Biodegradation of Cyromazine by Mycobacterium sp. M15: Performance, Degradation Pathways, and Key Enzymes

Cyromazine, a triazine insecticide, raises food safety concerns due to residues in vegetables like cowpeas. Microbial metabolism is key for pesticide elimination, but bacteria efficient in cyromazine degradation are limited, with uncharacterized enzymes. This study isolated a highly efficient cyromazine-degrading bacterium, Mycobacterium sp. M15, from a cowpea field. M15 utilized cyromazine as the sole carbon source for its growth and completely degraded 0.5 mM cyromazine within 24 h. The degradation pathway involved hydrolyzing cyromazine to N-cyclopropylammeline and further to N-cyclopropylammelide, with amino groups removed sequentially. The cyclopropylamine group in N-cyclopropionamide continued to hydrolyze to cyanuric acid. A protein, CriA, identified as an aminohydrolase in M15, degraded cyromazine to N-cyclopropylammeline. Using CriA reduced cyromazine residues on cowpea surfaces and completely degraded them in immersion solutions. These findings offer insights into cyromazine's microbial degradation mechanism and highlight the potential of cyromazine-degrading enzymes in enhancing food safety.