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SECTION II. APPLIED BIOTECHNOLOGY IN THE PHARMACEUTICAL INDUSTRY... 2833.2.2. Effect of soybean peptone concentrationNitrogen sources are essential nutrients for microbial growth and the biosynthesis of secondary metabolites, with different microbial strains exhibiting varying requirements for nitrogen sources. Previous studies have indicated that peptone derived from soybeans serves as an optimal nitrogen source for the production of vitamin K2 [9,10]. Building on this, the present study further investigates the impact of soybean peptone concentration on vitamin K2 synthesis by strain Bacillus subtilis BST2. As shown in Figure 3, increasing the soybean peptone concentration from 10 to 20 g/L enhanced vitamin K2 production by strain BST2, with the highest yield reaching 1476.3 %u00b5g/L. However, when the nitrogen source exceeded 20 g/L, a reduction in vitamin K2 production was observed.Figure 3. Effect of Soybean peptone concentration on vitamin K2 production by strain BST2