A bacterium has evolved into a new cellular structure inside algaeA brief summary:
1. A new cellular structure called a "nitroplast" has been discovered in a single-celled alga called Braarudosphaera bigelowii.
2. The nitroplast evolved from a nitrogen-fixing bacterium (UCYN-A) that has become an organelle within the algal cell.
3. This is only the fourth known case of a free-living bacterium evolving into an organelle in eukaryotic cells, the other three supposedly being mitochondria, chloroplasts, and chromatophores.
4. The research was conducted by Tyler Coale and colleagues at the University of California, Santa Cruz.
5. The study used soft X-ray tomography to observe how UCYN-A divides in sync with the algal cell, with each daughter cell inheriting one UCYN-A.
6. About half of the proteins in UCYN-A come from the algal host, indicating a high level of integration.
7. The nitroplast represents a new way for eukaryotic cells to fix nitrogen, a function previously thought to be exclusive to prokaryotes.
8. This discovery could have implications for understanding how to integrate nitrogen fixation into crop plants.
9. The document provides more detailed scientific background and context, including information about endosymbiosis, the evolution of organelles, and the importance of nitrogen fixation in biology.
10. It also includes additional perspectives from other scientists and more detailed explanations of the research methods and findings.
1. Evolutionary divergence:
- Around 91 million years ago, in the late Cretaceous period, the ancestral free-living cyanobacterium that would become UCYN-A entered into a symbiotic relationship with a prymnesiophyte algae.
- This initial symbiosis then diverged into at least two distinct lineages - UCYN-A1 and UCYN-A2 - each associating with a different but closely related prymnesiophyte host.
2. Genome reduction:
- As the symbiosis became more intimate, the UCYN-A genome underwent extensive reduction, losing many genes and pathways that became unnecessary in the symbiotic lifestyle.
- This included the loss of genes for photosystem II, carbon fixation via the Calvin cycle, and the tricarboxylic acid cycle.
3. Metabolic integration:
- The UCYN-A symbionts became specialized for nitrogen fixation, with the nitrogen fixation (nif) genes being among the most highly expressed.
- Energy production pathways (ATP synthase, cytochrome b6f, photosystem I) became tightly coupled to nitrogen fixation to provide the necessary ATP and reducing power.
4. Physical integration:
- UCYN-A cells became physically incorporated into their host cells.
- UCYN-A1 typically exists as 1-2 cells per host cell.
- UCYN-A2 forms a "symbiosome-like" structure with 3-10 cells inside the B. bigelowii host.
5. Partner fidelity:
- Each UCYN-A lineage developed strict specificity for its particular host species.
- This partner fidelity likely drove further co-evolution and specialization of each symbiotic pair.
6. Metabolic exchange:
- A mutualistic relationship developed where UCYN-A provides fixed nitrogen to the host, while the host likely provides fixed carbon and other nutrients to UCYN-A.
7. Gene expression adaptation:
- The UCYN-A gene expression became streamlined, with a strong focus on nitrogen fixation and associated energy production.
This merging represents a remarkable example of a supposed evolutionary transition from free-living organisms to obligate symbionts, with extensive metabolic and genomic integration between the partners. The process resulted in highly specialized nitrogen-fixing "organelles" within the prymnesiophyte hosts.
The endosymbiotic event described in the case of UCYN-A and Braarudosphaera bigelowii is fundamentally different from the proposed prokaryote-to-eukaryote transition in the endosymbiotic theory. 1. Pre-existing complexity:
- In the UCYN-A case, the host organism (B. bigelowii) is already a complex eukaryotic alga.
- The endosymbiotic theory for eukaryote origin proposes a transition from simple prokaryotes to complex eukaryotes, which is a much larger evolutionary leap.
2. Lack of intermediate forms:
- There is a lack of observable intermediate stages between prokaryotes and eukaryotes which is a major problem with the endosymbiotic theory.
- The UCYN-A case doesn't address this issue, as it involves two already distinct and complex organisms.
3. Complexity of eukaryotic features:
- The appearance of complex eukaryotic features is a challenge for the endosymbiotic theory. Here's a list of the main innovations found in eukaryotes that are not present in prokaryotes:
a. Nucleus
- Nuclear envelope with double membrane
- Nuclear pore complexes
- Chromosomes organized with histones
b. Endomembrane system
- Endoplasmic reticulum (rough and smooth)
- Golgi apparatus
- Lysosomes
- Vesicular transport system
c. Complex organelles
- Mitochondria
- Chloroplasts (in plants and algae)
- Peroxisomes
e. Cytoskeleton
- Microfilaments (actin)
- Intermediate filaments
- Microtubules
- Centrosomes and centrioles
f. Cell division mechanisms
- Mitosis with a spindle apparatus
- Meiosis and sexual reproduction
g. Membrane-bound compartments
- Vacuoles
- Specialized vesicles
h. Complex gene regulation
- Introns and exons
- Alternative splicing
- Epigenetic modifications
i. Linear chromosomes with telomeres
j. Larger cell size (typically 10-100 times larger than prokaryotes)
k. Complex cell signaling pathways
l. Cytoplasmic streaming
m. Phagocytosis and other complex forms of endocytosis
n. Flagella and cilia with "9+2" microtubule structure
o. Extracellular matrix production
p. Cell specialization and differentiation in multicellular organisms
q. Complex cell cycle regulation with checkpoints
r. Sophisticated DNA repair mechanisms
s. Membrane-bound cell surface receptors
t. Diverse membrane lipid composition
u. Ability to form complex multicellular organisms with specialized tissues and organs
These eukaryotic innovations represent a significant leap in cellular complexity compared to prokaryotes, and their sudden appearance poses a challenge for gradual evolutionary explanations, including the endosymbiotic theory.
- The UCYN-A event doesn't explain the origin of these complex features (nucleus, ER, Golgi, etc.) as they already exist in the host alga.
4. Membrane differences:
- There is a significant difference between eukaryotic and prokaryotic membranes.
- The UCYN-A case doesn't address this fundamental difference in cellular architecture.
5. Nuclear pore complexes and other eukaryote-specific structures:
- The origin of complex structures like nuclear pore complexes is not explained by the UCYN-A event.
- These structures already exist in the host alga, so this symbiosis doesn't shed light on their evolutionary origin.
6. Mitochondrial protein import and genome reduction:
- While the UCYN-A case shows some genome reduction and protein import, it doesn't address the extensive mitochondrial genome reduction and complex protein import systems seen in eukaryotes.
7. Origin of other organelles:
- The UCYN-A event doesn't explain the origin of other eukaryotic organelles like the endoplasmic reticulum, Golgi apparatus, or peroxisomes.
8. Cytoskeleton evolution:
- There are significant differences between eukaryotic and prokaryotic cytoskeletons.
- The UCYN-A case doesn't address this fundamental aspect of eukaryotic cell structure.
9. Eukaryotic gene content:
- Many eukaryotic genes have no clear prokaryotic homologs, which isn't explained by the UCYN-A event.
10. Mitochondrial-nuclear interdependence:
- There is complex interdependence between mitochondria and the nucleus in eukaryotes.
- While the UCYN-A case shows some integration, it doesn't approach the level of interdependence seen in eukaryotic cells with mitochondria.
11. Irreducible complexity:
- Many eukaryotic systems exhibit irreducible complexity.
- The UCYN-A event, occurring between two already complex organisms, doesn't address how these systems could have evolved gradually.
While the UCYN-A and B. bigelowii symbiosis is an interesting example of ongoing endosymbiosis, it occurs between two already complex organisms and doesn't address the fundamental challenges posed to the endosymbiotic theory for eukaryote origin. The pre-existence of eukaryotic complexity in this case means it cannot serve as a model for the proposed prokaryote-to-eukaryote transition.
A bacterium has evolved into a new cellular structure inside algaeA once-independent bacterium has evolved into an organelle that provides nitrogen to algal cells – an event so rare that there are only three other known cases
Michael Le Page 11 April 2024
https://www.newscientist.com/article/2426468-a-bacterium-has-evolved-into-a-new-cellular-structure-inside-algae/
In the 3.5 billion years since life first evolved on Earth, it was thought that once-free-living bacteria had merged with other organisms on just three occasions, making this an exceedingly rare evolutionary event. Now, a fourth example has been found, in a single-celled alga common in the oceans. These algae were thought to “fix” nitrogen – convert atmospheric nitrogen into useable ammonia – with the help of a bacterium. Tyler Coale at the University of California, Santa Cruz, and his colleagues have now shown that this bacterium has evolved into a new cellular structure, or organelle. It is the first known nitrogen-fixing organelle, or nitroplast, says Coale, and could be the key to the success of these algae. “It appears to be a successful strategy for them,” he says. “These are very widespread algae. We find them all over the world’s oceans.”
Read more Evolution is evolving: 13 ways we must rethink the theory of nature It is quite common for one species to live inside the cells of another in a mutually beneficial relationship called endosymbiosis. For instance, cells in the roots of legumes such as peas host nitrogen-fixing bacteria. The success of cockroaches is partly due to endosymbiotic bacteria that produce essential nutrients. Some cells even host multiple endosymbionts. While endosymbiotic relationships can become very close, in almost all cases, the organisms remain distinct. For example, legumes acquire their root bacteria from the soil. And while the cockroach bacteria are passed down in eggs, they live in specialised cells, not in every cell.
But in three cases, endosymbionts have merged with their hosts to become a fundamental part of them. Energy-producing mitochondria arose from the merger of a bacterium with another simple cell, forming the complex cells that gave rise to animals, plants and fungi. Plants arose when a cyanobacterium combined with a complex cell to form the chloroplast, the organelle that carries out photosynthesis. And around 60 million years ago, another cyanobacterium merged with an amoeba, forming a different photosynthetic organelle called a chromatophore, found only in a few species of Paulinella. It has been suspected for more than a decade that a cyanobacterium known as UCYN-A living within the single-celled alga Braarudosphaera bigelowii has become an organelle. However, studying the partnership was difficult until team member Kyoko Hagino at Kochi University in Japan found ways of keeping B. bigelowii alive in the lab. This allowed the team to use a technique called soft X-ray tomography to watch what happens as the algal cells divide. From this, it was discovered that UCYN-A divides in concert with the algal cell, with each daughter cell inheriting one UCYN-A. “We did not know how this association was maintained before this,” says Coale.
A radical new theory rewrites the story of how life on Earth began It has long been thought that the ingredients for life came together slowly, bit by bit. Now there is evidence it all happened at once in a chemical big bang
The team also found that around half of the 2000 or so different proteins inside UCYN-A come from the algal host, rather than being made within UCYN-A. Many of the imported proteins help UCYN-A fix nitrogen, says Coale. “I think it is being souped up by the algal cell to produce more nitrogen than it needs for itself.” There also seems to be a specialized system for delivering proteins to UCYN-A, as there is for other organelles. All the imported proteins have an extra section thought to be an “address label” marking them for delivery to UCYN-A. There is no universally accepted definition of an organelle, says Jeff Elhai at Virginia Commonwealth University, but many biologists regard coordinated division and the importing of proteins as key. “Both boxes are checked by Coale,” says Elhai. “Even to the semantic purists, UCYN-A must be counted as an organelle, joining mitochondria, chloroplasts and chromatophores.” The manufacture and use of nitrogen fertilizers is a major source of greenhouse gas emissions as well as an expense for farmers. So there is a lot of interest in modifying crop plants so they can fix their own nitrogen as legumes do. One way to achieve this would be to equip their cells with nitroplasts and Elhai has put together a proposal for how this could be done. But UCYN-A isn’t a good starting point because it is far too dependent on B. bigelowii, he says. Instead, Elhai envisages starting with cyanobacteria that have only just started down the road to becoming nitroplasts and don’t rely on imported proteins, so they could be easily added to a wide range of crop plants. Nevertheless, Elhai agrees with Coale that studying B. bigelowii could help us understand how to integrate nitrogen fixation into a plant cell.
The Nitroplast Revealed: A Nitrogen-fixing Organelle In A Marine Alga April 20, 2024 2
Evolution and function of the nitroplast – Multiple organelles in eukaryotic cells, including mitochondria, chloroplasts, and nitroplasts, evolved from the integration of endosymbiotic bacteria. In Braarudosphaera bigelowii, the chloroplast fixes inorganic carbon to produce glucose, which feeds the respiratory chain in mitochondria that produces adenosine triphosphate (ATP), which in turn fuels nitrogen fixation in the nitroplast. Glucose, ammonia, and ATP generated by the organelles, together with externally incorporated compounds (phosphorous, mineral nutrients, and vitamins), are the building blocks for cell metabolism, resulting in cell growth and division.
A nitrogen-fixing bacterial endosymbiont of marine algae is evolving into a nitrogen-fixing organelle, or nitroplast, according to a new study, thereby expanding a function that was thought to be exclusively carried out by prokaryotic cells to eukaryotes. Eukaryotic cells are remarkably complex and contain various organelles, which are specialized structures within a living cell that have specific biological functions. Two organelles, mitochondria and chloroplasts, play a key role in energy metabolism and photosynthesis, respectively, and likely evolved from the integration of endosymbiotic bacteria to the eukaryotic cell.
The robust volumetric relationship between partners of a marine planktonic nitrogen-fixing symbiosis reflects predictable, balanced, and quantitative interdependencies among CO2 fixation, respiration, and N2 fixation that maximize synchronized growth rate. Biological nitrogen (N2) fixation, the conversion of atmospheric N2 gas to biologically available ammonia, is a key metabolic process that maintains the fertility of aquatic and terrestrial systems. N2 fixation in eukaryotes is only known to exist through diverse symbiotic partnerships with prokaryotic microbes capable of N2 fixation. However, the nature of these symbiotic relationships is poorly understood, and, to date, a N2-fixing organelle in eukaryotic cells has yet to be described. Tyler Coale and colleagues investigated the interactions between Candidatus Atelocyanobacterium thalassa, or UCYN-A, a metabolically streamlined N2-fixing cyanobacterium. which is a known endosymbiont of the unicellular marine algae Braarudosphaera bigelowii.
Through subcellular images taken with soft X-ray tomography to visualize the algae’s cell morphology and division, Coale et al. observed a coordinated cell cycle in which endosymbiotic UCYN-A divided and is split evenly between daughter B. bigelowii cells, which is similar to the way chloroplast and mitochondria organelles are transmitted during cell division. Moreover, further proteomic and genomic analyses show that UCYN-A contains many proteins that are imported from the eukaryotic host cell’s nucleus, including those essential for cellular metabolism and control of the cell cycle. According to Coale et al., the findings suggest that UCYN-A has evolved beyond endosymbiosis and functions as an early evolutionary stage N2-fixing organelle. “The nitroplast represents a textbook case of a eukaryotic organelle that complements the energy, carbon, and nitrogen needs of the algal host and is another example of how ecology is the theater where evolution takes place,” writes Ramon Massana in a related Perspective.
The nitroplast: a nitrogen-fixing organelleA bacterial endosymbiont of microalgae evolved to an organelle 3
By Ramon Massana
Eukaryotic cells are notably complex, including by having various organelles, which are membrane-bound structures with specific functions. Two of these organelles, mitochondria and chloroplasts, which function in respiration and photosynthesis, evolved from the integration of endosymbiotic bacteria into the eukaryotic cell (1). In marine systems, some nitrogen-fixing bacteria are endosymbionts of microalgae, such as UCYN-A, a cyanobacterial symbiont of the unicellular algae Braarudosphaera bigelowii (2). On page XXX of this issue, Coale et al. (3) demonstrate a close integration of this endosymbiont into the architecture and function of the host cell, which are characteristics of organelles. These findings show that UCYN-A has evolved from a symbiont to a eukaryotic organelle for nitrogen fixation, the nitroplast, thereby expanding a function that was thought to be exclusively carried out by prokaryotic cells to eukaryotic cells.
Biological nitrogen fixation, which reduces atmospheric dinitrogen gas (N₂) into bioavailable ammonia (NH₃), is crucial in the nitrogen biogeochemical cycle as the only path to incorporate the abundant dinitrogen gas into biomass. This process represents a main driver of fertilization for aquatic and terrestrial systems, and is continuously studied to increase crop yields in agriculture (4). To directly benefit from the resulting ammonia, many photosynthetic organisms, from terrestrial plants to microalgae, incorporate nitrogen-fixing endosymbionts (5). This is the case of B. bigelowii and relatives (belonging to the algal class Prymnesiophyceae) carrying the nitrogen-fixing UCYN-A cyanobacteria. The latter symbiont lacks the genes for photosynthesis, whereas it is suitable for performing oxygenic photosynthesis while involved in a stable partnership with the host, providing it with fixed nitrogen and receiving fixed carbon in return (6). This symbiosis is now known to be very stable, widespread in sunlit coastal and oceanic waters, and to play a crucial role in the nitrogen biogeochemical cycle (6). However, establishing stable cultures of B. bigelowii and UCYN-A have limited studies on this symbiosis. Coale et al. successfully grew B. bigelowii in culture, which enabled them to further probe its interactions with UCYN-A. Tridimensional subcellular images taken with soft X-ray tomography were used to follow the development of the nucleus, mitochondria, chloroplasts, and UCYN-A during the cell cycle. The data revealed a coordinated fiber of events for the replication and fission of these four components that show that UCYN-A is as integrated within the eukaryotic cell architecture as the other three organelles. These findings also suggest that UCYN-A division is tightly controlled by the host and that the symbiont is transmitted to daughter cells during cell division. Furthermore, proteomics and comparative genomics analyses showed that UCYN-A contains many proteins that are imported from the eukaryotic host. These proteins are encoded in the host nucleus, translated in the host cytoplasm, signaled for transport to the nitroplast and complement metabolic pathways that appear incomplete in the UCYN-A genome, such as those involved in the synthesis of some amino acids, nucleotides, or cofactors. The synchronized division and the import of essential eukaryotic proteins indicate that UCYN-A has evolved beyond endosymbiosis (7) and that it can be instead considered a eukaryotic organelle under the full control of the host. The nitroplast takes the name proposed years ago for analogous systems (
and denotes its role in nitrogen fixation and its cyanobacterial origin (by analogy to plastids, also derived from cyanobacteria).
Distinguishing an endosymbiont from an organelle can be challenging (9), and each reported endosymbiosis may appear at a different stage of a putative endosymbiont-organelle continuum. Nevertheless, the nitroplast cellular integration and dependency supports the view that the nitroplast of B. bigelowii can be added to the short list of endosymbiosis-derived organelles. The evolutionary history of the nitroplast is analogous to that of mitochondria and chloroplasts, including gene loss, coordinated division, and subjugation to the host. Besides the mitochondria, chloroplast and nitroplast, there are few additional cases of endosymbiosis-derived organelles (10), such as the chromatophore of the amoeba Paulinella. In addition, the spheroid bodies of rhopalodiid diatoms, which resemble UCYN-A in many ways, may represent another example of an evolving nitroplast (11). Nonetheless, it is still intriguing that so few endosymbiosis-derived organelles are known, emphasizing how difficult it is to achieve this transition (12).
The transitions from endosymbionts to the various organelles happened independently at different times of eukaryotic evolution, and this influences their taxonomic coverage. Mitochondria acquisition (thought to have occurred around 2 billion years ago) predates the origin of the eukaryotic cell and these organelles are found throughout the eukaryotic tree of life, with some cases of secondary loss or modification. The primary endosymbiosis that originated the chloroplast also occurred in ancient times (likely around 1.5 billion years ago) in the supergroup Archaeplastida. Chloroplasts were later transferred to other eukaryotic supergroups by secondary or tertiary endosymbiosis. The establishment of the nitroplast is more recent, about 100 million years ago (13), and this may explain why this organelle is taxonomically constrained to prymnesiophytes. Even within this narrow host range, this variant has coevolved, revealing a remarkable relationship between organelle size and host size in related species (14). Given enough time, the nitroplast might be transferred to other lineages through secondary endosymbiosis, securing nitrogen supply to distant eukaryotes.
The study from Coale et al. shows that a revived endosymbiont is actually the nitroplast organelle, an optimal adaptation of the microalgae to thrive in nitrogen-limited waters. Like photosynthesis, a prokaryotic innovation that was incorporated by endosymbiosis into the eukaryotic cell and is now considered a eukaryotic function, these authors propose the claim that nitrogen fixation is no longer an exclusive prokaryotic function and that eukaryotes can fix nitrogen using their nitroplast. The nitroplast represents a textbook case of an eukaryotic organelle that complements the energy, carbon and nitrogen needs of the algal host (see the figure) and another example of how ecology is the theatre where evolution takes place.
Incredible Discovery of an Entirely New Organelle That Fixes Nitrogen 4
When it comes to life, and specifically the individual cells that make up much of life like us, one of the more mysterious and difficult questions to answer regards the complexity inside the cell and how various structures formed over time. Over billions of years of evolution, animal cells and plant cells, specifically eukaryotic cells, developed a lot of complexity that relies on a concept known as endosymbiosis. This is a kind of symbiotic relationship between various types of organisms providing for each other and getting something back in return.
The best example here is what you see in this video: mitochondria. Billions of years ago, mitochondria were most likely individual bacteria that were exceptional at producing energy, mostly in the form of a molecule known as ATP. Then, at some point, something happened and they essentially formed a symbiotic relationship with various cells, providing that extra energy to them and in return getting a lot of safety and essentially a house to live in (and possibly something else). So, over billions of years, modern cells evolved to use mitochondria as an essential organelle in pretty much every cell inside our body. There are over 80 trillion of them inside each of us, and basically almost every cell contains them. Something very similar happened to plant cells, specifically various algae and chloroplasts - another bacterium that was very good at photosynthesis became absorbed by various algae, with some eventually evolving into plants. Over billions of years, both mitochondria and chloroplasts became so specialized that they can't actually live outside of a typical cell. They require our cells for survival, and our cells even provide them with a lot of additional proteins in order to reproduce and copy themselves over many generations.
This process of ingestion of bacteria, where the whole cell and the ingested bacteria eventually become codependent, seems to have happened at least three times. The absorption of chloroplasts potentially was the first, with this beautiful picture of a typical moss showing us huge amounts of chloroplasts present in each of the cells. Then we had the absorption of mitochondria, which became essential for a lot of more complex life on the planet, basically responsible for producing a lot of energy but also for regulating many things in our body, making these organelles crucial for more complex life. More recently, researchers discovered the most recent such case from an organism known as Paulinella. This probably happened only 60 to maybe 100 million years ago, basically during the time of the dinosaurs, as opposed to billions of years ago when we believe mitochondria and chloroplasts became part of various cells. Approximately 60 million years ago, another cyanobacterium merged with an amoeba, forming a new organelle known as a chromatophore - essentially a completely separate photosynthetic organelle that seems to only exist in these specific organisms.
This idea of various specialized bacteria getting swallowed and merging with more complex cells, eventually becoming a part of them, seems to be a relatively common scenario in the evolution of complex life. This idea today is known as the Endosymbiotic Theory - basically, the process of ingesting bacteria in order to form this permanent relationship that then changes the cell and creates a new organism. Though mitochondria and chloroplasts still obviously have their own DNA, they're completely dependent on the cell they reside in. But so far, these examples only present us with two separate chemical reactions that life relies on: we have photosynthesis and we have the production of ATP, or the energy molecule. But we know that bacteria evolved to actually use a lot of other chemical reactions for survival on the planet. For example, something that plants rely on as well is the idea of nitrogen fixation. Plants need nitrogen for growth, and normally most plants get nitrogen by creating a kind of collaboration, or once again symbiosis, with nitrogen-fixing bacteria somewhere around the roots. This is sometimes referred to as the root microbiome, and it's kind of similar to what we have in our guts that essentially helps roots digest various types of matter and acquire different nutrients they need for growth.
But here, just like with our guts, the microbes don't live inside the cells; they basically live around the roots, forming their own communities. This type of bacterial symbiosis is extremely common. As I mentioned, we have something similar inside our guts, and pretty much most animals out there use bacteria for something to some extent. When it comes to nitrogen, it is a very crucial element, and it's actually kind of surprising that no life so far has developed an ability to basically integrate these bacteria into the cells, forming organelles kind of like mitochondria or chloroplasts. Or so we thought.
Transitioning into the actual topic that we're discussing today, it turns out something has done that. Researchers have just now discovered a new organism that seems to have nitrogen-fixing properties, and the organelle in this case is now going to be referred to as nitroplast. It fixates nitrogen, with all of this discovered in a single-cell algae known as Braarudosphaera bigelowii, and the cyanobacterium that seems to be present here, responsible for the fixation of nitrogen, is now referred to as UCYN-A.
The thing about the strange organism that possesses this organelle is that it's already kind of strange. It's essentially what's known as a coccolithophore. We actually discussed this in one of the previous videos (you can find it in the description), but in essence, these are some of the strangest looking organisms on the entire planet. They're all marine organisms; they essentially rely on oceans. They're also extremely successful and exist everywhere, and more importantly, they seem to form these unusual shield-like formations around the cell. It's not clear why; they're actually super diverse and do come in a lot of varieties and have definitely existed on the planet for over 100 million years. As a matter of fact, that previous video that I mentioned in the description talks about the ones that existed around the time dinosaurs perished. But despite their complexity and their overall numbers, we still barely know anything about them because they are super tiny and are also generally very different from a lot of other life. The organism we're discussing today looks like this: it contains unusual fivefold symmetry and contains 12 unusual pentagons forming a kind of dodecahedral structure, but only 10 micrometers in size. These organisms are also autotrophic; they basically feed themselves. By covering themselves with this calcium shell, they kind of protect themselves from possible hazards outside. This unusual shell is known as the coccosphere, although the real reason why the coccosphere exists is still unknown. It's actually one of the mysteries here.
Nevertheless, these organisms are super important because they capture a lot of calcium but also a lot of carbon. This is actually made out of calcium carbonate, and as a result, they form one of the biggest parts of the carbon cycle in the oceans, which is why so many scientists try to understand them a little bit better. This time, by using X-ray tomography and by watching these cells divide using individual frames, the researchers realized that as they divide, one of the unusual bacteria known as Atelocyanobacterium thalassa that lives inside of them seems to rely on a lot of genetic code and a lot of proteins from the whole cell. For example, they don't seem to have genes producing RuBisCO, which is usually essential, and they're also unable to fix carbon via photosynthesis. Yet the cell they live in can do all of this but just doesn't really have any nitrogen. So approximately 2,000 various proteins essential for this bacterium seem to come from the whole cell and not from the DNA inside. In other words, this is basically an actual organelle and not a bacterium anymore. And obviously, in return, it seems to fix nitrogen, allowing the whole cell to then use it for food.
So basically, this is the first ever known nitroplast. Instead of relying on some kind of a culture of bacteria like roots of plants, just like with mitochondria, this just became an organelle. Although obviously, it's not clear when all of this happened. But what's, I guess, more impressive is that this is not just like one or two examples here. We're actually talking about an extremely widespread organism pretty much found all over the planet, which basically means that this is a very successful evolutionary change that provides the host with some essential advantages. This is the fourth known organelle that used to be a bacteria. We have mitochondria, chloroplasts, chromatophores, and now nitroplasts. For actual plants, in other words, is there any way for us to replicate this and possibly genetically modify plants somehow in order to give them not just chloroplasts but also nitroplasts, which would then make them way more efficient at basically growing? But most importantly, it would suddenly make nitrogen fertilizers kind of useless. And since fertilizers are both expensive and generally are not very good for the environment, being able to somehow introduce nitroplasts into plants might actually change everything.
There's obviously no real way we can do this yet, but this unusual discovery could definitely present us with some options in the future. But because this is a super recent discovery, there's really not much else we know about this, and I'm sure there will be more discoveries in the next few months. And so, until then, or until we know something else, that's pretty much all I wanted to mention. Thank you for watching, subscribe, share this with someone who loves to learn about space and sciences, come back tomorrow to learn something else. Support this channel on Patreon, by joining Channel membership, or by buying the wonderful person t-shirt you can find in the description. Stay wonderful, I'll see you tomorrow, and as always, bye-bye.
This is a Braarudosphaera Bigelowii (Latin name) otherwise known as a coastal PhytoPlanktonic algae. It is so small that its diameter is just a couple of microns (the average cross-section of a human hair is 50 microns) Living geometry is truly amazing.
1. https://www.science.org/doi/10.1126/science.ado8571
2. https://astrobiology.com/2024/04/the-nitroplast-revealed-a-nitrogen-fixing-organelle-in-a-marine-alga.html
3. https://docs.google.com/viewerng/viewer?url=https://digital.csic.es/bitstream/10261/354070/3/Massana_2024_postprint.pdf
4. https://www.youtube.com/watch?v=eGkV_k8IcQ0
