Last week, I transformed home-prepared E. coli TOP10 cells. When checking the colonies, I noticed that some of them have yellow color. They did not grow on the randomly, but dependently on the transformation success. At least one of them was positive with colony PCR, I attached picture of pellet I took the next day.
What could it be? Is it some contamination (I work in a lab, where we work with various cyanobacteria and microalgea), which I managed to transform with my plasmid? Or did something happen to the E. coli?
Hi Dominique Liger !
It is a biosynthetic gene cluster for a lasso peptide from one cyanobacteria. At the end is also GFP, but I think that GFP expression looks differently :) Moreover, it is under tetracycline-inducible promoter, so it shouldn't be turned on.
I was actually thinking of GFP expressing clones. In my experience these are colored in the green/yellow-ish tones... But it can't explain the possible "leaky expression". Have you got PCR positives among the non yellow-ish clones?