Biotechnology suitable for the Red Planet

NASA, in collaboration with other top space agencies, aims to send its first human missions to Mars in the early 2030s, while companies like SpaceX could do so even earlier. Astronauts on Mars will need oxygen, water, food and other supplies. These will have to be obtained from Mars, as their importation from Earth would be impractical in the long run. In the Frontiers 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 biological systems that support biological life.

“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, cyanobacteria have retained their ability to grow in water containing only Mars-like dust and could This could help sustain long-term missions to Mars, “says lead author Dr. Cyprien Verseux, an astrobiologist who heads the Laboratory of Applied Space Microbiology 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 to support biological life in space missions, as all species produce oxygen through photosynthesis, while some can fix atmospheric nitrogen into nutrients. One difficulty is that they cannot rise directly in the Martian atmosphere, where the total pressure is less than 1% of that 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 – is too low for their metabolism. But recreating an Earth-like atmosphere would be costly: gas would have to be imported, while the cropping system would have to be robust – therefore difficult to transport – to withstand pressure differences: “Think of a pressure cooker. Says Verseux. Thus, the researchers looked for a middle ground: an atmosphere close to that of Mars, which allows cyanobacteria to grow well.

To find suitable atmospheric conditions, Verseux et al. developed a bioreactor called the Atmos (for the “Atmosphere Tester for Mars-Related Organic Systems”), in which cyanobacteria can be grown in artificial atmospheres at low pressure. Any input must come from the Red Planet itself: in addition to nitrogen and carbon dioxide, abundant gases in the Martian atmosphere, and water that could be extracted from ice, nutrients should come from “regolith,” the dust that covers the planets. and Earth-like months. Martian rule 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 vessels made of glass and steel, each of which is sterile, heated, pressure controlled and digitally monitored, while the indoor cultures are continuously stirred. The authors chose a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, as preliminary tests have shown that it would be particularly good at using Martian resources and helping other organisms grow. 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 raised 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. Cyanobacteria grew as well as under ambient air. Then they tested the combination of the modified atmosphere with the regolith. Because no regolith has ever been brought from Mars, they have instead used a substrate developed by the University of Central Florida (called the “Mars Global Simulant”) to create a growth environment. As controls, Anabaena were grown in standard environment, either in ambient air or under the same low-pressure artificial atmosphere.

Cyanobacteria grew well under all conditions, including regolith under a mixture of nitrogen and carbon dioxide at low pressure. As expected, they grew faster on a standard environment optimized for cyanobacteria than on Mars Global Simulant, in both atmospheres. But this is still a major success: while the standard environment should be imported from Earth, the rule is ubiquitous on Mars. “We want to use as nutrients the resources available on Mars and only on them,” says Verseux.

The dried Anabaena biomass was ground, suspended in sterile water, filtered and successfully used as a substrate for the growth of E. coli bacteria, demonstrating that sugars, amino acids and other nutrients can be extracted from them to feed other bacteria, which are less tools. resistant but tested 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 oxygen-producing cyanobacteria that fix nitrogen can be efficiently grown on Mars at low pressure under controlled conditions, with exclusively local ingredients.

Additional pipe improvements

These results represent an important advance. However, 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 optimal combination of pressure, carbon dioxide and nitrogen for growth, while testing other genera of cyanobacteria, perhaps genetically adapted for space missions. A Mars cultivation system must also be designed:

“Our bioreactor, Atmos, is not the cultivation system we would use on Mars: it is meant to test, on Earth, the conditions we would provide there. But our results will help guide the design of a Martian cultivation system. “For example, lower pressure means that we can develop a lighter structure that is easier to transport because 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.