Study finds space lettuce more susceptible to salmonella

In between shelf stable rehydrated meals, and white flour tortillas, sometimes an astronaut just needs a few leafy greens. But some innovative science has shown that when you mess with gravity, lettuce can become susceptible to bacterial infection.

The new study which involved putting lettuces into a simulated gravity free environment, was conducted at the University of Delaware.  

The research has been published in Scientific Reports and npj Microgravity.

Where there are humans, there are bacteria, even in space. Researchers have been trying for years to limit the bacterial and biofilm growth on the International Space Station (ISS), but it’s hard to keep a good bug down, and some thrive in the ISS.

Although lettuce was first grown (and eaten) by astronauts in space back in 2015, and – as far as we know – there have been no gastrointestinal issues yet, longer missions and more people means we should be prepared for any lettuce hiccups.

The researchers on these two new papers unfortunately didn’t have access to ISS grown lettuce. They instead simulating microgravity by slowly rotating plants around at between 2 and 4 rotations a minute, to ensure the plants couldn’t know which way was up. In the press release, the team describe it as “the speed of a rotisserie chicken on a spinner”.

“In effect, the plant would not know which way was up or down,” Noah Totsline, who undertook the work as a student, said. “We were kind of confusing their response to gravity.”

Of course, a slowly rotating plant isn’t true microgravity, but it does provide a way for the plants to lose their directionality.

Normally, when plants like lettuce are exposed to pathogens or threats, the stomata holes which normally let in air and let out water, close. In this paper, the team used a bacteria which causes Salmonella to test the plants’ responses.

However, the team found that when the plants were rotating, the stomata opened instead of closed.

“The fact that they were remaining open when we were presenting them with what would appear to be a stress was really unexpected,” Totsline said.

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To fix this, the researchers added a bacterial strain called Bacillus subtilis UD1022 which is known to help plants grow better and protect against pathogens.

In this case, that didn’t work either.  

“The failure of UD1022 to close stomata under simulated microgravity is both surprising and interesting and opens another can of worms,” said University of Delaware plant professor Harsh Bais.

“I suspect the ability of UD1022 to negate the stomata closure under microgravity simulation may overwhelm the plant and make the plant and UD1022 unable to communicate with each other, helping Salmonella invade a plant.”

For now, the astronauts on board the ISS probably don’t need to worry too much about their lettuce, but more research could be done to try and tweak the genetics of the plants to stop them opening their stomata in the same way.

“If, for example, we find one that closes their stomata compared to another we have already tested that opens their stomata, then we can try to compare the genetics of these two different cultivars,” Bais said.

“That will give us a lot of questions in terms of what is changing.”

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