Auxotroph/analog selection in amino acid processes: Which microorganism listed is commonly selected for resistance to the analog methyl tryptophan when developing overproducing strains for tryptophan pathways?

Introduction / Context:
Classical strain improvement for amino acid overproduction often uses antimetabolite (analog) resistance. Methyl tryptophan is a tryptophan analog that selects for deregulated enzymes or upregulated pathways in tryptophan biosynthesis.

Given Data / Assumptions:

• Target pathway: tryptophan biosynthesis.
• Selection pressure: methyl tryptophan resistance.
• We choose a microbe classically engineered by such selections.

Concept / Approach:
Escherichia coli is a model bacterium extensively engineered for aromatic amino acid production using analog resistance (e.g., 5-methyl tryptophan). Resistance can arise via mutations that relieve feedback inhibition in the anthranilate synthase complex or alter regulation of the trp operon, enabling higher tryptophan flux.

Step-by-Step Solution:
Map the analog to the aromatic pathway (shikimate → chorismate → tryptophan).Identify common industrial chassis used with such selection: E. coli.Select “E. coli” as the best-supported choice.

Verification / Alternative check:
Numerous publications report 5-methyl tryptophan–resistant E. coli yielding increased tryptophan titers; similar strategies extend to C. glutamicum, but E. coli is the archetype.

Why Other Options Are Wrong:
Yeasts listed (Candida, Hansenula) are less commonly associated with classical methyl tryptophan selections for tryptophan. B. subtilis has been engineered for other amino acids, but E. coli remains the canonical example for this analog.

Common Pitfalls:
Assuming any analog-resistant mutant will overproduce; careful screening and pathway balancing are required.

Final Answer:
E. coli.