#37

On the Cusp of Complexity

Microorganism bridges the simple and complex life.

By Jonathon Keats|Monday, November 30, 2015
RELATED TAGS: MICROBES & VIRUSES
complexity
complexity
Reprinted and adapted by permission from MacMillan Publishers Ltd: Nature doi:10.1038/nature14522 copyright 2015

When Norwegian researchers brought up a mud core from the floor of the Atlantic Ocean in 2010, they were orchestrating a family reunion. After 2 billion years of separation, a descendant of our distant common ancestor, a simple microorganism, has been discovered in the sediment by molecular biologists at Uppsala University in Sweden.

All nonviral life on Earth belongs to one of three domains. Complex organisms, distinguished by nucleated cells, collectively belong to Eukarya. The other two domains, genetically different yet both structurally simple, are Bacteria and Archaea. One of the great puzzles in biology is how simple life evolved to become complex. The Archaean discovered under the Atlantic — dubbed Lokiarchaeota in Nature in May — appears transitional, showing an unprecedented degree of genetic overlap with eukaryotes.

complexity-graph
complexity-graph
In our very extended family tree, Lokiarchaeota marks an important transition point in evolution: It’s still simple but shares some genes with more complex organisms.
Reprinted and adapted by permission from MacMillan Publishers Ltd: Nature doi:10.1038/nature14522 copyright 2015

For instance, Loki has genes that are nearly identical to those used by eukaryotes to build the cellular scaffold known as the cytoskeleton. Even more notable, Loki has genes that code for proteins involved in phagocytosis, the process by which one cell can swallow another — and widely believed to be the way eukaryotes acquired mitochondria, a cell’s power source.

Lead researcher Thijs Ettema was surprised to find such a close cousin in the first sample he sequenced. “This indicates that there probably is much more out there than meets the eye,” he says. “Most likely we’ll have to revise the biology textbooks a few more times in the near future.”

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