The laboratory technician wiped the leaf from the mud - and saw what the most important point of our history will explain.
Every second, the flow of solar energy falls to Earth, which is 10 thousand times the energy consumption of modern civilization. People collect the light with panels, store the charge in the batteries and adjust the power grid to the solar generation. Microbes mastered the energy of light billions of years ago, and the byproduct of this process changed the atmosphere of the planet.
About 2.4 billion years ago, some bacteria learned to use light to break down water and collect organic molecules from carbon dioxide. During the reaction, oxygen was released. At first, the gas simply went into the environment, but over time accumulated in the atmosphere and opened the way to organisms that use oxygen to generate energy.
Photosynthesis seems simple only in school textbooks for elementary classes. In the cell there is a thin system of proteins and pigments: some molecules catch photons, others transmit energy further, others conduct electrons through a chain of reactions. The entire mechanism is placed in structures less than one thousandth width of a human hair.
Modern microscopy and cell biology allow you to trace how the electron passes through photosynthetic proteins. With living cells, scientists have dealt in in some detail. With an ancient history, it is more difficult: oxygen photosynthesis appeared more than two billion years ago, and the early protein complexes have not been preserved as fossil parts that can be extracted and studied directly.
The main issue is related to the origin of photosynthetic systems. Plants, algae and cyanobacteria use related protein complexes, which means that this branch had a common ancestor. What was the body, which first learned to receive energy from light with the release of oxygen, scientists do not yet know.
To get closer to the answer, biologists are looking for living organisms that could have preserved ancient signs. For a long time, there were few suitable candidates: most modern cyanobacteria are too close to each other and give similar material for comparison. The Gloeobacteria line changed the situation. These photosynthetic bacteria separated from the rest of the cyanobacteria more than two billion years ago.
Gleobacteria do not serve as living fossils literally. Any line passes through mutations, selection and adaptation to the environment. But these bacteria have a set of traits that help restore early stages of the evolution of photosynthesis.
The band's newest representative, Anthocerotbitacter panamensis, was found almost by accident. The plant from the group of anthocerotes was brought from Panama to a laboratory in Ike, New York. When cleaning the surface from the microbial plaque under the microscope, a small green cell was noticed, not similar to conventional cyanobacteria.
The very find of an unknown bacterium did not surprise researchers: the microbial world is still not fully described. But the shape and color of the cell were knocked out of the usual picture. DNA analysis showed that the find refers to gleobacteria. The new species was named Anthocerotibacter panamensis in honor of Panama, where the specimen came from, and the bacterium itself was described in July 2021.
Even among gleobacteria, this type stands out. Anthocerotibacter panamensis separated from the closest known relatives about 1.4 billion years ago. For biologists, such a distance is important: if the key parts of the photosynthetic apparatus have not changed in a huge period, you can look for traces of early oxygen photosynthesis.
The internal device of the bacteria was studied using cryo-electron microscopy. Samples quickly freeze, and then consider cellular structures in detail, without gross destruction of the material. The images showed an important feature: Anthocerotbitacter panamensis has both photo systems, but no tylacoids.
Thilacoids are membrane compartments where plants and most modern cyanobacteria work the main part of the photosynthetic apparatus. In plants, terioids are inside chloroplasts and gather in stacks. Their membranes are covered with proteins and pigments that capture light, transmit energy and conduct electrons further.
Anthocerotibacter panamensis has no internal tilactoid system. Photosystems are located directly in the plasma membrane of the cell. The native species of Gloeoobacter violaceus, discovered in 1974, thilaoids are also absent. So, internal photosynthetic membranes could appear after the separation of gleobacteria from the general line.
In plants and many cyanobacteria, the light is first caught by pigments. The photon passes from the Sun to the Earth about 150 million kilometers, but the shortest part of this path is important for the cell: the energy is transmitted from the molecule to molecule until it gets into the reaction center.
In the photosystem II, the energy of light helps to tear the electrons out of the water molecules. Oxygen comes out as a byproduct, and electrons go into the transfer chain. This chain pumps protons through the membrane and creates a difference that triggers ATP synthase, an enzyme that collects adenosine triphosphate, or ATP.
Then the electrons reach the photosystem I and again receive energy from light. After that, the cell uses them to form the restorative molecules that are needed when assembleing sugars from carbon dioxide. Therefore, two photo systems work as a ligament: one takes electrons from the water, the other helps to direct energy in chemical bonds.
Over the billions of years, the reaction centers of the two photosystems have changed little. Light-processing antennas and additional pigments, on the contrary, the evolution was much more active. Therefore, the early history of photosynthesis is difficult to collect in one scheme: the nucleus of the mechanism is similar in different organisms, and the outer parts are very different.
Even the earliest photosynthetic organism could not just absorb light. The minimum working version had to catch photons, separate electrical charges and send electrons in metabolism. To do this, you need a protein complex with pigments, a reaction center and electron transfer pathways.
The living organisms have different variants of photosynthesis. Some bacteria use one photosystem and do not release oxygen. This process is called anoxigenic, or oxygen-free, photosynthesis. The widespread hypothesis says that the oxygen-free version appeared before the oxygen: first there was one photo system, then the corresponding genes doubled, and one copy eventually gave rise to the second photo system capable of working with water.
Even if the photo system I really appeared first, its early shape still had to be difficult. We needed protein subunits, a reaction center, pigments and antennas. Therefore, Anthocerotibacter panamensis attracted the attention of researchers: the photosystem I in the bacterium works, and some of the surrounding structures are more arranged than most modern cyanobacteria.
Light-gasing antennas Anthocerotibacter panamensis are especially different from the usual scheme. In most modern cyanobacteria, these antennas, or phycobisomas, depart from the tilactoid membrane with a wide semicircle. They consist of proteins and light-absorbing pigments, so help catch more photons.
In Anthocerotbitacter panamensis antenna in shape resembles a paddle. Experiments in 2023 showed that this form reduces the rate of photosynthesis in bacteria. A narrow antenna probably collects fewer photons than a wide fan complex in other cyanobacterias, so the cell receives less energy from light.
Later, a separate group of researchers studied in detail the photo system I in Anthoctortibacter panamensis. Scientists compared different parts of the complex and checked where evolution left an almost unchanged basis, and where they allowed noticeable restructuring.
The reaction center of the photo system, where chlorophyll pigments absorb light and trigger the transfer of electrons, differed from similar complexes of other gleobacteria only in small details. The main frame is preserved almost without large rebuildings. Noticeably more changes were found in light-processing proteins that bind pigments and enter an unusual antenna.
This separation explains a lot. The breakdown in the center of the photo system could destroy the whole process, so the working kernel almost did not change. External parts responsible for collecting light and setting up for the environment, transferred the perestroikas much more freely. For evolution, this is a convenient scheme: to preserve the main mechanism and change the details that help to live in different conditions.
For the reconstruction of early photosynthesis Anthocerotibacter panamensis is valuable precisely by a combination of signs. The bacterium does not have tylacoids, the antenna differs from most modern cyanobacteria, and the central photo system I is close to variants in other gleobacteria. In one living system, you can compare the features similar to ancient ones, and details that appeared later.
With the conclusions you have to be careful. Gleobacteria can not be perceived as a live picture of the world 2.5 billion times ago. After separating from the common ancestor, this line also changed. Any modern bacterium carries traces of selection, loss, adaptations and random changes, so one species does not close the issue of the origin of photosynthesis.
Therefore, researchers are looking for new species of gleobacteria around the world. There is not enough genomic data. We need organisms that can be grown in the laboratory, considered under a microscope and tested in experiments. The more related lines can be found, the more accurate the biologists will separate the ancient signs of Anthocerobibacter panamensis from the features that appeared later.
Particularly important are the types that have responded even earlier. Comparison of several lines will help to restore the order of changes: when an internal membrane system arose, how the antennas changed, how the two photo systems began to work together and which elements remained almost unchanged.
New findings can clarify the long-standing dispute about the procedure for the appearance of photo systems. The most common version begins the story with anoxigenic photosynthesis and attributes the oxygen variant to a later stage. But this scheme has a weak point: there are no direct data that would show how one photosystem would generate another. Both photosystems date back to the common ancestor, and an event where genes could double and disperse in function occurred too long ago.
In the works of 2019 and 2021, a more controversial version was offered: oxygen photosynthesis could have arisen very early, possibly earlier than commonly believed. The point of this idea is not that scientists have already found a ready answer. Rather, the authors show that the usual scenario is too easily turned into a filter for new data. If you count in advance the oxygen-free photosynthesis first, almost any find you want to embed in just such a sequence.
The problem rests with the age of the event. The genetic and protein traces of the first photosystems in billions of years could disappear along with the ancient lines of organisms. Therefore, a dispute cannot be resolved by one comparison of modern DNA or protein sequences. We need new organisms, new structures of photosystems and more examples that will show which parts of the mechanism are really ancient.
The Anthocerotibacter panamensis study does not close this dispute. But the work shows where to look for the following tips. If central photo systems have changed little, and the antennas and membrane structures were rebuilt more actively, the new gleobacteria can become rare landmarks in the history of the process that has changed the Earth’s atmosphere.
There is also a practical meaning for this story. Photosynthesis feeds almost the entire biosphere, but from an engineering point of view does not work too efficiently: plants lose most of the incoming energy at the intermediate stages, enzyme restrictions and protection from excess light. Scientists are trying to improve this process in order to increase crop yields, but it is risky to interfere with a complex photosynthetic chain.
Every second, the flow of solar energy falls to Earth, which is 10 thousand times the energy consumption of modern civilization. People collect the light with panels, store the charge in the batteries and adjust the power grid to the solar generation. Microbes mastered the energy of light billions of years ago, and the byproduct of this process changed the atmosphere of the planet.
About 2.4 billion years ago, some bacteria learned to use light to break down water and collect organic molecules from carbon dioxide. During the reaction, oxygen was released. At first, the gas simply went into the environment, but over time accumulated in the atmosphere and opened the way to organisms that use oxygen to generate energy.
Photosynthesis seems simple only in school textbooks for elementary classes. In the cell there is a thin system of proteins and pigments: some molecules catch photons, others transmit energy further, others conduct electrons through a chain of reactions. The entire mechanism is placed in structures less than one thousandth width of a human hair.
Modern microscopy and cell biology allow you to trace how the electron passes through photosynthetic proteins. With living cells, scientists have dealt in in some detail. With an ancient history, it is more difficult: oxygen photosynthesis appeared more than two billion years ago, and the early protein complexes have not been preserved as fossil parts that can be extracted and studied directly.
The main issue is related to the origin of photosynthetic systems. Plants, algae and cyanobacteria use related protein complexes, which means that this branch had a common ancestor. What was the body, which first learned to receive energy from light with the release of oxygen, scientists do not yet know.
To get closer to the answer, biologists are looking for living organisms that could have preserved ancient signs. For a long time, there were few suitable candidates: most modern cyanobacteria are too close to each other and give similar material for comparison. The Gloeobacteria line changed the situation. These photosynthetic bacteria separated from the rest of the cyanobacteria more than two billion years ago.
Gleobacteria do not serve as living fossils literally. Any line passes through mutations, selection and adaptation to the environment. But these bacteria have a set of traits that help restore early stages of the evolution of photosynthesis.
The band's newest representative, Anthocerotbitacter panamensis, was found almost by accident. The plant from the group of anthocerotes was brought from Panama to a laboratory in Ike, New York. When cleaning the surface from the microbial plaque under the microscope, a small green cell was noticed, not similar to conventional cyanobacteria.
The very find of an unknown bacterium did not surprise researchers: the microbial world is still not fully described. But the shape and color of the cell were knocked out of the usual picture. DNA analysis showed that the find refers to gleobacteria. The new species was named Anthocerotibacter panamensis in honor of Panama, where the specimen came from, and the bacterium itself was described in July 2021.
Even among gleobacteria, this type stands out. Anthocerotibacter panamensis separated from the closest known relatives about 1.4 billion years ago. For biologists, such a distance is important: if the key parts of the photosynthetic apparatus have not changed in a huge period, you can look for traces of early oxygen photosynthesis.
The internal device of the bacteria was studied using cryo-electron microscopy. Samples quickly freeze, and then consider cellular structures in detail, without gross destruction of the material. The images showed an important feature: Anthocerotbitacter panamensis has both photo systems, but no tylacoids.
Thilacoids are membrane compartments where plants and most modern cyanobacteria work the main part of the photosynthetic apparatus. In plants, terioids are inside chloroplasts and gather in stacks. Their membranes are covered with proteins and pigments that capture light, transmit energy and conduct electrons further.
Anthocerotibacter panamensis has no internal tilactoid system. Photosystems are located directly in the plasma membrane of the cell. The native species of Gloeoobacter violaceus, discovered in 1974, thilaoids are also absent. So, internal photosynthetic membranes could appear after the separation of gleobacteria from the general line.
In plants and many cyanobacteria, the light is first caught by pigments. The photon passes from the Sun to the Earth about 150 million kilometers, but the shortest part of this path is important for the cell: the energy is transmitted from the molecule to molecule until it gets into the reaction center.
In the photosystem II, the energy of light helps to tear the electrons out of the water molecules. Oxygen comes out as a byproduct, and electrons go into the transfer chain. This chain pumps protons through the membrane and creates a difference that triggers ATP synthase, an enzyme that collects adenosine triphosphate, or ATP.
Then the electrons reach the photosystem I and again receive energy from light. After that, the cell uses them to form the restorative molecules that are needed when assembleing sugars from carbon dioxide. Therefore, two photo systems work as a ligament: one takes electrons from the water, the other helps to direct energy in chemical bonds.
Over the billions of years, the reaction centers of the two photosystems have changed little. Light-processing antennas and additional pigments, on the contrary, the evolution was much more active. Therefore, the early history of photosynthesis is difficult to collect in one scheme: the nucleus of the mechanism is similar in different organisms, and the outer parts are very different.
Even the earliest photosynthetic organism could not just absorb light. The minimum working version had to catch photons, separate electrical charges and send electrons in metabolism. To do this, you need a protein complex with pigments, a reaction center and electron transfer pathways.
The living organisms have different variants of photosynthesis. Some bacteria use one photosystem and do not release oxygen. This process is called anoxigenic, or oxygen-free, photosynthesis. The widespread hypothesis says that the oxygen-free version appeared before the oxygen: first there was one photo system, then the corresponding genes doubled, and one copy eventually gave rise to the second photo system capable of working with water.
Even if the photo system I really appeared first, its early shape still had to be difficult. We needed protein subunits, a reaction center, pigments and antennas. Therefore, Anthocerotibacter panamensis attracted the attention of researchers: the photosystem I in the bacterium works, and some of the surrounding structures are more arranged than most modern cyanobacteria.
Light-gasing antennas Anthocerotibacter panamensis are especially different from the usual scheme. In most modern cyanobacteria, these antennas, or phycobisomas, depart from the tilactoid membrane with a wide semicircle. They consist of proteins and light-absorbing pigments, so help catch more photons.
In Anthocerotbitacter panamensis antenna in shape resembles a paddle. Experiments in 2023 showed that this form reduces the rate of photosynthesis in bacteria. A narrow antenna probably collects fewer photons than a wide fan complex in other cyanobacterias, so the cell receives less energy from light.
Later, a separate group of researchers studied in detail the photo system I in Anthoctortibacter panamensis. Scientists compared different parts of the complex and checked where evolution left an almost unchanged basis, and where they allowed noticeable restructuring.
The reaction center of the photo system, where chlorophyll pigments absorb light and trigger the transfer of electrons, differed from similar complexes of other gleobacteria only in small details. The main frame is preserved almost without large rebuildings. Noticeably more changes were found in light-processing proteins that bind pigments and enter an unusual antenna.
This separation explains a lot. The breakdown in the center of the photo system could destroy the whole process, so the working kernel almost did not change. External parts responsible for collecting light and setting up for the environment, transferred the perestroikas much more freely. For evolution, this is a convenient scheme: to preserve the main mechanism and change the details that help to live in different conditions.
For the reconstruction of early photosynthesis Anthocerotibacter panamensis is valuable precisely by a combination of signs. The bacterium does not have tylacoids, the antenna differs from most modern cyanobacteria, and the central photo system I is close to variants in other gleobacteria. In one living system, you can compare the features similar to ancient ones, and details that appeared later.
With the conclusions you have to be careful. Gleobacteria can not be perceived as a live picture of the world 2.5 billion times ago. After separating from the common ancestor, this line also changed. Any modern bacterium carries traces of selection, loss, adaptations and random changes, so one species does not close the issue of the origin of photosynthesis.
Therefore, researchers are looking for new species of gleobacteria around the world. There is not enough genomic data. We need organisms that can be grown in the laboratory, considered under a microscope and tested in experiments. The more related lines can be found, the more accurate the biologists will separate the ancient signs of Anthocerobibacter panamensis from the features that appeared later.
Particularly important are the types that have responded even earlier. Comparison of several lines will help to restore the order of changes: when an internal membrane system arose, how the antennas changed, how the two photo systems began to work together and which elements remained almost unchanged.
New findings can clarify the long-standing dispute about the procedure for the appearance of photo systems. The most common version begins the story with anoxigenic photosynthesis and attributes the oxygen variant to a later stage. But this scheme has a weak point: there are no direct data that would show how one photosystem would generate another. Both photosystems date back to the common ancestor, and an event where genes could double and disperse in function occurred too long ago.
In the works of 2019 and 2021, a more controversial version was offered: oxygen photosynthesis could have arisen very early, possibly earlier than commonly believed. The point of this idea is not that scientists have already found a ready answer. Rather, the authors show that the usual scenario is too easily turned into a filter for new data. If you count in advance the oxygen-free photosynthesis first, almost any find you want to embed in just such a sequence.
The problem rests with the age of the event. The genetic and protein traces of the first photosystems in billions of years could disappear along with the ancient lines of organisms. Therefore, a dispute cannot be resolved by one comparison of modern DNA or protein sequences. We need new organisms, new structures of photosystems and more examples that will show which parts of the mechanism are really ancient.
The Anthocerotibacter panamensis study does not close this dispute. But the work shows where to look for the following tips. If central photo systems have changed little, and the antennas and membrane structures were rebuilt more actively, the new gleobacteria can become rare landmarks in the history of the process that has changed the Earth’s atmosphere.
There is also a practical meaning for this story. Photosynthesis feeds almost the entire biosphere, but from an engineering point of view does not work too efficiently: plants lose most of the incoming energy at the intermediate stages, enzyme restrictions and protection from excess light. Scientists are trying to improve this process in order to increase crop yields, but it is risky to interfere with a complex photosynthetic chain.
