You are not just you, according to new research from biologists at Vanderbilt University. Rather, you are part of a “biomolecular network” of living organisms that includes all of the bacteria and other symbiotic microbes in your body combined to create a collective entity.
As such, the authors of the new PLOS Biology paper explain that microbiologists have developed a new term for these symbiotic systems (holobiont) and a second (hologenome) that describes the combined genetic material of all constituent organisms that comprise so-called individuals.
As Seth Bordenstein, associate professor of biological sciences at Vanderbilt, explained recently in a statement, “It’s a case of the whole being greater than the sum of its parts.” In the new paper, he and co-author Kevin Theis from the University of Michigan explore the basic concepts behind this concept and develop 10 principles that can be applied to the entire field of biology.
In this paradigm, humans, other animals, and plants are the hosts, and the microbes within their bodies have a significant impact on the holobiont’s development, the diseases it contracts, and the way that it behaves and socially interacts with its fellow holobionts. Both the holobiont and the hologenomes, they argue, are fundamental units of biological organization.
Expanding the rules of evolution to include host and symbiont
“One of the basic expectations from this conceptual framework,” Bordenstein said to redOrbit via email, “is that animal and plant experiments that do not account for what is happening at the microbiological level will be incomplete and, in some cases, will be misleading as well.”
For instance, by searching only for the genes in a nucleus that contribute to a disease, a new species, or a specific environmental adaptation, scientists “may well be missing the other half of the story – the contribution of the microbiome to those phenotypes as well,” he added.
As such, conducting experiments both in the presence of and in the absence of microbes should become a routine part of future studies, Bordenstein said via email. After all, he and Theis write in their study, natural selection and other evolutionary forces act on the hologenome, not just on the genome, and mutations in the microbiome that could affect the overall fitness of a holobiont are every bit as important as those that occur in the genome of the host.
This concept does not change the basic rules of evolution, the researchers said. Rather, this view upgrades the types of biological units that these rules may act upon, and provides holobionts with a way to respond to environmental challenges unavailable to individual organisms. They are able to change the composition of their bacterial communities, allowing microbial symbionts to make a toxin that can kill invading pathogens when the host itself is unable to do so.
“The development of these concepts are in their earliest phases,” Bordenstein explained. “[But] every subdiscipline is touched by the microbial world and we as a community are just starting to appreciate it. Just as animal and plant genetics has had a century long period of investigation, the next century may very well be defined by hologenomics in which genetics and microbiology offer a more accurate and cohesive vision of the macroscopic living world.”
(Image credit: Robert Brucker/Harvard)
Comments