. Implementation .
Overview
Climate change not only brings about the increase of global average temperature, but also leads to more frequent, widespread, and harsh extreme weather events. Among these disastrous weathers, the sudden drought and frost will pose a serious threat to people's lives, agriculture and forestry economy, and social development.
To reduce the immediate damage from frost and drought weather to agriculture, we designed a gene circuit and regulated the expression of target products, achieving the function of anti-icing and anti-drought. For anti-icing, the engineered bacteria are constructed to lighten the damage from unexpected cold or wet snaps, in which the designed gene circuits could respond to the temperatures plummeting and express antifreeze proteins to protect the plant tissue from frost. For anti-drought, another two engineered bacteria are constructed to synthesize bacterial cellulose and hyaluronic acid respectively, achieving a moisturizing function with the cross-linked material in the soil.
Proposed Implementation
Target users
Our target users involve workers in forestry, agriculture, and grassland, individual farmers and scientists were also included.
The sudden disastrous climate of frost and drought would trigger the death of vegetation and commercial crops, resulting in worse environmental problems and severe economic losses. For example, the taste of tea is not only different with the processing flow but also depends on the age of the tea tree and microflora around the tea root. If frost and drought kill the microflora and tea tree, the farmer has to recultivate new trees which would cost 3-5 years (please see Integrated Human Practice for details). The worst situation is that they will forever lose the exceptional taste of the tea before. Our product can alleviate the damage from the sudden disastrous climate of frost and drought to crops (please see Design for details).
Our comprehensive strategy provides a paradigm in antifreeze and water-retention strategies. This can be an invaluable platform for research groups (and iGEM teams) around the world to develop more and more devices and engineered strains to cope with damage from disastrous weather.
Usage
For antifreeze, the targeted part includes leaves and roots. Our product (freeze-dried powder of engineered bacteria) will be distributed to the soil during the irrigation process and colonized on the surface of the root of vegetation and commercial crops (please see Design for details). Our product can also be sprayed on the above-ground parts of the plant, such as the surface of leaves. Antifreeze protein produced by engineered bacteria can alleviate the damage from the sudden disastrous climate of frost.
For water retention, the cross-linked product of bacterial cellulose and hyaluronic acid from two engineered strains, which exhibit excellent water retention performance, was selected as water retention material. For large-scale farms, we can combine our drought-resistant bio-factories (FermentX, a well-design continuous fermentation bio-reactor with software and model controlling, please see Hardware and Software for details) with irrigation systems, making it extremely easy to apply our products to the soil. The water-retention material (liquid broth of engineered bacteria) can be also sprayed on the surface of leaves and buds to prevent moisture volatilization in a long-term drought.
Safety
If we apply the project in the actual environment in the future, there are two potential biosafety hazards associated with our engineered bacteria. One is the leakage of engineered bacteria into the environment, and the other is the potential horizontal gene transfer (HGT). These may pose potential risks to the environment and biodiversity. Thus, we design and develop the kill switch to ensure the bio-safety.
To avoid the leakage of engineered bacteria, MazF is selected as the toxin by cleaving the mRNA of bacteria inside. For the anti-icing part, we introduce the inverter to make engineered bacteria survive when arabinose is present and die when it runs out. So, the arabinose was added to the freeze-dried powder of engineered bacteria. When arabinose is exhausted, the expression of toxin protein kills the bacteria escaping from the working environment. For the anti-drought part, the arabinose was added to the cross-linked product produced by the engineered bacteria, which could induce the expression of MazF directly to kill the bacteria escaping from the working environment when glucose is exhausted.
To avoid horizontal gene transfer, the gene, expressing toxin protein CcdB, was inserted into a vector and its expression is regulated by a weak constitutive promoter J23109. At the same time, Gene ccdA, which encodes the corresponding antitoxin CcdA, is introduced into the genome of the engineered bacteria and its expression is regulated by a strong constitutive promoter J23106. The natural bacteria that absorb the vector from our bacteria will be killed by the toxin protein CcdB because it doesn't have the corresponding antitoxin protein CcdA.
Risk assessment
Since engineered bacteria are used when the project is implemented, there are potential risks to public health and the environment. Therefore, before we put our devices into production, testing, and applications outside the laboratory, extensive testing should be performed to ensure that our engineered bacteria are safe for humans and the environment.
Besides, China passed a new biosecurity law and it come into effect on April 15, 2021. The law establishes systems for biosecurity risk prevention and control, including risk monitoring and early warning, risk investigation and assessment, and information sharing. It also has provisions to prevent and respond to specific biosecurity risks, including major emerging infectious diseases, epidemics, and sudden outbreaks, and biotechnology research, development, and application. To keep our activities legal, applying for permits and approvals is necessary if we execute our proposed implementation.
