Yoshihiko Kuwana¹, Katsura Kojima¹, Hideki Sezutsu², Ken-ichi Nakajima²

¹Silk Materials Research Unit, ²Transgenic silkworm Research Unit

［Abstract］

A transgenic silkworm which produces new silk material combining the tensile strength and elasticity of spider dragline silk has been successfully generated. This new spider-type silk, “Tough Silk” is 1.5 times tougher as compared to normal silk. A processing method similar to normal silk has also been successfully applied in production of textile using “Tough Silk”.

［Keywords］

Keywords: garden spider, transgenic silkworm, dragline, toughness, silk

［Background］

Developing a transgenic silkworm which expresses the modified spider dragline protein in cocoon silk fibroin could facilitate in improving the tensile strength and elasticity of silk known for high quality natural fiber. Since spider dragline has excellent tensile properties, we cloned the cDNA of a dragline protein gene from a garden spider (Araneus ventricosus). In 2007, we succeeded in generating a transgenic silkworm using an experimental strain silkworm as host. However, because of the limitations presented by the poor physical properties of the silk produced, reeling of raw silk from the cocoons and weaving with the silk fibers could not be performed. Therefore for practical applications of transgenic silk, it is necessary to use a silkworm strain that can produce smooth, uniform silk such as the C515 in commercial strain and to introduce the dragline cDNA of Araneus ventricosus into that strain.

［Results and Discussion］

1. In order to generate transgenic silkworm, it is important to perform micro-injection of DNAs before cell division of diapause-broken eggs. However, it was quite difficult to break diapause of eggs artificially for micro-injection. We improved the traditional acid-treatment by adjusting the C515 strain, and finally succeeded in generating a transgenic silkworm expressing the spider dragline protein (Fig. 1).
   
2. The cocoons from the transgenic silkworm could be pulled into raw silk and mass production could be performed as shown in Fig. 2. Using densitometry, we calculated the amount of spider dragline protein against the total fibroin and that was about 1 % w/w. From the tensile test results, the toughness (breaking energy of a fiber) improved by 53.2 % as compared with native raw silk (Fig. 3).
   
3. The transgenic raw silk could be degummed in a usual industrial process. After degumming, the glossy and elasticity of the transgenic silk were the same as normal silk. A vest woven using the spider-dragline-protein containing silk demonstrates the utility of transgenic silk (Fig 4). This “Tough Silk” is 1.5 times tougher than normal silk and could provide a new strong and tough fiber for textile industry.
   
4. Although there are studies showing that spider dragline protein could be produced using bacteria, development of a tough fiber for industrial purposes has never been reported so far. Our “Tough Silk” produced by the transgenic silkworm is the first application of fibers which contains spider dragline proteins.

Fig. 1. Comparison of the dry cocoon shell weight of the experimental and “Tough Silk” strains.

 

Fig. 2. A processing method similar to normal silk has been successfully applied in the production of textile using “Tough Silk”.

 

Fig. 3. Comparison of toughness with other fiber materials shows that “Tough Silk” requires 1.5 times more energy to break than normal silk.

 

Fig. 4. A vest made of “Tough Silk”.

 

[Reference]

1. Kuwana Y, Sezutsu H, Nakajima K, Tamada Y, Kojima K (2014) High-toughness silk produced by a transgenic silkworm expressing spider (Araneus ventricosus) dragline silk protein PLoS ONE 9 (8):e105325