Science fiction stories have imagined future people living in underground cities on Mars, in hollowed-out asteroids, and in floating space stations far from the sun. But if humans are ever going to survive in one of these harsh, alien environments, they’ll need ways to grow food using limited resources — and photosynthesis, the hugely efficient but energy-inefficient process by which plants turn sunlight into sugar, might not cut it. .
Now some scientists are wondering if it’s possible to produce food more efficiently by skipping photosynthesis altogether and growing plants in the dark.
The idea sounds as science fiction as cities on Mars. But a team of researchers has taken a first step towards its realization with a study published in natural food in June. Research shows that it’s possible to grow algae, edible yeast and fungus-producing fungi in the dark by feeding them a carbon-based compound called acetate that doesn’t come from plants, but was made using solar electricity. Scientists hope that this method, a type of “artificial photosynthesis”, could open up new ways to produce food using less physical space and energy than traditional agriculture, including, perhaps, crops that can grow in the dark.
While other experts are skeptical that plant biology can be so radically redesigned, they are excited about the technology invented by the researchers and the team’s brainchild of how to make food production more efficient. .
“We need to find ways to grow plants more efficiently,” says study co-author Feng Jiao, a professor of chemical and biomolecular engineering at the University of Delaware. “Who [solution] is the best? I think the beauty of science is that we explore all the possibilities.
More efficient than nature
With the exception of a few extreme environments such as deep-sea hot springs, which are powered by the chemical energy of hydrogen sulfide bubbling up in cracks in the seafloor, all life on Earth is powered by the sun. Even top predators like tigers and sharks are part of complex food webs that trace back to plants and, in the oceans, to tiny green algae. These so-called primary producers have a biological superpower: the ability to create organic carbon from carbon dioxide via photosynthesis, a biochemical process fueled by sunlight.
But while photosynthesis is essential to life as we know it, it’s not very efficient: only about one percent of the sunlight that falls on plants is actually captured and used to make organic carbon. This inefficiency will pose a challenge if humans are ever to establish a self-sustaining presence in space, where it will be vital to produce food using as few resources as possible.
It’s also a problem on Earth today as the human population increases, putting pressure on farmers to get more calories from the same land.
Some scientists believe the solution is to genetically modify crops for more efficient photosynthesis. The researchers behind the new study propose something more unusual: replacing biological photosynthesis with a partially artificial process to turn sunlight into food. Their process is a version of artificial photosynthesis, a term that has been around for years and encompasses various approaches to converting sunlight, water and CO2 into liquid fuels and chemicals like formate, methanol and ethanol. hydrogen. The researchers behind the new study say their work represents the first time that an artificial photosynthesis system has been combined with an attempt to culture common food-producing organisms.
Their system is based on electrolysis or using an electric current to cause chemical reactions in a device called an electrolyzer. In their recent study, the researchers created a two-stage solar electrolyzer system that converts carbon dioxide and water into oxygen and acetate, a simple carbon-based compound.
The authors then introduced this acetate into Chlamydomonas reinhardtii, a photosynthetic green algae. They also gave acetate to nutritional yeast and mushroom-producing fungi, which do not photosynthesize themselves but generally need organic carbon made by plants to grow.
All of these organisms were able to take up acetate and grow in the dark, independent of sunlight or photosynthesis-derived carbon.
Compared to photosynthesis, the process was surprisingly efficient. Using artificial photosynthesis, green algae could convert solar energy into biomass about four times more efficiently than crops using biological photosynthesis. Yeast grown using this process was nearly 18 times more energy efficient than cultures.
“This is one of the main advantages of using artificial pathways over natural pathways,” says Jiao.
Growing crops in the dark?
Scientists already knew that the algae C. reinhardtii can grow on acetate in the dark – the organism is a mixotroph, meaning it can switch between making its own food through photosynthesis or eating organic carbon produced by other plants. But according to the study’s lead author, Robert Jinkerson of the University of California, Riverside, this is the first time C. reinhardtii was grown on acetate that did not come from recent photosynthesis or petroleum products, which are the fossil remains of ancient photosynthesis. It is significant.
“This is the first time that a photosynthetic organism, such as an algae or a plant, has grown independently of photosynthesis since its evolution,” says Jinkerson. “It’s completely decoupled.”
After growing algae without photosynthesis, the researchers turned to a more difficult question: Could they also grow cultivated plants?
Their first results are encouraging. In the dark, the researchers grew lettuce tissue in a liquid suspension containing acetate, confirming that it can absorb and metabolize an externally supplied carbon source.
And when they grew whole lettuce plants in the light (along with rice, canola, tomato, and several other crop species), but fed them extra acetate, they got discovered that plants incorporated acetate into their tissues. Acetate labeled with a heavy carbon isotope called carbon-13 could be traced to both amino acids and sugars, suggesting that plants can use it to support a variety of metabolic processes.
However, the study did not show that whole plants can be grown entirely on acetate without access to sunlight – in fact, the researchers’ experiments with lettuce indicated that too much acetate actually inhibits plant growth. plants. Jinkerson says his lab is currently working on genetic engineering and breeding plants to be more acetate tolerant. This will be necessary for the team’s artificial photosynthesis method to significantly support plant growth and food production.
Emma Kovak, a food and agriculture analyst at the Breakthrough Institute, says the authors’ findings represent a “first step toward the potential use of acetate to help feed plants for indoor production.” This could reduce the energy needed to run indoor farms if it allows growers to reduce indoor light levels. But “massive progress would be needed,” says Kovak, to allow plants to grow robustly using acetate, even in low light conditions.
Evan Groover, a synthetic biology doctoral student at the University of California, Berkeley, whose research focuses on genetically engineering plants to enhance photosynthesis, agrees.. The study “shows that plants can take up acetate, but it doesn’t prove that they are able to really thrive or synthesize food, fuel or drugs in any meaningful way,” Groover says. Accomplishing the latter, he says, would require “a complete reprogramming of factories.”
At the same time, Groover says he found the authors’ article “uplifting.”
“It shows us how we could capture light and carbon in weird, non-terrestrial environments, or environments where you can’t do traditional agriculture,” he says.
Food for deep space
An extraterrestrial environment could be where the researchers’ technology is first applied. The researchers submitted their concept of artificial photosynthesis to NASA’s Deep Space Food Challenge, which awards prizes and recognition to groups with innovative ideas for feeding astronauts on long-term space missions. Last fall, the team concept was named one of 18 US-based Phase 1 winners. In phase 2, these teams must build a prototype that actually produces food. The winners will be announced next year.
Winning the competition does not guarantee that a new food production technology will be piloted on a future space mission. Many technical details would need to be worked out first, says Lynn Rothschild, principal investigator at NASA’s Ames Research Center, who was not involved in the new study. Weight is a key factor – and artificial photosynthesis would likely require carrying new equipment, including additional solar panels and electrolysers, into space.
But Rothschild says it’s worth keeping an open mind about how any effort to redesign a fundamental biological process like photosynthesis might be applied, in space or on Earth: “The payoff can be anything that we haven’t imagined yet.”