Want to go to Mars? Then you could end up eating a lot of lettuce. But not any ordinary lettuce.
Researchers from the University of California, Davis, have genetically engineered lettuce to produce a drug based on a human hormone that keeps bones strong.
It is the latest development in the emerging field of designing food and drugs suitable for long-distance space travel.
Astronauts lose on average about 1 per cent of their bone mass a month in space.
“Right now, astronauts on the International Space Station (ISS) have certain exercise regimens to try to maintain bone mass,” said Kevin Yates, who presented the team’s work at the American Chemical Society meeting earlier this week.
“But they’re not typically on the International Space Station for more than six months.”
To prevent bone loss for that period of time, you’d not only need to commit to a serious workout, but you’d have to inject yourself with parathyroid hormone (PTH) every day.
So let us take a closer look at how this lettuce fits in with the future of space travel.
At the moment, astronauts onboard the ISS mainly eat ration packs, with the occasional fresh food delivery when a new spacecraft arrives.
This means “menu fatigue” quickly sets in, said Matthew Gilliham, director of the Waite Research Institute at the University of Adelaide.
“Astronauts lose 10 per cent of their body weight within the first few weeks of being on the space station, partly because of the monotonous diet,” said Professor Gilliham, who researches future foods but was not involved in this research.
So NASA has been experimenting with growing plants such as lettuce on the ISS.
“Lettuce is great because it grows pretty fast,” said Jenny Mortimer, who also studies future foods at the Waite Research Institute.
Growing plants in microgravity can be tricky. Some plants don’t grow in the right direction, and water can stick to the roots and leaves of plants and kill them.
NASA uses a system of fans and LED lights to keep their mini-garden alive.
Along with lettuce, they’ve also successfully grown barley, radishes, and, most recently, chilli.
“That added excitement to their food because they were putting chilli on absolutely everything,” Professor Gilliham said.
Spicing up the menu is not the only reason scientists are experimenting with growing their own veggies.
The cost of sending food to the ISS is estimated to be between $US 20,000-$40,000 per kilogram, with each crew member eating about 1.8 kilograms a day.
A crew going to Mars for three years would chew through about 10,000-11,000 kg of food.
Along with the cost of carrying and storing these tonnes of chow, most perishable vitamins such as vitamin B and C only last for 12 months.
Dr Mortimer said a DIY veggie patch would not only provide fresh flavour and nutrients for space travellers in the short term, but it would be particularly important for long-term habitation.
Beyond providing food, plants could be modified to become ‘home-grown’ sources of drugs and materials such as plastics.
“You can’t take everything with you,” she said.
“Plants are great because you can take seeds.”
How do you turn lettuce into a drug?
There’s been a big move over the past few years to start to produce molecules, drugs, and even plastics in biological organisms, Professor Gilliham said.
Plants are easier to grow and modify than single-celled organisms such as bacteria and yeast.
“You can put [the molecule] in different parts of the plant tissue, you could store it in different bits of the leaf that are less problematic to the plant for storing it,” he said.
Some medicines, such as dopamine used in Parkinson’s disease, and insulin used by people with diabetes, are produced by modifying plants such as tomatoes and then extracting and purifying the drug.
“But this team’s approach is different. They are producing the molecules in the plant and there is potential to feed that leaf to humans,” Professor Gilliham said.
The researchers attached a molecule to the genetic code of parathyroid hormone to keep it stable, then transferred this to the lettuce via a bacterium.
The idea is that astronauts could then eat the medication, rather than inject it.
“There will be some applications where lettuce would be the best option, but there will be others where you would need to purify,” Professor Gilliham said.
Because this plant has had genes added to it that have transformed it from a humble lettuce to an edible drug, it is classed as being genetically modified.
That means it can only be grown in controlled environments under current regulations.
“It would be a different story if you were using gene editing to modify a [known] medicinal plant … to make it suitable for space or other applications,” Professor Gilliham said.
“That would be non-GM — for instance, gene editing a hemp plant to produce certain compounds.”
When will we see this lettuce on the space menu?
A bunch of cos won’t be on the menu in the near future.
Preliminary results indicate that, on average, the plants produce about 10-12 milligrams of the modified hormone per kilogram of fresh lettuce.
That means an astronaut would currently need to eat eight cups of lettuce a day to get enough of the hormone to keep their bones strong.
“I don’t know if I’d want to share an astronaut capsule with someone who is eating that amount of lettuce,” Dr Mortimer joked.
The team will next try to tweak the lettuce to make it more efficient at producing the drug, so astronauts won’t have to eat as much.
They’d also like to see how it grows on the ISS.
And no-one knows what it tastes like yet because it hasn’t been tested for safety on either animals or humans.
“If you are taking medication, you want to be sure how much you’re taking,” Dr Mortimer said.
“When you think about dosage, you might want to do some purification, or have some control over what’s being produced.
“So that’s one question: Can we be very confident about the amount we are producing per leaf of lettuce?”
But with travel to Mars at least another decade off, the team has plenty of time to perfect their lettuce.
And if Professor Gilliham and Dr Mortimer have their way, lettuce might not be the only homegrown produce on the menu by then.
Is this the food of the future?
If you’ve ever played near a waterway in Australia, then you might be familiar with duckweed.
“It’s a really fascinating plant, it divides every two to three days so it grows on the surface,” Dr Mortimer said.
That means duckweed production can be scaled up really quickly.
Although it’s an aquatic plant, its closest relatives are wheat and barley. And it’s packed with nutrition.
“It’s got a good balance of protein, starch, and fats … and it’s pretty digestible,” she said.
“The World Health Organization has been interested in it as a food for a long time, but it doesn’t look particularly appetising.”
Not only does it take a much shorter time to grow than grain crops, you can eat every part of the plant, Professor Gilliham said.
“It is a zero-waste plant.”
Professor Gilliham said that not only could research into plants like lettuce and duckweed benefit space travellers in the future, it could provide more sustainable sources of food, drugs and other materials on Earth.
“It’s that example of using the lens of space to improve sustainability here on Earth,” he said.
ABC News, 27 March 2022