Wetenschap - 14 november 2002

ATO uses oyster mushrooms to make substrate

ATO uses oyster mushrooms to make substrate

Astronauts on Mars expedition will have to grow their own food

Twenty years from now the inevitable manned space mission to Mars will be a fact. The astronauts will spend five years away from planet Earth, and they will have to grow food for themselves in greenhouses. Wageningen research institute ATO is developing technology that will make this possible, with the help of oyster mushrooms.

"There's no way I would be an astronaut," declares Dr Cristina Soler Rivas. The mushroom researcher at the Agrotechnological Institute ATO is seated at a table in one of the Spartan research rooms. "Everything they will eat is made from this." Soler Rivas points to a sealed transparent plastic container on the table. She picks it up, smells it and shakes her head. "You can't smell it," she says, visibly relieved.

In the bottom of the container there is a dark brown paste. "You would be forgiven for thinking it is something else," says research leader Dr Harry Wichers. "And that is so." The researchers at ATO have christened the dark brown stuff Melissa cake, after the European Space Agency (ESA) Melissa project for which ATO and other research institutes are working on food provision for the astronauts.

The paste comes from a reactor in Gent in Belgium, where plant parts and human faeces have been processed to make a substrate. The stuff stinks to high heaven. It's so bad that Soler Rivas and Wichers try to do their laboratory work as quickly as possible. Nevertheless it's impossible to prevent the sewerage smells from reaching the corridors in the rest of the building. "We are used to getting angry looks," Wichers says resignedly. "And we understand why."

Wichers and Soler Rivas are doing research on food for the cosmonauts that will take part in the manned flight to Mars in ten or twenty years' time, or other deep space exploration. According to calculations the voyage to Mars will take a year. The astronauts will spend three years on the planet, until Earth and Mars are once again close enough for the return voyage to begin, which will also take another year.

Faeces

"We are working on technology that is meant for on Mars," explains Wichers. "On the journeys there and back the astronauts will live on food that they take with them. But that won't be possible on Mars, or on a manned space station that might orbit the planet. Human adults eat about ten times their own weight in a year Wichers calculates out loud. "That's about two kilos a day. There will be at least ten passengers to Mars, so that's twenty kilos a day. They won't be able to take food for the whole mission, so they'll have to grow their food in greenhouses, on this stuff," he says pointing at the transparent container.

The cake that will be used as a substrate in the greenhouses is made from human faeces and inedible vegetable waste from the greenhouse, which is then processed in a fermenting installation. Earlier tests carried out by ESA however showed that Melissa cake was not without its problems. There were too many undigested fibres which would accumulate in the greenhouses where the astronauts would grow their food. White rot fungi such as shii-take and oyster mushrooms can help solve this problem.

"White rot fungi manufacture enzymes such as peroxidases, phenyloxidases and aryl-alcoholoxidases," explains Soler Rivas. "This means they can break down fibres. We are now doing tests to see which white rot fungi do this best. In an earlier project we found at that shii-takes can do this, but oyster mushrooms work six times as fast. We are also doing experiments with a couple of inedible species that grow three times faster again, but that's mainly to determine the theoretical maximum of what we could achieve with white rot fungi." These inedible mushrooms are unlikely to be used - ESA is concerned that the undesirable waste they produce will end up in the closed system and therefore possible on the astronauts' plates.

Monotonous

Oyster mushrooms are the number one research topic. On the brown Melissa cake in the container there are thousands of transparent threads growing to form a round patch. These are the mycelium threads of a white rot fungus that is two weeks old. But the process needs speeding up, which can be done by using substances that occur naturally in plant cell walls, such as ferula acid. These cell wall components increase the release of fibre breaking enzymes in the fibre-eating fungi. Soler Rivas and Wichers are going to examine what happens if they add these substances to the brown paste.

"If you think of mushrooms you usually think of stems with caps," says Wichers. "But we are looking at the mushrooms in the first stages of growth. "We are not yet sure, but probably the fungi will not have to grow any bigger to be able to convert the cake into a suitable growing medium." So it is by no means certain that the astronauts will be able to add oyster mushrooms to their diet on Mars, although according to Soler Rivas they probably wouldn't be averse to the idea. The space diet will be very monotonous. "Food in space is awful. The ESA projects are examining four to six crops, including grain, beetroot, lettuce and soya. That's what you get every day. No salmon, no tapas, no wine, no beer, no chocolate. Who can stand that?"

Willem Koert

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