Undergraduate Researchers Successfully Transplant A Bacterial Immune System

Mar 21, 2018

In the Jackson lab at Utah State University, mixers whirr, protein purification machines beep, and shakers jiggle, all with one goal: isolating and describing the bacterial immune systems known as CRISPR.

Bacteria have immune systems to protect them against viruses, like our own which protects us against the flu. Information about previously encountered viruses is stored in the bacterial DNA which in simple terms helps to kill invading viruses. And when a bacteria encounters an unfamiliar virus, proteins usually insert information about this virus into the bacteria’s DNA to store for future reference.

It is those information inserting proteins that scientists use in animals, plants, and fungi to change their genes for a variety of reasons. It has only been used once in humans.

The most studied virus attacking protein, Cas9, was discovered in the bacteria that causes strep throat. But there are at least five more types of bacterial immune systems being researched right now. Ryan Jackson, an assistant professor at Utah State University's Department of Chemistry and Biochemistry, is interested in CRISPR Type IV.

“These type IV systems that we’re trying to understand are in bacteria that grow in really weird places and are difficult to grow in the lab,” Jackson said. “So, these are bacteria, but one of them grows in pH 1 conditions with heavy metals and is able to survive. The name of it tells you. It’s Acidithiobaccillus: Acidi, so acid, thio, sulfur, ferrooxidans, so it oxidizes iron to get its electrons.”

So, basically this bacteria consumes sulfur and iron. What a workhorse!

Obviously, Jackson couldn’t keep a sulfuric acid waste pond in his lab just to study CRISPR type IV. Enter his undergraduate researchers, Riannon Smith and Malena Garrett, biological engineering majors at Utah State University. They decided it would be easier to study this unique bacteria by transplanting Acidithiobaccillus ferrooxidan’s immune system into the more manageable E. coli. This way the weird bacteria’s immune system can live in a lab.

“We’ve had to do several cloning techniques to get the individual genes of the CRISPR into one single E. coli cell,” explained Garrett. “And then we also have another one that has the actual spacer repeat section. We’re doing that along with a tagged gene. We’re putting all of that into one single cell and then we’re trying to express the entire protein complex.”

After a year of work, Jackson, Smith and Garrett now have their model organism. Now what?

“Do the components assemble? We think the protein pieces of this immune system will come together and recruit an RNA guide used to bring this immune system to a DNA that would then get processed or cut. All that remains to be seen,” Jackson said.

If the immune system works then the Jackson lab will try to map the 3-D structure of the protein to better understand how they work. If all goes well, Jackson hopes that other researchers will be able to use this work horse bacteria alteration to develop CRISPR type IV into a gene editing tool.