Enzymatic properties of a bacterial microcystinase <scp>A</scp> produced in <scp> <i>Saccharomyces cerevisiae</i> </scp>

Microcystins (MCs) are toxins produced by cyanobacteria, posing a significant emerging threat to human and public health. Therefore, control strategies combining frequent toxin monitoring with removal techniques are urgently needed. In this context, microcystin degradation using the bacterial enzyme microcystinase A, originally derived from Sphingosinicella microcystinivorans B9, has been identified as a sustainable and effective approach. To facilitate access to the enzyme, the gene encoding microcystinase A was successfully expressed in the Saccharomyces cerevisiae PE-2 strain. The recombinant microcystinase A was produced as an intracellular enzyme and applied in MC degradation assays. Optimal conditions for enzymatic activity were identified at 42.2°C and pH 6.3. The maximum degradation rate of microcystin was determined to be 3.09 mg/L/h, and a K_m of 2.81 μM was obtained when assays were performed at 37°C and pH 7.4. The recombinant microcystinase A remained fully active for 2 h at 20°C. Exposure to 50°C for 1 h resulted in 60% residual activity, while 30 min at 65°C led to complete inactivation. The enzyme was also denatured when exposed to alkaline pH conditions. Therefore, this study provides key data on recombinant microcystinase A, supporting further investigations into its potential applications for MC degradation, particularly under mildly acidic conditions and temperatures up to 45°C.