Marine bacteria genomes reveal evolved tolerance to copper antifouling coatings

Copper has long been the maritime industry’s most trusted weapon against biofouling, the unwanted accumulation of barnacles, algae, tubeworms, and other marine organisms on ship hulls and submerged structures. Copper-based coatings are applied to marine surfaces specifically to slow bacterial growth and deter larger settlers, keeping vessels efficient and reducing drag. But a new peer-reviewed study published in Biointerphases, an AVS journal published by AIP Publishing, reports that marine bacteria have evolved to bypass these defenses. Researchers from the U.S. Naval Research Laboratory and Duke University examined the genetic characteristics of various bacterial species that survive on copper surfaces, a step the team says could lead to strategies for inhibiting the copper-resistant genes themselves. The findings arrive at a moment when port observations suggest resistance is spreading, and they signal that new methods for managing biofouling will be needed.

The research team, led by author Kenan Fears of the U.S. Naval Research Laboratory, had noticed a troubling trend in the field. “We have observed increasing copper resistance in some of the ports our team frequents over the past decade, particularly in ports with heavy tourist [or] industry shipping activity,” Fears said. That pattern raised a central question: which genetic pathways allow bacteria to survive in an environment loaded with one of the most toxic metals available to antifouling chemistry? The team wanted to identify the resistance pathways across a diverse microbial community, and in particular to provide insight into how members of a complex community could be acting symbiotically to resist toxic environments. Rather than studying a single laboratory strain, they chose to look at whole, naturally assembled communities exposed to real seawater conditions.

The experimental design was straightforward but revealing. The researchers placed pieces of polyvinyl chloride panels in the Chesapeake Bay, some coated with a copper-based antifouling coating and some left uncoated as controls. The panels were left in the bay, where bacterial growth accumulated on their surfaces over the exposure period. After two weeks, the team extracted DNA from the bacterial colonies that had grown on the panels and sequenced their genomes to identify genes associated with copper resistance. In parallel, they tested each colony’s tolerance against copper-based water treatments, allowing the researchers to link genetic markers to measurable survival under copper stress. This combination of genomic sequencing and direct tolerance assays gave the team a picture of both the potential and the realized copper resistance within each community.

The most striking result was how little difference the coating actually made. Surprisingly, the bacterial species had a lot in common regardless of whether they grew near the copper-based coating. The bacteria from the control colonies, the ones that did not initially grow on the copper-coated surfaces, were just as copper-resistant as those harvested directly from the treated panels. Even more remarkable, these communities could thrive at copper concentrations above 70 milligrams per liter. That figure is difficult to overstate. “To put that in perspective, the U.S. Environmental Protection Agency limit in seawater for a short-term spike in copper is 18 micrograms per liter,” Fears said. In other words, the bacteria tolerated copper concentrations nearly four thousand times higher than the regulatory threshold designed to protect marine life from a brief surge of the metal.

Such extreme tolerance points to a long evolutionary history rather than a recent adaptation to ship coatings alone. “Copper was not always in a water-soluble state; it only became so after oxygen accumulated in Earth’s atmosphere,” Fears said. This observation places the selection pressure in deep geological time. When the Great Oxidation Event transformed Earth’s atmosphere billions of years ago, insoluble copper species were converted into forms that could dissolve into water, exposing microbial life to bioavailable copper ions capable of disrupting proteins, membranes, and DNA. “However, as environmental copper loading has increased, the bacteria with the best defense mechanisms continued to reproduce,” Fears explained. The researchers interpret the extreme tolerance they measured as a likely marker of evolution and of bacteria adapting to their environments, with human activity in ports and shipping lanes adding a modern layer of selection on top of an ancient genetic toolkit.

From a mechanistic standpoint, copper resistance in bacteria typically involves genes that encode transport proteins capable of pumping the metal out of the cell, sequestration systems that bind copper ions before they can cause damage, and enzymatic pathways that convert toxic ionic copper into less harmful chemical forms. While the study’s sequencing work was designed to identify the copper-resistant genes carried by the Chesapeake Bay communities, the broader goal was to map the resistance pathways operating across a diverse community of species rather than in a single isolate. The finding that uncoated control colonies carried equivalent tolerance suggests these resistance genes are widespread in the environmental gene pool, circulating among bacteria in the bay and ready to be deployed whenever copper concentrations rise. It also hints at horizontal exchange and shared survival strategies within the microbial community, consistent with the team’s interest in how community members might act symbiotically to withstand toxic conditions.

The implications for shipbuilding and port management are significant. Biofouling increases hull roughness, which raises fuel consumption and greenhouse gas emissions, and it facilitates the transfer of invasive species between ports. If bacteria, the first colonizers of any submerged surface, can tolerate copper concentrations thousands of times above regulatory limits, then the copper leaching from antifouling coatings may no longer suppress the initial microbial film on which barnacles, tubeworms, and algae subsequently establish. A tolerant bacterial community can effectively neutralize the first line of defense, allowing macrofoulers to settle. This helps explain why copper-based coatings continue to require replacement and why the industry is under pressure to find alternatives, particularly as environmental regulations tighten around the release of copper into coastal waters.

The research team hopes to use their findings to target the molecular pathways that help bacteria express copper-resistant genes, weakening their ability to survive in copper-rich environments. Rather than simply increasing the dose of copper, an approach that risks further regulatory scrutiny and ecological harm, the strategy is to undermine the genetic machinery that makes tolerance possible. Fears outlined a forward-looking vision that goes beyond mere suppression. “Our research suggests the smarter path moving forward is to design antifouling coatings that select microbial communities that either help deter macrofouler settlement — like barnacles or tubeworms — or do not impede the release of biocidal compounds,” he said. In this framing, the goal is not a sterile hull but a managed one, where the microbial film that forms is compositionally steered so that it either repels larger organisms or allows existing biocides to reach their targets.

“With increasing regulatory pressure on copper use in antifouling coatings, there is an urgent need for alternatives,” Fears added, underscoring the practical stakes of the work. The study, titled “Extreme copper tolerance and genomic adaptation in early-stage marine biofilms,” was authored by Kailey N. Richard, Sara M. Tuck, Sophie M. Colston, Maryssa A. Beasley, W. Judson Hervey, Kevin Le, Sean Brown, Katherine J. Franz, and Kenan P. Fears, and it appeared in Biointerphases on October 13, 2026. What began as an evaluation of fouled panels in the Chesapeake Bay has yielded a clear warning: the genetic capacity to withstand copper is already present, and widely distributed, in marine bacterial communities that have never even touched a coated hull. Any next generation of antifouling technology will need to account for microbes that view one of humanity’s oldest maritime poisons as little more than a background condition of their world.

Subject of Research: Genomic adaptation and extreme copper tolerance in early-stage marine biofilm bacteria

Article Title: Bacteria DNA has evolved to withstand copper

Article References: Bacteria DNA has evolved to withstand copper. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: marine bacteria, copper resistance, biofouling, antifouling coatings, genomics, Chesapeake Bay, Biointerphases, U.S. Naval Research Laboratory, Duke University, heavy metals, microbial evolution, ship hulls