Spider silk from bacteria 
Escherichia coli bacteria have been genetically engineered to produce artificial spider dragline silk, which is five times stronger than steel and has multiple potential applications.
Sang Yup Lee at the Korea Advanced Institute of Science and Technology (KAIST) led the research to find a viable alternative to spider-farming, which is virtually impossible due to spiders’ territorial behaviour. The E. coli bacterium was an ideal target, as it is widely used in industry and its optimum growing conditions are well-known.
Firstly, the researchers identified the portion of spider DNA which coded for silk protein expression in the spider Nephila clavipes and inserted this into the DNA of E. coli. Initial attempts to get the bacteria to produce spider dragline silk proteins were unsuccessful, as the silk is rich in the amino acid glycine and the proteins have a high molecular weight and a highly repetitive nature. High levels of stress response proteins from the bacteria were observed.
Lee tells tce that analysis of enzymes within E. coli and experiments with increasing the levels of different elements within the process led to the researchers increasing the levels of tRNAGly, an important coding structure for the protein. The genes coding for the two types of tRNAGly were overexpressed in plasmids, small rings of coding DNA found within bacteria. Raising the tRNAGly pool led to increased cell growth of 30–50% and much higher production of the highest-weight silk proteins, which was further increased by raising the levels of glycine available.
“We could obtain appreciable expression of the 285 kilodalton spider silk protein, which is the largest recombinant silk protein ever produced in E. coli. That was really incredible,” says Lee.
Yields of protein were 0.5–2.7 g/l, but Lee says that in unpublished work they have achieved yields of 4 g/l. This is comparable to a previously reported method in tce for bee silk.
Sang Yup Lee at the Korea Advanced Institute of Science and Technology (KAIST) led the research to find a viable alternative to spider-farming, which is virtually impossible due to spiders’ territorial behaviour. The E. coli bacterium was an ideal target, as it is widely used in industry and its optimum growing conditions are well-known.
Firstly, the researchers identified the portion of spider DNA which coded for silk protein expression in the spider Nephila clavipes and inserted this into the DNA of E. coli. Initial attempts to get the bacteria to produce spider dragline silk proteins were unsuccessful, as the silk is rich in the amino acid glycine and the proteins have a high molecular weight and a highly repetitive nature. High levels of stress response proteins from the bacteria were observed.
Lee tells tce that analysis of enzymes within E. coli and experiments with increasing the levels of different elements within the process led to the researchers increasing the levels of tRNAGly, an important coding structure for the protein. The genes coding for the two types of tRNAGly were overexpressed in plasmids, small rings of coding DNA found within bacteria. Raising the tRNAGly pool led to increased cell growth of 30–50% and much higher production of the highest-weight silk proteins, which was further increased by raising the levels of glycine available.
“We could obtain appreciable expression of the 285 kilodalton spider silk protein, which is the largest recombinant silk protein ever produced in E. coli. That was really incredible,” says Lee.
Yields of protein were 0.5–2.7 g/l, but Lee says that in unpublished work they have achieved yields of 4 g/l. This is comparable to a previously reported method in tce for bee silk.
