Chapter 16, Problem 12P

Suppose you have six strains of E. coli. One is wild type, and each of the other five has a single one of the following mutations: lacZ^-, lacY^-, lacI^->, o^c>, and lacI^s> . For each of these six strains, describe the phenotype you would observe using the following assays. [Notes: (1) IPTG is a colorless synthetic molecule that acts as an inducer of lac operon expression but cannot serve as a carbon source for bacterial growth because it cannot be cleaved by β-galactosidase; (2) X-gal cannot serve as a carbon source for growth; (3) E. coli requires active lactose permease (the product of lacY) to allow lactose, X-gal, or IPTG into the cells.

a. Growth on medium in which the only carbon source was lactose.

b. Colony color in medium containing glycerol as the only carbon source, X-gal, and IPTG.

c. Colony color in medium containing glycerol as the only carbon source and X-gal, but no IPTG.

d. Colony color in medium containing high levels of glucose as the only carbon source, X-gal, and IPTG.

e. Colony color in medium containing high levels of glucose as the only carbon source and X-gal, but no IPTG.