Degradation and Detoxification of Nicosulfuron by a Pseudomonas Strain Isolated from a Contaminated Cornfield Soil

ABSTRACT

The dissipation and detoxification of nicosulfuron (NS) by Pseudomonas aeruginosa B9 isolated from a cornfield soil was investigated. The fastest decline of NS occurred at 40 µg ml^?1 in liquid media with 0.25% glucose plus 0.05% yeast extract (DT₅₀ = 4 days) with a notable pH reduction (pH ? 5). Bioassay tests showed considerable phytotoxicity of NS for Cress (Lepidium sativum L.) with 50% shoot growth inhibition (SGI) at 40 µg ml^?1. The dissipation of NS (40 µg ml^?1) by the B9 isolate reduced the SGI significantly (SGI: up to 45 ± 3%) compared to the non-inoculated media (SGI: up to 58 ± 4%). In soils with the B9 isolate, NS dissipation, especially at 0.3 µg g^?1, was faster with a more significant SGI reduction (k = 0.08 ± 0.00 day^?1; SGI = 2 ± 1%) compared to non-inoculated samples (k = 0.03 ± 0.00 day^?1; SGI = 8 ± 1%). NS initially inhibited soil respiration, microbial biomass carbon, and dehydrogenase activity. The effect was however transient, and these parameters recovered within 10 days, especially in the presence of the isolate. Overall, this study proves Pseudomonas aeruginosa B9 as a suitable candidate for bioremediation of NS in contaminated sites.     

Studies on the interactions between nicosulfuron and degradation enzymes

The interactions between nicosulfuron and two degradation enzymes (vegetative catalase 1 and manganese ABC transporter) from the Bacillus subtilis YB1 strain were studied and molecular docking simulations and surface plasmon resonance (SPR) were used to research their specific interaction patterns and affinities. The results showed that vegetative catalase 1 and manganese ABC transporter bound specifically to nicosulfuron and that the former binding ability was stronger than that of the latter. The manganese ABC transporter mainly interacted with nicosulfuron by strong hydrophobic interactions and hydrogen bonds (oxyanion hole), while vegetative catalase 1 formed a strong hydrophobic interaction with nicosulfuron in its main channel and hydrogen bond with nicosulfuron in the side chains. Vegetative catalase 1 and manganese ABC transporter catalyze nicosulfuron degradation, and molecular docking simulations and SPR are good methods for studying molecular interactions, which could make a foundation for the study of degradation mechanisms of enzymes.