Over the centuries, mariners have wondered how mussels manage to stick so tightly to the sides of ships.
Researchers at Purdue University say they might have figured out the mussels' secret: They extract iron from seawater to create their glue. The results could help scientists create new superglues and develop nontoxic paints to rid ship bottoms of barnacles and other pests.
Their four-year study analyzed the adhesive created by 800 blue mussels collected off the Maine coast - the kind that grow about four inches long and are staples at many East Coast seafood restaurants.
Jonathan Wilker, a 34-year-old chemistry professor and lead author, said he got the idea for the study while scuba diving off New England and Southern California before he came to landlocked Purdue four years ago. He showed that mussel glue is sticky enough to hold onto everything from a ship in a storm-tossed sea to a glass plate to a Teflon pan.
"You could have a Teflon ship, and [mussle glue] would still stick to it. It's amazing stuff. It's totally cool," said Wilker.
The study, published last month in a German scientific journal, follows decades of work by dozens of researchers who have tried to use mussels as models to come up with a water-resistant superglue.
But the researchers say theirs is the first study to firmly establish the use of a metal by any organism to create an adhesive. Barnacles, kelp and other organisms might use similar techniques.
"The impressive properties derived from metal-protein interactions may prove to be a prevalent theme in marine biomaterials," says the article in the journal Angewandte Chemie.
Some researchers remained skeptical. Iron's role in creating the glue has been suspected for years, but whether it is absolutely necessary is an open question, they say.
"With mussels, you're talking about very reactive proteins that do a lot of chemistry. They want to stick to things," said Timothy J. Deming, a chemistry professor at the University of California, Santa Barbara, who reviewed the study. "My gut feeling is, if you took the iron out of the process, they would still find a way to stick."
Wilker concedes that iron might not be the only key or necessary ingredient in every case. "We're saying iron is the only one we've identified so far. There could be others," he said.
Mussels, like clams, are bivalves that feed on plankton, which they filter from seawater. But unlike clams, they have a beard of tough fibers, known as byssal threads, that shoot out as they drift and attach to create a permanent home on a reef, rock or ship.
In the study, scientists placed 800 blue mussels on glass sheets in saltwater tanks and scraped off the adhesive plaque that the organism created to stick to the glass.
Researchers took proteins from the mussels and added different agents to see what would form the best "cross links" or bonding molecules. They found iron to be the most effective.
Wilker said the study could lead to the development of improved adhesives - for surgical procedures and everyday use. The results also could help create paints to replace the copper-based paints that discourage barnacles but foul harbors.
"If we can understand how these adhesives work, we could develop replacement materials and get rid of some of that copper," Wilker said.
The study might also help scientists understand and combat the blue mussel's smaller and nastier cousin - the thumbnail-sized zebra mussel, Wilker said.
Zebra mussels have cost power plants and municipal water systems millions of dollars since they showed up in the Great Lakes in the 1980s, arriving by way of discharges of European shipping ballast.
Unfortunately, zebra mussels have no natural enemies here, and developing a safe weapon to fight them will take time, said David Terlizzi, a marine scientist at the University of Maryland Marine Biotechnology Center in Baltimore.
"Whether this helps, we'll have to wait and see," Terlizzi said.