Lettuce in space

A study published in Frontiers in Plant Science has revealed that researchers have successfully cultivated a salad crop — red romaine lettuce — on board the International Space Station (ISS). Despite being grown under lower gravity and more intense radiation than on Earth, the space-grown lettuce is claimed to be safe to eat, free from disease-causing microbes and as nutritious as Earth-grown plants.

Astronauts in space currently live on processed, pre-packaged rations that have been sterilised by heating, freeze drying or irradiation. The US Space Agency NASA has been trying to determine how to grow safe, fresh food on board, as it would provide astronauts with additional potassium, and vitamins K, B1 and C — nutrients that are less abundant in pre-packaged rations and can degrade during long-term storage.

“The ability to grow food in a sustainable system that is safe for crew consumption will become critical as NASA moves toward longer missions. Salad-type, leafy greens can be grown and consumed fresh with few resources,” said Dr Christina Khodadad, researcher at the Kennedy Space Centre.

Astronauts Scott Kelly and Kjell Lindgren taste the lettuce grown on board the ISS in August 2014. Image credit: NASA.

Lettuce was grown on board the ISS from 2014–2016, with surface-sterilised seeds within Vegetable Production Systems (nickname Veggie), growth chambers equipped with LED lighting and a watering system designed to grow crops in space. The crops grew in the Veggie system for 33 to 56 days, before crew members ate part of the mature leaves, with no ill effects. The remainder was deep-frozen until transport back to Earth for chemical and biological analysis. Scientists had grown control plants on Earth under the same conditions, replicating the temperature, carbon dioxide and humidity on board the ISS.

The space-grown lettuce was similar to the Earth-grown controls, except in some trials, where it was richer in elements such as potassium, sodium, phosphorous, sulfur and zinc, as well as in phenolics, molecules with proven antiviral, anticancer and anti-inflammatory activity. Analysing the microbial communities of the plants revealed that Earth-grown plants had a diverse set of microbes, identifying the 15 most abundant microbial genera on the leaves and 20 in the roots, and found that the diversity and identity of these microbes was similar for space- and Earth-grown lettuce.

Astronaut Shane Kimbrough in front of the Veggie chamber on the ISS in November 2016. Image credit: NASA.

“The International Space Station is serving as a test bed for future long-duration missions, and these types of crop growth tests are helping to expand the suite of candidates that can be effectively grown in microgravity. Future tests will study other types of leafy crops as well as small fruits like pepper and tomatoes, to help provide supplemental fresh produce for the astronaut diet,” said Dr Gioia Massa, co-author and project scientist at the Kennedy Space Centre.

None of the detected bacteria genera are known to cause disease in humans, with further tests confirming that the leaves did not carry dangerous bacteria such as E. coli, Salmonella and S. aureus. Researchers found that lettuce grown in space-borne Veggie units is safe to eat. These findings could lead to further experiments with other crops on board the ISS, to help propel astronauts further into space.

Top image credit: NASA