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284 PROCEEDINGS OF INTERNATIONAL SCIENTIFIC CONFERENCE ON APPLIED BIOTECHNOLOGYFigure 4. Effect of Glycerol concentration on vitamin K2 production by strain BST23.2.3. Effect of glycerol concentration In Bacillus subtilis, glycerol serves as both a carbon source for cell growth and a precursor for menaquinone synthesis through various biosynthetic pathways, including the pentose phosphate pathway, the shikimate pathway, and the classical menaquinone pathway [11]. In this study, different glycerol concentrations (1%, 3%, 5%, and 7%) were tested, while other culture conditions were held constant. Following shake-flask fermentation, vitamin K2 production by strain BST2 was measured. The results (Figure 4) showed that the highest vitamin K2 yield was 1608.5 %u00b5g/L in medium containing 70 g/L glycerol, more than three times the yield obtained with 10 g/L glycerol (505.2 %u00b5g/L).3.2.4. Effect of fermentation timeBacillus subtilis BST2 was cultivated in a medium with optimized nutritional conditions, including 0.5 g/L K2HPO4, 20 g/L soybean peptone, and 70 g/L glycerol, to evaluate the effect