Key metabolic features of the organism from which all life evolved, and the type of environment in which it likely lived, are identified in a paper published online this week in Nature Microbiology. The genomic data analysis finds that the so-called last universal common ancestor (LUCA) was adapted to survive in warm, oxygen-free, mineral-rich environments, perhaps similar to hot springs we see on Earth today.
The concept of a LUCA for all cells is central to the study of early evolution and the origin of life. However, little information exists about how and where LUCA lived. William Martin and colleagues analysed the evolutionary relationships of 6.1 million prokaryotic (single-celled) protein-encoding genes to search for ancient genes that may have originated from LUCA.
Although only 355 protein groups met their strict criteria, they found this was enough to determine that LUCA was anaerobic (did not require oxygen for growth) and thermophilic (thrived at relatively high temperature), and used carbon dioxide, nitrogen and hydrogen to sustain its metabolic pathways. The authors find LUCA was also dependent on transition metals such as iron, and other elements such as selenium. Based on these evolutionary relationships, they conclude that some organisms alive today have similar lifestyles to LUCA, including the clostridia (Bacteria) and methanogens (Archaea). This work provides new evidence to support the theory that life on Earth today is descended from autotrophic organisms - which create nutritional organic substances from inorganic substances, such as CO2 - in a hydrothermal environment.
In an accompanying News & Views article, James McInerney writes: “When we look at the inferred metabolism of LUCA, we are looking at the dominant and most successful kind of metabolism on the planet before the Bacteria and Archaea diverged. This new study provides us with a very intriguing insight into life four billion years ago.”