Question

If two different auxotrophic strains are placed in a liquid medium culture tube, prototrophic strains can sometimes be subsequently recovered. Name several mechanisms by which this is possible.

Answer 1

There are several mechanisms by which prototrophic strains can be recovered when two different auxotrophic strains are placed in a liquid medium culture tube: complementation, reversion, and horizontal gene transfer.

Step-by-step explanation:

When two different auxotrophic strains are placed in a liquid medium culture tube, prototrophic strains can sometimes be subsequently recovered through several mechanisms:

1. Complementation: If each auxotrophic strain has a mutation in a different gene, they can complement each other's deficiencies when grown together. This allows for the recovery of prototrophic strains.
2. Reversion: In some cases, the auxotrophic mutation can revert back to the wild-type genotype, restoring the ability to produce the missing nutrient. This can occur through spontaneous mutations or genetic recombination events.
3. Horizontal gene transfer: Bacteria have the ability to transfer genes horizontally through mechanisms like conjugation, transformation, and transduction. If one of the auxotrophic strains acquires the gene for the missing nutrient from the other strain, it can become prototrophic.