Final answer:
A glucose-responsive promoter should be used for the expression of glucose-6-phosphatase in the engineered cell line to regulate its expression based on the availability of glucose as an energy source.
Step-by-step explanation:
The type of promoter that should be used for the expression of glucose-6-phosphatase in this engineered cell line is a promoter that is specific to glucose metabolism. One example of such a promoter is the glucose-responsive promoter, which is activated in the presence of glucose. This type of promoter would ensure that the expression of glucose-6-phosphatase is tightly regulated and only occurs when glucose is available as a energy source.