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NASA-Led Team Examines Mycobiome of Environment Mimicking Space Habitats

NEW YORK (GenomeWeb) – The presence of people alters the fungal diversity of a closed environment, such as one mimicking conditions in space, according to a new study.

Researchers from the NASA Jet Propulsion Laboratory at the California Institute of Technology sampled surfaces within a habitat that simulates the environment of a lunar or Martian lander for metagenomic — particularly fungal — analysis. As they reported today in the journal Microbiome, the researchers found that the introduction of people into the habitat led to an increase in fungi, including ones that could make people ill. Living in such a closed habitat is stressful and could make astronauts more susceptible to infection, the researchers added.

"Fungi are extremophiles that can survive harsh conditions and environments like deserts, caves, or nuclear accident sites, and they are known to be difficult to eradicate from other environments including indoor and closed spaces," author Kasthuri Venkateswaran from JPL said in a statement. "Characterizing and understanding possible changes to, and survival of, fungal species in environments like the [the inflatable lunar/Mars analog habitat] is of high importance since fungi are not only potentially hazardous to the inhabitants but could also deteriorate the habitats themselves."

Three crews of students lived in an inflatable lunar/Mars analog habitat (ILMAH) for 30 days. The ILMAH was closed off from the outside world for the duration of their stay, except for an exchange of filtered air. Prior to habitation, the surfaces were cleaned with a bleach solution, and during the experiment, the surfaces were cleaned weekly with antibacterial wipes. Eight surfaces in the habitat were sampled four times: on day zero, day 13, day 20, and day 30.

By culturing the samples, the researchers uncovered a significant increase in fungal abundance between the collection time points. They also found that the culturable fungal population was higher for the lab area of the ILMAH than the others. In particular, they identified Cladosporium cladosporioides, Epicoccum nigrum, and Aspergillus tubingensis among the culturable fungi.

At the same time, the researchers sequenced viable fungal samples to gauge the diversity of the full mycobiome. From this, they found that the most abundant phylum was Ascomycota, followed by Basidiomycota.

When they examined the samples over time, they observed variations in abundance and noted that during human occupation of the ILMAH, the fungal diversity changed. For instance, levels of Pleosporaceae varied from 96 percent on day zero to 47 percent on day 20, and up to 70 percent on day 30. While Pleosporaceae decreased on day 20, levels of Davidiellaceae, Dothioraceae, Saccharomycetales, and Trichocomaceae increased, as compared to other time points.

Similarly, Epicoccum, Alternaria, Pleosporales, and Cryptococcus were highly abundant at day zero, but decreased in numbers by day 20 before increasing again by day 30.

They further noted that Alternaria, Cladosporium, and Epicoccum — all of which they uncovered in their study — are common household fungi. Though the researchers said that Cladosporium cladosporioides rarely causes infections, they said it could lead to asthmatic reactions in people with weakened immune systems, such as astronauts.

"In-depth knowledge of the viable mycobiome will allow the development of required maintenance and cleaning procedures in a closed habitat like ILMAH and also prevent it from deteriorating and becoming a health hazards to its inhabitants," Venkateswaran said. "However, to be able to show that increased fungal diversity is a result of human presence, the mycobiome of the occupants will also need to be studied."