All spiders possess spinning glands and produce amazingly lightweight and strong threads called draglines that enable them to hang from ceilings or use it as a cocoon to protect their offspring or wrap their prey. These draglines are made from silk protein. They are used in manufacturing various materials but getting enough of it is difficult since each tiny spider only produces a small number of draglines.
Producing spider silk using photosynthetic bacteria
A team of researchers from the RIKEN Center for Sustainable Resource Science (CSRS) in Japan recently succeeded in producing spider silk using photosynthetic bacteria. The spider silk is said to be an ultralightweight, biocompatible, biodegradable, and tough material that has the potential to be used in manufacturing tear-resistant clothing, aerospace components, automobile parts, and other mechanical properties, reports Science Daily.
Their study, which appeared in the journal Communications Biology, highlights that silks made by arthropod species are biocompatible and biodegradable. Spider silk, in particular, is ultralightweight but is as strong as steel on a weight for weight basis. Dragline silk combines strength and toughness to an extraordinary degree.
Spider silk in medicine
Co-author Choon Pin Foon from Department of Material Chemistry of Kyoto University and RIKEN Biomacromolecules Research Team said the biocompatibility of spider silk makes it safe to be used in biomedical applications, like scaffolds for tissue engineering, implant devices, and drug delivery systems. For centuries, spider silk has been regarded as the strongest natural fiber used in medical applications. It was recognized to ease healing and connect the skin. Because of its antiseptic properties, spider silk is also known to be effective in clotting blood because of its vitamin K content.
However, since only a trace amount of spider silk can be collected from one spider and breeding large numbers of spiders is not easy, there have been attempts to produce artificial spider silk from various species.
Heterotrophic production of spider dragline silk proteins
For their study, Foon and team focused on the heterotrophic production of spider silk proteins using a marine photosynthetic purple bacterium called Rhodovulum sulfidophilum. A heterotroph is an organism that cannot manufacture its food and derive its intake of nutrition from other sources, animal matter, or mainly plants. In the food chain, heterotrophs are not producers but primary, secondary, and tertiary consumers.
They added that the Rhodovulum sulfidophilum bacteria is ideal for creating a sustainably bio-factory because it uses solar energy, requires nitrogen and carbon dioxide in the atmosphere, and grows in seawater. All of which is inexhaustible and abundant in the environment. Thus, the photosynthetic microbial cell factory promises a sustainable and green platform for biopolymers and proteins, including the spider silks.
MaSp1 or Mannan-binding lectin serine protease 1 is the main element of the Nephila spider silk thought to play a significant role in the strength of the spider draglines. This is why the researchers genetically engineered the bacterium to produce the MaSp1. After optimizing the gene sequence that they inserted into the genome of R. sulfidophilum, they were able to maximize the amount of silk that it could produce. Furthermore, the team found that a simple combination of yeast extract, nitrogen gas, a bicarbonate salt, irradiation with near-infrared light, and artificial seawater enables the bacterium to grow well. Thus, it resulted in the more efficient production of the silk protein.
Further observations also confirmed that the internal and surface structures of the fibers produce in R. sulfidophilum were the same as if it were naturally produced by spiders. Biomacromolecules Research Team’s Keiji Numata, one of the researchers, says that the marine photosynthetic microbial cell factors that produce biodegradable and bio-based materials through a carbon-neutral process can help us in accomplishing Sustainable Development Goals that have been adopted by the United Nations. Their findings can provide feasible solutions for food, water, and energy crises, global warming, and solid waste problems.
Tensile strength of spider silk
Paul Hillyard, the author of the Book of the Spider, explains via Earth Life that spider silk is about as strong as nylon for an equal diameter. Yet, it can stretch several times before breaking, thus more resilient than nylon itself. It is more difficult to break than a rubber. A typical strand of spider silk has a diameter of 0.00012 in (0.003 mm) compared with silkworm silk that is ten times as thick in diameter. Hillyard is not involved in the RIKEN study.
Global synthetic spider silk market and top players
According to market insights platform GuruFocus, the global synthetic spider market is valued at US$ 6665.6 this year and is expected to reach $19840 million by the end of 2026 at a compound annual growth rate of 16.7% between 2021 and 2026. The top manufacturers will be Bolt Threads, Kraig Biocraft Laboratories, Spiber, and AMSilk.
Bolt Threads, a manufacturer of spider silk fibers and fabrics using synthetic biology and microfabrication, is a key player in the biotechnology sector and has an estimated annual revenue of $13M. It has about 145 employees. Its CEO Dan Widmaier, PhD., received a CEO approval rating of 85/100. Data is provided by the business information site Owler.
Other silk spider fiber and fabrics manufacturer included by Owler include Kraig Biocraft Laboratories with an estimated annual revenue of $ <1M and 84/100 CEO rating, Spiber ($50M annual revenue, 66/100 CEO rating), AdvanSource International ($<1M,70/100), and Berkeley Advanced Biomaterials – BAB ($7.1M, 70/100).
Meanwhile, National Geographic shares that there are more than 45,000 known species of spiders in habitats all over the world. Their size ranges from the tiny Samoan moss spider (0.11 inch long) to a massive Goliath birdeater, which is a tarantula. The top places where people can find some of the world’s biggest spiders include the Amazon Rainforest in South America, Laos, Australia, New South Wales in Australia, Sonoran Desert in the USA, Sri Lanka, Brazil, Colombia, Florida, and Africa. According to an article published by The Travel, there are more than 3,000 species of spiders in the Amazon alone. The Golian Bird-Eating Tarantula is also found in the Amazon Rainforest. The Goliath birdeater (Theraphosa Blondi) can even be compared to a puppy dog and, just as the name suggests, birds are part of their diet. Nevertheless, they do not tragically harm humans.
Physicians, the military, police, and other groups are eager to find large quantities of dragline silk from spiders. They recognize that the material can be compacted or woven to make bulletproof clothing, medical sutures, replacement ligaments, ropes for rock climbers, and fishing line, among others. It's no wonder, then, why biotechnologists have turned to other sources of dragline silk as it would impracticable to harvest sufficient quantities of such material from the number of spiders we have in the world.