A powerful physical tool that could help scientists understand complex ecosystems | Sciences

Your gut is the home of bacterial madness. Hundreds of trillions of bacteria belonging to countless species interact with each other in complex ways that can keep you healthy and make you sick. Provoking these interactions may seem an impossible task.

Now, microbiologists have found help from an unexpected source: physics. A new experiment suggests that a powerful concept known as phase transition can predict the complexity of ecosystems – such as those made up of the bacteria in your stomach -. This discovery could help us keep our gut healthy and even protect other complex ecosystems like rainforests and coral reefs.

“It’s beautiful work,” says Fernanda Pinheiro, a physicist who studies bacterial ecology and physiology at Human Technopole, who was not involved in this work.

Phase transition in physics works like this: everything you really need to know about huge groups of particles – whether they are 1023 The molecules in a glass of water are liquid or solid, for example, or whether the myriad atoms in a metal will arrange themselves in a magnet—often controlled by a few simple factors, such as temperature and pressure. Theorists since the 1970s have similarly proposed two factors—the total number of species and the strength of interactions between species—that can predict whether complex living systems, such as the thousands of species in rainforests, will remain stable.

But testing such theories has proven difficult. This is because there is usually no way to manipulate population sizes or interactions between species in natural ecosystems. “You don’t have a handle that you can turn which makes lions eat zebras better,” says Sebi Cohn, an ecologist at the University of Chicago who was not involved in the study.

To solve this problem, Massachusetts Institute of Technology (MIT) physicist Jeff Gore and his colleagues created custom ecosystems in the lab. They took 24 species of bacteria from the soil of a Boston-area nature reserve and pulled another 24 species from the guts of nematodes. They cultured the microbes together in plastic wells and increased and decreased the concentration of nutrients to manipulate how strongly different species interact with each other. The more nutrients, the more different species compete.

Experimental ecosystems went through three distinct stages as the number of species in the mix increased or the intensity of interactions between species increased. At first, the numbers of each species remained stable. Then, when the number of species or interactions between species exceeded a certain threshold, the system suddenly entered a new phase in which some species began to become extinct. As the experimenters continued to add species and raise nutrient levels, the system moved into a third stage: populations of the remaining species began to fluctuate dramatically, indicating that the ecosystem as a whole had lost stability.

The result: Only two variables—the number of species and the average interaction strength—determine whether the mixture of different microbes will be stable or chaotic, says study author Jilyang Hu, a graduate student in mechanical engineering at MIT.

The paper published today in SciencesDo you First to report repeatable phase transitions Based on interactions of species and diversity in communities with more than a small handful of species, says Cohn.

Theorists have long suspected that fluctuations like the one Gore’s team found could allow large numbers of species to coexist, because when species numbers drop to a low level, they can create room for another species to grow. The study “gives reason to hope that such a stage could also exist in natural communities,” which may help explain why so many species are able to coexist in real-world ecosystems, says Daniel Fisher, a Stanford University physicist, who was not Well involved in the work.

But in nature, organisms live in environments with complex spatial structures and external influences not examined by Gore’s team, Fisher notes. For example, the alimentary canal is divided into different regions and is constantly flooded with nutrients, chemicals, and water. Because of this complexity, Fisher says, “Whether [the finding] Relevant to anything in the real world is largely up in the air.”

However, the work is “a very important step,” says Ofelia Ventorelli, a biochemist at the University of Wisconsin, Madison, who was not involved in the study. Advances, for example, could help researchers design a mix of gut bacteria that will remain healthy and resist the takeover of pathogens such as Clostridium difficileWhich can cause severe diarrhea, pain and even death, she said.

As a next step, Venturelli hopes to see researchers document microbial phase shifts in the guts of lab mice or other less artificial ecosystems. “I’d be very excited to test some of these ideas that Jeff’s team has discovered in more realistic environments.”

Pinheiro says the study could also provide a basis for testing how likely a bacterial community is to develop antibiotic resistance. “The fact that they find patterns” in microbial ecosystems, she says, “will inspire a lot of work.”

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