There are over 35,000 species of spider — and most make spider silk. So there’s a dazzling array of silks to choose from for making better bulletproof vests, medial sutures or fishing lines.
Spider silk is incredibly strong — it’s stronger than steel at the same weight and thickness. Someday, it could be used in a wide range of products from biodegradable fishing lines to medical sutures to bulletproof vests.
But different spiders make different kinds of silk — and even one spider has different types of silk for different purposes. Cheryl Hayashi is a biologist at the University of California, Riverside studying spider silk.
Cheryl Hayashi: I think that by studying these different silks and by looking at their silk genes, we’ll be better able to design these biomaterials that we can use. So for instance, spider silks vary in how stretchy they are, how strong they are, how long they last in the environment. . . And I think differences like that will make for different kinds of products that we can use.
Hayashi was recently awarded a three-year research grant to classify different kinds of spider silks. She’ll also search for the genetic codes responsible for silk production. Some of those genetic codes might eventually be put into other animals or plants so that they can produce spider silk.
There are over 35,000 species of spider — and most of them produce silk fibers. So there may be many different forms of silk spun by different spiders. And even within one spider species, there are different types of silk for different purposes. Scientists would like to know which types of spider silk are best for which kinds of applications.
Cheryl Hayashi — a biologist at the University of California, Riverside — was recently awarded a three year research grant to classify different kinds of spider silks based on their strength, stretchiness and durability. She’ll also search for the genetic codes responsible for producing silks. Hayashi says the study might even help her understand how the ability to create silk evolved in spiders.
Excerpts from interview with Dr. Cheryl Hayashi:
You’ve just gotten this new grant to do a project over the next 3 years. What are you hoping to accomplish with this project?
CH: My goals for this project are to try to identify and characterize a variety of silks that are spun by spiders. I want to characterize them both in terms of their performance properties and also identify the genes that are used to code for the proteins in the silk fibers. And, I want to better understand how silk genes have evolved in spiders. And, part of this work will also involve understanding the evolution of the spider themselves.
So, spiders make several types of silk?
CH: Oh yes, spiders make a whole variety of silks. The exact number of silks that spiders can make, well we don’t know the answer to that. That’s part of what in the long term I hope to try to understand. Individual spiders can spin more than one kind of silk, and different species of spiders can spin different kinds of silks from other species of spiders. So, the diversity of silks out there could be enormous.
So, are you going to be looking at specific silks or are you going to be categorizing many of them?
CH: Actually, both. I’m going to be trying to do both of those kinds of things. Because, since we need a better understanding of the categories of spider silks, I would need to first of all try to identify what are the different varieties of silks out there. There are some silks that have been pretty well characterized, such as the dragline silk. So for instance, I could look at the dragline silks from a whole variety of spider species. But, on the other hand, I would also want to find out, you know, exactly what are the different types of silks that are used by an assortment of species.
So, what is a dragline silk?
CH: Dragline silk is the trailing safety line that almost all spiders leave behind them. So for instance, you know when spiders drop down from, for instance, the edge of your roof or they drop down from a branch on a tree, they are always suspended by a little trailing safety thread, and that’s called the dragline. And, the dragline is also used by spiders to make the frame of their webs. So for instance, a spider that makes an orb web, the typical sort of circular, wagon-wheel web. All those webs have a frame that’s also made by the same dragline silk.
The orb web is the one that you said looks like a wagon wheel?
CH: Yeah, it’s a circular web with a capture spiral on it. If you think back to Charlotte’s Web, Charlotte was an orb weaving spider.
You said you were going to identify the genes that code these silks. How are you going to go about doing that?
CH: The way I do that is I take spiders and I remove their silk glands. And in the silk glands, the genes that encode the silk proteins are very highly expressed, because that’s, you know, the part of the spider that’s actively making, synthesizing silk protein. And so, by taking the silk glands from the spider, I can then using a variety of genetic techniques, I can actually look for spider silk protein gene sequences in those silk glands.
What does highly expressed mean?
CH: Highly expressed means the gene is actually activated, and the gene is actually turned on and is being used by the organism to make the specific protein. So for instance, you know, all our cells have the same genes in them, but depending on where the cell is in your body it’s making a different suite of proteins.
So, then the ones in the silk glands are going to be highly expressed because they are being used by the silk glands.
CH: Exactly, well for instance genes for venom proteins will be highly expressed in the venom glands of spiders.
Why do you think the average person should care about the project?
CH: Well, there are several reasons why I think the average person should care. First of all, there has been a lot of interest in spider silks as a novel biomaterial. So, in the future I fully expect to see a whole line of products out there made from spider silk — things like biodegradable fishing lines, medical sutures, different kinds of rope, and also things like bullet proof vests. People have been saying that spider silks might have a really good application there. So I think that in the near future we’re going to start seeing these spider silk products out there. And, basically, there’s a whole diversity of spiders out there and they are all doing something a little bit different. [10:25] I think that by studying these different silks and by looking at silk genes we’ll be better able to design these biomaterials that we can use. So for instance, spider silks vary in by how stretchy they are, how strong they are, how long they last in the environment-do the spiders use them on the order of one day and then replace the silk line or are they using them for years? And I think differences like that will make for different kinds of products that we can use.
So what are the advantages of using spider silk over other traditional materials for these products?
CH: Well, it turns out that the spider silks that have been looked at tend to have greater strength and toughness for the amount of material you have. So, basically by weight, spider silk, for instance, is much stronger and tougher than high tensile steel. And that has to do with the properties of spider silks when you account for how fine and light they are. A typical spider silk is one to two orders of magnitude thinner than human hair.
But it has a strength that’s greater than the same size in steel?
CH: Yes. If you could scale steel down to size of spider silk, spider silk is far superior. And similarly, if you could scale spider silk up to the size of a steel bar, it could be amazing what you could do with such a material. So people are looking into applications of what we call recombinant spider silk — spider silk that’s not made by spiders but we put spider silk into other organisms to mass produce spider silk. So the potential for spider silk for commercial technology I think is one of the main reasons why the average person should care about this. And, also all the research that I will be doing — all the genetic information, all the performance information-that will all be put on public databases, so other scientists, high school students could have access to all this data.
And, what do you think this field of research will look like in 20 years?
CH: That’s where I think things get really exciting. So right now it’s pretty time-consuming and also pretty expensive to clone each of these spider silk genes. I think that those techniques will just get better and more streamlined. So I expect that within the next ten years it will be very easy and routine to say catch a spider and characterize its silk properties and silk gene sequence. So, I hope that will be much easier, so for instance I could look at hundreds of spiders rather than about ten spiders in the period of a couple of years. Also, if you look forward to 20 years, you know if you think about how spiders use their silk, it’s one thing to study how the genes that make the silk proteins but I could hand you a blob of silk and we couldn’t really do too much with it. It would just be a blob of silk. And similarly for a spider they need to not only make silk proteins, but they need to be able to spin the silk into a fiber and then spin that fiber into the various kinds of web that they use. And so, in twenty years people might be looking at the genetics of web spinning behaviors. That would be a completely new avenue of research that right now is not accessible.
So it’s not just the components of the silk, it’s how it is spun.
CH: Exactly. When we look at the evolution of spiders and the evolution of how they use silk, there are three major components there. One is that spiders have to have the silk proteins, sort of the raw material for the silks. Second, spiders have to have the machinery to actually spin the silk proteins into a usable fiber. So, that would be their spinnerets and the different types of nozzles and tubes associated with those spinnerets that actually turn silk proteins into fibers. And the third thing is the behaviors. For instance, if you think about an orb web, it’s an amazing structure. What are the behavioral sequences used to construct such architecture? And what are the genes underlying those behaviors? And how have those genes changed over time?
CH: The biodiversity of spiders is really quite enormous. We have over 35,000 described species. That means species that have been named and that people have drawn pictures of in the scientific literature. So, that means there are far more spiders out there that have never been described. So if you just think about the biodiversity of spiders and the fact that they live in all terrestrial environments, you start realizing just how interesting this could be to look at the diversity of their silk genes. There are all kinds of spiders out there, they live in pretty much all terrestrial habitats, and they all do something a little different from each other.