Mara Leite
Background: With plans for crewed missions to Mars in the coming decades, forward contamination and planetary protection are becoming increasingly important topics in Planetary Science and Astrobiology. Forward contamination, the delivery of Earth microbes to other celestial bodies, can pollute the Martian surface and interfere with the search for indigenous Martian life. Vehicles and other equipment can be sterilized; however, bacteria associated with the human body (commensal bacteria) and thus carried by future astronauts cannot be removed. It is, therefore, vital to understand how these microbes may propagate onto the Martian surface. On Earth, an analogue of a Mars habitat has been constructed near Hanksville, in Southern Utah. The Mars Desert Research Station (MDRS) is used to carry out research on various subjects under simulated Martian conditions to better prepare for future missions on the Red Planet.
Objective: This study aims to determine the extent of microbial dispersal and leakage from inside the MDRS to the surrounding soil.
Methodology: We performed DNA sequencing and compared the microbial species present on swabs collected from inside the MDRS with microbial species present on soil samples outside the MDRS.
Results: In addition to bacteria and fungi, we also detected plants, including the henna tree, responsible for the henna dye commonly used to decorate hands.
Conclusion: Our findings suggest a low abundance of human-associated microbes in the soil. A study of this nature can improve our knowledge of microbial dispersion from space habitats onto a Mars analogue soil and can, therefore, help to mitigate the future risk of forward contamination on Mars.
The poster starts by mentioning that one of the major concerns of future crewed missions is Mars' contamination with terrestrial bacteria. To assess the risk of contamination that human-associated microbes can present to the Martian environment, we analysed one of the Mars analogue sites, which are sites on Earth that are geologically similar to Mars and used to conduct scientific research in a Mars-like environment.
The study, a collaboration between the University of Westminster and UCL, took place at the Mars Research Station (MDRS). The MDRS is located in Hanksville, Utah, USA, and it's used to perform 2-week simulated space missions. On the bottom of the slide, a photo of the MDRS and its five buildings is shown:
-the RAM (repair module)
-the Hab (living habitat)
-the GreenHab (greenhouse)
-the observatory
-the Science Dome
The second slide explains the importance of studying the contamination risk of Martian soil by human-associated microbes, also known as commensals. Although harmless, these microbes are residents of the human body. Astronauts will consequently carry them to Mars due to the impossibility of sterilizing humans. If leaked from habitational facilities, commensal microbes can forward contaminate the Martian soil and interfere with Martian microbial life detection. Forward contamination is the contamination of other celestial bodies with Earth's biological material, while backward contamination is the opposite, as illustrated in the image at the bottom of this column. This scheme from NASA shows Earth and another planet linked by a spacecraft traveling from and to Earth to illustrate these two concepts.
In other to evaluate the effect of human presence on the MDRS environment, one of the objectives was to determine the leakage extent of commensal microbes from inside The Hab to the exterior. This objective was achieved by comparing the microbial species present on swabs collected from surfaces inside the MDRS habitat with the microbial species present on a soil sample collected from outside the MDRS after DNA extraction and sequencing was performed on the samples. The objectives are followed by a succession of images that elucidates how commensal microbes through human touch can contaminate indoor surfaces and escape to the outdoors and soil.
Regarding sampling, all samples were collected at the end of Mission 174. The 3rd slide explains that the soil sample was collected adjacent to The Hab by scooping soil into a sterilized tube, while seven indoor swabs were collected from surfaces frequently touched by the crew:
-fridge door
-dining table
-computer keyboard
-handrail staircase
-dining table
-door handle of the extravehicular activity preparation room
-door handle of the workshop area
These locations can be seen on the habitat floor plan provided at the end of the column.
On the right column of this slide, a schematic representation of the methodology is shown, including the kit used for DNA extraction and the genes targeted in the DNA amplification and sequencing.
The last slide displays the general results. The left column has a graph that shows that fungi (orange) and bacteria (purple) were recovered from the majority of samples. Inside the Hab, fungi were more abundant than bacteria, while the soil had a similar abundance of bacteria and fungi. Plant-based food was also detected in some samples.
Our findings suggest a low abundance of human-associated microbes in the soil. Nonetheless, these types of studies can help us mitigate the risk of the dispersal of commensal microbes in crewed missions.