The great-grandparent of all living things, dubbed the Last Universal Common Ancestor (LUCA), was a sophisticated organism after all, with a complex structure recognizable as a cell, researchers say.
Many believe LUCA was little more than a crude assemblage of molecular parts, a chemical soup out of which evolution gradually constructed more complex forms. Some scientists still debate whether it was even a cell.
The study builds on several years of research into a once-overlooked feature of microbial cells, a region with a high concentration of polyphosphate, a type of energy currency in cells.
Researchers report that this polyphosphate storage site actually represents the first known universal organelle, a structure once thought to be absent from bacteria and their distantly related microbial cousins, the archaea.
This organelle, the evidence indicates, is present in the three domains of life: bacteria, archaea and eukaryotes (plants, animals, fungi, algae and everything else).
The existence of an organelle in bacteria goes against the traditional definition of these organisms, said University of Illinois crop sciences professor Manfredo Seufferheld, who led the study.
“This is the only organelle to our knowledge now that is common to eukaryotes, that is common to bacteria and that is most likely common to archaea,” Seufferheld said. “It is the only one that is universal.”
The study lends support to a hypothesis that LUCA may have been more complex even than the simplest organisms alive today, said James Whitfield, a professor of entomology at Illinois and a co-author on the study.
The study has been published in the journal Biology Direct.