Space salad: no soil needed for the „Veggie” chamber but plant pillows with clay like used on baseball fields

Astronaut Shane Kimbrough in front of the „Veggie” chamber on the ISS. Photo: Nasa

Nasa published research results about red romaine lettuce grown on board the International Space Station (ISS)

In a new study in Frontiers in Plant Science, Dr. Christina Khodadad, a researcher at the Kennedy Space Center, and co-authors report the successful cultivation of a salad crop – red romaine lettuce of the ,Outredgeous’ cultivar – on board the International Space Station (ISS). They show that space-grown lettuce is free of disease-causing microbes and safe to eat, and is at least as nutritious as Earth-grown plants. This is despite being grown under lower gravity and more intense radiation than on Earth.

Between 2014-2016, lettuce was grown on board the ISS from surface-sterilized seeds within Vegetable Production Systems (nicknamed „Veggie”), growth chambers equipped with LED lighting and a watering system, specifically designed to grow crops in space. Each plant had a „pillow” with a growth media inside that included controlled release fertilizer and a type of calcined clay also used on baseball fields. This clay increases aeration and helps the growth of plants.

Special concern was in respect of low gravity: therefore, seeds were placed in the pillows in a way that their roots grew downwards into the substance and their leaves grew up.
The crops were left undisturbed inside the Veggie units for 33 to 56 days, until 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.

As a control, the scientists grew control plants on Earth under the same conditions, which was possible because temperature, carbon dioxide, and humidity data were logged on board the ISS, and replicated in the Kennedy Space Center’s laboratories with a 24-48 hour delay.

Astronaut Christina Koch collecting and packing mizuna mustard greens. Photo: Nasa/JSC

Space-grown lettuce was similar in composition to the Earth-grown controls, except that in some (but not all) trials, space-grown plant tissue tended to be richer in elements such as potassium, sodium, phosphorus, sulphur, and zinc, as well as in phenolics, molecules with proven antiviral, anticancer, and anti-inflammatory activity.

Space- and Earth-grown lettuce also had similar levels of anthocyanin and other antioxidants, which can protect cells from damage by free, reactive oxygen radicals.

The researchers also examined the microbial communities growing on the plants. Typical Earth-grown plants harbor a diverse set of microbes. These may include specialized, beneficial guests called commensals, or haphazard associates. Because these can affect the health of plants and their suitability as food, the researchers used next-generation DNA sequencing technology to characterize the communities of fungi and bacteria growing on the lettuce.

They identified 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. This similarity was surprising, given the unique conditions in the ISS: the scientists had instead expected that these would favor the development of distinct microbial communities.

Importantly, none of the detected bacteria genera are known to cause disease in humans. Further tests confirmed that the leaves never carried any dangerous bacteria known to occasionally contaminate crops, such as coliform E. coli, Salmonella, and S. aureus, while the numbers of fungal and mould spores on them was also in the normal range for produce fit for human consumption.

The authors conclude that lettuce grown in space-borne Veggie units is safe to eat. These encouraging results open the door for experiments with other nutritious and tasty crops onboard the space station, to help propel astronauts further into space.

Apart from a welcome change in diet, fresh produce would provide astronauts on long time missions with additional nutrients that are less abundant in pre-packaged rations and tend to degrade during long-term storage.

Such missions are Artemis-III (scheduled to land humans on the lunar South pole by 2024), the current SpaceX program, and NASA’s first crewed flight to Mars, planned for the late 2020s.

Frontiers in Plant Science

„Veggie” chamber

Source: Nasa

(12.03.2020, USA: 03.12.2020)