Written by Lorenzo Mahoney ‘24
Edited by David Han ‘24
If you ask most people who the last person to walk on an extraterrestrial surface was, chances are that they won't even know the name of Gene Cernan. Moonwalking hasn’t been literal since 1972 but fifty years later, the possibility of exploration all the way to Mars has become a talking point and perhaps even an expectation for humanity moving forward. However, the massive challenge Martian travel poses requires a multidisciplinary research effort. The harsh, distinct conditions of a planet dozens of millions of miles away make each and every design feature for novel missions to the red planet critical. These crucial decisions carry weight, quite literally. Every pound of cargo for a shuttle bound towards Mars requires 99 additional pounds and costs $10,000 to overcome Earth’s gravity and supply enough propellant fuel to travel the vast distance (1). Limiting the transport mass is an overarching goal for successful and more sustainable space travel. Beyond rocket science, the environmental conditions of the journey and its destination pose constraints on material viability. The vacuum-like weightlessness compounds space’s massive temperature variations and high radiation levels (2). Space travel plans need to minimize weight while maximizing life forms with extreme tolerance: that’s where the world of microbes comes in.
A key component to making human travel to Mars possible is harnessing what’s abundant at the destination. Working under a framework of in situ resource utilization (ISRU), it is a question of how to connect Martian chemical resources into outputs functional for human nutrition, health, and habitation (3). On Mars, carbon dioxide and nitrogen gas are significant portions of the atmosphere. Hydrogen and oxygen gasses are not as readily available but can be manufactured through the hydrolysis of water (4). Frozen water on Mars is located on the poles and in-ground reservoirs under the topsoil. While plentiful groundwater might sound like a blessing, the high levels of perchlorate salts in Martian regolith, its geological surface, permeate into reservoirs and toxify them.
Searching for solutions, scientists refocused on our own planet. As far away as Mars is, some of its extreme features are replicated here on Earth. Rock and water samples from the hypersaline Big Soda Lake in Nevada yielded a collection of bacteria able to grow, replicate, and thrive in salty conditions resembling Mars’ water environments (5). Their survivability makes these specific bacteria powerful biological chassis, where their resistant genome can be the standard to which target genes are added to amplify specific functions. None of the Big Soda Lake organisms had the perchlorate reductase enzyme, which converts the salts into molecular oxygen gas (5). In the context of human survival on Mars, the ability to transform surface toxins into breathable gas would be incredibly valuable. No bacteria candidates with the enzyme have been shown to survive in Martian salinities either, but genetic engineering can combine function with survival now. Compared to more mechanical water-retrieving technologies like reverse osmosis machines, microbial approaches contain less mass and don’t require servicing or repair of manmade parts. Through a variety of organisms, biological systems can develop fuel, food, and pharmaceuticals from the most basic of compounds. As Dr. Lynn Rothschild, Brown faculty member and senior scientist at the NASA Ames Research Center, writes, “For millennia we have used biology to do chemistry on Earth. In the future, we will use biology to do chemistry beyond Earth.”(1)
For example, the Methanobacterium thermoautotrophicum was originally discovered in a waste-treatment facility sample of sludge (6). Cultivated in bioreactors, the rod-shaped bacterium can react with carbon dioxide and hydrogen to form methane ripe for fuel use. Whether using CO2 from crew members exhaling during initial travel or derived from Martian regolith during their stay, such extreme critters are being fine-tuned for this very function. Current estimates of scaled-up bioreactors with maximum chemical extraction from regolith forecast the ability of the bacteria to create the methane necessary for return travel in 153 days. Compared to delivering additional fuel from Earth, the ISRU return approach lessens fuel-apportioned traveling weight by 83% (4). Similarly, employing microbes in food production reaps massive reductions in the cost of transport. For a six-person crew to arrive, live, and return from Mars, current projections of vegetarian diets necessitate nearly 5000 kg of transported bulk and prepared items (7). Using saline-resistant cyanobacteria families to produce dry mass spirulina from photosynthesis could deliver nutrition for the entire stay and return at under 70% of the vegetarian wet-food approach (4).
Of course, eating dry-stock superfood supplements for every meal for multiple years is a fate worse than any bodybuilder could imagine. Infusing the spirulina approach with synthetic flavorings derived from organisms (vanillin from yeast, for example) could make the most weight-effective diet more bearable (8). Other synthetic biology discoveries are making it possible to develop standard pharmaceuticals in situ. A multi-year occupation on Mars would require resupplies of common drugs, as most rapidly degrade or expire in non-controlled conditions (9). Acetaminophen, a common over-the-counter pain reliever, has been synthesized in a variety of organisms by redirecting amino acid biosynthesis. In one such case, the introduction of a mushroom reductase gene into E. coli allowed the model organism to manufacture the relevant drug (10). While E. coli is not itself viable for intragalactic travel, proposed pathways in more suitable organisms have been achieved with comparable genes of interest. In a recent project, a group of Berkeley scientists was able to develop acetaminophen production in spirulina factor Arthrospira platensis, opening the doorway to combining space travel medicine into existing food supply models (11).
Across a variety of components vital to facilitating life beyond Earth, microbes are proving to successfully deliver substantial amounts of products for health and energy. Sampling Earthly environments similar to the high-salt, oxygen-lacking conditions on Mars has upturned a variety of organisms able to make the trip beyond our atmosphere. In a mission constrained by weight and volume, their microscopic size and rapid replication are ideal. Zooming in further, microbes’ genomes provide the background for bioengineering to weave genes into their genetic fiber, expanding their functions beyond what is found in nature. So, when there is another “giant step for mankind” onto Mars, some of the smallest organisms on Earth will have made the largest leap possible.
References
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2. Karouia F, Peyvan K, Pohorille A. Toward biotechnology in space: High-throughput instruments for in situ biological research beyond Earth. Biotechnology Advances. 2017 Nov 15;35(7):905–32.
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6. Zeikus JG, Wolee RS. Methanobacterium thermoautotrophicus sp. n., an Anaerobic, Autotrophic, Extreme Thermophile. J Bacteriol. 1972 Feb;109(2):707–13.
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9. Mehta P, Bhayani D. Impact of space environment on stability of medicines: Challenges and prospects. J Pharm Biomed Anal. 2017 Mar 20;136:111–9.
10. Shen X, Chen X, Wang J, Sun X, Dong S, Li Y, et al. Design and construction of an artificial pathway for biosynthesis of acetaminophen in Escherichia coli. Metab Eng. 2021 Nov;68:26–33.
11. Hilzinger JM, Freidline S, Sivanandan D, Cheng YF, Yamazaki S, Clark DS, et al. Acetaminophen production in the edible, filamentous cyanobacterium Arthrospira platensis [Internet]. bioRxiv; 2022 [cited 2022 Dec 1]. p. 2022.06.30.498297. Available from: https://www.biorxiv.org/content/10.1101/2022.06.30.498297v1
[Image] NASA-Apollo8-Dec24-Earthrise.jpeg [Internet] [Cited Dec 11 2022] Available from: https://en.wikipedia.org/wiki/Earthrise
[Image] web_feature_photo_petri_dish.jpeg [Internet] [Cited Dec 11 2022] Available from:https://science.nasa.gov/biological-physical/news-media/image-gallery/petri-dish-holding-microbial-isolates