FRIDAY, NOVEMBER 11, 2016
Corrosion reportedly costs the United States Department of Defense about $23 billion a year, and much of that is said to occur in marine environments, where chemical processes or bacteria oxidize the iron in steel on ships and other structures.
Bigelow Laboratory for Ocean Sciences, a nonprofit research institution in East Boothbay, ME, is working to help the U.S. Navy fight back against rust with research to understand the early stages of bacterial growth and its corrosive impact.
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“Understanding the basic microbiology of this process is a crucial part of figuring out how to mitigate it,” said Adam Mumford, who led a study of microbially driven corrosion for the Navy as a postdoctoral researcher at Bigelow Laboratory.
Environmental Simulation
The Navy project built on the institution’s earlier research that showed iron-oxidizing bacteria, which use iron as an energy source, are among the first microorganisms to colonize the surface of steel when it’s put into the ocean.
In this round of research, Bigelow researchers monitored the early stages of colonization and its role in corrosion, by placing pieces of steel in a container of seawater and adding Mariprofundus DIS-1, an iron-oxidizing bacterium. This experimental arrangement enabled the team to simulate environmental conditions and control oxygen levels.
From this setup, the scientists learned that the iron-oxidizing bacteria use the iron that’s released from the steel, but they don’t directly cause dramatic corrosion.
That doesn’t, however, mean those bacteria don’t play a significant role in starting the process, the laboratory noted.
“In the ocean, the initial colonization of steel is by iron oxidizers but other organisms eventually move in and take over,” said Senior Research Scientist David Emerson, who worked closely with Mumford on the study.
“We’re not yet certain how the initial colonizers make the steel surface more hospitable, but more damaging bacteria, such as sulfate-reducers, arrive next and can cause rapid pitting and corrosion of the steel.”
Bacterial Structures
According to Bigelow, the “complex microscopic structure” formed by the first colonizers appears to play a role in creating a more hospitable environment.
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| Bigelow Laboratory for Ocean Sciences |
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This 3D image shows the microscopic structure the bacteria build on steel surfaces in red; the bacteria cells are the green dots. |
As the bacteria process iron, it says, each cell builds a unique stalk of metallic and organic matter from the resulting waste. These stalks allow the bacteria to slowly move themselves through the environment and settle on a spot where they have access to the nutrients they need. They also drastically increase the surface area near the steel and create a new environment ready for colonization by other microbes, it adds.
These structures are incredibly delicate, Emerson explained, saying that it could be destroyed just by picking up the steel to move it to a microscope for examination.
However, Mumford developed a test container that allowed him to move intact structures to a confocal microscope, which uses a laser to excite fluorescent dyes that scientists add to samples.
He stained the bacteria cells green and the iron oxide stalks red. He then used the microscope to create a three-dimensional image of the steel’s surface, revealing the amazing structures this species creates.
Surprising Discovery
According to the scientists, one of the biggest surprises they uncovered is that this species of Mariprofundus does very well in oxygen-rich seawater.
Iron-oxidizing bacteria are generally found in very low oxygen environments, like those that may occur near hydrothermal vents on the seafloor, they explained.
However, the bacteria in this project were exposed to fully oxygenated seawater—such as that found in the near-surface waters that affect boats and marine infrastructure—“and it didn’t seem to slow them down,” the laboratory added.
To understand why, the team sequenced the genome of the bacterium and found genetic defenses against harmful byproducts that are created when iron and oxygen interact.
“This goes counter to what we’ve all been saying about iron oxidizers for a long time,” Emerson said. “This species is well-adapted to life in the fully oxygenated ocean, and it seems to create conditions on the surface of steel that make it easier for other, more corrosive bacteria to live there as well.”
The results of Mumford and Emerson’s research were recently published in Applied and Environmental Microbiology.
Tagged categories: Corrosion; Laboratory testing; Marine; Microbiologically Induced Corrosion (MIC); Quality Control; Research and development; U.S. Navy
