🧪 Origin of life: scientists resurrect a 3-billion-year-old enzyme

How can we know what life on Earth looked like more than three billion years ago, when rocks from that era are so rare and difficult to exploit? To answer this question, researchers have adopted an original method by bringing an ancestral enzyme back to life. This approach opens a new window onto our distant past and the search for life beyond our planet.

A team from the University of Wisconsin-Madison used synthetic biology to reconstruct a probable version of a 3.2-billion-year-old enzyme. Starting from modern enzymes, they traveled back in molecular time to reconstruct an ancient DNA, inserted it into modern microbes, which subsequently produced the ancestral enzyme.


The enzyme in question, nitrogenase, plays a fundamental role for life. According to scientists, without it, life forms as we know them would likely not exist. It transforms atmospheric nitrogen into compounds usable by cells, enabling the formation of DNA and proteins. This function was just as vital billions of years ago, when Earth was very different, with an atmosphere rich in carbon dioxide and methane.

Enzymes do not fossilize, but their activity can leave chemical imprints in ancient rocks. For nitrogenase, the nitrogen fixation process generates distinctive isotopic patterns. Geologists use these signatures to detect signs of past life. However, a lingering question remained: were these signatures the same billions of years ago as they are today? The recent study provides an answer.

Tests on the reconstructed ancient enzyme showed that its isotopic signature remains identical to that of modern versions, despite changes in its DNA sequence. This unexpected stability means the chemical traces found in Earth's rocks are reliable for identifying nitrogenase activity in the past. Consequently, this strengthens confidence in interpreting the geological record.

This work has implications for the search for extraterrestrial life. The team is part of the NASA-supported MUSE consortium, which aims to improve space missions through a better understanding of microbial evolution. By confirming that nitrogenase-related isotopes are a reliable biosignature on Earth, they provide a framework for evaluating similar signals on other planets.

The results, published in Nature Communications, pave the way for new explorations, both on our planet and in the cosmos.

Synthetic biology: a molecular time machine

Synthetic biology is a discipline that combines engineering and biology to design or modify biological systems. In this study, it enables the reconstruction of ancient enzymes starting from modern versions. Researchers analyze current DNA sequences to infer probable past forms, similar to tracing the evolution of a language.

This reconstruction is carried out in the laboratory using genetic engineering techniques. Scientists synthesize the DNA corresponding to the ancient enzyme, then introduce it into living microbes. The microbes then produce the enzyme, allowing its properties and function to be studied in a controlled environment.

This approach offers a major advantage: it allows hypotheses about the past to be tested directly, without relying solely on fossils or fragmentary rocks. By observing how these enzymes interact with their environment, we can better understand the conditions of early Earth and the evolution of biological mechanisms.