Amino acid biosynthesis in industry: for glutamic acid production by Corynebacterium glutamicum, what immediate metabolic precursor feeds directly into the glutamate pathway?

Introduction / Context:
Glutamic acid (glutamate) is produced at scale using Corynebacterium glutamicum, a workhorse of amino-acid fermentation. Understanding the central carbon intermediates that lead to glutamate accumulation helps explain process control (for example, biotin limitation or cell-membrane perturbation) used to drive secretion.

Given Data / Assumptions:

• Central metabolism funnels carbon through glycolysis and the tricarboxylic acid (TCA) cycle.
• Glutamate is synthesized by amination of 2-oxo-glutarate (alpha-ketoglutarate) via glutamate dehydrogenase or through the glutamine synthetase/glutamate synthase routes.
• “Immediate precursor” refers to the direct carbon skeleton donor to glutamate.

Concept / Approach:
In C. glutamicum, 2-oxo-glutarate is the TCA intermediate directly converted to glutamate. Process strategies often elevate intracellular pools of this ketoacid and shift redox/ammonium balance to favor aminating flux, thereby enhancing glutamate secretion to the broth.

Step-by-Step Solution:

Verification / Alternative check:
Biochemistry references confirm the alpha-ketoglutarate → glutamate step as the primary route, consistent with isotope-labeling studies in C. glutamicum.

Why Other Options Are Wrong:

• Lysine: Another amino acid; not a precursor to glutamate.
• Oxoacetate (oxaloacetate): Precursor for aspartate family, not glutamate directly.
• Citrate: Earlier TCA intermediate; requires further conversion to 2-oxo-glutarate.
• Pyruvate: Central node but not the immediate donor to glutamate.

Common Pitfalls:
Confusing oxaloacetate (aspartate family) with alpha-ketoglutarate (glutamate family); overlooking nitrogen assimilation coupling.

Final Answer:
2-oxo-glutarate