Abstract: To investigate the tolerance mechanisms of soil microorganisms to mesosulfuron-methyl and to screen for functional strains with environmental adaptability, a strain exhibiting tolerance to this herbicide was isolated and screened from soil with a long-term history of mesosulfuron-methyl application. The target strain was systematically identified through morphological observation, physiological and biochemical tests, and 16S rRNA gene sequence analysis. The results showed that the isolated strain J-1 was a Gram-positive, non-spore-forming bacterium, catalase-positive, capable of utilizing citrate, hydrolyzing starch, gelatin, and esculin, and decomposing urea, and growing well at 7% NaCl concentration. Based on 16S rRNA gene sequence homology analysis and phylogenetic tree analysis, strain J-1 exhibited the closest phylogenetic relationship to Microbacterium resistens. Combined with its physiological and biochemical characteristics, the strain was identified as Microbacterium resistens. This strain was able to stably survive and grow in both nutrient-rich (beef extract-peptone medium) and nutrient-limited (soil extract) conditions containing mesosulfuron-methyl (50 mg/L).

Key words: mesosulfuron-methyl, Microbacterium resistens, tolerance, isolation and identification