Protecting soybean yields from enrofloxacin toxicity: The role of Bradyrhizobium japonicum inoculation

Abstract

Soybean plants are sensitive to the antimicrobial enrofloxacin (Enro), demonstrating significant yield reductions when exposed to this pharmaceutical. In this study, we investigated the susceptibility and attenuation properties of a commercial Bradyrhizobium japonicum formulation on the deleterious effects of Enro on the growth and yield of soybean plants. Although environmentally representative concentrations of Enro in soil (200, 600, and 1000 μg kg−1) may be toxic to B. japonicum, effective symbiosis between the bacteria and soybean plants was observed even when plants were exposed to Enro concentrations close to those leading to bacterial death (1600 μg kg−1). While the antimicrobial decreased the number of nodules in plants, the increase in their mass assured the maintenance of nitrogenase activity and the provision of nitrogen to plants. The inoculation also increased the nitrogen status of leaves, ensuring the production of glutamate, which is related to the biosynthesis of proline, an antioxidant molecule that helps avoid oxidative bursts and related decreases in photosynthesis and growth. In addition, the inoculation prevented Enro-induced decreases in seed production. However, while the inoculation may prevent economic losses related to the production of soybeans in soils contaminated by Enro, it does not prevent the accumulation of the antimicrobial in edible parts of the plant, which poses hazardous toxicological effects.