Breaking down the microbiology world one bite at a time

Mars in a BOX – Microbes to survive Martian environment.

Written by:

Charlotte van de Velde

The first successful mission to Mars was already in 1964 by Mariner IV, which returned the first close-up pictures of the Martian surface. During the next fifty years, we continued to explore our neighbor planet and have successfully landed multiple Mars rovers to explore it in more detail. Curiosity and Opportunity (the latter now inoperative) would search for evidence of, amongst other things, ancient life (chemical building blocks, biosignatures) and water.

Recently, on the 18^th of February 2021, a new Mars rover called Perseverance landed on Mars. One of the main goals of this car-sized rover is to identify ancient Martian environments capable of supporting life and seeking out new evidence of former microbial life existing in those environments!

Rocket scour and wheel prints of Perseverance. Credit: NASA/JPL-Caltech

So far, researchers discovered that the Martian environment is very dry as well as having extremely low temperatures and pressure. Moreover, lacking a substantial atmosphere, different kinds of radiation such as UV, X-ray or Gamma rays are bombarding the planet’s surface. From a terrestrial standpoint, the Martian surface appears to be quite biocidal…

So why do we want to know if our earthly microbes would survive space travel and moreover, if they can grow on Mars? With crewed long-term missions to Mars planned in the future, microbes could be very helpful for our survival because they could help us produce food and material supplies independently from Earth. An example of this would be using fungal mycelium to help replace foam, timber, flooring and furnishings as mentioned in this interesting review. Maybe more important, we need to know if human-associated microbes would survive on the planet, as some are a health-risk for astronauts.

In a recent study performed by Marta Cortesão and colleagues, four microbes were tested for their survivability in Martian conditions. Typically, Mars-analog studies are performed in Mars-like environments on Earth where aridity, extreme temperatures and elevated radiation dominate the landscape.

Such a similar environment, however, can be found high above the Earth’s surface in the stratosphere (about 15~50 km above the surface). And this environment might be even more similar to what is found on Mars compared to Mars-like environments on Earth: intense, full spectrum UV radiation, high energy ionizing radiation, desiccation (extreme dryness), hypoxia (low oxygen levels) and ultralow temperatures and pressures. And this is precisely where the authors conducted their experiment.

MARSBOx (Microbes in Atmosphere for Radiation, Survival, and Biological Outcomes Experiment) payload (figure from original article).

Using a high-altitude scientific balloon, the authors sent MARSBOx (Microbes in Atmosphere for Radiation, Survival, and Biological Outcomes Experiment) to ~38 km altitude for seven hours. They looked at survival and metabolic response of four microorganisms relevant to astrobiology while monitoring radiation and other environmental factors.

Two bacterial extremophiles (Salinisphaera shabanensis and Buttiauxella sp.) were included to test the hypothesis that strains isolated from extreme Mars-analog environments on earth could survive. S. shabanensis can be found in extremely salty conditions at 1.3km below the surface of the sea. Buttiauxella is found in oxygen-deficient, nutrient-limited sulphidic spring water.

The fungus Aspergillus niger and the bacterium Staphylococcus capitis were included because they are human-associated and opportunistic pathogens. Moreover, these two microorganisms have already been detected inside the international space station (ISS) and are likely to travel to Mars in crewed space missions.

Sample preparation (figure adapted from original article).

Survival fraction
One of the four species, Buttiauxella, did not survive both the laboratory controls and the MARSBOX flight samples. The other three species did survive at different levels and were tested in several conditions:

Lab-conditions on earth (lab control, which means 5 months of dessication)
In a bottom layer in the MARSBOx where they were shielded from radiation
In the top layer where they received mars-like radiation.

For the fungus A. niger, both a thick layer of spores and a single (mono) layer of spores were tested.

Move the slider to change from the original version to the adapted version (figure from original article).

In the figure above you can see how many bacterial cells or fungal spores survived the harsh conditions. Both bacteria are very sensitive to radiation, as either one cell in a million was able to grow (S. shabanensis), or none at all (S. capitis). The spores of A. niger were quite resistant to all of the conditions: At least one per hundred spores survived!

Cell wall stress
The authors also looked at resistance against cell-wall stress of A. niger. They grew a certain number of spores and observed how well the fungus grew under stress conditions caused by an antifungal compound called Caspofungin and a cell wall stressor called Calcofluor White. As shown in the picture below, the UV-shielded spores show a decreased ability to cope with cell wall stress while the UV-exposed spores were highly sensitive and only grew when a high number of spores were initially placed on the plate.

Different reactions on cell well stress of *A. niger* (figure from original article).

In conclusion, three of the four species survived the journey! They could (temporarily) endure the harsh conditions of the stratosphere, and would potentially survive on the Martian surface. This study gives a better understanding of which microbes could survive in environments that are normally perceived as ‘lethal’.

But this experiment is just the beginning, as we don’t know yet what mechanisms these bacteria used to survive. One of the hypotheses for the survival of A. niger is that it has ‘sunscreen-like pigmentation’ or a cellular structure that protects it against the radiation. Future research could help scientists to determine WHY these microbes survived and WHAT mechanisms they had to use.

A next mission for MARSBOx is already scheduled: it will fly into the stratosphere from Antartica, where the conditions (radiation from the sun and cosmic rays) will be even more similar to those on Mars. And with renewed focus on Mars exploration, the need for additional Mars-analog studies will only increase in the coming years.