Sending germs to space

Space is harsh place that the human body cannot easily survive. Astronauts face extreme heat and cold, radiation, and low gravity. But there is another, sneakier danger. Tiny infectious microbes, or germs, can make astronauts sick.

Jennifer Barrila is a microbiologist who studies how infections work. But not just here on Earth… she wants to understand how germs infect their hosts in the low gravity of space. Barrila conducts experiments both in space and in her lab on Earth to unravel this mystery. Her work helps protect astronauts from getting sick in space. But it could also help us control diseases on Earth.

What do germs do in space?

In the early days of space travel, scientists noticed that astronauts are more likely to get sick in space. Low gravity, lack of sleep, and other stressors weaken the immune system. This lowers the body’s natural defenses and makes it easier for germs to infect the astronauts. Yet focusing on the human immune system only looks at half the picture.

Germs are also affected by the harsh space environment. For example, some germs become more infectious in space. Salmonella is a common germ that causes food poisoning when it gets inside our guts. Scientists grew Salmonella samples in space, then used the samples to infect mice back on Earth. The mice infected with the germs grown in space were less healthy than the mice infected with germs grown on Earth. But what about the germs changed to make them more infectious?

Early in her career, Barrila took part in a groundbreaking experiment to learn more about this question. She was involved in the first experiment where scientists infected human cells in space! In her lab, Barrila prepared samples of Salmonella, along with tiny samples of human gut tissue. She loaded them into an automated machine. Then, the experiment was sent off to the International Space Station. Once in space, the machine combined the Salmonella and human tissue samples. The infections began.

After six hours, a special liquid was added to the mix to completely freeze any activity. When her experiment returned to Earth, Barrila could see the infections exactly how they were in space. She looked at which genes were turned on or off in both the Salmonella and the human cells. She also examined the proteins inside the cells. Then, she compared what she found in the space samples to samples she infected on Earth.

What she found was unexpected. Normally, scientists can use certain genes to tell if a germ is highly infectious. They use them as markers to predict if a germ will be good at infecting. But when Barrila looked at the Salmonella that had been to space, she didn’t see the usual markers of a highly infectious germ. Something else caused the Salmonella to become more infectious in space: low gravity.

Fluid shear

In low gravity, the physical forces affecting our bodies, germs, and all other matter are very different than on Earth. But there is one type of physical force that has a huge impact on germs and infections, called fluid shear.

Fluid shear refers to how strongly a liquid rubs against another object. Imagine sitting in a lake with calm water. The water doesn’t move much around you, so this is a low fluid shear environment. Now imagine sitting in a river with water rushing past you. This is a high fluid shear environment, where the pressure and friction from the water is much stronger.

Inside the human body, fluid moves around differently depending on where it is in your body. For example, near the walls of our intestines, liquid moves very slowly, creating low fluid shear. But in the middle of our intestines, liquid flows more quickly, creating a high fluid shear environment. Low fluid shear is also found in the low gravity of space. Without the force of gravity to pull on liquids, they don’t move as rapidly past each other.

Barrila discovered that fluid shear is one of the key forces that impacts infections. Some germs like Salmonella, are more infectious in low fluid shear environments like space. Yet other germs are more infectious in high fluid shear environments.

Researching space on Earth

Space experiments can teach us a lot about infections in low gravity. But they are also costly, difficult, and very time consuming. To get around these challenges, Barrila developed a unique way to continue her research on Earth. She uses a special NASA technology, called a bioreactor. These bioreactors are small cylinder chambers that spin very fast. Barrila can create different amounts of fluid shear by changing how fast the bioreactors spin.

To mirror the environment of space, Barrila usually grows her cells in low-fluid shear. This lets her learn a lot about the germs, the infection, and the effects on the infected cells. Barrila measures how severe an infection is, how much damage it causes, and how well the host survives. The bioreactors are not a perfect model of space, but they help Barrila to run experiments quickly. She gains lots of valuable information that can guide her future experiments in space.

From infection to health

Illness in space can wreak havoc on crew and compromise mission objectives. Barrila’s research helps protect the health of astronauts during space missions. She is looking for ways to make germs less infectious and less dangerous. That way, astronauts have one less threat to worry about in the harsh space environment.

Barrila’s work can also help us control and prevent infection on Earth. Her bioreactors closely mimic what’s going on inside the human body, more so than if these cells were grown in a quiet Petri dish. In trying to recreate space, Barrila also recreated the environment near the walls of our intestines. Her research is revealing new ways that germs behave inside the human body. This helps scientists design better methods to treat and prevent infections both in space and on Earth.