Question

Researchers grew populations of identical Escherichia coli (E. coli) bacteria in a growth medium that contained a low concentration of glucose and a high concentration of citrate, a substance that is not typically consumed by E. coli. For thousands of generations, the bacteria used only glucose as an energy source and grew relatively slowly and to a low density because of the low concentration of glucose. After about 30,000 generations, one population emerged that began to rapidly grow to a much higher density. The researchers hypothesized that the bacteria evolved the ability to use citrate as an energy source and referred to them as Cit . To test the hypothesis, the researchers grew separate populations of the Cit bacteria and bacteria from the original population (Cit- ) in a growth medium that contained only citrate. Describe one outcome that would demonstrate that a given population has evolved.

Answer 1

To demonstrate that E. coli has evolved to use citrate, a population should grow in a citrate-only medium, with a color change in the growth medium indicating successful citrate utilization.

Step-by-step explanation:

An outcome that would demonstrate that a population of Escherichia coli (E. coli) has evolved to utilize citrate as an energy source would be their ability to grow in a medium that contains only citrate. In the experiment referenced, Cit+ bacteria that can consume citrate should thrive in citrate-only medium, demonstrating the presence of necessary enzymes such as citrate permease for transport and citrase for citrate catabolism. A positive result in this experiment would likely be indicated by a change in color of the broth as described, from green to blue due to the alkaline by-products of citrate metabolism indicating citrate utilization.