A Wayne State University School of Medicine researcher is among a network of scientists leading an emerging concept examining how the microbiome shapes the evolution of life, a movement that may lead to a new dawn in personalized medicine, prevention of inherited chronic disease and serve in the ongoing fight against preterm birth.

Kevin Theis, Ph.D., is an associate professor in the Department of Biochemistry, Microbiology and Immunology, and a member of the Holobiont Biology Network. In 2015, he and collaborator Seth Bordenstein, Ph.D., who directs the Microbiome Center at Pennsylvania State University, wrote two papers formalizing the concept in the context of neo-Darwinism, the modern version of Charles Darwin’s theory of evolution by natural selection that incorporates the theory of genetics. A decade later, the concept has gained the attention of one of the leading academic journals. 

“The disciplinary matrix of holobiont biology: Uniting life’s seen and unseen realms guides a conceptual advance in research,” is featured in a recent issue of Science, the journal of the American Association for the Advancement of Science.

Dr. Bordenstein, who wrote the Science article with Dr. Theis and other members of the Holobiont Biology Network, considers its publication a watershed moment. Holobiont biology recognizes animals, plants and other hosts as dynamic assemblages of interacting and/or interdependent host and microbial cells, just as the host body is recognized as a dynamic assemblage of its own interacting cells that forge anatomical structures with specialized functions.

Dr. Theis, a behavioral and microbial ecologist who joined the School of Medicine in 2015, researches host-microbe interactions to determine whether science and medicine can effectively manage the human microbiome in relation to maternal-fetal health and disease.

Microbes are crucial in shaping behaviors, immune systems and digestion, and can be inherited or exchanged during social interactions. Understanding the microbiome's role is crucial for personalized medicine and addressing chronic diseases, as microbes significantly influence phenotypes and health outcomes.

Dr. Theis’s lab at Wayne State is studying the microbial ecology of human reproduction to identify and ultimately manage polymicrobial causes of preterm birth, as well as how animal social behavior influences the structure and function of microbiomes, which provides natural animal model systems for addressing critical inquiries in human disease.

“We’re thinking about how the vaginal microbiome is contributing to whether or not a woman delivers preterm, or whether a woman has bacterial vaginosis, which obviously is going to influence their lifestyle, but could also lead to fertility issues and pregnancy issues,” he said.

The field of personalized medicine can especially benefit from incorporating microbiome data, he said, stressing the importance of considering both the host genome and the microbiome in diagnosing and treating chronic disease, because interactions can vary among individuals, influencing the likelihood of disease and the effectiveness of treatments.

Whether standing at a lectern in front of undergraduates or doctors, he uses the same approach when presenting the idea of the holobiont.

“I'll put up a picture, and one of the ones I often put up is a mother with a child, and I'll say, ‘Go ahead and tell me what you see here,’” he said. “No one has ever said that what they're looking at is an amalgam consortium of host and microbial cells and alleles. Then I give them the stat that they’ve probably all seen, which is that at least half the cells that are associated with your body are microbial in origin, and 99% of the unique genes associated with your body are microbial in origin.”

They also shape behaviors, including communication and scent production, essential for social interactions. Microbial presence influences phenotypes, the selective mechanism within natural selection, he said.

Failure to incorporate that information means potentially excluding information that could be of value from a medical standpoint.

“That doesn’t mean that every single ailment that we have as humans is due to the microbes that populate our body,” he said.

“Now, those only get transferred across generations if the hosts that are generating those phenotypes can pass those genes on,” Dr. Theis said. “People assume that the microbiome is just part of the environment and that we only come into contact with certain populations or communities of the environment, and that it’s not really heritable, that it’s so variable that it’s not heritable. But there are two potential explanations here. One is that we inherit large communities of our microbiome from our parents, but they're present at low relative abundances until the appropriate developmental stage shows itself. Another possibility is that, at least among social hosts like us, that when we go ahead and interact with one another at certain developmental stages, we actually exchange the microbes that would benefit us. If we don’t take into account the role that the genomes of those microbes have played in the phenotypes of the host that are competing for reproductive opportunities, we’re missing a large part of what makes the animal or the plant what it is, in that competitive environment.”

Some women have bacteria and have no problem with pregnancy. “But then you have other women who have the same bugs, but they are the ones who are going to deliver preterm, which is the leading cause of neonatal mortality and morbidity worldwide. And the reason may be because those bugs interact in a way with their genome differently than they interact with other individuals who have a different genome. Personalized medicine is going to be the approach where we say, ‘Okay, we know which bugs can be harmful, but it’s going to depend also on the background genomics of the host,” he added.

For more information on his research, visit https://kevinrtheis.wordpress.com/