Industrial microbiology — amino acid fermentation: Brevibacterium flavum (now Corynebacterium glutamicum) strains are widely engineered for amino acid production. Which amino acid listed below is classically produced using B. flavum in industrial fermenters?

Introduction / Context:
Amino acid fermentations are a cornerstone of industrial microbiology. Strains of Brevibacterium flavum (taxonomically aligned with Corynebacterium glutamicum) have been intensively optimized to overproduce specific amino acids used as feed additives, nutraceuticals, and flavor enhancers.

Given Data / Assumptions:

• Organism: Brevibacterium flavum.
• Process goal: overproduction of a defined amino acid at commercial scale.
• Options include several amino acids; only one fits classical, well-documented production with B. flavum without further qualifiers.

Concept / Approach:
B. flavum/C. glutamicum has been developed to produce multiple amino acids, most famously L-lysine and L-threonine through mutation/selection, pathway deregulation (feedback-resistant aspartokinase and homoserine dehydrogenase), and improved carbon flux. Among the options, L-threonine is a canonical product of B. flavum lines used industrially and frequently cited in classical process texts alongside L-lysine.

Step-by-Step Solution:
Identify the organism: B. flavum, renowned for aspartate-pathway amino acids.Map options to pathways: threonine derives from the aspartate family (aspartate → aspartyl-P → homoserine → threonine).Recall industrial precedence: B. flavum strains producing L-threonine are standard in large-scale operations.Choose the single best-supported classical answer: L-Threonine.

Verification / Alternative check:
Process literature and patent families on B. flavum/C. glutamicum repeatedly highlight lysine and threonine as flagship products; other amino acids require different hosts or more complex engineering.

Why Other Options Are Wrong:

• L-Proline: Typically associated with other hosts or specific engineered routes, not the classical B. flavum product.
• L-Isoleucine and L-Histidine: Possible in engineered microbes, but not the textbook association for B. flavum.
• All of the above/L-Arginine: Overly broad; not supported as the single standard association.

Common Pitfalls:
Assuming a single chassis efficiently produces all amino acids; pathway regulation and redox demands vary widely.

Final Answer:
L-Threonine.