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Salad is good for your health, generally speaking, so growing fresh vegetables in orbit seems like a winning way for space travelers to stay healthy. New research suggests that as nutritious as space salad is, it could pose a risk to astronauts.
The problem is that growing leafy plants like lettuce and spinach in space can be accompanied by bacteria, according to a new study from a team at the University of Delaware. In tests with plants grown in simulated microgravity, it was shown that they were actually more susceptible than normal to he Salmonella enterica pathogen.
We know that the International Space Station (ISS) is home to many aggressive bacteria and fungi, and if these space microbes were to cause widespread illness in an astronaut’s crew, it would mean lives are at risk.
“We don’t want the entire mission to fail just because of a food safety outbreak,” says plant biologist Harsh Bais of the University of Delaware.
Bais and his colleagues used a device called clinostat to perform some clever rotation tricks in the lab, putting the lettuce plants in a state similar to what they would be in microgravity. Then they added S. enterica bacteria to the leaves.
The interesting – and surprising – thing was that the little stomatal pores in lettuce it was opened to allow bacteria to invade. Normally, the job of stomata is to keep dangerous attackers away while also helping the plant breathe.
The researchers then added a more useful species of bacteria, one that generally protects plants from external stressors. Once again, the defenses did not work in microgravity, suggesting that there is something about this state that deactivates the chemical reactions that the lettuce would normally use to keep itself safe.
“The fact that (the stomas) stayed open when we presented them with what appeared to be stress was really unexpected.” says Plant scientist Noah Totsline of the University of Delaware.
“In effect, the plant wouldn’t know which direction was up or down. We were confusing its response to gravity.”
While previous studies have shown that space lettuce is as safe and nutritious as equivalent plants grown on Earth, the new research indicates that it may struggle to protect itself from infections in the usual way.
Add to that what we know about space bacteria being particularly nasty, and this is a potential problem. The team behind the study wants to see much more research to ensure our food is safe outside orbit, with genetic modifications being a possibility.
“We need to be prepared and reduce risks in space for those who live on the International Space Station now and for those who might live there in the future.” says Kali Kniel, a microbiologist at the University of Delaware.
“It is important to better understand how pathogenic bacteria react to microgravity so that appropriate mitigation strategies can be developed.”
The research has been published in Scientific Reports and NPJ Microgravity.