Astronauts need nutrition on longer space flights. One potential source? Their urine

You can’t get fresh salmon in space, but astronauts may one day be able to get the vital nutrients the fish provide — by recycling their urine and exhaled breaths.

Chemical engineers at Clemson University are bioengineering yeast to use human urine and breath to make omega-3 fatty acids, the vitamins humans need for heart, eye, and brain health that are found in fish such as salmon. It’s still in the early stages — and there are some significant hurdles to clear — but the process could one day be used to simultaneously recycle waste and keep astronauts healthy on multiyear space missions. The researchers will present their results Tuesday at the American Chemical Society’s annual meeting.

Mark Blenner, a biomolecular engineer at Clemson, received funding from NASA in 2015 for his research on Yarrowia lipolytica, a cousin of baker’s yeast that is good at making and storing large amounts of fatty acids and lipids.

“I like to say they’re a lot like I am, so they eat too much, and they want to store that as fat for later,” Blenner said.

The space agency was seeking ways to allow astronauts to spend more time in space on far-off missions. Blenner and his team borrowed genes from algae and phytoplankton, tiny marine organisms that excel at making omega-3s. They inserted those genes into yeast DNA, successfully engineering the yeast to produce some of the more important omega-3s for human health. Now, they’re tinkering with the yeast to get them to produce larger, more useful quantities of omega-3s.

To churn out omega-3s, yeast require a constant stream of nitrogen and carbon, which are readily available on Earth, but hard to come by on a space shuttle. That forced Blenner and his colleagues to think more creatively.

“You have to figure out, how do you basically start to recycle all the things you’ve brought with you for other needs?” he said.

Their answer? Astronaut waste. Specifically, urine and the carbon dioxide exhaled with every breath. In a manuscript submitted for publication, the team showed that their yeast grew better on urea from human urine than on other nitrogen sources like ammonium salt.

Securing a simple carbon source for the yeast has proven more challenging, since yeast can’t extract carbon directly from carbon dioxide. Right now, Blenner and his team are working with cyanobacteria, photosynthesizing bacteria that turn carbon dioxide into carbon-rich sugars.

There are other critical details to work out — Blenner and his colleagues still need to predict how the yeast will behave in the low-gravity, high-radiation space environment, which they’ll test by replicating conditions on a space station. They’ll also have to make the system light enough to send into space and simple enough for astronauts to fix if something goes wrong.

If it works, the system could be a game changer for long-term space travel. If the approach could be expanded beyond omega-3s, it could offer astronauts a potential way to produce their own vitamins and medications, some of which degrade quickly and can’t be stored for multiyear missions.

Others in the field say it’s an interesting approach to solving a difficult problem.

“The idea of recycling human waste in space is very critical and very important,” said Dongming Xie, a biochemical engineer at the University of Massachusetts, Lowell, who wasn’t involved in the research. Xie added that to live in space for years, humans have to figure out how to turn a spaceship into a “small Earth” by creating a sustainable, closed-loop system.

But Xie, who worked on a similar process involving the same yeast at DuPont, also pointed out that Blenner and his team have some hurdles to clear: They have to increase their omega-3 outputs and process the acids to make them fit for human consumption. Yeast also require oxygen to grow — which could be problematic on a space mission in which oxygen is limited.

Blenner and his team are working to tackle those issues as they modify the system to make it space-ready.

If that happens, astronauts in the future could find themselves launching into space with a healthy supply of yeast riding shotgun.