Lettuce grown in space could pose risks to astronauts, study says

Vegetables and leaves should be part of a healthy and balanced diet, including for astronauts on space missions. Therefore, for more than three years, NASA has included lettuce grown in space on the menu of professionals on board the International Space Station.

However, studies such as those published in Scientific Reports and on npj Microgravity suggest that lettuce grown in space may be more prone to being infected by bacteria such as Salmonella.

Researchers at the University of Delaware grew lettuce in conditions that mimicked a gravity-free environment, like on the International Space Station. According to scientists, the stomata, tiny pores present in lettuce leaves, opened wider when they came into contact with bacteria, instead of closing.

This is worrying because the International Space Station is an environment rich in bacteria and fungi that can harm astronauts' health, such as E. coli and the Salmonellawhich cause diseases such as urinary infections, hemorrhagic colitis and typhoid fever.

“The fact that the pores remained open when we presented them with what appeared to be a stressor [a bactéria] it was really unexpected,” says Noah Totsline, lead author of both studies.

How was the study carried out?

To carry out the studies, the researchers used a device called a clinostat to spin the lettuces in a centrifuge and make them lose their response to gravity, simulating a microgravity environment. Then they added a helper bacteria called B. subtilis UD1022 to test the suitability of leaves against pathogens.

This bacteria would help protect lettuce against infectious agents such as Salmonella. However, researchers discovered that the UD1022 it was not able to protect the leaves in space-like conditions. According to the authors, this would be the result of the bacteria's inability to trigger a biochemical response that would force the plant to close its stomata.

“The failure of UD1022 in closing stomata under simulated microgravity is both surprising and interesting,” said Harsh Bais, professor of plant biology and co-author of the studies. “I suspect that the ability of the UD1022 denying stomata closure under simulated microgravity can overwhelm the plant and render it unable to communicate with helper bacteria, helping to Salmonella to invade a plant”, he adds.

These results are worrying as they indicate a risk of astronauts becoming infected when consuming lettuce grown in space during space missions. Because it is a restricted environment and where around seven people live together, according to NASA, germ infections can cause great damage.

“We need to be prepared and reduce the risks in space for those living on the International Space Station now and for those who may live there in the future,” says Kali Kniel, professor of microbial food safety in the Department of Plant and Soil Sciences at the University of Delaware, and also co-author of the research.