Bacterial production of the enzymes needed for the synthesis of the amino acid tryptophan declines with increasing levels of tryptophan and increases as tryptophan levels decline. This is an example of

Answer: repressible operon

Explanation:

As tryptophan level increases in the bacteria growth media, the operator region of the operon is blocked to inhibit the functional gene responsible for the synthesis of enzymes that synthesize tryptophan. When tryptophan level decreases, the operator regiintis unblocked to allow synthesis of the enzyme ... This is known as a repressible operon