Having discovered the mechanism by which animals, like plants, carry out photosynthesis, scientists thought about the possibility of transferring a person to a full supply of solar energy.
Imagine what it would be like if people, like plants, could feed directly on solar energy. It would definitely make our life easier: the countless hours spent shopping, preparing and eating food could be spent on something else. Over-exploited agricultural land would return to natural ecosystems. The levels of hunger, malnutrition and disease spreading through the digestive tract would plummet.
However, humans and plants have not shared a common ancestor for hundreds of millions of years. Our biology is fundamentally different in almost every aspect, so it might seem like there is no way to design humans to do photosynthesis. Or is it still possible?
This problem is being thoroughly studied by some specialists in synthetic biology, who even tried to create their own plant-animal hybrids. While we are still far from creating a human being capable of photosynthesis, new research has uncovered an intriguing biological mechanism that could contribute to the development of this nascent field of science.
Recently, representatives of the Marine Biological Laboratory, located in the American village of Woods Hall, reported that scientists have solved the secret of Elysia chlorotica - a brilliant-green sea slug that looks like a plant leaf, feeds on the sun like a leaf, but is actually an animal.
It turns out that Elysia chlorotica maintains such a bright color by consuming algae and taking their genes for photosynthesis. It is the only known example of a multicellular organism to assign DNA from another organism.
Elysia chlorotica is a species of small sea slug that belongs to the marine gastropod molluscs. This is an animal capable of photosynthesis like plants.
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In a statement, co-author of the study, professor emeritus at the University of South Florida Sidney K. Pearce said: “It is impossible on Earth for genes in algae to function inside an animal's cell. And yet it happens. They allow the animal to get its nourishment from the sun. According to scientists, if people wanted to hack their own cells to make them capable of photosynthesis, a similar mechanism could be used to do this.
With regard to solar energy, we can say that people have been moving in the wrong evolutionary direction for a billion years. As the plants became thin and translucent, the animals became thick and opaque. Plants get their small but constant share of the sun's sap, while staying in one place, but people like to move, and for this they need energy-rich food.
If you look at the cells and the genetic code of humans and plants, it turns out that we are not that different. This striking similarity of life at its fundamental levels allows unusual things like the theft of photosynthesis by animals to happen. Today, thanks to the growing field of synthetic biology, we can be able to reproduce such phenomena in one evolutionary instant, making biopunk ideas for creating photosynthetic skin patches seem less fantastic.
According to Peirce, “Usually, when genes from one organism are transferred into cells of another, it does not work. But if it works, it can change a lot overnight. It's like accelerated evolution."
Sea slugs are not the only animals capable of photosynthesis through symbiotic relationships. Other classic examples of such creatures are corals, which store photosynthetic dinoflagellates in their cells, and spotted salamander, which uses algae to supply its embryos with solar energy.
However, sea slugs differ from similar animals in that they have found a way to exclude intermediaries and perform photosynthesis only for themselves, absorbing chloroplasts from algae and covering the walls of their digestive tract with them. After that, the hybrid of an animal and a plant can live for months, feeding only on sunlight. But how exactly the slugs maintain their stolen solar factories has remained a mystery until now.
Now Peirce and other study co-authors have found the answer to this question. It seems that slugs not only steal chloroplasts from algae, but also steal important DNA codes. In an article published in The Biological Bulletin, it appears that a gene that codes for an enzyme used to repair chloroplasts can help the slugs keep solar machines running long after eating algae.
Genetic expropriation may be rare in nature, but scientists have been experimenting with it in laboratories for years. By transferring genes from one organism to another, humans have created many new life forms, from corn, which produces its own pesticides, to plants that glow in the dark. With all of this in mind, is it crazy to think that we should follow nature's lead and endow animals - or even humans - with the ability to photosynthesize?
Biologist, designer, and writer Christina Agapakis, a PhD in synthetic biology from Harvard, has spent a lot of time pondering how to create a new symbiosis in which animal cells can photosynthesize. According to Agapakis, billions of years ago, plant ancestors absorbed chloroplasts, which were free-living bacteria.
Agapakis said the problem with creating a sun-eating organism is that a very large surface is needed to absorb enough sunlight. With the help of leaves, plants manage to absorb a huge amount of energy, relative to their size. Fleshy people, with their surface-to-volume ratio, most likely do not have the necessary carrying capacity.
“If you are wondering if you can acquire the ability to photosynthesize, my answer is that, firstly, you have to completely stop moving, and secondly, you have to become completely transparent,” says Agapakis, according to whose calculations, for photosynthesis, every human cell will need thousands of algae …
In fact, the sunshine-eating Elysia chlorotica may be the exception that proves the rule. The slug began to look and behave so much like a leaf that in many ways it became more a plant than an animal.
But even if a person cannot subsist on the sun alone, who said that from time to time he cannot supplement his diet with a small sun snack? In fact, most photosynthetic animals, including several of Elysia chlorotica's relatives, rely on more than just energy from the sun. They use their photosynthetic mechanism as a backup generator in case of food shortages. Thus, the ability to photosynthesize is insurance against hunger.
Perhaps humans could find a completely new application for photosynthesis. For example, according to Agapakis, “there might be green spots on human skin - a sun-activated wound healing system. Something that doesn't require as much energy as a person needs."
In the near future, a person will not be able to completely switch to providing only one sunlight - at least until he decides on cardinal modifications of the body - therefore, for now, we just have to continue to be inspired by the example of nature.