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Mikhail Tikhonov, an associate professor of physics in the Arts & Sciences department at Washington University in St. Louis, is not your typical physicist. Rather than concentrating on celestial bodies, nuclear interactions, or quantum formulas, he has committed much of his inquiry to an unusual and surprising realm: communities of microorganisms, such as bacteria found in soil.
“What is a physicist doing studying bacteria in soil? I receive that inquiry constantly,” Tikhonov remarked. “However, there’s a valid explanation. Physics involves applying mathematics to comprehend phenomena that elude our intuitive grasp. And with microorganisms, there are numerous chances to do just that.”
Tikhonov employs theoretical physics methods to investigate biological systems that are overly intricate for traditional ecological techniques. A recipient of a National Science Foundation CAREER award, he has already made significant contributions to several notable studies showcasing his strategies and methodologies. In July, he was a co-author on a Nature article demonstrating that a mathematical model can simplify the complexity of bacterial ecosystems in soil, making it feasible to foresee how these communities and the soils they reside in will react to environmental changes.
The ecology of bacteria presents genuinely puzzling situations, especially when juxtaposed with more conventional instances of ecological interactions, Tikhonov noted. “In a forest, you might encounter trees, rabbits, and perhaps a fox. It’s fairly clear that counting rabbits and foxes and examining their interactions is the ‘right’ level of analysis,” he explained. “For microbes, that’s anything but clear. Some assumptions we once held might actually be incorrect.”
In a microbial environment, borders fade, and the interactions among different entities become significantly more challenging to define. “Bacterial species are less clearly delineated than animal species,” Tikhonov stated. “Picture yourself observing a forest filled with rabbit-like foxes, fox-like rabbits, and everything in between. How would you even quantify the dynamics in such a system? Similarly, how can you make predictions when even a small soil patch contains literally hundreds of unique strains, all interacting with one another?”
This is where the theories and mathematical methods of physics come into play. As Tikhonov elucidated, physicists have successfully discovered “emergent simplicity” within highly intricate systems, be it in the structure of the cosmos or the flow of a river. In the instance of microbial communities, Tikhonov constructs models utilizing a physics-driven approach: You don’t need comprehensive knowledge to infer something.
His research targets a central inquiry: Which characteristics of ecosystems can be anticipated using physical models? “Instead of delving into minute details, we aim to step back and identify the coarse grains, the overarching traits that truly matter for the functionality and health of an ecosystem,” he remarked. “In terms of soil, identifying these attributes could assist humanity in better managing a resource essential for our existence.”
In the recent Nature paper, Tikhonov collaborated with colleagues at the University of Chicago to demonstrate that it was feasible to predict how the denitrification rate in soil — a critical component of the nitrogen cycle — would react to alterations in pH levels, a measure of acidity. Rather than attempting to anticipate how pH would influence each individual microbe or microbial species, the researchers discovered that the experimental outcomes were perfectly represented by a coarse-grained model treating all the varied denitrifiers as a single unit.
Approximately 1,500 painstaking experiments conducted by Kiseok Lee, a graduate student at the University of Chicago and co-author of the Nature article, revealed that the coarse-grained model accurately predicted every adjustment in pH, a finding that could have ramifications for agriculture and soil preservation. For instance, a deeper understanding of the relationship between soil bacteria and pH could enable farmers to achieve improved results from fertilizers, while mitigating harmful effects such as algal blooms resulting from nitrogen runoff. “It’s crucial to have experimental findings to ensure our theories are grounded in reality,” Tikhonov stated.
Tikhonov has applied his mathematical insights to address other intricate dilemmas. Earlier this year, he co-authored a paper proposing a novel approach to detecting signs of extraterrestrial life on other planets. Instead of searching for molecules or compounds associated with life as we know it, Tikhonov and his co-author suggested that scientists could seek recognizable energy patterns in extraterrestrial soil, air, or water.
His research holds numerous potential practical benefits, ranging from enhancing fertilizer application to shielding waterways from contamination. However, at present, Tikhonov is concentrating on the theoretical challenges.
“Microbes challenge some of our most fundamental biological principles and raise a plethora of open questions,” he remarked. “For a theorist, that’s an excellent position to be in.”
Originally published on the Ampersand website
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