Potentiated remediation of imazethapyr-contaminated soil by phosphate-doped biochar immobilized with Bacillus cereus MZ-1.

Microbial degradation represents a promising strategy for the remediation of pesticide-contaminated agricultural soils. However, the field performance of free degrading bacteria is often compromised by environmental fluctuations, poor colonization capacity, and intense competition from indigenous microorganisms. In this work, phosphoric acid-modified corn stover biochar was utilized as a support matrix to immobilize the imazethapyr (IMT)-degrading strain Bacillus cereus MZ-1, yielding a high-efficiency immobilized microbial inoculum for soil remediation. The immobilization process was optimized using response surface methodology, and under the optimal conditions (30 °C, 18 h incubation, 4:1 cell-to-biochar suspension ratio), the inoculum achieved 93.57% IMT removal efficiency. GFP labeling validated the stable colonization and ecological compatibility of strain MZ-1 in soil. When applied at 2% dosage under the optimal conditions (30 °C, 80% soil relative moisture, weakly alkaline pH), the inoculum markedly accelerated IMT dissipation, reducing its half-life from approximately 55 d to 20 d in brown loam and black soil. 16S rRNA sequencing results indicated that the immobilized microbial inoculant regulated the metabolic activity of soil microorganisms. It significantly upregulated fatty acid and carbohydrate metabolism, while causing no substantial changes to the soil microbial community structure compared with the control group. Pot experiments further confirmed that the inoculum effectively alleviated IMT phytotoxicity to succeeding maize, restoring plant growth and physiological performance. Overall, this biochar-immobilized microbial system provides an eco-friendly and high-performance approach for remediating IMT-contaminated agricultural soils.