Journal of Advanced Microbiology

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Abstract: Milk-clotting enzyme has an important role in the process of cheese procution and maturation.

In this study, a bacterium producing extracellular milk-clotting enzyme was isolated from the soil in Tibetan

Plateau and identified as Bacillus licheniformis using 16S rDNA. Then the milk-clotting enzyme from B.

licheniformis HN1 was purified to 26.25-fold with 18.39 % recovery by precipitation in ammonium sulfate and

ion-exchange chromatography. The molecular mass of the enzyme was 51.9 kDa as determined by SDS-PAGE,

and the result of pepstatin A inhibition treatment showed that this enzyme was an aspartic proteas. The enzyme

was active in the pH range 5.5-9.5 and was inactivated completely by heating at 60°C for 20 min. The highest

level of enzyme activity was obtained at 55°C, pH 5.5, and in the presence of 20 mM CaCl2. The high level of milkclotting

activity coupled with a low level of thermal stability suggested that the milk-clotting enzyme from

licheniformis HN1 was a potential substitute for calf rennet.