How Microbes Are Eating Our Deep-Sea Infrastructure
In the crushing darkness of the deep sea, an unseen battle is taking place between human engineering and nature's smallest inhabitants—and the microbes are winning.
Imagine a piece of industrial steel, thick and resilient, designed to withstand decades of punishment in the ocean's depths. Now imagine that same steel being slowly, methodically consumed by organisms so tiny they're invisible to the naked eye. This isn't science fiction—it's the reality of microbially induced corrosion (MIC), a process that costs global industries trillions of dollars annually and poses a significant threat to our expanding footprint in the deep sea .
Microbially induced corrosion accounts for approximately 20% of all corrosion damage worldwide, with economic impacts estimated at trillions of dollars annually.
As humanity ventures deeper into the oceans for resources, energy, and exploration, we're discovering that the extreme environments of the abyss present unique challenges. The deep sea is characterized by near-freezing temperatures, low oxygen levels, and crushing hydrostatic pressures that would deform most submarines. Until recently, we understood very little about how these conditions affect the longevity of the metallic structures we deploy there 1 .
A groundbreaking 10-year study has now shed light on this invisible war, revealing how specific sulfur-cycling microorganisms are accelerating the corrosion of mild steel in the deep sea, causing damage that far exceeds what would be expected from chemical processes alone. The discoveries are changing how scientists view corrosion in one of Earth's most extreme environments 1 2 .
Microbially influenced corrosion isn't caused by a single villain, but by a diverse cast of microscopic characters, each playing a specialized role in breaking down metal.
The most notorious corrosion culprits, these anaerobic microorganisms thrive without oxygen and respire using sulfate instead. They produce hydrogen sulfide as a metabolic byproduct, which reacts with metal surfaces to form corrosive metal sulfides.
In marine sediments, SRB account for more than 50% of sulfate reduction, and over 60 types are known to exist in marine environments .
These microorganisms perform the opposite function of SRB, oxidizing reduced sulfur compounds to produce sulfuric acid. This dramatically lowers the pH of the surrounding environment, creating highly corrosive conditions that can accelerate metal dissolution .
These bacteria directly use metal as an electron donor for energy metabolism. Iron-oxidizing bacteria, for instance, accelerate the oxidation of ferrous ions, while manganese-oxidizing bacteria catalyze the conversion of soluble manganese to insoluble oxides, both processes contributing to corrosion .
Various microorganisms produce organic acids as metabolic byproducts, creating localized acidic environments that eat away at both metals and concrete surfaces. Some fungal species have been shown to cause more degradation than certain bacteria, demonstrating their significant corrosive potential 3 9 .
In 2008, researchers deployed mild steel mooring chain links at a depth of 1,988 meters in the cold, dark waters of the deep sea 1 . The environment was characterized by:
The chain links were left undisturbed for ten years, creating a natural laboratory to observe long-term corrosion processes in the deep sea. In 2018, the researchers retrieved the chains using a remotely operated vehicle, carefully packaging them to prevent contamination during their journey to the surface 1 .
Back in the laboratory, the researchers employed an impressive array of techniques to uncover what had happened to the chains during their decade in the deep:
Using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) to examine corrosion products and ultrastructural features 1 .
Employing shotgun metagenomics and 16S amplicon analysis to identify the microbial communities on the corroded surfaces 1 .
Utilizing X-ray diffraction (XRD) to identify crystalline corrosion products 1 .
Applying quantitative PCR to measure the abundance of specific genes, particularly the dsrB gene used by sulfate-reducing bacteria 1 .
Using flux-balance analysis to reconstruct the metabolic networks of corrosion communities 1 .
The results revealed a fascinating story of biological warfare against steel, with several key discoveries:
The steel surfaces showed intensive and highly localized corrosion, with the characteristic pitting and structural features typical of microbially induced corrosion. The corrosion rate observed was significantly higher than what could be expected from purely abiotic (non-biological) corrosion mechanisms under these environmental conditions 1 .
Perhaps most remarkably, the microbiome on the chain links differed considerably from that of the surrounding sediment. The metal surfaces had selected for specific metal-corroding biofilms dominated by sulfur-cycling bacteria, creating a specialized community optimized for corrosion 1 .
By reconstructing the core metabolism of the microbiome, the researchers developed a mechanistic model that combines both biotic and abiotic corrosion. The model suggests that sulfate reduction and sulfur disproportionation play key roles in deep-sea corrosion, with sulfur-cycling microorganisms potentially gaining energy by accelerating the reaction between metallic iron and elemental sulfur 1 2 .
Understanding microbial corrosion requires specialized tools and techniques. Here are some of the essential components used in this field of research:
| Tool/Technique | Primary Function | Application in MIC Research |
|---|---|---|
| Scanning Electron Microscopy (SEM) | High-resolution surface imaging | Visualizing corrosion patterns and biofilm structures on metal surfaces |
| Energy-Dispersive X-ray Spectroscopy (EDS) | Elemental composition analysis | Identifying corrosion products and their chemical makeup |
| X-ray Diffraction (XRD) | Crystalline phase identification | Determining the mineral composition of corrosion products |
| Shotgun Metagenomics | Comprehensive microbiome analysis | Identifying all microorganisms present in a corrosion biofilm |
| Quantitative PCR (qPCR) | Gene quantification | Measuring abundance of specific corrosion-related genes (e.g., dsrB for SRB) |
| Flux-Balance Analysis | Metabolic modeling | Reconstructing the metabolic networks of corrosion communities |
The deep-sea environment presents unique challenges for materials that don't exist in shallow waters:
High hydrostatic pressure appears to accelerate the initiation of metastable pitting while decreasing the probability of pit growth, increasing the susceptibility of steel materials to uniform corrosion 1 .
The near-freezing temperatures and low oxygen levels of the deep sea would normally slow corrosion, yet the observed rates were higher than expected, suggesting microbial activity is overcoming these limitations 1 .
Deep-sea microorganisms are specifically adapted to thrive under high pressure, making them fundamentally different from their shallow-water counterparts in both physiology and metabolic activity 1 .
The findings from this decade-long study have significant implications for various industries looking to expand into deep-sea environments:
Understanding MIC mechanisms enables better material selection and engineering design for deep-sea infrastructure, potentially incorporating corrosion-resistant materials like specific stainless steel grades, copper alloys, or protective coatings 9 .
With knowledge of the specific microorganisms involved, industries can develop targeted monitoring programs to detect early signs of corrosion and implement preventive maintenance strategies 5 .
Corrosion already costs global economies trillions of dollars annually, with an estimated 20% of this damage attributed to microbiologically influenced corrosion . As we expand into deeper waters, these costs could escalate without proper mitigation strategies.
The silent war beneath the waves continues unabated. As we push further into the deep sea for resources, energy, and scientific knowledge, understanding our microscopic adversaries becomes increasingly crucial. The ten-year study on sulfate-dependent corrosion of mild steel represents a significant advancement in this understanding, revealing the sophisticated mechanisms through which sulfur-cycling microorganisms accelerate corrosion in the deep sea.
What emerges clearly is that in the extreme environment of the deep sea, the rules of corrosion are different—shaped as much by biology as by chemistry. The microbes have adapted to thrive under conditions we once considered too extreme for significant biological activity, and they've turned our infrastructure into an energy source.
Future innovations in material science, perhaps inspired by nature's own corrosion resistance strategies, may eventually give us the upper hand. But for now, each piece of steel we lower into the deep joins an invisible battlefield, where the smallest organisms continue to demonstrate their remarkable ability to reshape our world—one microscopic pit at a time.
This article was based on the study "Sulfate-dependant microbially induced corrosion of mild steel in the deep sea: a 10-year microbiome study" published in Microbiome journal, which garnered significant scientific attention with 49 citations and over 7,500 accesses since its publication in 2022 6 .