Battling Biocorrosion in Duluth-Superior Harbor
University of Minnesota researchers develop novel bioactive coating to protect valuable port infrastructure.
by Annamarie Rutledge
Duluth’s shipping industry has always been vulnerable to shifts in global commodity prices. But the Great Lakes busiest transportation corridor also faces a threat much closer to home. Corrosion, accelerated by bacteria in the harbor, is slowly eating away at the 14 miles of port infrastructure that form Duluth-Superior Harbor (DSH).
“Biocorrosion is so severe in some places that the steel looks like swiss cheese,” says Randall Hicks, a biology professor at University of Minnesota Duluth (UMD) who has studied the problem over the past decade. Biocorrosion in DSH damages about 50,000 pounds of steel per year, while replacement of the port’s infrastructure has been estimated at more than $100 million.
Hicks understood that solving the biocorrosion problem required a better understanding of the bacteria living in the harbor waters—the same microorganisms that contribute to slimy goo, which clings to the rocks and steel structures along the shoreline.
Iron-oxidizing microbes in the harbor colonize steel structures and produce biofilms composed of algae, diatoms, and bacteria. Under the surface of the biofilm, the activity of sulfate-reducing bacteria and precipitated copper accelerates the corrosion, creating pits and holes that weaken the steel infrastructure. To the naked eye, the tubercles that form look like blisters on the steel.
During the winter, ice scraping against the steel removes some tubercles and exposes the corroded steel surface again, which may also accelerate the corrosion. “Controlling biocorrosion in this harbor is difficult. Not only is it very cold in the winter but there’s a lot of ice formation,” Hicks said.
Hicks was testing coatings to help mitigate this biocorrosion when he received a phone call from Mikael Elias, a bioremediation researcher at the University of Minnesota BioTechnology Institute (BTI).
Elias, a molecular biologist, was engineering an enzyme he thought might help prevent biocorrosion. “I saw an article in BTI’s Gateway magazine about Randall Hicks’ biocorrosion research and wondered if he would be interested in testing this enzyme,” Elias said. The Elias lab’s lactonase enzyme interferes with quorum sensing, a mechanism for bacterial cell communication that is critical for biofilm formation. “Imagine bacteria have cell phones to communicate and there’s a device that scrambles the signal,” Elias said, “the bacteria are still there but they can no longer communicate.” Unable to communicate, the bacteria fail to create biofilms on the protected surfaces.
Enzymes capable of interfering with microbial signaling were found about two decades ago, yet their lack of activity and stability did not allow for
practical applications yet. The molecules weren’t stable in nature and once outside the test tube they were ineffective. “This is where our lab came in to stabilize them,” Elias said.”
Elias and his team studied enzymes from extreme organisms living in geysers and hot springs. They used this information to re-engineer their lactonase and increase its thermal stability. Even after mixing lactonase with commercial coatings, the enzyme remained active. From there, “we just had to think, where would this be useful? And one place is biocorrosion.”
Hicks, whose work is also supported by the Minnesota Sea Grant Program, was starting lab tests using biochemical coatings that might inhibit steel corrosion when he received Elias’ call. He thought the enzyme might reduce biocorrosion by disrupting microbial communities and preventing attachment. “It turned out that it gave us some of the best results in terms of reducing corrosion tubercles,” Hicks said. Elias’ molecule outcompeted most biochemicals Hicks was testing at the time. In the lab study, the enzymatic coating reduced biocorrosion by 50 percent and was effective against the freshwater bacterial biofilm.
With MnDRIVE funding provided by the Minnesota State Legislature, the team has begun a two-year study to see how the enzyme coating performs over longer periods of time. “The coating we’re looking at is environmentally friendly,” Hicks said. “The question is whether it’s durable enough in harsh field conditions over a longer period of time.” If the molecule succeeds, the next step will be to license the technology. In preparation for commercialization, the team filed for a patent. The Elias lab re-engineered the molecule to increase compatibility with existing coatings and lower manufacturing costs.
Elias has also found that the coating seems to also reduce biofouling, the accumulation of larger organisms like mussels and barnacles on underwater structures. Biofouling causes physical damage, mechanical interference, and reduced fuel inefficiency from increased drag. In the United States alone, biocorrosion and biofouling result in $200 billion in maintenance costs annually.
Biocorrosion and biofouling impose a significant burden on recreational boaters and cabin owners as well. The coating can be applied to boats, docks, anchors, and chains, thereby reducing the cost of maintenance and replacement. In fact, Elias considers the solution a platform technology with Global potential. “It has applications beyond biocorrosion and beyond Minnesota,” Elias said. “It can be applied to many different fields, including agriculture and medicine. Essentially, anywhere bacteria are a problem.”
Research funding was provided by MnDRIVE: Advancing Industry, Conserving Our Environment, Minnesota Sea Grant, Great Lakes Maritime Research Institute, US Army Corps of Engineers, University of Minnesota Center for Urban and Regional Affairs, and Duluth Seaway Port Authority