How and why microbes promote and protect against stress

ASU professor uses evolutionary theory to examine relationship between microbes in the human body and stress

December 14, 2020

More than half of the human body is not actually human: The body hosts approximately 100 trillion microbes. These bacteria, yeast and viruses, which make up the human microbiome, affect more than physical health. They also influence behavior and emotions.

Some microbes prosper when the body is under stress, while other microbes contribute to buffering the body against stress. Athena Aktipis, associate professor of psychology at Arizona State University, used evolutionary theory to examine the reciprocal relationship between microbes in the human body and stress. The paper was published in BioEssays on Dec. 7. The human body and the 100 trillion bacteria, yeast and viruses that make up the microbiome have a reciprocal relationship that can be illustrated by the evolutionary goals of microbes. A microbe that prospers when the body is under stress is shown: It uses the increase in blood glucose levels that accompany stress to rapidly replicate. Graphic by Neil Smith. Download Full Image

“Microbes have access to physiological systems that can give them the power to stress us out, and there is evidence that contributing to the human body’s stress response serves their evolutionary goals,” Aktipis said. “This means that microbes can potentially change our physiology to keep the stress response going, ensuring their access to resources so they can proliferate.

"One example of a microbe that can benefit from host stress is the bacterium E. coli. We call microbes like these ‘stress microbes,’ and the microbes that can provide resilience against stress, like some species of Lactobacillus, ‘resilience microbes’ because there is evidence that they affect our physiology in these ways, possibly for their own evolutionary benefit.”


Stress-loving microbes both contribute to and benefit from the physiological changes that happen in the human body in response to stress, such as high blood glucose levels, increased permeability of the intestines and suppressed immune system responses. These microbes use what evolutionary biologists call a fast life history strategy. Organisms with fast life histories benefit from big bursts of resources, like the increase in blood sugar that happens when people experience stress, and also replicate quickly and – in the case of microbes – without regard for their host. But the body only benefits from the stress response in specific situations, like escaping danger. In other situations, the body does not benefit from the stress response, setting up a figurative tug-of-war between host and microbe.

“All organisms have their own evolutionary interests, and different resources and environments lead to optimal survival and reproduction," Aktipis said. "What is best for the host is not always what is best for the microbe, and we think this is what might be going on with some pathogenic ‘stress microbes.’ Sometimes the host response can lead to escalation of the conflict, which can lead to chronic inflammation as the host’s immune system tries in vain to deal with microbes that are causing a problem in the body. Stress can encourage this kind of dysregulated environment in the host that allows some microbes to thrive.”

Video by ASU Department of Psychology

Not all microbes in the microbiome benefit from a stressed host. Many do better in a stable environment, relying on a slow life history strategy that prioritizes surviving over reproducing. Microbes like these both alter and benefit from physiological processes that help protect the host from stress. Some, like Lactobacillus reuteri, contribute to increased production of the hormone oxytocin, which is associated with feeling calm and connected with others. 

“Microbes alter host behavior – whether it be by promoting stress or contributing to resilience against it – in ways that increase the odds they will be able to reproduce,” Aktipis said. “The composition of our microbiomes influences us in myriad ways: It can change the way we feel in terms of stress and our mental health and influence how we respond to the world around us. But it is a two way street; the way we behave — including what we eat, whether we exercise, and how we manage our stress — also affects the composition of our microbiomes. By changing our behavior, we can affect which microbes are thriving inside us.” 

Diego Beltran, a psychology graduate student, also contributed to the paper.

Science writer, Psychology Department


ASU Thunderbird grad prepares to globalize her management career with a humanist focus

December 14, 2020

Editor's note: This story is part of a series of profiles of notable fall 2020 graduates.

Before attending the Thunderbird School of Global Management at ASU, Makenna Flynn had already started developing a global mindset and empathy skills through her work at a local refugee resettlement office. Thunderbird graduate Makenna Flynn plans to pursue her master’s in management in the school’s 4+1 program. Thunderbird graduate Makenna Flynn plans to pursue her master’s in management in the school’s 4+1 program. Photo by Charlie Leight/ASU Now Download Full Image

She expanded her worldview by listening to the stories of struggle, triumph and tragedy shared there by refugees and employees. Flynn learned about the adversity that caused them to flee their home countries, places such as Iraq, Myanmar, Afghanistan, El Salvador and Somalia — where poverty and violence have turned many citizens into refugees in recent years.

When Flynn relayed to her adviser at Paradise Valley Community College how she felt hearing these stories, he suggested a Thunderbird at ASU program. Flynn did some research on the school and says she immediately felt connected. She chose ASU with the goal of earning a Thunderbird master’s degree after completing her undergraduate studies.

As a first-generation college student, Flynn was elated with the expanded learning opportunities outside the classroom. She spent a month in Argentina immersing herself in the culture and gathering more stories from residents. She saw the impact of globalization on a traditional culture, allowing her to contextualize what she was learning in the classroom and deepening her understanding of the dynamics of the global economy.

Flynn is a recipient of an ASU Young Alumni Scholarship, APS Scholarship and a Lentz Scholarship. She will continue her studies at ASU after graduation to earn her Master of Global Management in one year instead of two through Thunderbird’s 4+1 program.

She hopes to work in storytelling marketing in a social enterprise or business that makes a positive impact in its communities. Flynn will continue to collect and share stories about people from all over the world, narratives that she believes create the new human connections needed to build inclusive, sustainable prosperity in international communities through global cooperation. 

Question: What was your “aha” moment, when you realized you wanted to study the field you majored in?

Answer: In high school, I participated in a leadership program called the Hugh O’Brian World Leadership Congress (WLC). During this weeklong congress, one of the days was spent learning about major global issues. I heard professors speak about the right to an education and learned more about the global refugee crisis. After the mini courses, I felt the need to educate myself further and find out how to make a positive difference. And the more I researched, the more I realized the opportunities available for businesses to be that difference in the world.

Q: What’s something you learned while at ASU — in the classroom or otherwise — that surprised you or changed your perspective?

A: I have learned the importance of knowing how to manage stress. For a while, I would overload myself with extra coursework, part-time jobs and extracurricular activities without ever really taking time for myself. This past year, I have spent more time doing the activities that I love like hiking, exploring Arizona with friends, playing basketball or holding a movie night with my family. Setting aside this time to recharge has allowed me to focus more fully on my academics and professional development than before. 

Q: Which professor taught you the most important lesson while at ASU?

A: My communications professor, Professor Kenneth Kunkel, taught me the importance of not tying my sense of self-worth to my grades. When I entered his class, I would be so focused on trying to get the “A” that I would often miss out on the creative side of public speaking. It wasn’t until my advanced public speaking class where I realized my strength as a speaker lies in creating unique content, not simply following the rubric and adding no personal material.

Q: What’s the best piece of advice you’d give to those still in school?

A: Explore various interests, especially in your undergraduate degree. While my major was global management, I spent my electives exploring world philosophies, developing my public speaking skills, learning about astrology and other hobbies of mine. This interdisciplinary education gave me a much richer perspective in my core business coursework.

Q: What was your favorite spot on campus, whether for studying, meeting friends or just thinking about life? 

A: My favorite spot to study is at the West campus on the grassy area outside of the Casa de Oro residential hall. I love to roll out a blanket, turn some music on and spend the afternoon studying and hanging out with friends.

Q: If someone gave you $40 million to solve one problem on our planet, what would you tackle?

A: I would invest $40 million into producing alternatives to unsustainable development. Dams, mines and tourist attractions (among other industries) often displace Indigenous communities and negatively impact the environment. Finding more sustainable solutions will have positive impacts across sectors and for most stakeholders.

Written by Joanna Furst