What observation distinguishes bacterial colonies on LB/amp and LB/amp/ara plates?

The observation that colonies on LB/amp/ara plates glow green under UV light is crucial because it indicates the successful expression of the green fluorescent protein (GFP). In this experimental setup, the addition of arabinose (ara) to the LB medium acts as an inducer that triggers the expression of the gfp gene in bacteria that harbor the plasmid containing this gene. Consequently, when exposed to UV light, those colonies express GFP and exhibit fluorescence, distinguishing them from colonies grown on LB/amp plates that do not contain the arabinose and thus do not express the fluorescent protein.

While other options touch on various growth characteristics of bacterial colonies, they do not directly relate to the fundamental purpose of the experiment, which is to observe the expression of GFP. The ability to see green fluorescence is a powerful visual confirmation of successful genetic transformation and induction, making this observation particularly significant in the context of GFP purification and analysis.