!First Humans on Mars – Artist Concept
Artist’s concept of astronauts and habitats on Mars. New research shows Earth microbes can survive individual Martian hazards and evade human immune detection. Credit: NASA/JPL-Caltech
NIJMEGEN, Netherlands Human pathogens can withstand individual harsh conditions on Mars and, in doing so, undergo changes that make them harder for the immune system to recognize. That is the central finding of a new PhD thesis from Tommaso Zaccaria at Radboud University, signaling a significant challenge for long duration crewed missions to the Red Planet.
“Our microbial companions will travel with us wherever we go, and we need to understand how they behave in alien environments,” Zaccaria said.
The research tested four known Earth pathogens including the bacteria responsible for pneumonia and wound infections, exposing them one by one to individual Martian hazards: extremely low atmospheric pressure, complete desiccation, intense ultraviolet radiation, and high concentration brines containing perchlorates (toxic salts abundant in Martian soil). Under these isolated conditions, some bacterial strains survived desiccation for up to 16 days.
But Mars does not present a single hazard; it combines all of them at once. When Zaccaria’s team stacked the conditions together to simulate real Martian surface reality, survival dropped sharply from 16 days to just one day.
Shrinking Pathogens and a Weakened Immune Response
The more troubling finding emerged when the surviving microbes were introduced to human immune cells. Bacteria that endured Martian conditions physically shrank in size, and these compacted cells triggered a markedly weaker response from peripheral blood mononuclear cells (PBMCs), the immune system’s frontline soldiers.
The immune cells produced fewer cytokines and less reactive oxygen species, the molecular weapons normally deployed against invaders. The adapted bacteria essentially flew under the radar.
“In effect, the harsh environment may select for or induce bacterial characteristics that help them evade immune detection, potentially making them more dangerous to astronauts,” the authors noted.
Lunar and Martian Dust: A Respiratory Risk
Zaccaria also investigated the threat of extraterrestrial dust. Using Lunar Mare Simulant and Martian Global Simulant, his team exposed human airway epithelial cells and living mice to the particles. The results mirrored symptoms Apollo astronauts called “lunar hay fever”: local tissue inflammation, neutrophilia (a surge of white blood cells indicating tissue damage), and increased activity in genes that control mucus production and lung fibroids, a precursor to chronic respiratory disease.
Lunar dust proved more damaging than Martian dust despite the latter’s toxic perchlorate content, likely due to the sharper, more jagged edges of lunar regolith particles.
Planetary Protection and the Yeast Problem
A third arm of the thesis examined planetary protection protocols. Zaccaria tested how well eukaryotes such as yeasts survive during robotic transit to the icy moons of Jupiter and Saturn. Yeasts showed the highest survival rates among all tested microbes. Some species, including Rhodotorula frigidalcoholis, deliberately stalled their own growth cycle to prioritize DNA repair.
Current planetary protection protocols run their sterilization tests in series (one condition at a time) rather than in parallel (all conditions simultaneously). Because Zaccaria’s experiments used the same serial approach, the work serves as a valid validation: the protocols likely underestimate the resilience of eukaryotic organisms like yeasts.
The Bottom Line for Mars Missions
As NASA and other space agencies push toward crewed Mars missions, the research underscores a dual challenge. The same environmental pressures that kill most terrestrial microbes may also toughen the survivors into more elusive pathogens. And the dust that will inevitably be tracked into habitats poses a measurable respiratory danger.
“Mars isn’t a one off environmental condition,” Zaccaria said. “It combines some of the deadliest known things life can be subjected to. As we expand out into space, we are going to need a better understanding of our biological companions, whether wanted or unwanted, and how they survive these conditions.”
The thesis is published through Radboud University and has been accepted for publication in the journal mBio.