Astronauts may need to reconsider eating salads in space

Space lettuce is very popular on the International Space Station (ISS), where astronauts enjoy the leafy greens in a space garden called Veggie, and even munch on a piece of red leaf lettuce they grow themselves.

However, scientists have discovered that lettuce grown in a simulated microgravity environment on Earth is more susceptible to infections such as E. coli or salmonella than lettuce grown in space and may not be safe for astronauts.

A paper recently published in Scientific reports She revealed that a group of researchers grew plants in a device called a clinostat, which rotated them like a roasted chicken so that they lost their sense of direction. Gizmodo mentioned.

“In fact, the plant didn't know which direction was up or down,” Noah Totslein, lead author of the new paper, said in a statement. “We were kind of confounding their response to gravity.”

Plants have gravity-sensitive cells that cause their roots to grow downward, while the plant grows upward. However, in microgravity environments, a plant's natural defense against stressors is less effective.

Stomata, small pores in leaves and stems, help with breathing and close when they sense stressors such as bacteria. During their carnival ride on the clinostat, the plants became disoriented and opened their pores in the presence of bacteria, according to the research.

“The fact that they remained open when we were putting them through what appeared to be stress was really unexpected,” Totsline said.

From the experiment, the researchers concluded that bacteria such as Salmonella can invade leaf tissue more easily in simulated microgravity conditions, such as those on the International Space Station.

A 2020 study of the first lettuce crop grown on the International Space Station between 2014 and 2016 revealed that although lettuce had the same nutritional content as the Earth-based variety, it showed higher levels of bacteria.

Despite efforts to mitigate microgravity, the closed-air environment of the International Space Station with astronauts living in its headquarters may expose plants to pathogens, which could impact the plant system, a nutritious food source for future missions to the Moon or Mars.

The researchers propose modifying the genetics of space lettuce to prevent stomata from opening more widely in space, thus reducing the risk of bacterial infection for astronauts who consume the greens.

They are currently testing different varieties of lettuce in a simulated microgravity environment.