Team:XHD-Wuhan-China/Implementation
Proposed Implementation
Introduction
Deinococcus radiodurans (DR) is widely used in various extreme environments due to its amazing radiation resistance, special cell structure, super DNA repair ability, efficient antioxidant defense system and cell purification system. It may survive in the harsh environment of Mars. Because there are lots of insoluble phosphates on Mars, plants can’t effectively absorb phosphorus, so our project design was to use DR to improve the content of phosphorus in Martian soil. Therefore, we constructed the phosphate dissolving system, phosphate dissolving plus system, and GDH-Pro system in DR，which can achieve different degrees of phosphate dissolving effects.
In this project, We successfully constructed three phosphate dissolving systems with different efficiencies: Phosphate dissolving system, Phosphate dissolving Plus system, and GDH-Pro system, and verified the function of three phosphate dissolving systems to decrease pH and dissolve phosphate, we also completed evaluation and comparison of various systems. DR with function of dissolving phosphate, can be applied to the following aspects:
Figure 1. The phenotype of Deinococcus radiodurans.
Transformation of Martian soil
Microbial landing on Mars is the first step of human migration to Mars. The Martian soil contains a large amount of phosphorus in the form of dolomite (Ca9NaMg(PO4)7) and chlorapatite (Ca5(PO4)3Cl ). Among them, chlorapatite is very similar to fluorapatite ( Ca5(PO4)3F), the most important phosphate rock on earth. Moreover, the biological toxicity of chlorapatite is less than that of fluorapatite. Therefore, it is possible to directly use phosphorus from Mars as a source of phosphorus fertilizer for Martian agriculture.
However, the above-mentioned phosphates belong to insoluble phosphates and are not easy to be directly absorbed and utilized by plants. In order to meet the needs of crops growth, phosphorus must be released from insoluble phosphorus minerals. However, ordinary microorganisms can't adapt to the harsh environment of Mars. Our modified DR can survive in the outdoor soil of Mars, directly transform the surface soil of Mars, so that the absorbable phosphorus content can meet the needs of normal plants growth, and can be applied to Mars exploration and migration.
Researchers can use DR R1 and modified DR to test the resistance in hash environments such as radiation exposure, high temperature environment and low temperature environment switching, proving it can adapt to the harsh environment of Mars. Cultivating the modified DR in the Martian soil is the prerequisite for transforming the Martian soil, In addition, researchers can also test whether the modified DR can grow normally in the simulated Martian soil.
New chassis organism for iGEM
In the past years, many teams had plans to transform the Martian soil. However, the chassis organisms they used were all Escherichia coli, and the actual survival chance on Mars was very low. The DR we used is the most promising species to survive in the Martian environment, and has the strongest reliability in the actual application scenarios of soil modification on Mars. At the same time, we introduced DR into the iGEM species library for the first time, and provided mature gene expression systems, providing an important solution for environmental modification in extreme condition.
As a supplement to phosphate fertilizer
Phosphorus is an essential mineral element for plant growth, but the content of phosphorus in soil that can be directly absorbed and utilized by plants is very low. Most of phosphorus exists in the form of insoluble inorganic phosphorus. However, the large use of phosphate fertilizer is easy to cause serious pollution to the environment. Therefore, bioavailability of soil insoluble phosphorus has been a hot topic for researchers for a long time. It is a preferred method to release insoluble phosphorus from soil by microorganisms with phosphate solubilizing effect, so as to reduce the input of phosphate fertilizer and enrich phosphorus in soil.
As for the molecular biological mechanism of phosphate solubilizing microorganisms, previous studies have shown that it mainly secretes gluconic acid and decrease the pH of soil. The secretion of gluconic acid involves GDH and PQQ, so we chose DR which could synthesize PQQ by itself as chassis organism. At the same time, DR could adapt to various extreme environments, and the range of soil that could be transformed was also greatly increased.
With the function of dissolving phosphate, DR could improve the phosphorus content of soil, reduce the use of phosphate fertilizer, avoid excessive pollution to the soil environment, and also reduce the planting cost.
Possible challenges and difficulties
The research on the genetic background of DR is not as clear as that of E. coli, so we need to consult more article and explore more in functional design. Moreover, the growth cycle of DR is longer than that of E. coli, and the cultivation time and experimental process will be more time-consuming. In this project, we completed most of the experiments. However, we have not yet verified whether the DR with a phosphate dissolving system still has amazing resistance to radiation and various extreme environments, which determines whether our modified DR could survive on Mars. Meanwhile, the following problems need to be solved in the process of DR modification:
1. The special cell structure of DR require special plasmid transformation method
2. The genetic stability of related strains needs further evaluation
3. Soil testing similar to Martian soil composition is required
4. The growth cycle of DR is longer and the observation of experimental results is slow
References
Adcock, C. T., Hausrath, E. M., & Forster, P. M.. (2013). Readily available phosphate from minerals in early aqueous environments on mars. Nature Geoscience, 6(10), 824-827.
Ahemad, Munees. Phosphate-solubilizing bacteria-assisted phytoremediation of metalliferous soils: a review[J]. Biotech, 2015, 5(2):111-121.
Khairnar N P , Misra H S , Apte S K . Pyrroloquinoline-quinone synthesized in Escherichia coli by pyrroloquinoline-quinone synthase of Deinococcus radiodurans plays a role beyond mineral phosphate solubilization.[J]. Biochemical & Biophysical Research Communications, 2003, 312(2):303-308.
Xiao-Fei C , Meng N , Fei F , et al. Research Progress on the Radiation-resistant Mechanisms of Deinococcus radiodurans[J]. Biotechnology Bulletin, 2017.
