Scientists have harnessed a jellyfish protein and a common bacterium to create a living tool known as GFP E. coli. This combination of a glowing protein with a laboratory workhorse bacterium allows scientists to visually track processes that were once unseen. The creation of glowing bacteria is a foundational technique that illuminates the microscopic world of genes and proteins.
Understanding Green Fluorescent Protein
The “GFP” in GFP E. coli stands for Green Fluorescent Protein. This molecule was discovered in the crystal jellyfish, Aequorea victoria, which produces a green glow. The protein has a unique barrel-like structure that absorbs blue or ultraviolet light and then emits it as bright green light, a process called fluorescence.
Unlike many biological markers requiring added chemicals to work, GFP generates its own fluorescence once the protein is formed. This simplicity allows it to be used in many living organisms, from bacteria to human cells. The gene for GFP can be isolated and used as a visual tag.
The gene for GFP can be attached to the gene of another protein a scientist wants to study. The cell then reads the combined instructions, producing a single “fusion protein” that glows. This allows researchers to see exactly where their protein of interest is located within a cell and monitor its activity by following the green light.
E. coli as a Biological Tool
Escherichia coli, or E. coli, is the other half of this biological tool. While some strains cause illness, the versions used in laboratories are cultivated to be harmless. These lab strains are “workhorses” of molecular biology because they are inexpensive, grow rapidly, and have a simple genetic makeup.
An E. coli cell can double its population in as little as 20 minutes, allowing researchers to grow huge numbers of them overnight. This rapid growth means that experiments involving genetic modification can provide results in days instead of weeks. Its straightforward genetics also make it easier for scientists to introduce new DNA.
E. coli is also highly receptive to genetic transformation, the process of inserting foreign DNA into the cell. This capability is what allows researchers to introduce the GFP gene and turn the bacterium into a factory for the glowing protein.
How Scientists Create GFP E. coli
The technique to create glowing E. coli relies on plasmids, which are small, circular pieces of DNA that exist separately from the main chromosome. Scientists use these plasmids as vehicles, or “vectors,” to carry new genes into E. coli.
First, researchers use molecular tools to cut open a plasmid and insert the gene that codes for GFP. In addition to the GFP gene, scientists include a second gene on the same plasmid that provides resistance to a specific antibiotic, such as ampicillin. This antibiotic resistance gene acts as a selection tool.
The engineered plasmids are then mixed with E. coli. To get the bacteria to take up the plasmids, scientists perform a “heat shock.” The bacteria are first chilled in a solution containing calcium chloride, making their cell membranes more permeable, and then briefly exposed to a high temperature. This encourages the bacteria to take up the plasmids in a process known as transformation.
To separate the transformed bacteria from the untransformed ones, scientists use the antibiotic resistance gene. After the heat shock, all bacteria are spread onto an agar plate containing the antibiotic. Only bacteria that took up the plasmid with the resistance gene survive and multiply. Since the GFP gene is on the same plasmid, every surviving colony can produce the glowing protein.
The Utility of Glowing E. coli in Research
Once created, GFP E. coli serves as a tool for scientific investigations, most commonly as a “reporter gene.” The visible glow of GFP reports on the activity of other genes. By linking the GFP gene to a specific gene of interest, scientists can use the intensity of the green fluorescence as a direct indicator of how active that gene is. A bright glow means the gene is being turned “on” at a high level.
This technique is useful for studying gene regulation, the system that controls when genes are turned on and off. To do this, scientists place the GFP gene under the control of an “inducible promoter.” A promoter is a stretch of DNA that acts as a switch for a gene, and an inducible promoter is a switch that is only flipped in the presence of a specific chemical.
A common example involves a promoter activated by the sugar arabinose. In this system, the E. coli will only produce GFP and glow green when arabinose is added to their growth medium.
This gives researchers precise control to turn the glow on and off, allowing them to study how different conditions affect gene activity. This method is used to understand genetic processes and to screen for new medicines that might alter gene expression.