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Is Space Salad Safe? Scientists Say, Maybe Not.

Posted in Our Blog on March 30, 2024

Along with freeze dried, powdered, gelled, or liquified foods, powdered coffee is a staple on the International Space Station (ISS). An astronaut’s diet can be pretty bland.

To diversify their meals on the ISS, hydroponically grown lettuce has been propagated onsite for at least the last 3 years. However, a recent study shows there could be a space-centric danger not encountered in Earth’s gravity.

Why Grow Lettuce in Space?

The spectrum of available foods to astronauts has grown over the years, though fresh food is still not generally available. Many fresh foods just cannot conform to the restrictions aboard the ISS and spacecraft. Most of what an astronaut eats is freeze dried or similarly packaged and can be rather bland and lack diversity.

In fact, while not the only contributing factor, astronauts often experience significant weight loss on missions to the space station.

To combat this, experiments were performed to see if leafy greens could be grown in space. Turns out, they can! Lettuce does grow rather successfully hydroponically in the microgravity environment. But at a cost.

The initial studies showed a greater than normal bacterial growth. At the time, the bacteria found in those studies were not human pathogens, so not much was thought about it. Should astronauts get foodborne illnesses in space, it could be disastrous.

What’s the Worst That Could Happen?

Keeping astronauts healthy is a priority. Every minute is carefully scheduled and mission critical. Each member of the team has important tasks that must be done. Every astronaut is part of a well-tuned machine.

Unplanned deviations can cause serious issues aboard the ISS.

Not to mention the existing constraints on bathroom procedures. Let that thought sink in a moment.

Having an astronaut down due to foodborne illness is inconvenient at best, and catastrophic at worst. Especially since most foodborne illness is spread via fecal-oral route and typical hand hygiene procedures are not an option in space.

No warm soapy water out of atmosphere.

With certain human pathogens commonly associated with foodborne illnesses such as Salmonella eterica, E. coli, and Shigella sonnei already aboard the ISS, serious food safety risks already exist.

Why Is There More Bacterial Growth in Space?

The hydroponic methods used to grow lettuce in space are pretty much the same as those used to grow the leafy greens on Earth. So what is the reason for the greater than average bacterial growth?

Initially, scientists thought it was the increased humidity of the environment or the higher temperatures experienced. Turns out, the answer is more biological.

Plants Behave Differently in Space!

A recent study revealed that it isn’t the method that resulted in greater bacterial growth, but how the plants behave in microgravity.

A microgravity simulation was created Earth-side by putting hydroponically grown plants on a sort of carousel/Ferris wheel contraption, similar to those used to make rotisserie chickens. This activity was thought to add stress to the plant – an action that would normally prompt the plant to close their stomata to defend itself.

Stomata are the pores that a plant “breathes” through. It takes in carbon dioxide and releases oxygen through these pores.

Instead of the stress causing the plant to close their stomata, scientists found that under simulated microgravity, lettuce plants opened their stomata widely. They did not close them.

“The fact that they [lettuce plants] were remaining open when we were presenting them with what would appear to be a stress was really unexpected,” said Noah Totsline, an alumnus of the University of Delaware’s Department of Plant and Soil Sciences and lead author of the papers published on the study.

Why is this such a big deal?

Open Stomata is a Common Pathway

Open stomata pores leave the plant vulnerable to bacterial invasion. For this reason, plants often restrict their stomata during periods of stress to prevent this infection. While not impossible to breach, restricted stomata offer some defense against harmful microbes.

Certain bacteria, such as S. enterica manipulate one of the pathways that regulates stomatal closure. In doing so, they ensure the stomata are open and can make their way inside the plant.

Once inside the plant, no amount of washing will remove the pathogen from the leaves. The bacteria are inside the leaves, not on them.

Other Potential Concerns

While foodborne illness is a significant concern aboard the ISS and in situations where food may be hydroponically grown in space, it isn’t the only concern that these studies brought to light.

The stomata are used in photosynthesis. Photosynthesis is essentially the process plants use to take in carbon dioxide from the atmosphere and release oxygen as a byproduct.

Significant amounts of the plant hormone, auxin, was found in the plants exposed to microgravity. This auxin hormone contributes to stomata remaining open, even under dark conditions. As a result, photosynthetic efficiency is potentially compromised, as is CO2 uptake and phytoremediation aboard spacecraft.

These activities have been thought to help contribute to life-support activities in space. If this is compromised, additional life-control options will need to be employed.

Should Astronauts Trust Space Salad?

Ultimately, should astronauts trust space salad? There is no single answer to that question.

Lettuces grown in microgravity are significantly more likely to become infected with harmful human pathogens in the environment than those grown Earth-side. The existence of commonly known foodborne bacterial pathogens aboard the ISS suggests that the risk of infection is high.

So far there have been no known cases of foodborne illness aboard the ISS, so they must be doing something right in preventing astronauts from becoming sick.

What Does This Mean for Crops Grown in Space?

If humans are to eventually become a multi-planetary species, taking food crops along for the ride will be essential. Plants may evolve to keep their stomata open, or they may eventually adapt to the microgravity environment.

Only time will tell on this topic. But one thing is certain. Additional research must be done to better understand how plants and pathogens behave in space.

Want to Know More About Food Safety ?

If you’d like to know more about food safety, check out the Make Food Safe Blog. We regularly update trending topics, foodborne infections in the news, recalls, and more! Stay tuned for quality information to help keep your family safe, while The Lange Law Firm, PLLC strives to Make Food Safe!

By: Heather Van Tassell (content writer, non-lawyer)