DIAUXIC GROWTH OF AZOTOBACTER-VINELANDII ON GALACTOSE AND GLUCOSE - REGULATION OF GLUCOSE-TRANSPORT BY ANOTHER HEXOSE

The growth curve of Azotobacter vinelandii was biphasic when the organ ism was grown in a medium containing a mixture of galactose and glucos e. Galactose was the primary carbon source; glucose was also consumed, but the rate at which it was consumed was lower than the rate at whic h galactose was consumed during the first phase of growth. Metabolic p athways for both sugars were induced. Cell cultures exhibited a second lag period as galactose was depleted. The length of this lag phase va ried from 2 to 10 h depending on the pregrowth history of the cells. T he second log growth phase occurred at the expense of the remaining gl ucose in the medium and was accompanied by induction of the high-maxim um rate of metabolism glucose-induced glucose permease and increases i n the levels of glucose metabolic enzymes. The second lag phase of dia uxie may have been due to the time required for induction of the gluco se-induced glucose permease.