Diauxic growth curve

A diauxic growth curve refers to the growth curve generated by an organism which has two growth peaks. The theory behind the diauxic growth curve stems from Jacques Monod's Ph.D. research in 1940.

A simple example involves the bacterium E. coli, the best understood bacterium. The bacterium is grown on a growth media containing two types of sugars, one of which is easier to metabolize than the other (for example glucose and lactose). First, the bacterium will metabolize all the glucose, and grow at a higher speed. Eventually, when all the glucose has been consumed, the bacterium will begin the process of expressing the genes to metabolize the lactose. This will only occur when all glucose in the media has been consumed. For these reasons, diauxic growth occurs in multiple phases.

The first phase is the fast growth phase, since the bacterium is consuming (in the case of the above example) exclusively glucose, and is capable of rapid growth. The second phase is a lag phase while the genes used in lactose metabolism are expressed and observable cell growth stops. This is followed by another growth phase which is slower than the first because of the use of lactose as the primary energy source. The final stage is the saturation phase.