Biotech suitable for the red planet

NASA, in partnership with other leading space agencies, plans to send its first human missions to Mars in the early 2030s, while companies like SpaceX may be even sooner. Astronauts on Mars need oxygen, water, food and other consumables. These will have to come from Mars, as it would be impractical to import them from Earth in the long run. In Frontiers in Microbiology, scientists show for the first time that Anabaena cyanobacteria can be grown using only local gases, water and other nutrients and under 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 atmosphere of Mars, at a low total pressure, as their source of carbon and nitrogen. Under these conditions, cyanobacteria retained their ability to grow in water containing only Martian dust. and are used to feed other microbes, which could help make long-term missions to Mars sustainable, ” said lead author Dr. the University of Bremen, Germany.

Low pressure atmosphere

Cyanobacteria have long been the target of candidates to boost biological life support during space missions, as all species produce oxygen through photosynthesis, while some can bind atmospheric nitrogen into nutrients. One difficulty is that they cannot grow directly in the atmosphere of Mars, where the total pressure is less than 1% 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: gases would have to be imported, while the culture system would have to be robust – and therefore heavy on cargo – to withstand the pressure differences: “Think of a pressure cooker,” says Verseux. So the researchers looked for a middle ground: an atmosphere close to that of Mars in which the cyanobacteria can grow well.

To find suitable atmospheric conditions, Verseux et al. Developed a bioreactor called Atmos (for “Atmosphere Tester for Mars-bound Organic Systems”), in which cyanobacteria can be grown under low pressure in artificial atmospheres. Every input must come from the Red Planet itself: in addition to nitrogen and carbon dioxide, gases abundant in the atmosphere of Mars and water that can be extracted from ice, nutrients must come from “regolith,” the dust that makes up Earth-like planets and mane covered. . Regolith from Mars has been shown to be rich in nutrients such as phosphorus, sulfur and calcium.

Anabaena: Versatile cyanobacteria grown on Martian dust

Atmos has nine 1-liter glass and steel vessels, each sterile, heated, pressure-controlled and digitally monitored, while continuously stirring the cultures inside. The authors chose a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, because preliminary tests showed it would be particularly good at using Martian resources and helping other organisms grow. Closely related species have been shown to be edible, capable of genetic engineering, and able to form specialized dormant 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 lower than on Earth. The cyanobacteria both grew under ambient air. They then tested the combination of the modified atmosphere with regolith. Since regolith was never brought from Mars, they instead used a substrate developed by the University of Central Florida (called “Mars Global Simulant”) to create a growth medium. As controls, Anabaena were grown in standard medium, either at ambient air or under the same artificial low pressure atmosphere.

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

Dried Anabaena biomass was ground, suspended in sterile water, filtered and successfully used as a substrate for cultivating E. coli bacteria, proving that sugars, amino acids and other nutrients can be extracted from it to feed other bacteria, which are less are robust yet proven biotechnology tools. For example, E. coli could be more easily manipulated than Anabaena to produce certain food and drugs on Mars that Anabaena cannot.

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

Further refinements in the pipeline

These results are an important step forward. 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 efficiently on Mars,” says Verseux. They propose optimizing the combination of pressure, carbon dioxide and nitrogen for growth, while testing other types of cyanobacteria, perhaps genetically tuned for space missions. A cultivation 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 on Earth the conditions we would provide there. But our results will help design a culture system on Mars. means that we can develop a lighter construction that is easier to transport because it does not have to withstand major differences between indoors and outdoors, ”concludes Verseux.

The project was funded by the Alexander von Humboldt Foundation.