Question

E. coli is grown in nutrient broth in a shaker and is harvested by centrifugation in mid- exponential growth phase. After washing, half of the cells are placed back into fresh nutrient broth and the other half are placed into fresh glucose-salts minimal medium. All other conditions are kept the same Sketch growth curves for the two cultures that clearly diagram the probable differences one would observe.

Answer 1

The microbes in mid-exponential phase have undegone molecular transformations which help them in utilizing the nutrients present in the media to further increase their rate of growth.

According to the information, a set of microbes from mid-exponential growth are transferred to fresh nutrient broth. This will increase the growth rate of these microbes as now less number of microbes will be available to consume the nutrients of fresh growth medium. This will increase the rate of growth of these microbes and they will re-appear in the exponential phase as shown below:

Growth rate

Secondarily, the set of microbes which are transferred to a minimal medium of glucose salts will impair the growth of these microbes since glucose remains primary source of metabolic sugar for these microbes. Thus, the graph will appear as below:

Lag phase Time