Genetics - How Green Plates Work

Jeff Lawrence (G05)

1. Green plates are poorly buffered rich plates with an excess of glucose and two pH indicator dyes.

2. Being rich media, auxotrophic strains grow, but the dyes can interfere with strains mutant for replication and recombination functions.

3. The excess glucose causes the strains to make more acid than usual. When a strain lyses, the acid released causes the plate to turn dark green. In addition, normal colonies will turn the plate dark after sufficiently long period (more than 24 hours). Therefore, green plates must be examined promptly.

- Single, phage-infected strains lyse and make small, dark-green colonies.
- Normal cells will make larger, light green colonies. These colonies are phage-free, but may contain lysogens.
5. Strains may be cross struck over phage on green plates. The portion of the streak before the phage will be healthy and light. After contacting the phage, normal cells will lyse, so the portion of the streak after the phage will be spotty and dark. Lysogens are immune to phage, and will look healthy on both sides of the streak.
Last Update: Thursday June 19 2014
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