Vitamin B12 (cobalamin) biotechnology: Which microorganism among the following can produce vitamin B12 using methanol as the carbon source?

Introduction / Context:
Vitamin B12 (cobalamin) is an industrially important cofactor produced microbially. Some production routes exploit methylotrophic organisms capable of growing on one-carbon substrates such as methanol. Identifying which organisms can synthesize B12 under these conditions reflects knowledge of specialized metabolisms beyond common fermenters.

Given Data / Assumptions:

• The carbon source is methanol, indicating methylotrophy is relevant.
• Options include methanogenic archaea/bacteria and a historical methylotroph designation.
• We focus on organisms documented for vitamin B12 formation on methanol.

Concept / Approach:
Among the listed organisms, Protaminobacter ruber is associated historically with growth on methanol and cobalamin formation. In contrast, many methanogens (for example, Methanobacterium spp.) utilize CO2/H2 or acetate routes and are not the standard organisms cited for B12 production on methanol in industrial contexts. Therefore, the correct selection is Protaminobacter ruber.

Step-by-Step Solution:

Verification / Alternative check:
Classical fermentation literature mentions methylotrophic bacteria, including strains attributed historically to Protaminobacter, in experimental B12 formation using methanol; modern taxonomy may have updated names, but the exam-style pairing remains.

Why Other Options Are Wrong:

• Methanobacterium soehngenii and Methanobacillus omelianski are linked to methanogenesis and syntrophic growth, not standard B12 production on methanol.
• “All of the above” overgeneralizes capabilities across metabolically distinct groups.
• “None” contradicts methylotroph reports.

Common Pitfalls:
Assuming all methanol-utilizing microbes are equal in secondary metabolite production; conflating methanogenesis with aerobic methylotrophy used in vitamin fermentations.

Final Answer:
Protaminobacter ruber