comparison was made with a strain G2.8 of the genus Enterobacter, belong to the species Enterobacter cloacae. This strain also belongs to the collection of strains of the Laboratório de Metagenômica-UFGD, was isolated in soil with a history of application of fipronil. Using the two bacteria, growth and degradation kinetics of fipronil at 600 mg.L-1 were performed. The growth was evaluated through the dry biomass and the degradation was analyzed by GC/MS, evaluating besides the degradation of fipronil the formation and quantification of its metabolites. Isolates E1 and G2.8 degraded fipronil at a percentage of 94 and 96%, respectively. However, using the GENES statistical program, no statistical variance was observed throught ANOVA and, when compared with their respective controls, a difference was verified by the DMS-t 5% mean test. The E1 presented formation of both the fipronil sulfide metabolite formed from enzymatic reduction reactions and fipronil sulfone formed from enzymatic oxidation reactions. The G2.8 presented higher formation of fipronil sulfide. The results obtained in this study demonstrate that the studied strains have a high biodegradation efficiency of fipronil when compared to the results of the literature.