Biotechnology adapted to the red planet

NASA, working with other major space agencies, is aiming to send its first human missions to Mars in the early 2030s, while companies like SpaceX may do so even earlier. Astronauts on Mars will need oxygen, water, food, and other consumables. These will have to come from Mars, because importing them from Earth would not be practical in the long run. In Frontiers in microbiology, scientists show for the first time that Anabaena cyanobacteria can be cultivated with only 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 low total pressure, as a source of carbon and nitrogen. Under these conditions, the cyanobacteria have retained their ability to develop in water containing only dust similar to that of Mars and could still be used to feed other microbes. This could help make long-term missions to Mars sustainable, “says lead author Dr Cyprien Verseux, astrobiologist who directs the Applied Space Microbiology Laboratory at the Center for Applied Space Technology and Microgravity (ZARM) at the University of Bremen, Germany.

Low pressure atmosphere

Cyanobacteria have long been targeted as candidates for the biological support of life on 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 that of Earth – 6 to 11 hPa, too low for the presence of liquid water – while the partial pressure of nitrogen gas – 0.2 to 0.3 hPa – is too low for their metabolism. But recreating an Earth-like atmosphere would be expensive: the gases would have to be imported, while the growing system would have to be robust – therefore heavy to carry – to withstand the pressure differences: “Think of a pressure cooker,” says Verseux. The researchers therefore sought a common ground: an atmosphere close to that of Mars which allows cyanobacteria to develop well.

To find suitable atmospheric conditions, Verseux et al. has developed a bioreactor called Atmos (for “Atmosphere Tester for Mars-bound Organic Systems”), in which cyanobacteria can be cultivated in artificial atmospheres at low pressure. All input must come from the red planet itself: apart from nitrogen and carbon dioxide, gases abundant in the Martian atmosphere and water that could be extracted from ice, nutrients should come from “regolith. , The dust covering the Earth-like planets and moons. . Martian regolith has been shown to be rich in nutrients such as phosphorus, sulfur and calcium.

Anabaena: polyvalent cyanobacteria grown on Mars-like dust

Atmos has nine 1L glass and steel containers, each sterile, heated, pressure controlled, and digitally controlled, while the cultures inside are continuously agitated. The authors chose a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, as preliminary tests have shown it to be particularly effective in utilizing Martian resources and helping cultivate other organisms. Closely related species have been shown to be edible, suitable for genetic engineering, and able to form specialized dormant cells to survive harsh conditions.

Poureux 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 lower than on Earth. The cyanobacteria have grown as well as in the ambient air. Then they tested the combination of the modified atmosphere with the regolith. Since no regolith was ever brought from Mars, they used a substrate developed by the University of Central Florida (called “Mars Global Simulant”) to create a growth medium. As controls, the Anabaena were cultured in a standard medium, either in ambient air or under the same artificial atmosphere at low pressure.

Cyanobacteria grew well under all conditions, including regolith under the mixture rich in nitrogen and carbon dioxide at low pressure. As expected, they grew faster on a standard medium optimized for cyanobacteria than on Mars Global Simulant, under either atmosphere. But it remains a major success: while standard media should be imported from Earth, regolith is ubiquitous on Mars. “We want to use the resources available on Mars as nutrients, and only these,” explains Verseux.

The dried biomass of Anabaena has been crushed, suspended in sterile water, filtered and successfully used as a substrate for the growth of E. coli bacteria, proving that sugars, amino acids and other nutrients can be extracted from it to feed other bacteria, which are less robust but proven tools for biotechnology. For example, E. coli could be modified more easily than Anabaena to produce certain food and medicine products on Mars that Anabaena cannot.

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

Other improvements in progress

These results are an important step forward. But the authors warn that more 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 refining the optimum combination of pressure, carbon dioxide and nitrogen for growth, while testing other genera of cyanobacteria, possibly genetically adapted for space missions. A culture system for Mars must also be designed:

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

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The project was funded by the Alexander von Humboldt Foundation.