Isolation, Identification of Three Prometryn-Degrading Strains and Their Synthetic Consortium: Degradation Characteristics and Soil Remediation Potential

Prometryn, a methylthio-s-triazine herbicide, persists widely in agricultural soils after long-term application, causing crop phytotoxicity and potential human health risks, and microbial degradation offers an eco-friendly, cost-effective strategy for remediation. In this study, three prometryn-degrading bacterial strains were isolated from long-term contaminated cornfield soil in Harbin, China, and identified as Pseudomonas sp. ZM-1, Achromobacter sp. ZM-2 and Stenotrophomonas sp. ZM-3 based on morphological, biochemical and 16S rDNA sequence analysis; strain ZM-3 is, to the best of our knowledge, the first reported pure-culture Stenotrophomonas isolate with confirmed prometryn-degrading capability. The three strains degraded 97.3%, 85.1% and 92.8% of 100 mg·L−1 prometryn within 48 h respectively. The 1:1:1 synthetic consortium removed 96.8% of prometryn in 15 h, showing markedly superior degradation efficiency compared with single strains, and its 12-h degradation rate reached 96.87% with a half-life of 2.2 h following response surface optimization. In soil microcosms spiked with 20 mg·kg−1 prometryn, the consortium reduced the pollutant half-life from 58.2 days to 7.8 days and achieved 96.3% removal after 30 days, alongside enhanced soil dehydrogenase, catalase and urease activities. High-throughput 16S rRNA gene sequencing revealed directional succession of the soil bacterial community, enrichment of core degrading taxa, and predicted enrichment of xenobiotic biodegradation pathways during remediation. Maize pot experiments confirmed that the consortium significantly alleviated prometryn phytotoxicity at the tested concentration, restoring plant growth parameters to 95–97% of the uncontaminated control. This study provides an efficient synthetic microbial consortium for bioremediation of prometryn-contaminated agricultural soils.