Team:HUST-China/Description

iGEM_2019
banana-tree
Inspiration
One day, our team leader heard an article about Manila hemp. As a member of the banana family, Manila hemp fibers have many excellent characteristics. So he thought if Manila hemp belongs to banana family, whether the fiber of banana stalk has the same properties and can extract high-quality fiber.

Fortunately, one of our team members is from Guangdong Province. His hometown is a banana producing area. Almost every family has planted a large number of bananas. Once he heard that the whole body of the banana planted is treasure. The banana leaf can also be used to deal with the wound, can be used to wrap traditional Chinese rice-pudding. Banana root is a kind of medicinal material. It can clear away heat and detoxify. Ancient Chinese medicine is also used to treat calculus. But only the stalk of banana, it can make some coarse linen cloth clothes before. Now, with the fiber of chemical industry, no one will choose such clothes. And every year, a large number of banana stalks are cut down, which can only be used as fertilizer in the field for the next year.

After the he told us about this problem, we looked up relevant information and found that 410 million people in the world eat bananas as staple food, and the annual stalk output reached 8.8 billion tons.



We also consulted our college's teachers who are studying ramie degumming technology. They also think that biological treatment of banana stalk to extract fiber is a problem worthy of study. And their ramie and our banana stalk have some similarities. We can do our research based on their relatively mature technology.

So we decided to use biological fermentation to make banana stalk into fine fiber, which can become people's beautiful clothes again in the future.

banana-tree
Description
Banana, a fruit with magical and hidden treasure.
According to Food and Agriculture Organization of the United Nations (FAO), the world's largest producers of bananas in 2017 were India and China, which together accounted for approximately 38% of total production.

In southern China, there grows massive banana trees, and every year after harvesting the fruit, the false stem of the banana tree will be cut off and abandoned on the farm, becoming a kind of agricultural waste.

By searching for the relative information on the internet and communicating with the banana planters, we aware that banana stems are not only huge in scale but also a treasurable raw material resource waiting to be treated and utilized.

The stalk contains abundant industrial precursor and crude materials, including cellulose, lignin, saccharides, proteins, and trace element.



Figure1&2: Banana are staple food for many people[1]
Bananas’ castoff application[2]
Textile
Banana fiber is widely found in banana stalk, banana leaves and fruit shafts, which are natural cellulose fibers, and banana fibers have the characteristics of natural hemp fibers. It is a new environmental-friendly material for waste utilization.



Figure3&4: People use banana fiber to weave clothes[3][4]
Papermaking
The quality of banana fiber pulp is relatively stable. With the improvement of technology, its mechanical strengths are close to bamboo pulp, and banana stalk can be recycled as a new papermaking material. What's more, the emissions on its production line are environmentally friendly.



Figure 5&6: Banana fiber are used in papermaking industry[5]
Fertilizer
The banana stalk waste residue and the microorganisms are put together to produce organic fertilizer, which increases the soil organic matter and improves the soil condition. Achieve the soil circulation of the trace elements.



Figure7&8: Stalk waste can be used as fertilizer[5]
Feed
Banana pseudo stems are rich in nutrients, and protein feed using banana stalks as the main raw material can meet the growth needs of feeding animals.



Figure9&10: Banana relative materials can feed animals[5][6]
Energy
It is rich in a large amount of sugars that can be used to ferment ethanol or biodiesel, which is a green energy source.



Figure11&12: Derivations like ethanol are green energy[1]
Comprehensive Utilization
Lignin is separated and degraded to produce benzene-containing substances, which have great application prospects. According to all the information we have collected, we think it’s necessary and meaningful to treat banana stem. Nowadays most of the banana stems are treated by chemical, such as strong acid and alkali. Chemical-treating not only produce a lot of pollution, but also is low in profit, and the products are poor quality. So we decide to design a green and environmental friendly biological method to process banana stem.

What do we want to get from recycling the bananas’ castoff, especially their stalk?
We focus on cellulose, a kind of polysaccharide which is widely found in plants, as our project goal. Cellulose is the most abundant and renewable natural organic polymer in nature. Besides plants, we can find it in marine organisms and microorganisms either. The chemical structure of cellulose is a large molecule, which is formed by glucose units with beta-1, 4-glycoside bond connecting them. In nature, plant cell wall is the main source of cellulose. [7]

We searched the related reference to look for the information about the cellulose of banana’s stalk, and we found that the content of cellulose in banana is close to ramie, which used widely in textile, and we inferred that the cellulose in banana can be utilized. Hence, we decided to extract the cellulose of the banana. But there are other problems. Compared with ramie, the banana has more lignin (A material mainly located between cellulose fibers as an anti-compression agent, consist of three kinds of phenylpropane units), so we had to remove it. Another content in stalk—pectin (a group of poly-galacturonic acids)—also need to be removed. Therefore, we designed a system which help us to handle this problem.

How we design the system?
First, in order to remove the lignin and pectin in banana stalk, we need special enzyme to decomposed them. By searching lots of reference, we chose small laccase (hereinafter called SLAC), versatile peroxidase (VP) , and pectate lyase (one kind of pectate lyase called PelA). Our goal is to transferred these three genes which is corresponding with the three kinds of enzymes into our model microorganism, the Pichia pastoris.

So, we designed a secrete regulatory system, which use a kinds of signal peptide to make it, and we chose the unique signal peptide corresponding to different enzymes from the six signal peptides we prepared in advance. And in order to regulate the pH in fermentation process, we created a pH responding regulation system, by using some interesting pH-induced promoters. This part we will show elaborately in our design part.

Reference:
[1] https://image.baidu.com

[2] Recent Achievements and Analysis of Comprehensive Utilization of Banana Stalk Wastes, Chinese Journal of Tropical Agriculture, 2013, 33(7):63-67

[3] http://i-want.tw/project/view/id/1466

[4] https://www.walkerland.com.tw/article/view/68039?page=

[5] https://unsplash.com

[6] http://news.cctv.com/world/20070313/106440.shtml

[7] FU Shiyu Progress in Cellulose Research State Key Lab of Pulp and Paper Engineering,South China University of Technology,Guangzhou,Guangdong Province,510640