Two origins of life: Free-living cells may have emerged twice as bacteria and archaea diverged

This study by an international team of biologists investigates the origins of life on Earth, specifically focusing on the emergence of free-living cells and the divergence of bacteria and archaea. The researchers found evidence that two independent origins of life existed for these free-living cells. They believe that if we could travel back 4 billion years in time, we would see two distinct kinds of cells, pioneer bacteria and pioneer archaea, attempting life outside the confines of a hydrothermal vent.

The team studied genomes, protein structures, and chemical reactions to understand the earliest phases of microbial evolution before the emergence of free-living cells. They compared the chemical reactions that cells use to create essential building blocks such as amino acids, RNA bases, and vitamins, which are collectively known as metabolism. These chemical reactions are universally conserved, meaning they have remained the same since the origin of life.

The researchers discovered that the last universal ancestor of all cells, LUCA, possessed enzymes for only about half of the reactions in metabolism. The other half was catalyzed by metals in the environment where LUCA originated. Metals naturally found in hydrothermal vents can replace a significant number of enzymes in metabolism. This led the researchers to conclude that early biochemical evolution was a hybrid of enzymatic and metal catalysts.

The study also identified a new source of energy for metabolic reactions: phosphite and palladium, a metal catalyst found in hydrothermal vents. When phosphite is reacted with organic compounds in the presence of palladium, metabolic phosphorylation reactions occur, replacing the need for ATP and enzymes. This discovery makes early evolution easier to understand, as it provides an alternative energy source in extreme environments like hydrothermal vents.

The researchers used an innovative method to order metabolic reactions from the simplest to the most complex, which helped them understand the order in which these reactions likely arose during the origin of life. This new approach is expected to be helpful in deciphering the complex network of 420 reactions that make up metabolism.

In conclusion, the findings of this study suggest that while there is a single origin of the genetic code, there were two independent origins of life: the emergence of free-living bacteria and archaea. This research sheds light on the complex interplay between enzymes and metal catalysts in the early stages of life, providing valuable insights into the processes that led to the evolution of life as we know it today.