This Strange Microbe May Mark One of Life's Great Leaps - The New York Times - 0 views
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A bizarre tentacled microbe discovered on the floor of the Pacific Ocean may help explain the origins of complex life on this planet and solve one of the deepest mysteries in biology, scientists reported on Wednesday.Two billion years ago, simple cells gave rise to far more complex cells. Biologists have struggled for decades to learn how it happened.
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The new species, called Prometheoarchaeum, turns out to be just such a transitional form, helping to explain the origins of all animals, plants, fungi — and, of course, humans. The research was reported in the journal Nature.
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Species that share these complex cells are known as eukaryotes, and they all descend from a common ancestor that lived an estimated two billion years ago.Before then, the world was home only to bacteria and a group of small, simple organisms called archaea. Bacteria and archaea have no nuclei, lysosomes, mitochondria or skeletons
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In the late 1900s, researchers discovered that mitochondria were free-living bacteria at some point in the past. Somehow they were drawn inside another cell, providing new fuel for their host. In 2015, Thijs Ettema of Uppsala University in Sweden and his colleagues discovered fragments of DNA in sediments retrieved from the Arctic Ocean. The fragments contained genes from a species of archaea that seemed to be closely related to eukaryotes.Dr. Ettema and his colleagues named them Asgard archaea. (Asgard is the home of the Norse gods.) DNA from these mystery microbes turned up in a river in North Carolina, hot springs in New Zealand and other places around the world.
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Masaru K. Nobu, a microbiologist at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, and his colleagues managed to grow these organisms in a lab. The effort took more than a decade.The microbes, which are adapted to life in the cold seafloor, have a slow-motion existence. Prometheoarchaeum can take as long as 25 days to divide. By contrast, E. coli divides once every 20 minutes.
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In the lab, the researchers mimicked the conditions in the seafloor by putting the sediment in a chamber without any oxygen. They pumped in methane and extracted deadly waste gases that might kill the resident microbes.The mud contained many kinds of microbes. But by 2015, the researchers had isolated an intriguing new species of archaea. And when Dr. Ettema and colleagues announced the discovery of Asgard archaea DNA, the Japanese researchers were shocked. Their new, living microbe belonged to that group.The researchers then undertook more painstaking research to understand the new species and link it to the evolution of eukaryotes.The researchers named the microbe Prometheoarchaeum syntrophicum, in honor of Prometheus, the Greek god who gave humans fire — after fashioning them from clay.
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This finding suggests that the proteins that eukaryotes used to build complex cells started out doing other things, and only later were assigned new jobs.Dr. Nobu and his colleagues are now trying to figure out what those original jobs were. It’s possible, he said, that Prometheoarchaeum creates its tentacles with genes later used by eukaryotes to build cellular skeletons.
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Before the discovery of Prometheoarchaeum, some researchers suspected that the ancestors of eukaryotes lived as predators, swallowing up smaller microbes. They might have engulfed the first mitochondria this way.
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Instead of hunting prey, Prometheoarchaeum seems to make its living by slurping up fragments of proteins floating by. Its partners feed on its waste. They, in turn, provide Prometheoarchaeum with vitamins and other essential compounds.