When is the bacterial pellet observed under UV light?

The bacterial pellet is observed under UV light after adding lysozyme because lysozyme functions to break down the cell walls of bacteria, allowing the green fluorescent protein (GFP) within the cells to be released. This protein has inherent fluorescence, meaning that once the cell walls are disrupted, the GFP becomes accessible and can be detected under UV light.

This step is crucial in purification processes where the target protein, GFP, is liberated from the bacterial cells for subsequent purification steps. Observing the pellet under UV light after lysozyme treatment helps confirm that the lysis of cells has occurred effectively, and that the fluorescent protein is present and is made available for isolation, highlighting its properties in research applications.

While the bacterial pellet is present after centrifugation, at that stage, it does not exhibit fluorescence until the lysozyme has been added and has acted on the cells. Other options do not provide the means to observe fluorescence directly related to the presence of GFP. For instance, the addition of TE solution or freezing the sample does not facilitate the illumination of the GFP itself in a manner similar to direct interaction with lysozyme.