Mechanisms on the Combined Remediation of Sulfonylurea Herbicides Contaminated Soil by Chenggangzhangella sp. BI-1 and Cucumber

Sulfonylurea herbicides, widely used in agriculture, persisted long in soil, has raised considerable environmental concerns. Microbial remediation is effective in decomposing organic pollutants. However, researches on microbe-plant combined remediation of contaminated soil based on rhizosphere environment remains limited. In this study, the influence of cucumber root exudates on degrading strain Chenggangzhangella sp. BI-1 was investigated. Additionally, the treatment of cucumber seeds coating with strain BI-1 was employed to study its effects on cucumber stress resistance, herbicides degradation in rhizosphere soil, and the structure of the bacterial community. The results showed that root exudates significantly enhanced BI-1 degradation efficiency towards tribenuron-methyl, chlorimuron-ethyl, and bensulfuron-methyl. Liquid chromatography-mass spectrometry analysis identified 15 amino acids, 55 organic acids, and 4 vitamins in root exudates. Among these, lysine, glutamic acid, vitamin C, succinic acid, and tartaric acid significantly promoted colonization of strain BI-1 on roots. Transcriptomic analysis revealed that 1524 genes in strain BI-1 were significantly upregulated by root exudates, while 1643 genes downregulated, associated with nutrient metabolism, chemotaxis and genetic information processing. After coating treatment under the optimal conditions of 0.8 g·10 mL-1 carboxymethyl cellulose sodium, inoculation-seeds ratio of 1:35 and coating time of 57 min, cucumber seeds were planted in soil contaminated (3.0 mg/kg), the degradation rates reached 75.3% (tribenuron-methyl), 71.3% (chlorimuron-ethyl), and 77.7% (bensulfuron-methyl) after 14 d, which were significantly higher than those in the non-coating treatment. Meanwhile, the coating treatment reduced the malondialdehyde content in cucumber leaves and increased the activities of peroxidase, superoxide dismutase and catalase. It also significantly altered the relative abundances of cucumber rhizosphere bacteria, improving the richness and diversity of bacterial community. Functional prediction via FAPROTAX indicated that the coating treatment increased the relative abundance of functions such as aerobic chemoheterotrophy, thereby facilitating herbicides degradation. This study could provide a basis for the bioremediation of contaminated soils.