What were the first forms of life? In a promising new paper, scientists describe a strategy to answer this question by examining the earliest evolution of electron transport chains, a universal metabolic strategy with a very ancient history. The article was published in the journal Proceedings of the National Academy of Sciences.

Despite decades of progress, the origin of life remains one of science’s greatest unsolved problems. “The most basic features of biology, namely that organisms consist of cells, transmit genetic information through DNA, and use protein enzymes for metabolism, emerged as a result of certain processes very early in evolutionary history,” says Aaron Goldman. , Associate Professor of Biology at Oberlin College.

“Understanding how these basic biological systems formed for the first time will allow us to better understand not only how life functions at its most fundamental level, but also what life really is and how we can search for it beyond Earth.”

The question of how life first emerged is often studied by laboratory experiments that simulate the environment of early Earth’s times and look for chemicals that can create the same kinds of biomolecules and metabolic reactions we see in organisms today. This is known as the bottom-up approach because it works with ingredients available on the prebiotic Earth. While these so-called “prebiotic chemistry” experiments have successfully shown how life “could have arisen,” they cannot tell us how life actually “arose.”

Meanwhile, other research is using evolutionary biology techniques to reconstruct what early life forms might have looked like based on evidence of modern life. This is known as the top-down approach and can tell us about the history of life on Earth.

However, top-down studies can only look at the fact that there are genes that are still present in organisms today and thus trace back to the origin of life. Despite its limitations, top-down and bottom-up research share the common goal of discovering the origins of life, and ideally their responses should come together under a common set of circumstances.

A new paper by Goldman, Lori Barge (an astrobiology researcher at NASA’s Jet Propulsion Laboratory (JPL)) and colleagues attempts to fill this methodological gap. The authors argue that a combination of top-down evolutionary reconstructions of early life forms and top-down laboratory studies of plausible pathways for the origin of life could be used to uncover how life really arose on early Earth.

In their paper, entitled “Electron transport chains as a window into the earliest stages of evolution,” the authors describe a central phenomenon of modern life that can be studied through a combination of both bottom-up and top-down research: electron transport chains.

Electron transport chains are a type of metabolic system used to produce usable forms of chemical energy by organisms throughout the tree of life, from bacteria to humans. Many different types of electron transport chains are specialized for each life form and the energy metabolism they use: for example, our mitochondria contain the electron transport chain associated with our heterotrophic (food-consuming) energy metabolism; plants, on the other hand, have a completely different electron transport chain associated with photosynthesis (production of energy from sunlight).

Throughout the microbial world, organisms use a wide variety of electron transport chains associated with various energy metabolisms. Despite these differences, however, the authors describe evidence from top-down studies that this type of metabolic strategy was used by the earliest life forms, and present several models of ancestral electron transport chains that can be traced back to very early evolutionary history. They also examine existing evidence to suggest that electron transport chain-like chemistry may have been facilitated by early Earth’s minerals and ocean water before life as we know it.

Inspired by these observations, the authors outline future research strategies that synthesize top-down and bottom-up studies of the earliest history of electron transport circuits to better understand ancient energy metabolism and the origins of life in general. This research marks the culmination of five years earlier work by an interdisciplinary, multi-institutional team led by JPL’s Barge to investigate how metabolic reactions might have occurred under geological conditions on early Earth.

The team’s previous work included, for example, specific electron transport chain reactions triggered by minerals (led by JPL research scientist Jessica Weber); how ancient enzymes were able to incorporate prebiotic chemistry into their active sites (led by Goldman); and microbial metabolism in a highly energy-constrained environment (led by Doug Larrow of the University of Southern California).

“The emergence of metabolism is an interdisciplinary question, so we need an interdisciplinary team to study it,” says Barge. “Our work used chemistry, geology, biology and computer modeling techniques to combine these top-down and bottom-up approaches, and this type of collaboration will be important for future studies of prebiotic metabolic pathways.” Source