Earth Microbes Could Sabotage the Journey to Mars

A new study found a healthy community of microbes in the ISS, but this doesn’t mean that a journey to Mars would be safe for the microbe and human travellers.

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Dec 11 2017, 4:00pm

The year 2018 will mark two decades since of the launch of the first piece of the International Space Station, and the beginning of the first long-term human habitats in outer space. Since then, over two hundred astronauts have lived aboard the ISS—but for every human who goes to space, there are trillions of microbial passengers, both inside and outside her body.

For years, scientists have been studying how isolation affects astronauts inside a spacecraft. However, researchers are only beginning to uncode the ways microbial communities respond to containment in environments shared with humans.

A new study published in the journal PeerJ found that the ISS is home to a diverse selection of microbes across fifteen different surfaces, including vents, keyboards, and handles. These findings surprised researchers, who hail from six biology laboratories across the United States.

“We hypothesized that there might be a relatively low microbial diversity on the ISS,” the paper reads. “We note that Shannon diversity (which takes into account both the number of species present, and how evenly our sequences are distributed throughout those species) is actually relatively high on the ISS.”

On Earth or in space, a confined environment is a risk to the health of microbes, and by extension, of humans. When you remove all interactions with new people, animals, and outdoor environments, you remove interactions with new microbes. Competition among the remaining microbes becomes more fierce as a result, which isn’t good for the ecosystem’s overall health.

Studies on Earth have shown that too little microbial diversity in a human environment, like a house, is correlated with a higher risk for allergic reactions and diseases like asthma and Irritable Bowel Syndrome. Since the stress of spaceflight suppresses astronauts’ immune systems, any additional risk of illness is extremely serious.

It’s noteworthy that the microbe samples for the PeerJ study were only collected over the three-month period of Expedition 39, which flew in 2014, and each astronaut was only on the ISS for six months. The estimated amount of time it would take for a round-trip to Mars and back is seventeen months. So what happens when the same people and microbes are in a confined space for that long?

Research published in October in the journal Microbiome examines just that, albeit in a simulation here on Earth. The research paper details an experiment that took place from June 2010 to November 2011, when six Russian men locked themselves in a mock spacecraft designed to imitate the confined living conditions of a 520-day mission to Mars.

The spacecraft, called the Mars500, was located inside the Russian Academy of Sciences site in the heart of Moscow. It included a gym, operating room, greenhouse, and even a Martian surface simulator. The volunteers weren’t allowed to leave the habitat, or so much as open a window.


Every month, researchers took microbial samples from twenty Mars500 locations. Of these samples, 162 were airborne, and 198 were on surfaces like the greenhouse wall and toilet bowl.

The authors of the paper, from eight universities scattered across Europe, join a larger body of scientists who are dedicated to understanding how microbes colonize spacecrafts and how they could colonize other planets. However, authors of the Microbiome paper not were focused on the diversity of bacteria inside the bodies of its human occupants, but in the mock spacecraft itself.

Unsurprisingly, within the Mars500 spacecraft, microbial diversity gradually eroded. The “Marstronauts” changed their protocol for cleaning the spacecraft prototype a few times, which the Mars500 researchers say probably contributed to the drop.

Lead author Petra Schwendner, a professor from the University of Edinburgh, didn’t personally find the drop alarming. “Due to the appropriate measures, the microbial community was under control at any [given] time point,” she said in an email.

Schwendner said the human crew was never at much risk, or maybe any risk period, because microbial diversity in the Mars500 was never so low that its community dynamics violated the human system standards for the ISS, which outlines the lowest safe microbial diversity for a spacecraft. “Despite the fact that we were able to locate some microbial hotspots, we were quite relieved to find that the overall bacterial counts were within the acceptable limits,” she said.

The Mars500 research tested how a spacecraft’s containment affects its microbes, not space-driven factors like weightlessness or radiation. It also didn’t look at the astronauts’ microbiomes, or the collection of microbes inside their bodies. When you consider space and human microbiomes, a slew of different problems arise.

Luis Zea, a bioastronautics researcher at the University of Colorado who did not participate in the study, has found that microbes in space tend to reproduce more frequently than those on Earth. He told me over the phone that microbes in space are also more resistant to antibiotics and better at infecting hosts.

“Do we know how bacteria will change in spaceflight behavior for long periods of time?
In most cases, we have an idea, but we don’t really know.” Zea said. “[The Mars500 study] stresses the importance that we do these kinds of analyses in space as well.”

Brown University’s Leonard A. Mermel has researched microbial epidemiology for NASA. He told me that while he was impressed with the study of the Mars500 habitat, there's more to learn from experiments on Earth and in orbit before we can safely go to Mars, as people such as Elon Musk are planning.

“I don’t know if the acceleration of knowledge regarding the microbiome has kept up with how you build a spacecraft,” Mermel said. “If there’s not enough knowledge, the risk is for [human development] not going right is greater.”

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