Understanding the origin of life on Earth has long been a subject of fascination and inquiry. Scientists have made significant progress in identifying the last universal common ancestor (Luca) and reconstructing its genome. In a recent study published in Nature Ecology & Evolution, an international team of researchers used a combination of scientific methods to recreate Luca’s genome and explore how its genes might have allowed it to thrive.
To achieve this, the team analyzed a set of 700 genomes from different groups of bacteria and archaea, excluding eukaryotes (plants, animals, and fungi) since they are thought to have evolved later. By sorting these genes into families based on their function in modern organisms and using a database called KEGG, researchers could understand the metabolic pathways of these ancient organisms.
The team then built phylogenetic trees to understand the relationships between different species and how they evolved over time. They also constructed a separate set of 57 genes common to all 700 organisms and likely present in almost all life. These genes have remained relatively unchanged for billions of years, allowing researchers to estimate Luca’s age.
Using these 57 genes, scientists built a species tree showing the Darwinian relationships between different organisms. By combining this with gene trees from KEGG and modeling rates of gene duplication, transfer, and loss, researchers could calculate the likelihood of different gene families being present in Luca.
Reconstructing Luca’s genome allowed scientists to estimate its metabolism as if it were alive today. They envision Luca as a complex organism like modern bacteria and archaea with a small genome. However, they did not find evidence for photosynthesis or nitrogen fixation, suggesting that Luca might have had different metabolic pathways than its modern counterparts.
The team also attempted to estimate Luca’s age using genes thought to have duplicated before Luca together with fossil information. By tracing the evolutionary timeline of these paralogous genes, researchers estimated that Luca roamed the Earth around 4.2 billion years ago.
While this reconstruction is not without limitations and may change as more data becomes available, it sets a new standard for understanding Luca’s role in the origin of life on Earth. The study highlights the importance of continued research to better comprehend how life has evolved since the formation of our planet.
Source: https://theconversation.com/how-we-reconstructed-the-ancestor-of-all-life-on-earth-236452