Ancient Microbial Respiratory System Reveals How We Adapted To Earth’s Changing Atmosphere

Huilin Li et all.VARI

Over the few billion years since life emerged on Earth, our planet’s atmospheric composition has seen its fair share of changes. This forced the creatures inhabiting it to adjust the way they breathe in order to keep up with the changing environmental conditions.

However, the way they pulled it off has been a “longstanding mystery in biology,” says Huilin Li, from the Van Andel Research Institute (VARI) in Grand Rapids, Michigan. Until now, that is.

Li, who is a professor at VARI’s Center for Epigenetics, has just published a study investigating the ancient respiratory system of a marine microbe called Pyrococcus furiosus.

This heat-loving microbe thrives in the boiling water of underwater volcanic vents, where it has dwelled for billions of years. Yet the environment that P. furiosus calls home is a chaotic place ruled by extreme temperatures and populated with noxious gases.

Although completely inhospitable to most creatures, this environment is the perfect place to study the evolution of various biomechanisms because it’s very similar to the atmospheric conditions that our planet had to offer when it was much younger and much more volatile, notes a VARI news release.

The new study, conducted by an international team of scientists from VARI, the University of Georgia (UGA) and Washington State University, compared the microbe’s respiratory system — a molecular mechanism known as MBH, which regulates microbial respiration — with its modern counterpart, Complex I, found in modern-day humans.

The research, featured today in the journal Cell, documents the similarities between MBH and Complex I, as well as the major differences that make the latter stand out due to its more recent adaptations to the environment.

According to study co-author Michael Adams, from UGA’s Department of Biochemistry and Molecular Biology, the structure of the MBH can help researchers understand how Complex I evolved and how it works in humans.

“Nature is really good at finding molecules that work and then modifying them and using them over and over again. This is a prime example.”

Using VARI’s high-powered Titan Krios cryo-electron microscope (cryo-EM), the team managed to observe MBH’s structure in unprecedented detail. The Krios has advanced capabilities that allow the microscope to image molecules one-ten-thousandth the width of a human hair.

With the help of this powerful microscope, the researchers obtained the first-ever image of the MBH (pictured above) and uncovered that, though its structure is surprisingly similar to that of Complex I, the ancient respiratory system has a much simpler method of converting electrical energy into chemical energy.

“The determination of MBH’s structure fills in some important missing pieces that reveal how life adjusted to sweeping changes in the environment throughout the millennia,” said Li.

Another difference between MBH and Complex I is that the latter possesses “several extra loops that allow it to interact with more molecules,” shows the VARI news release. The team believes that this adaptation occurred as a result of a change in the planet’s atmospheric composition.

In addition, the two molecular mechanisms have different metabolisms, the study revealed. While Complex I helps humans inhale oxygen and exhale carbon dioxide, MBH allows P. furiosus to expel hydrogen gas.

“It is amazing to see these two distantly related systems reorganize their shared elements to adjust to their different living conditions,” said Hongjun Yu, from VARI’s Cryo-EM Structural Biology Laboratory.

“It looks as if nature is playing with its own building blocks,” he added.