Abstract: This study aimed at determining the enzymatic properties of recombinant CotA laccase and evaluating its potential for the degradation of aflatoxin M1 (AFM1). Our analysis demonstrated that the cotA gene of Bacillus pumilus E-1- 1-1 was 1 486 bp long, encoding 495 amino acids and having no signal peptide, and its putative protein molecular mass was 58 kDa. The optimum temperature for the recombinant laccase was 40 ℃, and the optimum pH was 4.0. The Km value was 3.01 mmol/L, and the Vmax value was 0.795 mmol/(L·min). Metal ions and chemical reagents had different effects on its enzymatic activity. K+, Na+, ethanol and SDS inhibited the enzymatic activity obviously with percentage inhibition of 31.0%, 13.6%, 64.5% and 100%, respectively. In contrast, Mn2+ and Zn2+ promoted the enzymatic activity by 33.0% and 23.9%, respectively. After 72 hours of reaction with this enzyme, the content of AFM1 in milk decreased by 54.3%, accompanied by a decrease in the toxicity of 9.1%. From this study, we concluded that CotA laccase from B. pumilus can have a great potential as an AFM1-degrading enzyme.

Key words: CotA protein, laccase, aflatoxin M1 (AFM1), biological detoxification, Bacillus pumilus