Even if manage to mitigate the many challenges of travelling through space, touching down at our destination does not mean the challenges are over. Far from it.
Whether it’s the moon, Mars, or — who knows — other extraterrestrial territories, we’ll need to build a base, recycle as much as we can, make sure we have food, and so on.
Especially for semi-permanent space settlements or scientific outposts, self-sustainability is critical. Loop-closure is the term that refers to the recycling and reuse of resources. As you can imagine, it’s the ultimate goal for any space mission that seeks to establish a toehold on non-earth soil. In an ideal scenario, we add in-situ resource utilisation (or ISRU) to the closed loops.
This means that our intrepid space colonists learn to make use of the resources that are available wherever they have landed.
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There are several hurdles to clear before we can travel to space outposts with closed loops and ISRU, though. The lack of deployable technologies and the costs of taking things to space look like a killer one-two punch.
But what if we could take something very small and very light, with all the functional prowess of a biological Swiss army knife? Enter microbes.
Bio-alchemy in space
Nature’s true alchemists hide among the microbes — an umbrella term that includes bacteria, viruses, fungi, and assorted tiny critters. Several of these microorganisms are adept at taking some molecules and turning them into other ones.
All organisms do this, but certain microbes have taken it to another level. Can we leverage, enhance, or tweak their abilities to help us build sustainable space habitats? It certainly seems so. In 2021, a group of scientists concluded that: “microorganisms will continue to play an increasingly critical role in astronaut health, habitat sustainability and mission success.”
A recent comprehensive paper sets out a roadmap of how to best use microbial support in space exploration.
Habitat air bioremediation uses microbes to remove carbon dioxide from the air and convert it into oxygen and organic matter that can be used to produce food or other materials. For example, researchers are testing cyanobacteria like Anabaena sp. PCC 7938 in Mars-like conditions to capture carbon dioxide and fix nitrogen.
Can’t plants do this? Yes, but if we’ve learned anything from the novel/movie The Martian it’s that growing plants in Martial soil is tricky (although microbes could help here, we’ll get to that soon). So initially, microbes might be the better option.
Ask anyone with a toddler would know, it’s surprising how much biological waste even a tiny human can produce. Human waste management is a major challenge for space exploration and most current solutions (for example on the ISS) focus on how to compact, sterilise, and dispose of human waste, rather than recycling it.
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However, solid human waste could be used as fertiliser or — it might not sound tasty — useful nutrients can be extracted from them. The European Space Agency (ESA) has a long-running project called MELiSSA (Micro-Ecological Life Support System Alternative) that investigates how diverse types of waste streams, including human ones, could be upcycled using microorganisms.
No space colony or outpost will ever be sustainable and self-sufficient if it can’t produce its own food. Bringing along livestock in the shuttle is not much of an option. But seeds of major crops? That isn’t a problem. However, remember The Martian. Earth plants don’t exactly grow well in lunar or Martian soil.
Here too, microbes can help. Plants have microbiomes. Especially the microbe communities in, on, and around their roots contribute — sometimes greatly — to nutrient uptake, growth, and pest prevention. Tailoring the microbes associated with the crops space explorers take along can lead to ‘agricultural probiotics’ that could be used to inoculate the extraterrestrial soil to make it more hospitable to plants.
Pharmacy and biomining
Image having a pharmaceutical foundry in space. No more dependence on the drug supply space explorers carried along and tailored medication on demand. Microbes have been used on Earth for the production of pharmaceuticals and they can be genetically engineered to produce pharmaceuticals.
For example, the cyanobacterium Synechocystis sp. PCC 6803 can produce acetaminophen, a versatile drug to treat infection and pain.
The human gut microbiome is relevant here as well. Human-associated bacteria can synthesise a range of secondary metabolites, including antibiotics. Vice versa, tailored probiotics might somewhat support human health in challenging environments through the gut microbiome.
In biomining, microorganisms extract valuable metals from minerals and waste, and it could provide a cost-effective supply of resources in space. For example, chemolithoautotrophs — microorganisms that oxidise iron and sulphur — could potentially bio-mine sulphide minerals on Mars.
Microbial extraction of rare earth elements and other metals has already been demonstrated on the ISS, but more research is needed to improve the scalability and performance of these systems. Similar approaches can help in recycling electrical waste and soil remediation.
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Building and powering
Microbes themselves can build infrastructure for space explorers. For example, MICP, or microbially induced calcite precipitation, involves microorganisms precipitating calcium carbonate, which can be used as a binding agent. This process can also help in the bioremediation of toxic compounds and CO2 sequestration.
Another option is myco-architecture. Fungal mycelia can form dense networks that combine with other materials, like regolith, to form mycelium-based composites. NASA is looking into fungi to construct furniture and habitat shells for the Martian and lunar surfaces.
Finally, certain anaerobic bacteria can reduce organic waste to generate electric current. Microbial fuel cells (MFC) utilise microbes to convert chemically bound energy into electricity.
Off to Mars, then? Not yet. To efficiently harvest microbial alchemy, there are a few more advances we need. Microbial processes depend on various factors such as temperature, pressure, pH, gravity, and radiation, among others.
Many of the processes described above will require bioreactors, which provide a controlled environment for the microbes. These bioreactors need to be designed to provide an appropriate environment for specific processes, and they need to provide us with means of tracking the processes we’re interested in. Most bioreactors also need water, which, depending on where our explorers touch down, could be in short supply.
Microbes are magical, but they are also tricky. They might ‘out-evolve’ the functions we’re dependent on, or they could turn virulent. So, on top of close tracking, the option to contain and isolate microbes gone wrong, ideally without having to shut everything down, is important.
Those challenges, though, are being addressed as you read this. Bioreactors and microbial engineering are gaining momentum in the context of terrestrial applications, such as soil remediation, carbon capture and sequestration, and hydrogen production.
Microbially-mediated sustainability can work both on Earth and elsewhere.