Evolution: origin of eukaryotes: Archaea hard to grow (Evolution)

by David Turell @, Monday, August 12, 2019, 15:07 (362 days ago) @ David Turell

An organism that took 12 years in the lab to grow offers new insight on eukaryote/Archaea possible relationship:


"Patience proved the key ingredient to what researchers are saying may be an important discovery about how complex life evolved. After 12 years of trying, a team in Japan has grown an organism from mud on the seabed that they say could explain how simple microbes evolved into more sophisticated eukaryotes. Eukaryotes are the group that includes humans, other animals, plants, and many single-celled organisms. The microbe can produce branched appendages, which may have helped it corral and envelop bacteria that helped it—and, eventually, all eukaryotes—thrive in a world full of oxygen.


"The prevailing thinking is that roughly 2 billion years ago, a microbe belonging to a group called the Asgard archaea absorbed a bacterium called an alphaproteobacterium, which settled inside and became mitochondria, producing power for its host by consuming oxygen as fuel. But isolating and growing Asgard archaea has proved a challenge, as they tend to live in inhospitable environments such as deep-sea mud. They also grow very slowly, so they are hard to detect. Most evidence of their existence so far has been fragments of DNA with distinctive sequences.


"DNA analyses of samples from the tube indicated it included an Asgard archaeon, the microbe they were hoping to grow. It took about 20 days for the numbers of this microbe to double—bacteria commonly double in less than an hour—but eventually, they got enough of the organism to study it. “It was really a gargantuan task,” says David Baum, an evolutionary biologist at the University of Wisconsin in Madison, who was not involved with the work.


"Experiments with this single-cell organism suggest it usually—if not always—grows in association with another microbe that makes methane, Imachi, Takai, and colleagues report today in a preprint on bioRxiv. The researchers further discovered that Prometheoarchaeum breaks down amino acids for food and releases hydrogen, which feeds its partner. That methanemaker in turn helps Prometheoarchaeum thrive by chewing through the hydrogen, the researchers say; a buildup of hydrogen could otherwise cause even slower growth of Prometheoarchaeum. The complex partnership is another reason why the Asgard arcahaea are so hard to grow in the lab.


"Having grown the microbe, the researchers used an electron microscope to image it, revealing multiple branched appendages. The team hypothesizes that, eons ago, an archaeon encircled the protomitochondrion and put it to work. The researchers propose that as the concentration of oxygen increased on early Earth, archaea like Prometheoarchaeum took in oxygen-using partners and did better than other microbes.


"Ettema cautions that the archaeal ancestor to eukaryotic cells that lived 2 billion years ago may not have looked and acted just like Prometheoarchaeum. Moreover, DNA studies indicate that other archaea are more closely related to eukaryotes than this one. He expects, however, that the 12 years the Japanese team devoted to culturing this microbe will help him and others isolate and grow related archaea in the lab: “I’m sure it will not take 12 years to get the next Asgard into culture.'”

Comment: Still not well understood, but an amazing advance in studying descendants of early life

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