Comparable to the birth of a plant!The fourth leap of life on earth is taking place on this algae–Fast Technology–Technology changes the future

I wonder if you have ever thought about how complex life on earth evolved?

In the past, biologists generally believed that the evolution of life from simplicity to complexity was a natural and inevitable occurrence, but in fact,Life on Earth has gone through a very long period of simple life—approximately more than half of the age of the Earth.

on the other hand,There is a huge gap between simple life and complex life forms on the earth now, and there is no “intermediate” at all. This is not like a step-by-step transformation from simplicity to complexity.

If life was a gradual process from simple to complex, then we would still have many life forms that cross the chasm living on the earth today.

Therefore, the evolution of life on earth from simplicity to complexity should be a qualitative leap. From simplicity to complexity,

We can now know,The essence of this leap is that life found mitochondria, which turned simple prokaryotic cells into more complex eukaryotic cells, and then complex life forms emerged.

Figure: Schematic diagram of mitochondria

Once cells have mitochondria, they can overcome a fundamental barrier that prevents prokaryotes such as bacteria and archaea from growing larger—a barrier to energy use.

ATP, the cell's universal energy currency, is manufactured in the cell membrane. As a cell gets larger, its surface area to volume ratio decreases, leaving less membrane available.

In other words, as prokaryotic cells get larger, their energy needs quickly exceed their supply and they become unable to sustain themselves.

Eukaryotic cells with mitochondria can overcome this problem by adding more mitochondria, and it's very easy to do because mitochondria themselves have the ability to replicate themselves.

All complex life on earth today descends from a common ancestor – a prokaryotic cell that acquired mitochondria.

Because it has the blessing of mitochondria, it can evolve freely. They can accumulate larger and more complex genomes, making complex life possible.

Figure: The structures of current chloroplasts and photosynthetic cyanobacteria are basically the same.

There was another qualitative leap in the history of life on earth, that is, life acquired chloroplasts about 1 billion years ago. This change in eukaryotic cells laid the foundation for the birth of plants.

There are several different hypotheses about how organisms on earth acquired mitochondria and chloroplasts, but for now, the most recognized one is the endosymbiosis hypothesis.

This hypothesis holds that eukaryotic cells phagocytose bacteria with special abilities, and these bacteria live in a mutually beneficial symbiosis with eukaryotic cells in their bodies.

But over time, the symbiosis became so intense that those bacteria completely transformed into parts of the eukaryotic cell – called organelles, which perform the cell's specific functions.

In addition to mitochondria and chloroplasts, there is currently another known example of an organism obtaining an organelle through this method (eukaryotic phagocytosis of bacteria), which is called chromoplasts.

This example is relatively unknown, but its existence makes it possible for cephalopods such as squid and octopuses to change color.

However, whether it is mitochondria, chloroplasts, or chromoplasts, they have been determined to be organelles, not separate bacteria.

Recently, two seminal articles published in Cell and Science revealed thatAn organelle is being born, produced symbiotically by eukaryotic cells engulfing prokaryotic bacteria, possibly for the fourth time in the known history of life on Earth.

This organelle, now named the nitroplast, gives eukaryotes the ability to fix nitrogen—converting nitrogen molecules in the atmosphere into nitrogen-containing compounds needed for life.

Before the discovery of nitrosomes, eukaryotes were considered to have no nitrogen-fixing ability, so if our food crops are to increase production, the application of nitrogen fertilizer is essential.

You might say, doesn’t soybean plant have the ability to fix nitrogen?

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Pictured: The roots of soybeans

In fact, they are not fixing nitrogen by themselves, but through symbiosis with bacteria. If you have seen the roots of soybeans, you will know that there are pieces of nodule-like tissue on the roots of soybeans. These are the nitrogen-fixing bacteria that live in symbiosis with soybeans – — Caused by rhizobia.

Life on earth found a way to fix nitrogen much earlier than we thought – nitrogen-fixing bacteria may have even appeared before the earliest photosynthetic bacteria, and nitrogen enzymes are believed to have appeared at least 2.2 to 1.5 billion years ago.

Although bacteria learned to fix nitrogen early, eukaryotes never acquired this ability. Before nitrosomes, biologists believed that all nitrogen-fixing eukaryotes did so because of symbiosis.

Before the publication of these two articles, scientists also believed that “nitrosomes” were just a type of algae endosymbiotic bacteria.

The one marked in black is nitrosome. Source: Tyler Coale

What bacteria do nitrosomes come from?

In 1998, a team led by Jonathan Zehr, a professor at the University of California, Santa Cruz, discovered a new species of cyanobacteria with the ability to fix nitrogen in the Pacific Ocean.

The team named this new nitrogen-fixing cyanobacteria UCYN-A, which is the predecessor of nitrosomes, or “wild mode”.

Almost at the same time that UCYN-A was discovered, Kyoko Hagino, a paleontologist at Kochi University in Japan, began actively trying to cultivate an algae with the ability to fix nitrogen in the laboratory – this algae is called raarudosphaera bigelowii, which finally proved to be UCYN-A host organism.

After more than ten years of hard work, Kyoko Hagino successfully cultivated this kind of algae containing UCYN-A in the laboratory, which helped later study the extraordinary symbiotic relationship between the two.

Nitrosomes that divide as host cells divide. Source: Valentina Loconte

Why is UCYN-A already a cellular organelle?

Cell organelles are also defined, and they need to meet at least two criteria:Must be inherited through cell division and rely on proteins provided by the host cell.

The article published in “Cell” revealed that UCYN-A and its host algae cell growth are synchronous and controlled by the exchange of nutrients, which is very consistent with the standards of a cell organelle.

The article published in Science revealed that UCYN-A obtains proteins from host algae cells, indicating that UCYN-A has given up some of its own cellular mechanisms and instead relies on the host to function.

This meets the second criterion, because the bacteria begin to discard their own DNA and rely on the mother cell, which is what happens to the organelles.

All these findings confirm that UCYN-A in raarudosphaera bigelowii has become an organelle (nitrosome) rather than an independent bacterium.

Picture: Archaea

at last

Compared with mitochondria and chloroplasts, which have existed for billions of years, nitrosomes are a very “young” organelle. They may have only begun to gradually evolve in eukaryotic cells in the last 100 million years.

At present, no one knows whether nitrosomes will have as profound an impact on the evolution of life on earth as mitochondria, chloroplasts, and chromoplasts, but one thing is clear, nitrosomes will certainly not be the last.

There must be many bacteria after it and before it that are being or have been transformed by eukaryotic cells – some may even be older than mitochondria, but their influence is not great and they have not been discovered.

Original report: https://www.iflscience.com/the-once-in-an-eon-event-that-gave-earth-plants-has-happened-again-73878

literature:

1.https://doi.org/10.1126/science.adk1075

2. https://doi.org/10.1016/j.cell.2024.02.016