This activity shows in one lab period how bacteria can be genetically modified. Genetic modification is a powerful tool wherein DNA from one organism is added to the DNA of a different species. The results of genetic modification in agriculture have resulted in plants that can make their own pesticides and resist herbicides. In this lesson, green fluorescent protein (GFP) is inserted or added to non-virulent E. coli bacteria.
The source of GFP is a jellyfish, Aequorea victoria. This protein allows the jellyfish to fluoresce and glow in the dark. The mechanism to transform the bacteria is by the use of a plasmid. The kit comes with a plasmid that contains the GFP, antibiotic resistance and a gene regulation system that turns the production of the protein on in the presence of arabinose, a monosaccharide. The plasmid is added to the bacteria in solution, then conditions are created to encourage the bacteria to uptake the plasmid. The bacteria is then grown overnight on various media that act as controls, and/or select for transformed cells.
As always when using bacteria in the lab, sterile technique should be used when transferring materials by sterile pipette or sterile loops. The condition for uptake of the plasmid by the bacteria is critical for success in this lab. The process, called heat shock, can be compared to how skin pores close in extreme cold, open in warmth and close again quickly when exposed to cold once more. Bacteria also have pore spaces that will be closed in the cold, opened in the heat and closed again tightly to hold in the plasmid if it crossed the membrane. The transformation solution used with the bacteria also sets up a charge differential across the membrane that attracts the plasmid to cross the membrane. The colonies in suspension will be held on ice, then in a water bath at 42°C for 50 seconds, then immediately back on ice.
Once students complete the procedure, have them complete the table with their predictions about bacteria growth and fluorescence.
