Team:ICJFLS/Description
Background
In 2020, the "most stringent plastic restriction ban" in China's was issued. It is said that the use of non degradable disposable plastic straw will be prohibited in China's catering industry by the end of 2020. A report entitled “Plastic & Climate: The Hidden Costs of a Plastic Planet” triggered public discussion. The report pointed out that the production and incineration of plastic in 2019 produced more than 850 million metric tons of greenhouse gases—equal to the emissions from 189 five-hundred-megawatt coal power plants. According to the current trend, the annual emission will increase to 1.34 billion tons by 2030. By 2050, the greenhouse gas emissions from plastic could reach over 56 billion tons, equal to 14% of the entire remaining carbon budget. In addition, the harmful gases and pollutants produced by plastics in the stages of production, transportation and incineration will also affect water sources, soil and even organisms.
As people pay more and more attention to environmental protection, the plastic ban storm quickly swept the world. The British government announced earlier this year that it plans to push for a new "plastic ban" in England. The European Commission proposed a "plastic restriction" plan in May, recommending banning disposable plastic products like plastic straws.
In fact, plastic straw is one of the most commonly used tableware in the catering industry, especially in beverage stores. The data showed that the annual use of plastic straws in China was about 46 billion in 2019, and about 500 million plastic straws were discarded every day in the United States, and about 8.5 billion plastic straws every year were discarded in the United Kingdom. The plastic degradation time may be as long as 500 years. These plastic straw have caused serious harm to the ecological environment and animals. One straws into the turtle's nasal cavity almost killed the turtle.
With the increasing voice of global plastic ban, the environmental pollution of plastic straw has been paid more and more attention.
Under the background of plastic restriction ban, businesses chose mainly the paper straw and polylactic acid (PLA) straw. However, the paper straw has some defects such as broken, low strength, easy softening, heat resistance, peculiar smell and safety. The surveys showed that 56% of respondents were unwilling to use paper straw, 31.2% of the respondents didn't support for the paper straw, and 76.6% of the respondents believed that the paper straw affected their interest in drinking milk tea and other drinks. PLA straw is not heat-resistant and UV resistant. The price is relatively expensive and the storage time is short. Few shops use PLA straw. Therefore, there were a long way on accepting the paper straw and PLA straw instead of the plastic straw. It is really a very intractable problem for businesses and customers. However, the environmental cost of plastic straw is too high, and finding a better alternative is still the most important issue.
Inspiration coming from milk tea drink and 2020 IGEM project
We young students like to drink milk tea. Since the paper straw used for drinking milk tea will be soft in a short time, the merchant will give us 2 or more paper straws. We also felt bad tastes about the paper straw. We thought that there is any other type of straw. Paper straw is so difficult to use. Why do we have to use it?
We got internet search and found that there are starch straws which have no harm to environments. However, starch mainly comes from food. It was not good choice to use food to make starch papers since there are many poor and hungry people in the world. Are there any ways to deal with it? synthetic biology?
We thought of cellulose synthesis of our 2020 iGEM project, and interestingly, cellulose is as a support material of straw. So, we got the idea on biosynthesis of amylose, the most important component of starch for making straw. Amylose has good gel strength, low water holding capacity and poor water absorption and can form a film with good plasticity, which features are suit for making straw. We are very excited that we will solve the two main components of the starch straw using synthetic biology method. We decided to carry out this project.
Useful application of synthetic biology for amylose straw
At present, the technology of preparing starch straw from grain starch is feasible, which can be made by starch heating, gelatinization, cooling and aging, and drying. There are two components in grain starch which are amylose and amylopectin. Interestingly, amylose is more suitable for making straw because of its stronger tensile strength, better process ability and extrusion and film forming, which can increase the brittleness and strength of straw.
Through biosynthesis of amylose, it can not only solve the white pollution, but also save food and ensure the health of national diet.
Another great advantage of using synthetic biology method to synthesis amylose is that amylose is difficult to be purified from starch.
Amylose straw is a good choice.
Project goal
Our project goal is that amylose was synthesized in E. coli through synthetic biological technology, combined with the biosynthetic cellulose achievements of 2020 iGEM, which laid a foundation for the preparation of amylose straw.
Starch consists of amylopectin and amylose. Amylopectin is a branched glucose polymer with α-1,6 glucosidic bonds that connect linear chains, which is synthesized by the catalytic action of several enzymes, such as ADP glucose pyrophosphorylase (AGPase), starch synthases (SSs), starch branching enzymes (BEs), and starch debranching enzymes (DBEs). Differently, amylose is essentially linear and composed of 1,4-linked α-D-glucose chains; AGPase and granule-bound starch synthase (GBSS) are involved in amylose production.
To realize the production of amylose synthesis in E. coli, we synthesized 2 genes related to the synthesis of amylose, which were ADP glucose pyrophosphorylase (AGPase) containing 2 subunits, ADG1 and APL1, and granule-bound starch synthase 1 (GBSS1) based on the sequence from Arabidopsis thaliana.
Using a degradable material to produce straw will be a good idea. After many searching, we found that the amylose produced from bacteria can satisfy our needs for making a straw.
References:
[1]Plastic & Health: The Hidden Costs of a Plastic Planet (February 2019). https://www.ciel.org/wp-content/uploads/2019/02/Plastic-and-Health-The-Hidden-Costs-of-a-Plastic-Planet-February-2019.pdf
[2]Chen Yanling. Ban Plastic, Starting with Plastic Straws [J]. Environmental Economy, 2018, 31(15):24.