Overview
Toulouse is known as the French capital of aerospace, housing up to 25% of Europe’s industry jobs in this sector1. With our project “Biomoon”, we aim to contribute to the future establishment of permanent moon bases. A major issue towards this goal is to sustainably provide astronauts with food from local resources. To tackle this challenge, we propose a system that will enable fresh food, such as vegetables, fruits and legumes to grow on regolith, i.e, the unconsolidated rock composing the lunar soil. However, regolith is a stressful environment for plants which grow poorly on it.
Our solution is to engineer Pseudomonas fluorescens, a plant growth-promoting rhizobacteria, to act as a biostimulant. Biomoon will be deployed through 4 modules: one about valorizing astronauts' wastes as a bacterial substrate and three to solve the soil problems (biofilm formation, nitrogen source for plants and response to stress).
Living in permanent moon bases
Currently, food in space is sent freeze-dried in canisters in order to feed astronauts on missions, which is not sustainable in the long run. Alternatively, the growth of plants in space has been well studied2, with most of the cultures being hydroponic. However, this specific type of plant growth poses several problems in a scenario of prolonged space travel:
- Plants need large amounts of water, exceeding by far the very small quantities found on the moon. As a matter of fact, NASA’s SOFIA mission detected quantities about 100 times smaller than those in the Sahara desert3.
- All nutrients for plants need to come from the watering system, meaning that they would need to be shipped regularly, which is prohibitive.
- Not all crops are suitable. While leafy greens and herbs tend to do well, root vegetables and grains, which are significantly more nutritious, can be more challenging to grow in hydroponic systems.
To tackle these constraints in mind, BioMoon offers an innovative solution to grow plants on lunar regolith
Regolith: a porous mineral source lacking in nitrates and carbon, a deadly combination for plants
The term regolith was first coined by geologist George P. Merril in 1897 to refer to “unconsolidated material”. Lunar Regolith has been heavily studied and its composition is well known, so much that you can order it online!
Studies have revealed that several macro and micronutrients are present in regolith: phosphorus, potassium, calcium, magnesium, manganese and copper, although not all of them are readily accessible for plants, like phosphorus which is present as insoluble inorganic phosphate4. Albeit carbon can be found in CO2 form inside space stations, nitrates, essential to plants, are not present in regolith. Overall, plants have been proven to poorly grow on regolith but they present stress-associated symptoms (abiotic stress can, in this case, come from an alkaline pH, heavy metals, reactive oxygen species (ROS) and osmotic pressure).5, 6.
![Lunar base with one astronaut](https://static.igem.wiki/teams/5108/project-description/apollo-11-footprint.jpg)
Pseudomonas fluorescens, a plant-growth promoting bacterium
Regarding the poor availability of nutrients and the stress conditions on the regolith, the use of a biostimulant is relevant. According to the European Commission, plant biostimulant means a product stimulating plant nutrition processes independently of the product’s nutrient content with the sole aim of improving one or more of the following characteristics of the plant or the plant rhizosphere:
- Nutrient use efficiency,
- Tolerance to abiotic stress,
- Quality traits,
- Availability of confined nutrients in soil or rhizosphere7.
One specific type of biostimulant is microorganisms : bacteria known under the designation PGPR (Plant Growth-Promoting Rhizobacteria) enhance growth and general health of plants.
Pseudomonas fluorescens is a Gram negative bacterium identified as PGPR with many interesting properties in our context:
- Its capacity to solubilize phosphorus, enhancing its uptake by the plant.
- The production of phytohormones like IAA (indole-3-acetic acid) and gibberellins, improving germination, root development and growth of the plant.
- The production of siderophores, especially pyoverdine (that gives the bacterium its fluorescence), which are iron-chelating compounds. These may protect the plants from the high level of iron present on regolith8.
- Its capacity to form biofilm which should enhance the water retention of regolith.
BioMoon: a Pseudomonas fluorescens based biostimulant to grow plants on lunar regolith
Pseudomonas fluorescens on regolith
P. fluorescens has already proved its ability to enhance plant growth on poor soils such as regolith, especially by making phosphorus available in the soil9. However, its full potential remains to be exploited in the context of lunar agriculture. Given the limitations of the wild-type strain, we will create an engineered strain that fulfills all requirements to boost plant growth on the lunar soil while using astronaut waste as a source of carbon and nitrogen.
An engineered P. fluorescens to enable lunar agriculture
Module 1
Human waste as the carbon and nitrogen source: creatinine metabolism
Creatinine is a human waste naturally present in urine originating from the degradation of creatine. In 24 hours, up to 1 g of creatinine is produced by a person in good health. Unlike urea and water, this urinary waste is not valorized in any of the space projects we are aware of. On the International Space Station (ISS), 98% of water present in urine is recovered and the leftover, called urine brine (containing mainly concentrated urea and creatinine), is discarded10. While other projects focus on the use of urea to feed bacteria, creatinine has never been investigated as a carbon source11.
Some species of Pseudomonas are able to use creatinine as their sole carbon and nitrogen sources12, but this has not been evidenced for Pseudomonas fluorescens. As these other Pseudomonas strains lack the many advantageous features of P. fluorescens as a plant-growth promoting bacterium, three optimized genes need to be introduced. crnA to convert creatinine into creatine, creA to convert creatine into sarcosine, and soxA to convert sarcosine into glycine that can be used as carbon and nitrogen sources.
![Module1 Illustration](https://static.igem.wiki/teams/5108/project-description/full-module1-img.png)
Module 2
Water retention through biofilm formation
One major goal of our project is to enhance the water retention capacity of regolith since its porosity does not allow the storage of water for long periods. To tackle this problem, we chose to modify the signaling pathway Wsp (wrinkly spreader phenotype) involved in biofilm formation. In this system, the protein WspF acts as a repressor forming a negative feedback loop. It has been demonstrated in P. aeruginosa that inactivating the gene wspF promoted the formation of biofilm13. To inactivate wspF in P. fluorescens, we are planning to use the CRISPR interference (CRISPRi) technology . The dead Cas9 chosen is the one from Streptococcus pasteurianus14.
![Module1 Illustration](https://static.igem.wiki/teams/5108/project-description/module2-img-full-final.png)
Module 3
Nitrogen supply for plants through nitrification and nitration
To grow, plants need macro and micronutrients, among which nitrates are the main and preferential nitrogen source15. Because regolith does not contain nitrogen, we will engineer P. fluorescens to enable the production of nitrates from ammonia originating from the degradation of creatinine. Specifically, we will implement the nitratation-nitrification pathway composed of three enzymes: AmoCAB to convert ammonia into hydroxylamine, Hao to convert hydroxylamine into nitrogen monoxide spontaneously oxidized into nitrite, and Nxr to convert nitrite into nitrate16.
![Module1 Illustration](https://static.igem.wiki/teams/5108/project-description/module3-full-img.png)
Module 4
Oxidative, osmotic, basic pH, and heavy metal stresses
Regolith is a hostile environment for both the plants and the bacteria. This comes from its composition, rich in oxides and heavy metals, as well as its alkaline pH. To help P. fluorescens overcome the stress it is exposed to, we intend to stimulate the global stress response by overexpressing the native stress factors hfq and rpoS17. The protein Hfq is a chaperone, while RpoS is a transcription factor involved in the stress response.
In addition, we want to specifically reduce oxidative stress related damages by overexpressing the catalase KatB18 that degrades oxygen peroxide, the principal factor of oxidative stress.
![Module1 Illustration](https://static.igem.wiki/teams/5108/project-description/module4-full-img.png)
Summary
To summarize, Biomoon is a project that will allow growing essential plants on the moon to ensure the success and sustainability of manned lunar bases. The project combines cutting-edge approaches in synthetic biology and metabolic engineering. Importantly, it has been designed to be integrated in ongoing efforts to optimize material cycles in space installations.
![Lunar base with one astronaut](https://static.igem.wiki/teams/5108/project-description/final-image-description.jpg)
- La filière spatiale sur Toulouse métropole. (n.d.). enseignementsup-recherche.gouv.fr.
- Growing plants in space - NASA. (n.d.). NASA.
- There’s water on the moon? - NASA Science. (n.d.).
- Noble, S. (2009, March 17). The Lunar regolith. NASA Technical Reports Server (NTRS).
- Paul, A., et al., (2022). Plants grown in Apollo lunar regolith present stress-associated transcriptomes that inform prospects for lunar exploration. Communications Biology, 5(1). doi:10.1038/s42003-022-03334-8
- Duri, L. G., Caporale, A. G., Rouphael, Y., Vingiani, S., Palladino, M., De Pascale, S., & Adamo, P. (2022b). The Potential for lunar and Martian regolith simulants to Sustain plant Growth: A Multidisciplinary Overview. Frontiers in Astronomy and Space Sciences, 8. doi:10.3389/fspas.2021.747821
- Regulation (EU) 2019/1009 of the European parliament and the Council of 5 June 2019 laying down rules on the making available on the market of EU fertilising products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 and repealing Regulation (EC) No 2003/2003
- David, B. V., et al., (2018). Pseudomonas fluorescens : A Plant-Growth-Promoting Rhizobacterium (PGPR) With Potential Role in Biocontrol of Pests of Crops. In Elsevier eBooks (pp. 221–243). doi:10.1016/b978-0-444-63987-5.00010-4
- Williamson, J., et al., (2023, July 16). Status of ISS water management and recovery.
- Wyss, M., & Kaddurah-Daouk, R. (2000). Creatine and creatinine metabolism. Physiological Reviews, 80(3), 1107–1213. doi:10.1152/physrev.2000.80.3.1107
- Hickman, J. W., et al., (2005). A chemosensory system that regulates biofilm formation through modulation of cyclic diguanylate levels. Proceedings of the National Academy of Sciences of the United States of America, 102(40), 14422–14427. doi:10.1073/pnas.0507170102
- Tan, S. Z., et al., (2018). A robust CRISPR interference gene repression system in pseudomonas. Journal of Bacteriology, 200(7). doi:10.1128/jb.00575-17
- Fredes, I., et al., (2019). Nitrate signaling and the control of Arabidopsis growth and development. Current Opinion in Plant Biology, 47, 112–118. doi:10.1016/j.pbi.2018.10.004
- Verbeelen, T., et al., (2021). Development of nitrogen recycling strategies for bioregenerative life support systems in space. Frontiers in Microbiology, 12. doi:10.3389/fmicb.2021.700810
- Wu, P., et al., (2021). Stress preadaptation and overexpression of rpoS and hfq genes increase stress resistance of Pseudomonas fluorescens ATCC13525. Microbiological Research, 250, 126804. doi:10.1016/j.micres.2021.126804
- Katsuwon, J., & Anderson, A. J. (1990). Catalase and superoxide dismutase of Root-Colonizing saprophytic fluorescent pseudomonads. Applied and Environmental Microbiology, 56(11), 3576–3582. doi:10.1128/aem.56.11.3576-3582.1990