Phylogenomics supports a cellularly structured urancestor

Cells and viruses are structured and harbor complex organization. This manifests in intra- and extracellular compartments such as reticuli and periplasmic spaces, storage and energy-harvesting organelles such as acidocalcisomes and mitochondria, and specialized structures that hold genomic repositories such as nuclei and capsids. Structural phylogenomic reconstruction of the protein repertoire of the common ancestor of life, the urancestor, suggests these entities that existed 2.9 billion years ago were not only complex from a structural and functional point of view, but were also cellularly structured. We also provide support to the existence of urancestral storage organelles that were analogous to acidocalcisomes. These cellular structures probably accumulated compounds that stored energy in their phosphoanhydride bonds, such as polyphosphates. These energy-rich compounds necessary for thioester and pyrophosphate intermediates would have channeled the abundant redox energy of early Earth to the early metabolic needs of the primordial cells. Our findings are compatible with a relatively complex urancestral cell and with abundant microfossil evidence supporting the existence of primordial microbial communities as far back as 3.4 billion years ago. Results highlight the centrality of the cellular compartment and bioenergetics in the early evolutionary stages of life.