Inside the white-walled cleanrooms at NASA’s Jet Propulsion Laboratory, technicians suit up in full-body garments, pass through air showers, and work under HEPA-filtered airflow rated to trap 99.97% of particles. The rooms meet ISO Class 5 to 8 standards, among the strictest contamination controls on Earth. Yet a growing stack of peer-reviewed research shows that fungi, organisms long overlooked in planetary protection planning, persist in these facilities and may possess the biological toolkit to survive a seven-month cruise to Mars.
The findings, drawn from studies published between 2021 and early 2025, are forcing a reassessment of how NASA and the broader spacefaring community think about forward contamination: the risk of accidentally seeding another world with Earth life. As of May 2026, no formal revision to NASA’s bioburden standards has been publicly announced, but researchers involved in the work argue that the current framework, built almost entirely around bacterial spore counts, is incomplete.
Fungi that refuse to leave the cleanroom
A 2022 study published in Frontiers in Microbiology cataloged the fungal populations inside JPL’s Spacecraft Assembly Facility and Kennedy Space Center, revealing a mycobiome far more diverse than earlier bacterial-focused surveys had suggested. Genera such as Penicillium, Aspergillus, and Cladosporium turned up repeatedly. The authors noted that fungi had been “significantly under-studied” in planetary protection research, leaving a blind spot in the models used to estimate how much biological material rides along on outbound spacecraft.
Separate research published in Microbiome during the Mars 2020 assembly period confirmed that cleanroom microbial communities are more complex than standard bioburden counts capture. That study found that the controlled conditions inside these facilities do not simply reduce life; they reshape it. As microbiologist Christine Moissl-Eichinger and colleagues have documented in studies of spacecraft-associated environments, cleanroom conditions paradoxically select for hardier organisms: microbes that tolerate low humidity, nutrient scarcity, and chemical cleaning agents gain a competitive edge, effectively turning the cleanroom into a selection pressure for stress-hardy life.
A NASA technical report archived on the agency’s Scientific and Technical Information server tested whether that hardiness translates to space-relevant conditions. Researchers dried select cleanroom bacterial isolates, exposed them to high vacuum at roughly 1×10⁻⁶ Torr, and hit them with repeated doses of proton radiation. Some survived. The report’s conclusion was blunt: cleanroom environments can select for organisms tolerant of deep-space conditions, meaning the very protocols designed to protect other worlds may inadvertently breed contaminants capable of reaching them.
Simulating the trip to Mars
A 2025 paper in Frontiers in Microbiology pushed the question further by subjecting cleanroom bacterial isolates to combined space-like stresses, layering desiccation, vacuum, and radiation in sequences that approximate an interplanetary cruise. The authors tied their results directly to planetary protection policy, arguing that protocols need updating before crewed Mars missions move from planning to hardware. Their central point: organisms conditioned by years of cleanroom life can endure exposure scenarios that mimic the journey between Earth and Mars, making them credible candidates for accidental transfer. While that study focused on bacteria rather than fungi, its demonstration that cleanroom selection pressures produce space-tolerant microbes strengthens the broader case that fungal residents of the same environments deserve equivalent scrutiny.
Earlier foundational work, published in Applied and Environmental Microbiology, had already shown that spacecraft-associated microbes respond very differently to simulated Martian UV radiation, with some isolates proving far more resistant than others. That study cautioned against blanket assumptions about UV sterilization on the Martian surface. But it predates the more recent mycobiome surveys, and its organism-specific findings have not been replicated with the fungal species now known to inhabit cleanrooms.
What the evidence does not yet show
The strongest survival data published to date centers on bacteria, not fungi. While the Frontiers in Microbiology mycobiome study confirmed that diverse fungal species persist in cleanrooms, no publicly available peer-reviewed paper has reported specific fungal survival rates under a full simulation of Mars atmospheric conditions, including the planet’s CO₂-rich, low-pressure environment. Fungi and bacteria differ in cell architecture, spore formation, and stress-response pathways, so bacterial survival data cannot be mapped directly onto fungal species without new experiments.
Policy movement has also been difficult to track. The technical papers and journal articles call for updated safeguards, and a Nature research highlight on novel extremotolerant cleanroom bacteria framed the persistence of these organisms as a growing concern. But as of spring 2026, no publicly released statement from NASA leadership has outlined specific revisions to bioburden standards in response to the fungal findings. Whether the agency is actively drafting new protocols, consulting with the Committee on Space Research (COSPAR), the international body that sets planetary protection categories under the Outer Space Treaty, or treating the research as preliminary input remains unclear from the public record.
Post-2020 sampling data from Artemis-era assembly facilities has not appeared in accessible peer-reviewed literature. The cleanroom studies available draw primarily from JPL and KSC environments used for earlier missions. Whether microbial communities in newer or reconfigured facilities differ in composition or resilience is unknown. Cost estimates for expanded fungal monitoring are likewise absent from NASA technical reports or budget documents.
It is also worth noting that planetary protection requirements apply to all Mars-bound hardware, not only spacecraft built by NASA. Commercial partners assembling vehicles or payloads for Mars missions would face the same COSPAR-derived contamination limits, a point that gains relevance as private companies take on larger roles in deep-space exploration.
What researchers say should happen next
The published literature converges on several practical steps. First, routine cleanroom monitoring should expand to include fungal biomarkers, not just bacterial colony counts, closing the gap that current assessments leave open. Second, combined-stress exposure testing, like the layered desiccation-vacuum-radiation protocols used in recent studies, should be applied specifically to the fungal genera most commonly found in assembly facilities. Without organism-specific survival data, risk models will continue to rely on indirect comparisons.
Third, future facility design could incorporate lessons from microbial ecology. Minimizing surface niches, adjusting humidity cycling, and rethinking material choices in cleanroom construction might limit the inadvertent selection of stress-tolerant species. The goal would not be a sterile room, an impossibility at any realistic scale, but a room that does not preferentially cultivate the organisms most likely to survive spaceflight.
A narrow gap with large consequences
None of this means Mars is destined to be colonized by stowaway molds the moment a crewed vehicle lands. The studies show that some cleanroom microbes are tougher than decades of planetary protection planning assumed, and that fungi have been left out of contamination models that were built around bacterial benchmarks. The gap between those assumptions and the microbial reality inside spacecraft assembly rooms is narrow but consequential. Closing it before the first crewed vehicles depart for Mars is not a theoretical exercise. It is an engineering and policy problem with a deadline that, mission by mission, keeps getting closer.
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*This article was researched with the help of AI, with human editors creating the final content.
