Finding novel ways to generate helpful compounds from the waste products of astronauts will enable them to sustain travel into deep space.
A tiny organism has big potential to produce both life-sustaining food and construction materials for astronauts on their long journey to Mars.
Yeast strains of Yarrowia lipolytica that naturally like to feed on urine have been bioengineered to produce omega-3 fatty acids, which are essential to human health, as well as polyesters that can be made into moldable shapes.
Generating tools and products from waste compounds is more efficient for a space mission than stockpiling food and supplies, which take up precious cargo room and require extra fuel to escape Earth’s gravity. But the innovation could also serve people on Earth in places where resources are limited, said Mark Blenner, an assistant professor of chemical and biomolecular engineering at Clemson University.
“In poorer countries, we think this might be an interesting way to reduce waste production,” Blenner told Seeker.
A yeast-based system could make good economic sense for remote military bases, too, where the price of fuel to ship supplies can cost hundreds of dollars per gallon.
In lab experiments, Blenner and his team used the genetically engineered yeast to produce 50 mg of omega-3s and 250 mg of plastic. The results, presented this week at the 254th National Meeting & Exposition of the American Chemical Society, are a proof-of-concept demonstration that yeast could play an important role in the future of space travel.
“Space is the ultimate resource-poor environment,” Blenner remarked.
His lab has been working with Yarrowia lipolytica for years because it’s been well-studied in scientific experiments and is a type of yeast that likes to feed on a wide range of compounds. In nature, strains of Yarrowia lipolytica tend to grow on cheese, and it has also been found growing on oil spills.
The yeast also likes feeding on urea, a compound in urine. Urine from astronauts is already collected in spacecraft like the International Space Station, where it’s filtered and turned into drinking water. The unused parts, like urea, could be fed to yeast.
Under normal conditions, yeast produces fatty acids, but not the kind that are essential to humans. Using gene-editing tools, including CRISPR-Cas 9 — which allows scientists to remove and replace genetic material from DNA — Blenner and his team added four genes to the yeast to get it to produce omega-3 fatty acids, which are necessary for heart, eye, and brain health.
The researchers also performed additional genetic engineering to increase the flow of carbon in the cell, which promotes the accumulation of the omega-3s there, and to block cell functions that cause the yeast to consume the omega-3s it has produced.
In addition to urea, the yeast need sugar and carbon to produce the omega-3s. For the purposes of this experiment, Blenner and his colleagues found that photosynthesizing bacteria, called cynobacteria, were a good source of these additional compounds. These bacteria convert CO2 to energy to live and can be cultivated in vats, much like algae.
On a spaceship, the cynobacteria would be suspended in a solution of trace salts and nutrients and grown in a vessel. Carbon dioxide from the air, generated by the exhalations of astronauts, would be piped into the vat, which the cynobacteria would feed on and convert into sugars. When it came time to feed the yeast, the astronauts would heat the cynobacteria to break down its cellular structure and release the sugars, which would be mixed with urea in a solution and fed to the yeast in a separate vessel.
As the yeast grow, they’d create the omega-3 fatty acids, which store up inside their cell walls. Ideally the yeast would be engineered to accumulate a large percentage of their body weight as omega-3s. How they’d be consumed is still an outstanding question.
“They’re full of protein and amino acids and omega-3s,” said Blenner. “You could technically eat that, as long as the astronauts would like the taste of it, which is a question.”
On Earth, the yeast could be dried and crushed up and turned into feedstock for fish farms, where sources of protein are becoming increasingly depleted along with wild fish populations.
Using similar gene-editing techniques, Blenner and his team have also gotten the yeast to produce molecules that link together inside the yeast to form polyester polymers. These accumulate inside the yeast as tiny granules. If the scientists can figure out a way to get the yeast to store up large amounts of these granules, the organisms could be mixed with a solution and turned into a kind of plastic ink for a 3D printer that is capable of printing a variety of components, whether in space or here at home.
A similar process could be adopted by military outposts in remote areas to print a range of parts to keep the base operating.
How astronauts would ultimately use these items in space remains an open question for Blenner. One thing he’s sure of, though, is that the systems cannot be complicated.
“The more complicated the system, the more modes of failure there are,” he said. “And the more modes of failure there, are the more likely it is that something will fail.
When you’re millions of miles from Earth, failure isn’t an option.
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