Signal and Noise

Enzyme-based coatings developed at the University of Minnesota help protect port infrastructure by disrupting the signals underwater bacteria use to communicate.

By Nick Minor and Kristal Leebrick

In any seaport or freshwater marina around the world, just beneath the surface, and you’ll find an ongoing battle between the boats, docks, bridges—anything made of steel—and a cast of aquatic bacteria in search of a submerged surface to call home. The biocorrosion created by these bacterial hitchhikers is especially dire in cold climates where winter brings the added wear and tear of scraping ice. And Duluth-Superior Harbor is ground zero, as aquatic bacteria corrode nearly 50,000 pounds of steel there each year.

Two University of Minnesota scientists—Randall Hicks, a microbial ecologist in Duluth, and Mikael Elias, a biochemist in the Twin Cities—have developed an enzyme coating they believe could rewrite the story of biocorrosion in Duluth and around the world. Their work shows extraordinary promise in helping prevent biocorrosion in seaports and could have the added bonus of being environmentally friendly.

The scientists’ collaboration began in late 2016, after Elias read about Hicks’s and postdoctoral associate Simon Huang’s work on testing anti-biocorrosion coatings in Gateway, published by the University of Minnesota BioTechnology Institute. The timing was auspicious for Elias. He and his students had recently engineered an enzyme that breaks down the chemical signals bacteria use to coordinate and build things like biofilm, a matrix of proteins and carbohydrates that can lead to biocorrosion. The interruption of those signals is like overlaying an impenetrable static onto construction workers’ walkie-talkies. Without the ability to communicate, the bacteria can’t coordinate enough to build anything.

Communication-disrupting enzymes are well-known and widely available, yet their potential ability to prevent bio-induced corrosion was unknown. In addition, in order to prevent biocorrosion in the Duluth-Superior Harbor, an enzyme needs to be hardy enough to withstand organic solvents of paints, temperature shifts that can kill most plants and animals, and endure scrapes from massive winter ice flows. This is where Elias’ specialty—protein engineering—came into play. Elias refined the enzyme to such an extent that it is now “so stable that we can dilute them into paint, a very harsh treatment for a protein,” says Elias, “and they still remain active.”

After reading about Hicks’s and Huang’s work, Elias reached out and asked if Hicks could squeeze one more coating into his tests. From there, the duo started with a two-month, proof-of-concept test in the lab, made possible through funding from the University’s MnDRIVE Environment initiative, which supports promising research on environmental remediation. In this short-term test, the enzyme, which was suspended in a durable acrylic, outperformed every other coating Hicks had been examining. But the real test lay ahead. After presenting the enzyme coating to companies like PPG, BASF, and Ecolab, Elias and Hicks heard the same message over and over: The companies needed to know if it would remain effective for years, not just two months.

Elias and Hicks received a much larger “demonstration grant” from MnDRIVE, which supported two years of testing, including testing in the Duluth-Superior Harbor. The work exceeded all expectations: over those two years, the enzyme coating was more effective at preventing biocorrosion than any other available coatings and it appears to do no harm to the environment as it kills nothing outright. Currently, 85 percent of the market for anti-biocorrosion coatings is dominated by toxic copper oxide paints. As with nearly every other coating available, copper oxide paints work by brute force, killing the organisms responsible for biocorrosion. Copper oxide’s toxicity to biocorrosive organisms also means it’s toxic to other living things.

Copper oxide paints were technically banned by multiple U.S. states. “But, because there is no alternative,” explains Elias, “the ban is constantly being pushed back.” Copper oxide, a heavy metal and potent environmental toxin, has been accumulating in portside ecosystems around the world for decades.

“The alternative that we’re working on,” says Elias, “is ecological because it’s a protein. A protein, by definition, is biodegradable. It’s amino acids.” The enzyme’s approach—disrupting the communication between bacteria that get biocorrosion started—is utterly novel.

The enzyme coating could rewrite the story of biocorrosion in Duluth and enable additional infrastructure protections to take effect. The aquatic ecosystem around the Duluth-Superior Harbor, along with similar portside ecosystems around the world, could start to recover from decades of copper pollution.

Based on their initial work, the team received funding from the Minnesota Sea Grant and Minnesota Aquatic Invasive Species Research Center-LCCMR to study the coatings’ ability to inhibit biofouling and the adhesion of aquatic invasive species to underwater surfaces.

“This may just be another arrow in the quill of possible coatings that could be used,” Hicks explains cautiously, “but potential applications are certainly way beyond Lake Superior. The market could be potentially unlimited.”