Scientists Grew Our Closest Microbial Relatives for the First Time

Every cell in your body has a nucleus, a neat little room where your DNA is kept. So do the cells of a mango tree, a mushroom and a mosquito. Biologists call all such life eukaryotes. But in Earth's distant past, there were no such cells at all. Life was only simple microbes. So where did the first complex cell come from?

This week, a team of Japanese scientists brought us one big step closer to the answer. For the first time ever, they have grown in the lab a group of microbes called Heimdallarchaeia, which are considered the closest living relatives of the microbe that gave rise to all complex life, including us.

Who announced it?

The study was led by Dr Hiroyuki Imachi and Dr Masaru K. Nobu of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). It was published in the journal Nature on 28 October 2026 (29 October in Japan), and JAMSTEC announced it in a press release on 29 October 2026.

First, what are archaea?

Life on Earth is usually split into three big groups: bacteria, archaea and eukaryotes. Bacteria and archaea are tiny single cells without a nucleus. Eukaryotes, the group that includes animals, plants and fungi, have a nucleus and many other inner compartments.

For years, scientists have suspected that the first eukaryote was born when an archaeal cell teamed up with a bacterium. Over a very long time, that bacterium ended up living inside the archaeal cell and became the mitochondrion, the "power station" found in our cells today. The archaea in question belong to a group once nicknamed Asgard archaea (after the home of the Norse gods) and now formally called Promethearchaeota. Heimdallarchaeia, named after the Norse god Heimdall, are a branch of this group, and DNA studies suggest eukaryotes arose from within them.

There was one big problem: nobody had ever grown Heimdallarchaeia in a lab. Everything known about them came from bits of DNA pulled out of mud and water. So scientists could only guess what they looked like and how they lived.

Microbes from a gas well, fed on milk powder

The JAMSTEC team has done this kind of patient work before. In 2020, the same group became the first to grow any member of the Asgard family, a strain called MK-D1, from deep-sea sediment.

This time, according to the Nature paper, they went to a natural gas production well on the Boso Peninsula in Chiba, Japan. Salty, methane-rich groundwater rises up this well, and a slimy layer of microbes, called a biofilm, grows on its walls. Because the water periodically erupts like a small geyser, the water level drops and the biofilm gets briefly exposed to air. That made it a perfect place to look for microbes that might cope with a little oxygen.

Back in the lab, the scientists fed their cultures tiny amounts of protein-rich food, including casamino acids and powdered milk, and added antibiotics to kill off competing bacteria. It was slow, careful work. The paper says it took about three years after the first sampling to isolate the first strain in a purified culture.

They ended up with two strains, called HC1 and SC1. The team has proposed the names Candidatus Margulisarchaeum peptidiphilum and Candidatus Flexarchaeum multiprotrusionum for them.

The big surprise: simple inside, fancy outside

Some researchers had expected these close cousins of eukaryotes to already have complex inner structures, maybe even something like a primitive nucleus. That is not what the microscopes showed.

Both strains turned out to be simple on the inside. They had no nucleus and no permanent inner compartments, just like ordinary archaea. But on the outside, they were remarkable. Most cells grew long, branching arms (scientists call them protrusions) that often made up more than half of the cell's total volume. These arms were used to grab on to partner microbes, methane-making archaea that the strains cannot live without.

This partnership is a give-and-take. The Heimdallarchaeia break down proteins and release hydrogen, and their partners eat that hydrogen.

JAMSTEC says this suggests the ancestor of complex cells may have first become complex on the outside, using these arms to build close partnerships, long before a nucleus and other inner rooms appeared.

The oxygen twist

Another debate was about oxygen. Some scientists had proposed that the ancestor of eukaryotes could already breathe oxygen, like we do. Strain HC1 does carry genes linked to using oxygen, so it seemed possible.

But the experiments said otherwise. Both strains are anaerobic, which means they live without oxygen, and they are harmed by it. Interestingly, HC1 could survive small amounts of oxygen, but only when oxygen-using bacteria were present to mop up the oxygen. The team thinks HC1's oxygen-related genes help it detoxify oxygen rather than breathe it.

This fits a fascinating idea: perhaps the bacterium that later became our mitochondria first helped the ancient archaeal host by protecting it from oxygen. One of these archaea may have eventually taken that bacterial partner inside, setting off the changes that led to the first complex cell.

Why it matters

These microbes live a very different life from typical bacteria. One strain doubles only once every 7 to 12 days, and the other every 14 to 20 days. The researchers also noticed that when given more food, the cells grew bigger instead of dividing faster. That is unlike typical simple microbes and more like the cells of eukaryotes.

Most importantly, scientists now have living cells to study instead of just DNA clues. These two strains give researchers a real-life model for experiments on how a simple microbe turned into the complex cells that make up every plant, animal and human.

The researchers are careful to point out that this is a picture of today's cousins, not the ancient ancestor itself. Still, for the first time, we can watch our closest microbial relatives live, eat and hold hands with their partners under a microscope. That is a remarkable window into our own deepest origins.