Nitrogen is essential to all known life forms on Earth. Now, scientists say this common element may also help explain how the earliest life evolved on Earth, and how life developed elsewhere in the universe.
“All living things need nitrogen to survive,” said Lance Seifert, a biochemist at Utah State University. “Nitrogen is all around us, but we don’t have direct access to it.” “Enzymes called nitrogenases enable nitrogen fixation, converting nitrogen into a form that plants, animals, humans, and other life forms can access. And we are only beginning to understand how far these nitrogenases have evolved over Earth’s 4 billion-year history.”
In a study published in nature communicationsSeefeld, USU senior scientist Derek Harris, and collaborators in the NASA-funded Metal Utilization and Selection (MUSE) project at the University of Wisconsin-Madison used synthetic biology to work backwards from modern nitrogenases to reconstruct possible ancestral versions of these enzymes.
Reconstitution of ancient nitrogen-fixing enzymes
“Our role in the study was to characterize a library of synthetically reconstructed ancestral nitrogenase genes,” Harris says. “Under controlled laboratory conditions, we measured nitrogen isotope fractionation in the cellular biomass of genetically engineered strains.”
This study allowed scientists to examine how ancient nitrogenases worked billions of years ago.
Professor Seefeld is a professor and chair of USU’s Department of Chemistry and Biochemistry and has spent more than 30 years studying the structure and function of nitrogenase. Being able to recreate ancient forms of these enzymes represents an important advance in efforts to understand the origins of life on Earth and potentially other worlds, he says.
“Until now, science has relied on ancient rocks and fossils to study early life,” he says. “Our Earth was very different billions of years ago. Modern microorganisms access atmospheric nitrogen sources through just one type of enzyme, nitrogenase. Studies of fossilized enzymes assume that ancient enzymes produced the same isotopic signature as modern enzymes.”
New clues about early Earth
Seefeld says the reconstituted nitrogenase provides a new way to investigate what conditions were like on Earth and in the atmosphere in the distant past.
“Understanding both ancient and modern nitrogenases is essential to addressing current agricultural challenges in a changing climate, including areas at risk of starvation due to drought and lack of access to commercial fertilizers,” he says.
This discovery may have practical applications outside of Earth. Seefeld, who has also participated in other NASA-funded projects, said this research will contribute to ongoing efforts to determine how food can be grown in space and on Mars.
Implications for the search for extraterrestrial life
Betul Kashar, a professor of bacteriology at the University of Wisconsin-Madison and director of the MUSE project and corresponding author of the study, said the results provide a clearer picture of how life survived and evolved before oxygen-dependent organisms transformed the planet.
“The search for life begins right here at home. Our home is 4 billion years old,” she says. “So we need to understand our own past. If we want to understand the life ahead and other lives, we need to understand the life in front of us.”
