From a spider gene to a silken thread

The spinnerets in the abdomen of the spider produce a fine, strong thread. The spider weaves this into a web, uses it to abseil, or forms it into a cocoon for egg deposition.

Researchers identify the specific segment of the spider’s genome thatcontains the genetic blueprint for the silk protein used to spin its thread. The aim is to copy this gene segment.

A plasmid is created, first on the computer, then in the laboratory. This ring-shaped DNA molecule containing the blueprint for the pro-tein is introduced into coliform bacteria using electrical pulses.

In addition to its own DNA, the bacterium’s cell interior now contains the plasmid with the blueprint for the silk protein.

The bacteria that have successfully taken up the plasmid and its protein blueprint are placed onto a nutrient medium in Petri dishes. The bacteria multiply rapidly in the warmth of an incubator.

In a bioreactor, the bacteria are fed with nutrients and sugar and continue to multiply. Adding a specific substance initiates the production of silk protein.

The silk protein must now be isolated from the biomass in a downstream process. Through multiple separation steps, the silk protein is enriched and the latte-colored liquid gradually becomes lighter.

After the last purification step, the protein must be dried. This takes place in a spray dryer in which the water evaporates. What’s left is a white powder.

In the spinning mill, the protein powder is stirred into a solvent. The mass, which resembles viscous honey, must be degassed and filtered to exclude impurities.

The solution is pressed through a spinneret into an agglomeration bath, causing the protein to solidify and the molecules to align. The fine filaments are stretched and combined to form a thread. The silk thread is passed through a water bath, dried on heated rollers and wound onto a bobbin. Fully wound, the bobbin holds one kilometer of thread, which weighs just nine grams.

The biotechnologically produced silk thread has a wide range of applications and has so far mainly been used in the textile industry—either as an innovative new fiber or as a more sustainable alternative to conventionally produced silk from Asia. For example, the material is currently used in the door handles that are installed in the interior of the Mercedes-Benz VISION EQXX concept car. The Parisian luxury brand Balenciaga produces blouses made from fermented spider silk. And the Omega watch brand is already weaving the