A New Description of Our Last Universal Ancestor

A New Description of Our Last Universal Ancestor
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Meet LUCA.

LUCA is, or rather was, a single-celled organism that lived in an oxygen-free hot spring. Its enzymes were packed with iron along with traces of other transition metals, hinting that LUCA's watery home was also rich in these metals. Within this cozy, metallic habitat, it fed on hydrogen and absorbed carbon dioxide and nitrogen from its surroundings, converting them to organic compounds in the proces. In many respects, LUCA was very similar to modern-day extremophiles dwelling near hydrothermal vents in the deep ocean.

Why should you care about LUCA? Because -- in a sense -- LUCA was your great, great, great, great, great, great (etc.) grandparent; the Last Universal Common Ancestor of all life on Earth. Between 3.5 and 3.8 billion years old! Respect your elders. (Figure Below: LUCA is the black line at the bottom.)

LUCA was just described in new detail in the journal Nature Microbiology. Madeline Weiss and Filipa Sousa led a team based out of Heinrich Heine University Düsseldorf in Germany. Together, they compiled gene families that exist in at least two species of Bacteria and two species of Archaea (Bacteria and Archaea being the most basic forms of life on Earth) and arranged them into phylogenetic trees. 286,514 gene families made the cut. Examining the trees, the researchers found that only 355 gene families descended from a common evolutionary ancestor and weren't shared with any other group.

"These 355 proteins were probably present in LUCA and thus provide a glimpse of LUCA’s genome," they reasoned.

Most of the genes previously had their functions sussed out, and these painted the aforementioned picture of LUCA.

"This new study provides us with a very intriguing insight into life 4 billion years ago," James O. McInerney an esteemed biologist at the University of Manchester, wrote in an accompanying news article. "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."

The study also supports the idea that life likely began near hydrothermal vents, where primitive cells may have been boiled into existence out of the building blocks of life. 

Source: Weiss et. al. "The physiology and habitat of the last universal common ancestor." Nature Microbiology. 25 July 2016. DOI: 10.1038/NMICROBIOL.2016.139

(Images: Jon Sullivan, NASA Astrobiology Institute)

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