ACETATE METABOLISM BY ESCHERICHIA-COLI IN HIGH-CELL-DENSITY FERMENTATION

Little is known about the cellular physiology of Escherichia coli at h igh cell densities (e.g., greater than 50 g [dry cell weight] per lite r), particularly in relation to the cellular response to different gro wth conditions. E. coli W3100 cultures were grown under identical phys ical and nutritional conditions, by using a computer-controlled fermen tation system which maintains the glucose concentration at 0.5 g/liter , to high cell densities at pH values of 6.0, 6.5, 7.0, and 7.5. The d ata suggest a relationship between the pH of the environment and the a mount of acetate excreted by the organism during growth. At pH values of 6.0 and 6.5, the acetate reached a concentration of 6 g/liter, wher eas at pH 7.5, the acetate reached a concentration of 12 g/liter. Furt hermore, at pH values of 6.0 to 7.0, the E. coli culture undergoes a d ramatic metabolic switch in which oxygen and glucose consumption and C O2 evolution all temporarily decrease by 50 to 80%, with a concomitant initiation of acetate utilization. After a 30-min pause in which appr oximately 50% of the available acetate is consumed, the culture recove rs and resumes consuming glucose and oxygen and producing acetate and CO2 at preswitch levels. During the switch period, the specific activi ty of isocitrate lyase typically increases approximately fourfold.