Bacterial strategies to evade natural or human-imposed antibiotics are varied and include membrane-bound efflux pumps that export antibiotics from the cell. A review of efflux pumps [Grkovic, S., et al. (2002)] states that, because energy is required to drive the pumps, activating them in the absence of the antibiotic has a selective disadvantage. The review also states that a given antibiotic may play a role in the regulation of efflux by interacting with either an activator protein or a repressor protein, depending on the system involved. How might such systems be categorized in terms of negative control (inducible or repressible) or positive control (inducible or repressible)?

Identify which of the following lac operon haploid genotypes transcribe operon genes inducibly and which transcribe genes constitutively. Indicate whether the strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).

I⁻ P⁺ O⁺ Z⁺ Y⁺

Identify which of the following lac operon haploid genotypes transcribe operon genes inducibly and which transcribe genes constitutively. Indicate whether the strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).

I⁺ P⁺ Oᶜ Z⁻ Y⁺

Identify which of the following lac operon haploid genotypes transcribe operon genes inducibly and which transcribe genes constitutively. Indicate whether the strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).

I⁺ P⁺ O⁺ Z⁺ Y⁻

Complete the accompanying table, indicating whether functionally active -galactosidase and permease are produced in the presence and absence of lactose. Use '+' to indicate the presence of a functional enzyme and '−' to indicate its absence. Indicate whether the partial diploid strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are constitutively transcribed, and the strain grows on lactose medium. List two possible genotypes for this phenotype.

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are inducibly transcribed, but the strain is unable to grow on a lactose medium. List one possible genotype for this phenotype.

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are never transcribed above a basal level, and the strain is unable to grow on a lactose medium. List two possible genotypes for this phenotype.

List possible genotypes for lac operon haploids that have the following phenotypic characteristics:

The operon genes are constitutively transcribed, but the strain is unable to grow on a lactose medium. List two possible genotypes for this phenotype.