Vitamin B12 fermentation — productive species: Among vitamin B12–producing “Pseudomonads” historically cited, which species is recognized as the most productive for industrial cobalamin biosynthesis?

Introduction / Context:
Industrial vitamin B12 (cobalamin) production has employed several bacteria. Productivity depends on robust corrinoid biosynthesis, cobalt handling, and oxygen control during fermentation.

Given Data / Assumptions:

• We are comparing historically named “Pseudomonas” species for B12 output.
• Industrial productivity is the criterion.
• Taxonomic names have evolved, but classical literature remains influential in process teaching.

Concept / Approach:
Pseudomonas denitrificans (reclassified in some texts) is a well-known producer used in industrial B12 fermentations, often contrasted with Propionibacterium shermanii processes. It supports high titers under controlled aeration and cobalt supplementation.

Step-by-Step Solution:
Identify the species linked to strong cobalamin production in classical sources.Select P. denitrificans as the most productive among the listed “Pseudomonads.”Exclude species not documented for high B12 output.

Verification / Alternative check:
Industrial case studies and patents have detailed optimization of P. denitrificans for cobalamin yields.

Why Other Options Are Wrong:

• P. ovalis/P. aureofaciens: Not recognized as major B12 platforms.
• None of these: Incorrect; a high producer is known.

Common Pitfalls:
Overlooking oxygen regime control; B12 biosynthesis is oxygen-sensitive at key steps.

Final Answer:
P. denitrificans.