Vitamin B12 (cobalamin) fermentation: which of the following microorganisms have been used as production strains for vitamin B12?

Introduction / Context:
Vitamin B12 (cobalamin) is an industrially important cofactor used in food fortification and pharmaceuticals. Multiple microbial genera are known to synthesize corrinoids, and a range of organisms have been tested or deployed as production strains depending on yield, downstream processing, and regulatory acceptance.

Given Data / Assumptions:

• Historically and experimentally, several bacteria and actinomycetes have produced cobalamins or closely related corrinoids.
• Modern large-scale processes often use Propionibacterium species or Pseudomonas denitrificans, but other organisms remain documented producers in the literature.
• The question asks which listed organisms have been used—not which is the single best modern industrial choice.

Concept / Approach:
Evaluate each candidate for reported B12 or corrinoid production capability. Bacillus megaterium and several Streptomyces species have been studied for cobalamin biosynthesis, even if not today’s dominant commercial strains. Therefore, when the scope includes organisms that “have been used” in research or pilot production, “All of these” is justified.

Step-by-Step Solution:

Verification / Alternative check:
Fermentation reviews discuss diverse producers; while modern processes prefer specific strains for yield and safety, multiple genera have been explored historically.

Why Other Options Are Wrong:

• Individual organisms (a–c): Each alone is incomplete relative to the question’s inclusive scope.
• None of these: Contradicted by known literature on microbial corrinoid production.

Common Pitfalls:
Confusing “current commercial standard” with “organisms ever used”; overlooking that research and early industrial practices included many species before process optimization converged on a few.

Final Answer:
All of these