In industrial microbiology and fermentation process design, which statement about phosphate repression and how to deal with it in production strains and media optimization is correct?

Introduction / Context:
Phosphate repression is a classic regulatory effect in industrial microbiology in which elevated inorganic phosphate suppresses the biosynthesis of many secondary metabolites (for example, antibiotics and alkaloids). Understanding whether this repression can be mitigated by medium design or by choosing special production strains is crucial for yield optimization in fermentation processes.

Given Data / Assumptions:

• The topic is phosphate repression affecting product formation.
• We compare the roles of nutrient medium optimization versus relying on “deregulated” production strains (i.e., strains less sensitive to phosphate control).
• Objective: identify the correct statement about mitigation strategy.

Concept / Approach:
High phosphate often represses gene clusters for secondary metabolism. Two broad levers exist: (1) medium design that limits available phosphate or controls its release, and (2) using strains that are genetically deregulated with respect to the phosphate control system. In practice, careful nutrient optimization can substantially reduce repression, while deregulated strains are commonly favored as “production strains” because they remain productive even when phosphate fluctuates.

Step-by-Step Solution:

Verification / Alternative check:
Process development literature consistently reports improved titers via phosphate-limited media and via strains selected or engineered for reduced sensitivity to phosphate control. Both strategies are used together in many industrial settings.

Why Other Options Are Wrong:

• Options (a) and (d): say optimization cannot help; this contradicts extensive fermentation practice.
• Option (c): recommends “regulated” strains for production; production commonly prefers deregulated strains to keep titers robust.

Common Pitfalls:
Assuming that only genetics or only medium can solve repression; most successful processes combine both. Also, confusing “deregulated strains” with “deregulated medium” (the latter is a misuse of terms).

Final Answer:
Phosphate repression can be eliminated by optimization of the nutrient medium; deregulated medium must be used as production strains.