The relative of all living things, dubbed the Last Universal Common Ancestor (LUCA), was a sophisticated organism with a complex structure recognizable as a cell, according to a new paper in the journal Biology Direct.
Prior theories have held that this great-grandparent of all living things was little more than a crude assemblage of molecular parts, a chemical soup out of which evolution gradually constructed more complex forms. This latest research suggests that was not the case, although LUCA was not a multi-celled creature.
“LUCA was probably a single celled organism because the extracellular machinery needed for multicellularity was developed in eukaryotes (organisms whose cells contain microstructures) very late in evolution,” lead author Manfredo Seufferheld told Discovery News.
“We do not know its appearance, but we hypothesize it looked very much like an archaeum,” added Seufferheld, who is a professor of crop sciences at the University of Illinois.
The archaea are a group of microorganisms that are somewhat similar to, but genetically distinct from, bacteria.
The study builds on research into a once-overlooked feature of microbial cells, a region with a high concentration of polyphosphate. Seufferheld and colleagues Kyung Kim, James Whitfield, Alejandro Valerio and Gustavo Caetano-Anolles made the determinations after studying this region of cells which is a type of energy currency.
Through genetic analysis, including the construction of “family trees,” the researchers demonstrated how this polyphosphate storage site actually represents the first known universal organelle. Such specialized subunits, organelles, were once thought to be absent from bacteria and their distantly related microbial cousins, the archaea.
The evidence now indicates the organelle dates back to LUCA, before the three main branches of the tree of life appeared. It is therefore likely present in the three primary domains of today’s Earthly life. These are bacteria, archaea and eukaryotes (plants, animals, fungi, algae and everything else).
“We hypothesize that LUCA developed this organelle very early in evolution so that it could have a sustainable source of energy stored in its cellular make-up,” Seufferheld explained, adding that mitochondria (organelles functioning as cellular power plants) “were later developed and replaced the major energetic role” of the polyphosphate storage site when Earth became oxygenated.
The findings add to what is already suspected about LUCA, thought to have emerged about 3.8 billion years ago.
Nicolas Lartillot, a bio-informatics professor at the University of Montreal, and his team also conducted genetic and tree of life analyses. These suggest early life on Earth was composed of ribonucleic acid (RNA) rather than DNA. RNA is particularly sensitive to heat, so this provides yet another clue about LUCA.
Lartillot said that “our data suggests that LUCA was actually sensitive to warmer temperatures and lived in a climate below 50 degrees.”
He said this negates the idea “that LUCA was a heat-loving or hyperthermophilic organism. A bit like one of those weird organisms living in the hot vents along the continental ridges deep in the oceans today.”
Instead, LUCA may not have been able to exist under such extreme heat conditions.
Whatever the temperature, it is believed LUCA was already at a developmental stage that allowed for advanced protein synthesis.
“It is possible that having efficient cells capable of faster replication through more efficient protein synthesis could have triggered more cellular variants and the emergence of lineages,” Caetano-Anolles said, thereby providing an explanation for how LUCA may have given rise to the three main branches of the tree of life.