Thriving without oxygen
Could the organisms that may potentially help us mitigate climate change have been responsible for the origin of complex life? To answer this question, we have to travel back to the largest mass extinction known on Earth—not when the dinosaurs were wiped out but further back, to the end of the Permian period, about 250 million years ago. The oceans were completely full of organic debris, to the point where it would have been difficult just to see your hand in front of your face. With no organisms capable of decomposing organic matter, it was just accumulating in an anaerobic—devoid of oxygen—environment. Eventually, thanks to years of evolution, a microorganism emerged that provided an essential link in the carbon cycle, where organic matter could be decomposed, producing methane as a byproduct. The resulting change in the Earth’s atmosphere cleared the way for complex life as we know it.
“With all that methane in the atmosphere, which is 30 times more potent as a greenhouse gas than carbon dioxide, we had the mother of all greenhouse effects occurring,” said James Ferry, Stanley Person Professor of Biochemistry and Molecular Biology. “The Earth warmed up and killed off 90 percent of all living things.”
Ferry studies the modern-day descendant of this microorganism, Methanosarcina acetivorans, a single-celled methanogen commonly found in anaerobic environments like the ocean floor and in rice paddies, where it converts decaying material into methane in order to produce energy.
“Methanogens produce about 1 billion metric tons of methane annually, which plays a critical role in modern-day climate change,” said Ferry. “By understanding the biochemistry of methanogens, we hope to be able to predict some aspects of climate change and to possibly even inhibit the production of methane by this organism.”
In 2018, Ferry’s lab identified key enzymes essential for M. acetivorans to reverse the biochemical pathway that produces methane. “We demonstrated key reactions that the organism uses to not only make methane but to use it, too,” said Ferry.
As it turns out, the microbe can consume methane in the presence of iron to create carbon dioxide, which could theoretically allow researchers to harness this pathway to manipulate the relative levels of these two greenhouse gases. Because methane is a more potent greenhouse gas than carbon dioxide—and can thus trap more heat in the atmosphere—this microbe could be an important tool in the fight to slow climate change.
At the same time, methanogens are also capable of making acetic acid from carbon monoxide. “It’s a starting material for the synthesis and production of all sorts of useful things, like polymers that can make clothing, pharmaceuticals, and entrepreneurial goodies,” said Ferry.
While ancestors of M. acetivorans might have been responsible for the largest extinction on record, their contributions to the atmosphere also paved the way for complex life. As for the future, this methanogen might just be part of the solution for keeping the next extinction at bay.