The utilization of mixed sugars in continuous fermentation. I.

A strain of Klebsiella aerogenes was selected which gave marked diauxic growth in a batch system on a mixture of glucose and lactose in a simple salts medium; the diauxic lag was 15–20 hr. at 30°C. The growth of this organism on glucose and lactose was studied in a single‐stream two‐stage continuous‐stirred fermentor system over a wide range of flow rates. Glucose was metabolized instantaneously to give very low reactor concentrations at all flow rates, but the time lag before lactose was attacked, when present for the first time, was never less than 40 hr. at low feed rates, rising to 60 hr. at higher rates. The adaptation to lactose of cells in the first vessel lagged behind that in the second vessel but eventually both sugars were completely utilized in the first vessel except at very high dilution rates. At these feed rates, lactose utilization was not only prevented completely in the first vessel but also could be delayed almost indefinitely in the second vessel at the highest dilution rates; thus the lactose passed unchanged through both vessels. Once the enzymes required for lactose utilization had been induced, this ability to use lactose was retained, even in the absence of lactose, for very long periods of time under continuous conditions. Thus on presenting lactose for the second and subsequent occasions it was immediately metabolized. The significance of these results is discussed.