Alexandra Purdy 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 ability to break down food to produce energy.

Now, Purdy has won a $513,187 collaborative grant from the National Science Foundation to study how gut bacteria affect the health of their host organisms. The research by Purdy and her co-investigator, 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 our intestines, humans naturally carry between one and three pounds of bacteria. This collection of bacteriacalled the gut microbiome—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 disease-causing bacteria. Unfortunately for us, the disease-causing bacteria (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 disease-causing bacterium—Vibrio cholerae—eats the molecule acetate, the main ingredient in vinegar. Acetate is one of a group of molecules 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.

Together, the Purdy and Sharp labs grant will also study other bacteria with genes that are “programmed” to eat acetate, including the disease-causing 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.

Tracking the interactions between various strains of bacteria and their hosts is far simpler in fruit flies than it would be in human beings or even in mice. Already, Purdy and Sharp have discovered the existence of 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, the Purdy and Sharp labs will shed new light on the role of the microbiome in causing organisms to thrive or decline. In keeping with NSF grant requirements, Purdy and Sharp will also provide authentic research experiences for undergraduate students, both in their labs and through their courses. As Purdy says, “When the students realize they are doing something that is new [to the broader scientific community] and that they’re actually answering questions about the natural world, that’s really exciting for them.”

The grant project also 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,” beams Purdy. “I feel like I’m revealing to people a world they didn’t know was there. It’s a particularly fun place to be.”


Purdy answers Strunk's questions about her research.

Can you explain the research the NSF grant will fund in the Purdy lab? In a nutshell, we are looking at how bacteria consume molecules when they are in the gut of an organism.  The molecule we focus on is acetate, which is produced by your normal gut bacteria from the fiber or plants that we eat.  

Is having acetate in our guts is a good thing? Yes, having more of these molecules is a good thing. They provide energy for the cells that line the gut. The bacteria we study in the Purdy lab “eat” the acetate, and, when they eat too much, this can have negative effects on the host organism.

What kinds of organisms are “hosts” for the bacteria that you study in your lab? We primarily use fruit flies, because they are simple, small and inexpensive. They also allow us to detect interactions between the bacteria and their hosts that might be hidden in larger hosts. 

Is it better for the host organism if the bacteria’s acetate-eating genes are switched off? Not necessarily. In my microbiology course, the students and I are also looking at how another acetate-eating bacterium, Vibrio fischeri, lives in harmony with a tiny Hawaiian squid. The V. cholerae bacterium actually glows in a special organ of the squid, and this protects the squid from predators. 

How does this research translate to people? It’s been found that children with cholera are more likely to die from the disease if they have lower amounts of short-chain fatty acids in their feces. One possible explanation for this is that cholera may be deadlier in people who are losing more of their acetate to the acetate-eating bacteria. Our research may one day help inform future interventions to prevent cholera.

What does getting the NSF grant mean for your students? It provides additional stipends for students to work across the school year and summer. It provides a research assistant in the lab, which means I can give more opportunities to students, and that there is always a presence in the lab when I’m teaching or writing. Amherst undergraduates will benefit from the added research opportunities. They will also be a part of the collaborations this grant fosters with my co-grantee, and with other colleagues at the Universities of Wisconsin and Massachusetts.