Astronauts on the International Space Station (ISS) have been enjoying fresh salads grown in orbit since 2021. NASA has been experimenting with growing lettuce and other leafy greens in controlled chambers that provide optimal conditions for plant growth. However, a new study by researchers at the University of Delaware suggests that space salads could pose a health risk for astronauts, as plants are more vulnerable to bacterial infections in microgravity.
The study, published in Scientific Reports and npj Microgravity, found that lettuce grown under simulated microgravity was more susceptible to Salmonella, a common foodborne pathogen that can cause diarrhea, fever, and abdominal cramps. The researchers used a device called a clinostat to rotate plants at a constant speed, mimicking the weightless environment of the ISS. They then exposed the plants to Salmonella and observed how they responded.
Plants have a hard time defending themselves in microgravity
Plants have a natural defense mechanism against pathogens, which involves closing their stomata, the tiny pores on their leaves and stems that allow them to breathe and transpire. When plants sense a threat, such as bacteria, they close their stomata to prevent the entry of the invaders. However, the researchers found that plants grown under microgravity did the opposite: they opened their stomata wider, making them more vulnerable to infection.
The researchers speculated that this abnormal response could be due to the altered gravity perception of the plants. Plants use their roots to sense gravity and orient themselves accordingly. In microgravity, their roots are confused and cannot tell which way is up or down. This could affect their signaling pathways and hormone levels, leading to changes in their stomatal behavior.
Space salads could jeopardize future missions
The findings of the study have important implications for the safety and sustainability of space missions. Growing plants in space is not only a way to provide fresh food for astronauts, but also a potential source of oxygen, water, and psychological benefits. However, if plants are more prone to contamination by harmful microbes, they could pose a serious health risk for the crew.
The researchers suggested that more studies are needed to understand the mechanisms and consequences of plant-microbe interactions in space. They also recommended that astronauts should wash their space salads thoroughly before eating them, and that plant growth chambers should be sanitized regularly to prevent the spread of pathogens.