Fig. 10

Putative metabolic pathway involved in l-serine accumulation. Serine sulfhydrase is shown as an example of pyridoxal phosphate enzymes. In this pathway, l-serine can be accumulated when the supply of pyridoxal-5-phosphate (P5P) is insufficient, which is caused by Zn²⁺ deficiency. As nicotinic acid and folic acid have been reported to promote pyridoxine biosynthesis [14], synergistic effect of Zn²⁺, nicotinic acid, and folic acid on colony morphology observed in present is accountable if this pathway is involved in the morphogenesis