Spiderworms: Using Silkworms as Hosts to Produce a Hybrid Silkworm-Spider Silk Fiber

Spider silk has received significant attention due to its fascinating mechanical properties. Given the solitary and cannibalistic behavior of spiders, spider silk farming is impractical. Unlike spiders, silkworms are capable of producing large quantities of a fibrous product in a manner mimetic to spiders, and there already exists an industry to process cocoons into threads and textiles for many applications. The combination of silk farming (sericulture), a millennia old practice, and modern advancements in genetic engineering has given rise to an innovative biomaterial inspired by nature; transgenic silkworm silk. This project focuses on the creation of chimeric silkworm-spider silk fibers through the genetic modification of silkworms. Advanced genetic engineering techniques were used to introduce the minor ampullate spider silk (MiSp) genes into the silkworm genome. A subset of these transgenic silkworms was cross-bred with other transgenic silkworms containing the same spider silk gene in a different section of the silkworm genome to create hybrid, dual-transgenic silkworms. The transgenic silk samples showed increased mechanical properties compared to native silkworm fibers, with the strongest fibers approaching or surpassing the mechanical properties of native spider silk. The transgenic silk retained the elasticity of the native silkworm silk and gained the strength of the spider silk. Ultimately, genetic engineering opens the door to mass produce synthetic spider silk in an established organism and industry, and the results of this project demonstrate that the properties of silkworm silk can be predictably altered through this technology

Silkworms with Spider Silklike Fibers Using Synthetic Silkworm Chow Containing Calcium Lignosulfonate, Carbon Nanotubes, and Graphene

Silkworm silk has become increasingly relevant for material applications. However, the industry as a whole is retracting because of problems with mass production. One of the key problems is the inconsistent properties of the silk. A means by which to improve the silk material properties is through enhanced sericulture techniques. One possible technique is altering the feed of the silkworms to include single-wall carbon nanotubes (SWNTs) or graphene (GR). Recently published results have demonstrated substantial improvement in fiber mechanical properties. However, the effect of the surfactant used to incorporate those materials into the feed on the fiber mechanical properties in comparison to normal silkworm silk has not been studied or reported. Thus, the total effect of feeding the SWNT and GR in the presence of surfactants on silkworms is not understood. Our study focuses on the surfactant [calcium lignosulfonate (LGS)] and demonstrates that it alone results in appreciable improvement of mechanical properties in comparison to nontreated silkworm silk. Furthermore, our study demonstrates that mixing the LGS, SWNT, and GR directly into the artificial diet of silkworms yields improved mechanical properties without decline below the control silk at high doses of SWNT or GR. Combined, we present evidence that mixing surfactants, in this case LGS, directly with the diet of silkworms creates a high-quality fiber product that can exceed 1 GPa in tensile strength. With the addition of nanocarbons, either SWNT or GR, the improvement is even greater and consistently surpasses control fibers. However, feeding LGS alone is a more economical and practical choice to consistently improve the mechanical properties of silkworm fiber

CRISPR/Cas9 Initiated Transgenic Silkworms as a Natural Spinner of Spider Silk

With a similar fiber spinning apparatus to spiders, silkworms are a potential host to spin spider silk-like fibers. In recent studies, it is still a challenge to incorporate and express native-size spider silk genes at a precise location in the genome of heterologous hosts. A fixed-point insertion and expression strategy has been designed in this study to overcome this limitation. Through CRISPR/Cas9 initiated non-homologous end joining, native-size spider silk genes (major ampullate spidroin 1 (MaSp1) and minor ampullate spidroin 1 (MiSp1) of Nephila clavipes) have been successfully integrated at defined locations in the fibroin heavy or light chain genes of silkworms. This is also the first report of using precise replacement through CRISPR/Cas9 and expressing native-size MaSp1 or MiSp1 using endogenous fibroin heavy/light chain promoters in silkworms. The transgenic spider/silkworm fibers exhibit improved mechanical properties approaching natural spider dragline silks. The strategy may also facilitate the integration and expression of large exogenous proteins at defined sites within a heterologous expression system

CRISPR/Cas9 Initiated Transgenic Silkworms as a Natural Spinner of Spider Silk

Using transgenic silkworms with their natural spinning apparatus has proven to be a promising way to spin spider silk-like fibers. The challenges are incorporating native-size spider silk proteins and achieving an inheritable transgenic silkworm strain. In this study, a CRISPR/Cas9 initiated fixed-point strategy was used to successfully incorporate spider silk protein genes into the Bombyx mori genome. Native-size spider silk genes (up to 10 kb) were inserted into an intron of the fibroin heavy or light chain (FibH or FibL) ensuring that any sequence changes induced by the CRISPR/Cas9 would not impact protein production. The resulting fibers are as strong as native spider silks (1.2 GPa tensile strength). The transgenic silkworms have been tracked for several generations with normal inheritance of the transgenes. This strategy demonstrates the feasibility of using silkworms as a natural spider silk spinner for industrial production of high-performance fibers