Biotech suitable for the Red Planet

NASA, in collaboration with other leading space agencies, intends to send its first human missions to Mars in the early 2030s, while companies like SpaceX may do so even earlier. Astronauts on Mars need oxygen, water, food and other consumables. It will have to be obtained from Mars, because its importation from Earth will 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 at low pressure. This makes it much easier to develop sustainable biological life support systems.

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

Low pressure atmosphere

Cyanobacteria have long been targeted as candidates to drive biological life support for space emissions, as all species produce oxygen through photosynthesis, while some can dissolve atmospheric nitrogen into nutrients. One problem is that they cannot grow directly in the atmosphere of Mars, 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 partial pressure of nitrogen gas – 0.2 to 0.3 hPa – are too low for their metabolism. But recreating an earth-like atmosphere will be costly: gases must be introduced, while the culture system must be robust – hence heavy to load – to withstand the pressure differences: “Think of a pressure cooker,” says Verseux. The researchers were therefore looking for a middle ground: an atmosphere near Mars that allows the cyanobacteria to grow well.

To find suitable atmospheric conditions, Verseux et al. develops a bioreactor called Atmos (for “Atmosphere Tester for Mars-bound Organic Systems”), in which cyanobacteria can be grown in artificial atmospheres at low pressure. Any input must come from the Red Planet: in addition to nitrogen and carbon dioxide, gases abundant in the Martian atmosphere, and water that can be extracted from ice, nutrients must come from ‘regolith’, the substance that covers Earth-like planets and moons. . The regolith of Mars has been shown to be rich in nutrients such as phosphorus, sulfur and calcium.

Anabaena: versatile cyanobacteria that grow on Martian matter

Atmos has nine 1 L barrels of glass and steel, each sterile, heated, pressure-controlled and digitally monitored, while constantly stirring the cultures inside. The authors selected a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, because preliminary tests have shown that it would be particularly good to use Mars resources and to grow other organisms. Closely related species have been shown to be edible, suitable for genetic engineering and capable of forming specialized resting cells to survive difficult conditions.

Verseux and his colleagues cultivated Anabaena for ten 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 grew under the ambient air as well. Then they tested the combination of the modified atmosphere with regolith. Because a regolith was never 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, Anabaena was grown in standard medium, either in the air or under the same artificial atmosphere under low pressure.

The cyanobacteria have grown well under all conditions, including in regolith under the nitrogen- and carbon dioxide-rich mixture under low pressure. As expected, they grew faster on standard medium optimized for cyanobacteria than on Mars Global Simulant, under any atmosphere. But it is still a great success: although standard medium must be imported from Earth, regolith is ubiquitous on Mars. “We want to use resources on Mars as nutrients, and only those,” Verseux says.

Dried Anabaena biomass has been 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 it to kill other bacteria, which are less nourish. hardy but proven tools for biotechnology. E. coli, for example, can be more easily designed than Anabaena to produce food products and medicines on Mars that Anabaena cannot.

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

Further refinement in the pipeline

These results are an important advance. 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 that the combination of pressure, carbon dioxide and nitrogen be optimally tuned to grow, while testing other genera of cyanobacteria, perhaps genetically modified for space shipments. A breeding system for Mars must also be designed:

“Our bioreactor, Atmos, is not the cultivation system we would use on Mars; it is meant to test the conditions on earth we would offer there. But our results will help guide the design of a Mars cultivation system. “The lower pressure means we can develop a lighter structure that can be transported more easily, as it does 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.