Key Points:
- Decontamination in cleanrooms used by NASA to build and study spacecraft focus mainly on bacteria.
- Researchers recently identified fungi in samples from spacecraft-associated environments, including cleanrooms.
- Conidia, a type of asexual reproductive spore, grown from those fungi survived after exposure to simulations of the harsh conditions of Mars and space travel.
- The findings suggest decontamination strategies should expand beyond traditional bacteria.
Washington, D.C.-Scientists have long known that fungi are resilient, but a new study suggests that some strains might survive every step of the long, brutal trip to Mars.
In a paper published this week in Applied and Environmental Microbiology, researchers isolated fungal microbes from NASA cleanrooms-facilities used in the assembly, testing and launch of spacecraft-that had persisted after decontamination. When subjected to simulations of the harsh pressure, temperature and radiation conditions of space travel and Mars, asexual reproductive spores called conidia, of the fungus Aspergillus calidoustus, survived.
"This does not mean contamination of Mars is likely, but it helps us better quantify potential microbial survival risks," said microbiologist and study leader Kasthuri Venkateswaran, Ph.D. He is a former senior scientist in the Biotechnology and Planetary Protection Group (BPP) of NASA's Jet Propulsion Laboratory. The group implements NASA policies on various missions for avoiding extraterrestrial cross-contamination with Earth's microbes, and vice versa. "Microorganisms can possess extraordinary resilience to environmental stresses."
Researchers have long sought to understand fungal survival under space conditions. This study is the first to show that microbial eukaryotes-which have a nucleus, like fungi-could persist through every part of a mission to Mars, from preparation to space travel to robotic exploration, Venkateswaran said.
BPP researchers study how microbes survive and adapt under harsh space conditions, and how they might be detected and monitored. Their work includes analyzing strategies for decontaminating environments associated with spacecraft, though Venkateswaran pointed out that germicidal techniques are usually assessed by studying resilient bacteria, not fungi.
Microbial monitoring is a critical step in assembling spacecraft components and subsystems. For the new study, the researchers first generated conidia from 27 fungal strains that had been isolated from assembly facilities used in the Mars 2020 program, which led to the landing of the Perseverance rover on the red planet. They also included 2 organisms-bacterial and fungal-known to be able to survive high levels of radiation.
They then subjected these fungal conidia to the intense conditions of space travel and Mars, including low temperature, ultraviolet and ionizing radiation, low atmospheric pressure and exposure to Martian regolith (the loose, dusty rock material on its surface). The conidia of A. calidoustus, which had been isolated from NASA cleanrooms, tolerated these harsh tests, and only the combination of extreme low temperature and high radiation was able to kill the fungus, the researchers found. "Microbial survival is not determined by a single environmental stress but rather by combinations of stress tolerance mechanisms," Venkateswaran said.
The study positions A. calidoustus as a strong candidate for a microbe that could survive the extreme clean conditions of the spacecraft associated environments, hitch a ride in a spacecraft and persist on robotic systems exploring the Martian surface. It builds on previous studies that have identified bacteria and fungi in NASA spacecraft-associated surfaces after decontamination.
"Together, these investigations help refine NASA's planetary protection strategies and microbial risk assessment approaches for current and future space exploration missions," Venkateswaran said.
