Control of Vitamin B 6 Biosynthesis in Escherichia coli

Pyridoxineless mutants ofEscherichia coli B which specifically require pyridoxal or pyridoxamine for growth can be divided into classes according to their growth responses in enriched media. Members of the slowest growing class synthesize vitamin B6 at the fastest rates when starved for pyridoxal in glycerol minimal medium. After 80 min of synthesis at 4 × 10−10 moles of vitamin B6 per mg of cells per hr, the rate increases four- to fivefold and continues at the new rate for several hours. The shift to the new rate is prevented by chloramphenicol, thus suggesting that a derepression mechanism exists to control vitamin B6 synthesis in addition to the previously discovered feedback control.