Industrial microbiology: At commercial scale, how are amino acids typically overproduced and efficiently released from cells?

Introduction / Context:
Amino acids such as lysine, glutamate, and threonine are manufactured at large scale by microbial fermentation. Two classic strategies are used together: push the metabolic pathway to overproduce the desired product and pull the product out of the cell efficiently to avoid feedback inhibition and product toxicity.

Given Data / Assumptions:

• Objective: maximize amino acid titer, rate, and yield.
• Microbial hosts (e.g., Corynebacterium, E. coli) are engineered for flux toward target amino acids.
• Export or release mechanisms reduce intracellular accumulation.

Concept / Approach:
Regulatory mutants remove or blunt natural controls that limit pathway flux. Examples include feedback-resistant aspartate kinase for lysine/threonine and relief of repression systems. Separately, altering membrane transport or permeability, or introducing exporters, improves secretion. Combining these increases net productivity by improving both synthesis and mass transfer.

Step-by-Step Solution:

Verification / Alternative check:
Industrial case studies for monosodium glutamate and lysine report improved titers after combining deregulated enzymes with export systems or controlled permeability changes.

Why Other Options Are Wrong:

• Regulatory mutants only: improves production but may still be limited by export.
• Permeability only: without overproduction, secretion gains are modest.
• None of the above: inconsistent with well-established practice.

Common Pitfalls:
Over-leakage can harm growth; optimization balances cell health with secretion. Also, uncontrolled mutations may hurt stability; robust strains use targeted edits.

Final Answer:
Both (a) and (b)