Question

The microbe Pseudomonas denitrificans produces the vitamin:
(a) K
(b) D
(c) ${ B }_{ 2 }$
(d) ${ B }_{ 12 }$

Answer 1

Hint: Some vitamins are found in foods that may not be consumed by certain sections of the society, for example, vitamins present in meat. Hence, these vitamins can be produced by certain microorganisms and added to the diet as supplements and help in physiological metabolism.

Complete step by step answer:
- Vitamin ${ B }_{ 12 }$ or cobalamin is an essential vitamin that has a role in DNA synthesis, lipid and amino acid metabolism, maturation of RBCs in bone marrow, and synthesis of myelin.
- The microbe Pseudomonas denitrificans produces the vitamin ${ B }_{ 12 }$. Vitamin ${ B }_{ 12 }$ is primarily available in milk, animal meat, fish, and eggs. Hence, people who do not consume these products require vitamin ${ B }_{ 12 }$ from external sources.
- Pseudomonas denitrificans is a Gram-negative, polar flagellated, rod-shaped, aerobic bacterium that overproduces cobalamin.
- The genes responsible for the overproduction of cobalamin are the cob genes.
So, the correct answer is ‘${ B }_{ 12 }$’.

Additional information:
- P. denitrificans also carries out denitrification when present in the soil. It reduces nitrate to nitrogen gas as a part of the nitrogen cycle.
- The biologically active forms of the vitamin ${ B }_{ 12 }$ are methylcobalamin and adenosylcobalamin. Cyanocobalamin is a manufactured form.
- It plays an important role in folate metabolism and in the synthesis of the citric acid cycle intermediate, succinyl-CoA.

Note:
- There are two main biosynthetic pathways to synthesize cobalamin; the aerobic and anaerobic pathways. The aerobic pathway is followed by P. denitrificans and others while the anaerobic pathway is followed by S. typhimurium and others.
- A salvage pathway to synthesize it is also found in bacteria and archaea.
- Deficiency of cobalamin in humans may cause limb neuropathy or pernicious anemia, a type of megaloblastic anemia.