Assistant Professor of Biology Alexandra Purdy
Assistant Professor of Biology Alexandra Purdy is conducting research that may one day help improve treatments for cholera. Photo by Jessica Scranton

There’s a saying that goes, “Pay attention to the little things, because one day you may realize they were the big things.” Assistant Professor of Biology Alexandra Purdy has devoted her career to uncovering the enormous impact of some very little things: the trillions of microorganisms that live on and in the human body and that influence everything—from our immune
systems to our digestion.

Now, with more than $500,000 in collaborative grant money from the National Science Foundation, she is studying how gut bacteria affect the health of their host organisms. The research by Purdy and colleague Josh Sharp of Northern Michigan University may one day help improve treatments for cholera, a disease that affects hundreds of thousands of people each year. 

In the intestines, each human being naturally carries between 1 and 3 pounds of bacteria. Called the gut microbiome, this collection of bacteria is integral to staying healthy and alive. The definition of a “good” microbiome is still murky, but it’s clear that helpful bacteria play a role in defending us against pathogens, which are disease-causing bacteria. Unfortunately for us, pathogens have a workaround: if they are able to take up, or “eat,” the molecules that our microbiomes secrete, they can wreak havoc and multiply.

Purdy’s grant project focuses on what happens when a specific pathogen—Vibrio cholerae—eats the molecule acetate, “which is produced by our normal gut bacteria from the fiber or plants that we eat,” she says. Acetate is one of a group known as short-chain fatty acids, which are associated with positive gut health. The health of the host organisms—fruit flies, in the Purdy lab—can suffer if the V. cholerae consume their gut acetate in great enough quantities. 

What does this research suggest about human health? “Cholera may be deadlier in people who are losing more of their acetate to the acetate-eating bacteria,” Purdy says.

Purdy and Sharp will also study other bacteria that are naturally “programmed” to eat acetate, including Pseudomonas aeruginosa, which can be devastating to the lungs of cystic fibrosis patients and to burned flesh. The question in both labs will be how scientists might target the regulatory systems in disease-causing bacteria, to cause them to eat less.

Already, Purdy and Sharp have discovered a special biochemical pathway in V. cholerae that appears to “flip the switch” on the bacterium’s gene and create the conditions for disease. Over the next four years, they hope to shed light on the role of the microbiome in causing organisms to thrive or decline. 

Amherst students will take part in Purdy’s research. In addition, the grant project includes funding for mentoring and the creation of educational programming for elementary and middle-school students. 

“I’m excited to talk about the role of microbiology and the role of microbes in our life,” Purdy says. “I feel like I’m revealing to people a world they didn’t know was there.”