Biotechnology suitable for the red planet

NASA, in collaboration with other leading space agencies, aims to send its first human missions to Mars in the early 2030s, while companies like SpaceX can do so even earlier. Astronauts on Mars will need oxygen, water, food and other consumables. These will have to come from Mars, because importing from Earth would be impractical in the long run. In Frontiers in microbiology, scientists show for the first time that Anabaena cyanobacteria can be grown only with local gases, water and other nutrients and at low pressure. This makes it much easier to develop sustainable biological life support systems.

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

Low pressure atmosphere

Cyanobacteria have been targeted by candidates to boost life support in space missions, as all species produce oxygen through photosynthesis, while some can fix atmospheric nitrogen into nutrients. One difficulty is that they cannot grow directly in the Martian atmosphere, where the total pressure is less than 1% of the Earth (6 to 11 hPa, too low for the presence of liquid water), while the pressure Partial nitrogen nitrogen is 0.2 to 0.3 hPa: it is too low for its metabolism. But recreating an Earth-like atmosphere would be costly: gases would have to be imported, while the cropping system would have to be robust (hence heavy for freight transport) to withstand pressure differences: “Think of a pressure cooker. “says Verseux. So the researchers looked for a midpoint: an atmosphere close to that of Mars that would allow cyanobacteria to grow well.

To find the right atmospheric conditions, Verseux et al. developed a bioreactor called Atmos (for “Atmosphere Tester for Mars-bound Organic Systems”), in which cyanobacteria can be grown in low-pressure artificial atmospheres. Any input must come from the red planet itself: apart from nitrogen and carbon dioxide, the abundant gases in the Martian atmosphere, and the water that could be extracted from the ice, the nutrients should come from the “regolith,” the dust covering Earth-like planets and 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 1L glass and steel containers, each of which is sterile, heated, pressure-controlled and digitally controlled, while indoor crops are continuously stirred. The authors chose a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, because preliminary tests showed that it would be especially good to use Martian resources and help grow other organisms. Closely related species have been shown to be edible, genetically engineered, and capable of forming specialized latent cells to survive harsh conditions.

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

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

Dried Anabaena biomass was ground, suspended in sterile water, filtered and successfully used as a substrate for the culture of E. coli bacteria, demonstrating that sugars, amino acids and other nutrients can be extracted by feed other bacteria, which are less resistant but proven tools for biotechnology. For example, E. coli could be more easily designed than Anabaena to produce some food and medicine on Mars that Anabaena cannot.

The researchers conclude that nitrogen-fixing, oxygen-producing cyanobacteria can be efficiently grown on Mars at low pressure under controlled conditions, with exclusively local ingredients.

More improvements to the pipe

These results are an important breakthrough. But the authors warn that additional studies are needed: “We want to move from this proof of concept to a system that can be used on Mars efficiently,” says Verseux. They suggest refining the optimal combination of pressure, carbon dioxide and nitrogen for growth, while testing other genera of cyanobacteria, perhaps genetically adapted for space missions. A cropping system for Mars must also be designed:

“Our bioreactor, Atmos, is not the culture system we would use on Mars: it is intended to test the conditions we would provide on Earth. But our results will help guide the design of a Martian culture system. For example, lower pressure means we can develop a lighter structure that can be transported more easily, as it will not have to withstand large differences between inside and outside, ”concludes Verseux.

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The project was funded by the Alexander von Humboldt Foundation.