The Comparison of Tolerance Capability of Nitrogen-Fixing Bacteria to Chemical and Biological Pesticides

Abstract

Due to concerns about the adverse effects of synthetic pesticides on the environment and human health, there is a growing preference for environmentally friendly and safe pesticides. However, hard evidence to verify their low-risk characteristics is scarce. This work attempted to compare the effects of a chemical pesticide (alpha-cypermethrin) and a biopesticide (emamectin benzoate) on the growth of indigenous nitrogen-fixing bacteria. These bacterial strains were isolated from the rhizosphere of bean plant samples obtained from farmers? fields where these two pesticides were sprayed on bean crops. The results revealed that at the field-recommended concentration of both pesticides, the growth of the isolates in both nutrient-rich and nitrogen-free media remained largely unaffected. However, the bacteria?s absolute growth inhibition was recorded as the pesticide concentration increased. When the Tryptic Soy Broth medium was supplemented with a pesticide concentration 10 times higher than the recommended dose, up to 85.7% of the isolated strains were completely inhibited in growth when exposed to alpha-cypermethrin. In contrast, only 17.9% of bacterial strains were completely inhibited when exposed to emamectin benzoate. In a nitrogen-free medium, the proportion of inhibited bacteria was absolute when the medium was supplemented with alpha-cypermethrin and emamectin benzoate at a dosage 10 times higher than the recommended concentration, which reached 92.9% and 28.6%, respectively. The strains that exhibited higher tolerance to both pesticides were identified as Niallia nealsonii ND15 and Rhizobium subbaraonis ND27. Our findings emphasize the importance of minimizing pesticide accumulation in the soil to protect the viability of soil-beneficial bacteria and ensure soil quality for safe and sustainable crop production.. KEYWORDS :Alpha-cypermethrin, Emamectin benzoate, N-fixing bacteria, Pesticides tolerance, Toxicity assessment