Microgravity Makes Lettuce More Vulnerable to Pathogens, Affecting Future Space Missions
Lettuce, a staple in a balanced diet, may not be the healthiest choice for astronauts aboard the International Space Station (ISS). New research has revealed that microgravity, the condition in which ISS astronauts live, can make lettuce more susceptible to pathogens, potentially leading to foodborne illnesses. This discovery could have significant implications for future crewed space missions to the moon and Mars.
Currently, ISS crew members have access to salad greens grown on the space station in controlled chambers. They can also consume items sent from Earth. However, the ISS is known to harbor various pathogens, including bacteria and fungi, which can cause diseases. If these pathogens colonize the lettuce tissue and are consumed by astronauts, it can result in illness.
NASA, other space agencies, and private space companies like SpaceX are concerned about the possibility of a foodborne illness outbreak during a mission. Such an event could not only jeopardize the health of astronauts but also risk billions of dollars of investment.
Scientists from the University of Delaware conducted research to understand how microgravity affects lettuce and whether it makes salad vegetables more vulnerable to illness-causing organisms. They simulated microgravity conditions using a device called a clinostat and exposed the plants to rotation.
Plants have the ability to sense gravity through their roots and exhibit a growth response known as “gravitropism.” The research team discovered that plants grown in simulated microgravity were more susceptible to colonization by the pathogen Salmonella.
Plants have tiny pores called “stomata” on their stems and leaves that allow for gas exchange. When exposed to stressors like bacteria, these pores usually close as a defense mechanism. However, in rotation-induced microgravity, the plants’ stomata remained open when exposed to bacteria, making them more prone to salmonella invasion compared to plants on Earth.
Noah Totsline, a scientist from the University of Delaware, expressed surprise at this unexpected behavior. The rotation-induced microgravity confused the plants’ sense of directionality and affected their response to stressors like bacteria. Totsline explained that the plants were “kind of confusing their response to gravity” because they couldn’t determine which way was up or down.
The research team also tested the use of a “helper bacteria” called B. subtilis UD1022, which aids plant growth and defends against bacterial colonizers. However, they found that UD1022 failed to protect plants from salmonella in microgravity. It is speculated that the bacteria’s inability to trigger stomata closure may be the reason for this failure.
To mitigate the risk of contamination due to wider stomata opening in microgravity, the team suggests starting with sterilized seeds to reduce the presence of microbes on plants. However, there is still a possibility of microbes entering the space environment and contaminating the plants. Another approach could involve genetically modifying the plants to prevent them from opening their stomata wider in space. Scientists are currently evaluating different lettuce species with varied genetics to understand their response to microgravity.
The team’s research, published on the Springer Scientific Reports website, sheds light on the vulnerability of lettuce to pathogens in microgravity environments. By understanding these factors, scientists can develop strategies to ensure the safety of astronauts during future space missions.
