For fermentative production of vitamin B12 (cobalamin) by Streptomyces olivaceus, which inorganic precursor salt is typically supplied to support cobalt insertion?

Introduction / Context:
Vitamin B12 (cobalamin) contains a central cobalt ion chelated within the corrin ring. Industrial fermentations therefore supplement cobalt to enable efficient biosynthesis. The question asks which salt is commonly used as a precursor for Streptomyces olivaceus processes.

Given Data / Assumptions:

• Organism: Streptomyces olivaceus.
• Need: a soluble, bioavailable cobalt source.
• Media typically include trace metals; cobalt must be controlled to avoid toxicity while ensuring supply.

Concept / Approach:
Cobalt chloride (CoCl2) is widely used as a cobalt source due to its solubility and ease of dosing at trace levels. Cobalt sulphate may also serve in some processes, but CoCl2 is the more commonly cited in classic media formulations for cobalamin production. Calcium salts listed do not provide cobalt and thus are irrelevant to corrin cobaltation.

Step-by-Step Solution:
Identify the essential requirement: cobalt ion for cobalamin core.Select a soluble cobalt salt compatible with fermentation media.Cobalt chloride satisfies solubility and availability criteria.Conclude that cobalt chloride is the appropriate precursor.

Verification / Alternative check:
Standard fermentation media and patents list CoCl2 as a trace additive for B12 production across multiple producing species.

Why Other Options Are Wrong:
Cobalt sulphate: possible, but not the most commonly referenced in classic recipes for S. olivaceus.Calcium chloride / sulphate: provide calcium, not cobalt; cannot support B12 cobalt insertion.

Common Pitfalls:
Over-supplying cobalt (toxic) or neglecting the need for dimethylbenzimidazole and other cofactors in full B12 biosynthesis.

Final Answer:
Cobalt chloride