Fifteen bacterial colonies growing on a complete medium are transferred to a minimal medium. Twelve of the colonies grow on minimal medium.

The three colonies that do not grow on minimal medium are transferred to minimal medium supplemented with the amino acid serine  and all three colonies grow. Characterize these three colonies.

Key Concepts

Minimal Medium

Minimal medium is a growth medium that contains only the essential nutrients required for the growth of microorganisms, such as bacteria. It typically includes a carbon source, nitrogen, salts, and water, but lacks additional growth factors like amino acids or vitamins. Bacteria that can grow on minimal medium are capable of synthesizing all necessary compounds from these basic nutrients.

Amino Acid Supplementation

Amino acid supplementation involves adding specific amino acids to a growth medium to support the growth of organisms that cannot synthesize them. In this case, the addition of serine allowed the three colonies to grow, indicating that these colonies are likely auxotrophic for serine, meaning they lack the ability to produce it and require it from their environment.

Auxotrophy vs. Prototrophy

Auxotrophy refers to the condition of an organism that cannot synthesize a particular compound required for its growth, necessitating its supplementation in the growth medium. In contrast, prototrophic organisms can synthesize all necessary compounds from minimal media. The three colonies that failed to grow on minimal medium but thrived with serine supplementation are characterized as auxotrophic for serine.