Team:CAU China/Description
Description
Background:
“The Soil is the Great Parent of All.”
As students from China Agricultural University, we have long been taught about the importance of soil, the mother of agriculture and Chinese cultivation culture. However, we must accept the fact that our soil has been going through serious degradation for decades, and saline-alkaline soil is one of these major threats.
As its name implies, saline-alkaline soil refers to the soil that contains heavy soluble salt and alkali. The saline-alkaline land can pose great threats to agriculture industry, including drought, flood, and infertility. Besides, few plants or bacteria can survive in such a harsh environment, resulting in a damaged soil ecosystem and Earth Cycles.
In our motherland, China, the saline-alkaline land has become an increasingly noticeable problem. The area of saline-alkaline land in China has reached 99 million hectares (Sumner and Shum 1998), ranking third in the world. What’s worse, the once normal soil in other regions is slowly developing into saline-alkaline soil due to overcultivation or lack of protection (Wang, Wu et al. 2004).
(Source From: Qingdao Saline-Alkali Tolerant Rice Research and Development Center)
Meanwhile, saline-alkaline soil is widely distributed throughout the world as well. According to UNESCO, the global saline-alkaline land covers 9.54 billion hectares and accounts for one fifth of the cultivated area, posing a threat to global agriculture and ecology.
As for previous solutions, people have tried to use the combination of irrigation and leaching, chemical improvement and planting salt-tolerant crops, which have achieved some good results. However, there are still problems in their cost and efficiency (Ming, Xiufen et al. 1997). According to the latest view, biological measures, which means to restore saline-alkaline land by microorganisms or engineered plants, is a better solution compared to irrigation, chemical or agricultural methods, and that’s why CAU_China has chosen to deal with saline-alkaline problem in this year’s iGEM competition.
Inspirations:
When choosing our final project, some work done previously in soil restoration have inspired us greatly:
- Prof. Feng Gu from College of Resources and Environmental Sciences, China Agricultural University, is an expert in environment restoration. He told us that the soil problems are closely linked to the population issue all over the world. He also pointed out that using synthetic biology is probably the most efficient way to improve soil, since the traditional agricultural method, such as planting Nostoc flagelliforme, takes at least 120 years to improve saline-alkaline soil.
- An example of saline-alkaline soil improvement with Bacillus subtilis has been reported in 2018 (Zhou, Hou et al. 2018). According to their work, Bacillus subtilis can obviously improve soil salinization, improve the water holding capacity of the soil and increase the soil aggregate. The key to its function is the water-retaining agent, gamma-polyglutamic-acid (γ-PGA). We got inspiration from this research and did further surveys, then finally considered γ-PGA as the target product that our bacteria need to synthesize.
Also, some previous iGEM projects have inspired us as well:
- JNU-China, 2019: Their project goals involve the production of γ-PGA by Corynebacterium glutamicum with a high yield, which verified that the assumption of using the genes capA/capB/capC to get γ-PGA in our project is feasible.
- XJTU-China, 2020: Their project background is about the soil desertification, which is closely related to soil salinization. Their synthetic biological method in soil restoration and induced lethality greatly inspired us.
To sum up, the saline-alkaline soil is a serious global problem related to agricultural industry, ecosystems, and even population issues. Current methods may have some effect, but they still have disadvantages in efficiency and long-term effect. Under such a background, synthetic biological measures stand out due to its potential in generating valuable products continuously and interacting with plants’ roots and bacteria in soil environment. There are some previous researchers who used bacteria or even synthetic biology in soil restoration, and their results proved a promising future for this method. That’s why we think our project will be a useful application of synthetic biology, for it is meaningful, well-grounded, and stands a good chance of success.
Our Solution:
This year, CAU_China decided to focus on a safe, efficient and low-cost treatment of saline-alkaline soil by synthetic biological means. The general goal of our project is to build a new bacterial agent that can not only improve the saline-alkaline soil, but can also prevent secondary salinization and ensure biosafety.
In previous brainstorming, we’ve found the viscous polymer, gamma-polyglutamic-acid(γ-PGA), which can generate hydrogen ion through dissociation and can therefore neutralize the alkali and absorb exchangeable sodium ion in soil colloids, resulting in soil restoration. Besides, it can also form soil aggregate (a good structure of soil), improve water-holding capacity of the soil and benefit plants’ roots. Hence, we think γ-PGA is just the very target product we need to find for this project.
There are two bacteria related to γ-PGA: Bacillus subtilis, which can synthesize γ-PGA if they are fed with the raw material, glutamic acid. And Corynebacterium glutamicum, which can synthesize glutamic acid at high yield itself.
Initially, we want to design a symbiotic system in which C.glutamicum can provide glutamic acid and B.subtilis can produce γ-PGA. However, during further discussion with experts, our team's instructor Yang Jinshui pointed out that these two bacteria are not known mutually beneficial symbiotic relationship in soil, and if they are isolated in space, the treatment efficiency will be greatly reduced. Therefore, we finally chose Corynebacterium glutamicum as our chassis and we want to make sure it can synthesize γ-PGA alone through engineering.
Consequently, our detailed goals and solutions are as follows:
- Make Corynebacterium glutamicum able to synthesize γ-PGA by itself
Plan: Transfer the γ-PGA producing genes from Bacillus subtilis into Corynebacterium glutamicum - Make Corynebacterium glutamicum able to synthesize γ-PGA at high yield
Plan: Modify the TCA cycle in Corynebacterium glutamicum to get more glutamic acid for γ-PGA synthesis - Ensure biosafety
Plan: Design a kill switch that can be turned on by low salinity and normal pH; Insert genes into the genome of our engineered bacteria - Take others' opinions or attitudes into full consideration
Plan: Integrated human practices, including background research, interviews and on-site visits
Besides, to complete our project, we also spent great efforts in education, modelling, and collaboration.
Until now, we have already finished some verification experiments and the construction of our gene circuits. However, due to time limit, we are still testing our gene circuit and make improvements accordingly. We have also worked hard in integrated human practices, education, communication, collaboration, partnership, modelling, inclusivity and so on.
How COVID-19 Impacted Our Project
The occasional outbreaks of COVID-19 all over China have greatly changed the way we push our project ahead. Due to the restriction policy, some of our team members can't return to the lab in summer and this posed a challenge to our wet lab work. Besides, we had to give up many human practice chances, such as offline gatherings and on-site visits, due to the pandemic.
Fortunately, we managed to make up for these losses through joint efforts, online meetings and email interviews. However, our project still has some flaws due to the lack of offline experience and we plan to continue doing wet lab work and polishing our human practices in the following year.
References
[1] Hansmeier N , Tzu‐Chiao Chao, A Pühler, et al. The cytosolic, cell surface and extracellular proteomes of the biotechnologically important soil bacterium Corynebacterium efficiens YS-314 in comparison to those of Corynebacterium glutamicum ATCC 13032[J]. Proteomics, 2010, 6(1).[2] Zhang J . Review of Improvment and Utilization of Saline alkali Soil[J]. JOURNAL OF SHANDONG FORESTRY ENCE AND TECHNOLOGY, 1997.
[3] Sumner, T. and S. B. Shum (1998). From documents to discourse: shifting conceptions of scholarly publishing. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. Los Angeles, California, USA, ACM Press/Addison-Wesley Publishing Co.: 95–102.
[4] TENGHong-fen, HUJie, ZHOUYue, et al. Modelling and mapping soil erosion potential in China[J]. Journal of Integrative Agriculture, 2019(2):251-264.
[5] Wang C Y , Zhi-Jie W U , Shi Y L , et al. The Resource of Saline Soil in the Northeast China[J]. Chinese Journal of Soil Science, 2004.
[6] Wicke B , Smeets E , Dornburg V , et al. The global technical and economic potential of bioenergy from salt-affected soils[J]. Energy & Environmental Science, 2011, 4(8):2669-. 2681.
[7] Zhou B , Hou Y , Wang Q . Characteristics of water and salt migration in process of improving saline alkali soil with bacillus subtilis[J]. Transactions of the Chinese Society of Agricultural Engineering, 2018, 34(6):104-110.