Insights on the isolation, identification, and degradation characteristics of three bacterial strains against mandipropamid and their application potential for polluted soil remediation

Abstract

Bacteria-induced biodegradation techniques have become an effective approach for removing pesticide residues from polluted soils. However, their effect on chiral fungicides must be systematically evaluated and the efficiency and risk of each chiral enantiomer must be better understood. In this study, we isolated and enriched seven bacterial strains that are able to degrade mandipropamid from contaminated soil samples. Three bacterial strains with high degradation efficiency (63.6%-73.4%) were screened and identified as Pseudomonas sp. (M01), Mycolicibacterium parafortuitum (MW05), and Stenotrophomonas maltophilia (MW09) by morphological and 16S rRNA gene sequencing analyses. The degradation characteristics of three strains (M01, MW05, and MW09) was investigated and it was revealed that pH, temperature, and initial concentration of mandipropamid significantly impacted their degradation efficiency. The optimal conditions for degradation were a nutrient source of mandipropamid and an inoculation amount of 5%. We used a Box-Behnken model experiment and an analysis of variance to determine the most suitable conditions for degrading mandipropamid at various pH, temperature, and initial concentration levels. A response surface methodology analysis showed that the three strains had the highest mandipropamid degradation efficiency (> 96%) under various conditions (pH: 7.15-7.71, temperature: 28.61-30.76 °C, initial concentration: 5.524-5.934 mg/L). Mycelial, intracellular, and extracellular enzymes also had an impact on the degradation of mandipropamid enantiomers by the three strains. In soil remediation trials, the three bacterial strains could effectively enantioselectively degrade rac-mandipropamid residues in polluted sterilized and natural soil samples (R-enantiomer was degraded faster) and influence the activity of urease and β-glucosidase in the soil. The results revealed several candidate bacterial strains for mandipropamid biodegradation and provide information on mandipropamid biological detoxification in soil environments.

Keywords: Degradation efficiency; Influence factor; Mandipropamid; Soil remediation; bacteria strains.