Team:XJTU-China/Implementation
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XJTU-China
Implementation
Our project this year aims to solve the problem of soil desertification. We hope to improve the ecological environment by inhibiting the process of land desertification by our engineering strains. Our sand fixers alliance will provide a more convenient and effective strategy for desertification control, contributing to a more green and sustainable earth for people and other species.
Based on our design, a symbiotic system of engineered Bacillus subtilis and cyanobacteria Nostoc sp. will be developed, to effectively produce extracellular polysaccharide to form biological soil crusts in the tough condition of desert. Initially Bacillus subtilis are cultured in ampicillin-resistant LB medium, and Nostoc sp. strains are cultured in BG11 medium. They are diluted and mixed after they grow to the logarithmic phase. The concentrations of the two bacteria were determined by blood cell counting method and colorimetric method respectively. Bacillus subtilis are diluted to 106~108 CFU/mL and Nostoc sp. to 5~10 μg/mL. The mixed bacterial liquid was sprayed evenly on the surface of desertified soil at the concentration of 200 mL/m2. Depending on the desert condition, sodium alginate can be added in the bacterial solution to improve the compressive strength of biological crusts and increase the growth efficiency of the initial symbiotic system. When the soil crust on the land surface reaches a certain thickness with the help of our sand fixers alliance (See modeling results) after some times, the barren land then is available to allow some algal crusts to grow and replaced our system gradually. After our symbiotic strain completes its mission, the number and species of microorganisms and plants in the region will be restored to the same as the normal ecological environment, to green the desert again.
In terms of biosafety, the Bacillus subtilis and Nostoc sp. we use are classified in biosafety level 1 (BSL-1), and they are harmless to humans. And they are also strains that already exist in the natural soil environment and will avoid the risk of species invasion. However, we should also consider their unlimited growth in the environment, and the symbiotic system of Bacillus subtilis and Nostoc sp. are well balanced to avoid this issue. Meanwhile, the dead Nostoc sp. will produce phycotoxins, which are harmful to animals and humans, but our Bacillus subtilis can secrete extracellular peptides to degrade phycotoxins, thereby reducing the risk. Moreover, we also consider the possible strains and genetic leakage, but with our suicide switch and anti-escape system, Bacillus subtilis that escapes and spreads will die to ensure the safety.
What’s more, there are still some kinds of challenges in our project. We also need to test the time period and delivery area of the strains inoculated in the desert environment so that they can achieve the highest efficiency. In addition, under natural conditions, our engineering bacteria are at risk of plasmids loss gradually. The engineering bacteria without plasmid cannot produce EPS normally and efficiently, so they will not be able to perform the function as expected. However, we can avoid this problem by integrating the constructed circuit into the genome by genome editing tools like CRISPR-Cas.