Biotechnology suitable for the Red Planet

PICTURE: A: Atmosphere of the bioreactor (“Atmospheric tester for the Mars-related organic system”). B: One ship in Atmos. C: Schematic representation of the design more

Credit: C. Verseux / ZARM

NASA, in collaboration with other leading space agencies, wants to send its first human missions to Mars in the early 2030s, while companies like SpaceX could do so earlier. Astronauts on Mars will need oxygen, water, food and other supplies. They would have to procure them from Mars, because importing them from Earth would be impractical in the long run. In Boundaries in microbiology, scientists show for the first time that Anabaena cyanobacteria can only be grown with local gases, water and other nutrients and under low pressure. This greatly facilitates the development of sustainable biological life support systems.

“Here we show that cyanobacteria can use gases available in the Martian atmosphere, at low total pressure, as a source of carbon and nitrogen. Under these conditions, cyanobacteria have retained the ability to grow in water containing only Mars-like dust and can still be used to feed other microbes “It could help in long-term missions to Mars, sustainable,” says lead author Dr. Cyprien Verseux, an astrobiologist who runs the Laboratory for Applied Space Microbiology at the Center for Applied Space Technology and Microgravity (ZARM), University of Bremen, Germany.

Low pressure atmosphere

Cyanobacteria have long been targeted as candidates to promote biological life support in space missions, as all species produce oxygen by photosynthesis, while some can fix atmospheric nitrogen to nutrients. The difficulty is that they cannot grow directly in the Martian atmosphere, where the total pressure is less than 1% of Earth’s – 6 to 11 hPa, too low for the presence of liquid water – while the partial pressure of nitrogen gas is 0.2 to 0.3 hPa – too low is for their metabolism. But re-creating an Earth-like atmosphere would be expensive: gases should be introduced, while the culture system should be robust – therefore, heavy to load – to resist pressure differences: “Imagine a pressure cooker,” Verseux says. So the researchers were looking for an environment: an atmosphere close to Mars that allows cyanobacteria to grow well.

To find suitable atmospheric conditions, Verseux et al. developed a bioreactor called the Atmos (for “Atmospheric Organizer for the Organic System Connected to Mars”), in which cyanobacteria can be grown in an artificial atmosphere under low pressure. Any intake must come from the Red Planet itself: apart from nitrogen and carbon dioxide, gases abundant in the Martian atmosphere and water that can be extracted from ice, nutrients should come from “regolith”, dust that covers planets and Earth-like moons. . Martian regolith has been shown to be rich in nutrients such as phosphorus, sulfur and calcium.

Anabaena: versatile cyanobacteria grown on Mars-like dust

Atmos has nine 1 L containers made of glass and steel, each of which is sterile, heated, pressurized and digitally monitored, while the cultures in it are constantly mixed. The authors chose a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, because preliminary tests have shown that it would be especially good to use Martian resources and help in the cultivation of other organisms. Closely related edible have been shown to be edible, genetically engineered, and capable of forming specialized dormant cells to survive harsh conditions.

Verseux and his colleagues first grew Anabaena for 10 days in a mixture of 96% nitrogen and 4% carbon dioxide at a pressure of 100 hPa – ten times lower than on Earth. Cyanobacteria grew as well as under ambient air. They then tested a combination of a modified atmosphere with regolith. Since no regolith was ever brought from Mars, they instead used a substrate developed by the University of Central Florida (called the “Mars Global Simulant”) to create a medium for growth. As a control, Anabaena was grown in standard medium, either in ambient air or in the same artificial atmosphere under low pressure.

Cyanobacteria grew well in all conditions, including regolith in a mixture rich in nitrogen and carbon dioxide at low pressure. As expected, they grew faster on a standard medium optimized for cyanobacteria than on the Mars Global Simulant, in any atmosphere. But this is still the main success: although the standard medium should be imported from Earth, regolith is ubiquitous on Mars. “We want to use as nutrients available on Mars, and only those,” Verseux says.

Dried Anabaena biomass is ground, suspended in sterile water, filtered and successfully used as a substrate for the cultivation of E. coli bacteria, proving that sugars, amino acids and other nutrients can be extracted from them to feed other bacteria that are less durable but proven tools. for biotechnology. For example, E. coli can be constructed more easily than Anabaena to produce some food and medicine on Mars that Anabaena cannot.

The researchers conclude that cyanobacteria that produce oxygen and produce oxygen can be efficiently grown on Mars under controlled conditions, with exclusively local ingredients.

Further training in preparation

These results are important advances. But the authors warn that further studies are needed: “We want to move from this proof of concept to a system that can be used effectively on Mars,” says Verseux. They suggest fine-tuning the combination of pressure, carbon dioxide and nitrogen optimal for growth, while testing other genera of cyanobacteria, perhaps genetically adapted for space missions. It is necessary to design a breeding system for Mars:

“Our Atmos bioreactor is not the breeding system we would use on Mars: it should test the conditions we would provide there on Earth. But our results will help guide the design of the Martian breeding system. For example, lower pressure means we can develop a lighter structure. it is easier to transport, because it will not have to withstand large differences between and inside, ”concludes Verseux.

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The project was funded by the Alexander von Humboldt Foundation.

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