Our Solution: Martian Mycrops
(Mycrops = mycelium + crops)
Purple bead: Perchlorate
Blue bead: Perchlorate-reducing bacteria
Purple string: fungal hyphae
Purple paper: liquid film surrounding hyphae
Green paper: compost/peat additive
Yellow paper: Martian regolith
Green leaves on poles: tepary beans (sample organism)
We can use the hyphae of filamentous hydrophilic fungi to disperse perchlorate-reducing bacteria throughout Martian regolith. The bacteria can then metabolize perchlorate and convert it into harmless chloride and oxygen.
Prototype Video
How It Works
1) Soil Amendment
Martian regolith doesn't have enough nutrients or water retention to support growth. It will first be amended with nitrate-containing compost/peat, which will feed both the bacteria and the fungi. It may also be amended with an oxygen-containing polymer and any additional nutrients required by the specific fungal strain.
2) Bacterial Inoculation
The perchlorate-reducing bacteria Azospira suillum will be introduced into the liquid film surrounding the fungal hyphae by allowing the two to grow/replicate together in a petri dish. This method has been previously used in other similar experiments.
3) Transplantation
Inoculated fungi will be transplanted into the amended regolith and allowed to grow in climate-controlled conditions with regular watering. The fungi will grow toward food sources like compost and gradually take up the full volume of the regolith.
Drawn Diagram of Perchlorate Degredation
4) Degradation
After transplantation, the bacteria will start to degrade the perchlorate available nearby. As the mycelium grows, a chemical gradient in the liquid biofilm will be created by higher perchlorate concentrations further away from the bacteria, causing them to move toward these higher concentrations.
5) Testing
The perchlorate concentrations in soil will be tested before use to ensure that they fall below the toxicity threshold.
6) Planting
After the regolith has been cleansed of perchlorate, it is ready to be planted in. A member of the legume family, such as tepary beans, will be used first since tepary beans grow quickly, produce oxygen, amend the soil with nitrogen, are edible, and are heat and drought resistant.
Choosing a Fungal Strain
Perchlorate-reducing bacteria are facultative anaerobes, meaning that they can only reduce perchlorate in the absence of oxygen. In contrast, most fungi are obligate aerobes, meaning they need oxygen to survive. How can we solve this problem?
Aerobic fungi & oxic soil
Some aerobic fungi, such as Coprinopsis cinerea, create anoxic microniches, allowing anaerobic bacteria to grow in small pockets without oxygen while the mycelium is exposed to atmospheric oxygen. However, the bacteria may migrate out of the pockets, since they prefer to use oxygen over perchlorates.
B) Aerobic fungi & anoxic soil
MacDonald et al. (2020) developed an oxygen delivery polymer that enabled plants to germinate in an anaerobic environment. A similar technique could be applied to allow aerobic fungi to grow in an anaerobic environment, but further research is required to validate this possibility.
C) Anaerobic fungi & anoxic soil
Although rare, anaerobic fungi do exist, such as Tritirachium candoliense, which was isolated from an anoxic pocket in the Arabian Sea, or Fusarium oxysporum, which is a facultatively anaerobic crop pathogen. Anaerobic fungi could survive in a completely anoxic environment, allowing perchlorate-reducing bacteria to function without any risk of interference from oxygen. The soil will be flash-heated before use to kill any pathogenic fungi after perchlorate levels are sufficiently low.
Images from Xiong et al. (2022), MacDonald et al. (2020), and Manohar et al. (2014) respectively
Experimentation
We will experiment with various strains of fungi to measure their efficacy at surviving in Martian regolith and dispersing Azospira suillum. Ideal fungi must be capable of hyphal transport, resistant to high perchlorate concentrations, hydrophilic, and fast-growing. Purpureocillium lilacinum, F. oxysporum, and Lyophyllum sp. Karsten are some initial candidates we have identified for testing.