The term deep-sea generally refers to oceans at depths below 200 meters (Danovaro et al., 2020; Li et al., 2023). The deep-sea ecosystem includes hydrothermal vents, cold seeps, whale fall ecosystems, seamounts, oceanic trench ecosystems and abyssal plain (Feng et al., 2022; Simon-Lledó et al., 2023). It also includes incredible volumes of deep-sea water column, as shown in Figure 1B. It is characterized by perpetual darkness, temperatures ranging from −1.0 to 4.0°C or up to 400°C in hydrothermal vents, high pressure, and oligotrophic conditions, making it an extreme environment (Emery, 2001; Feng et al., 2022). Extreme environments are typically characterized by factors such as temperature, pH, pressure, salinity, toxicity, and radiation levels. These environments support a diverse range of microorganisms, known as extremophiles, that have adapted to survive under such conditions (Li et al., 2013). Compared to more familiar environments such as the atmosphere or shallow marine settings, the deep-sea environment has significantly reduced dissolved oxygen levels, which alters corrosion dynamics. Thus, conventional corrosion protection methods are often inadequate to meet the protective requirements of deep-sea equipment (Duan et al., 2023). Figure 1A illustrates representative deep-sea operational equipment, including exploration tools such as remotely operated vehicles and manned submersibles, as well as subsea engineering systems for underwater operations, deep-sea oil and gas production, and mineral resource extraction (Muñoz-Royo et al., 2021; Chen et al., 2024).

Microorganisms in deep-sea environments are highly specialized and form the foundation of biogeochemical and energy cycles, making them indispensable to deep-sea ecosystems. Exploring the different types of microorganisms in various deep-sea regions, along with their physiological and metabolic characteristics, can provide a theoretical foundation for investigating the corresponding corrosion and mineralization mechanisms. These microorganisms include thermophiles, psychrophiles, acidophiles, alkaliphiles, halophiles, and piezophiles, each adapted to extreme environmental conditions. The different microbial types detected in extreme deep-sea environments are shown in Table 1. Since more than 99% of these microorganisms lack closely related described species, significant challenges remain in understanding their diversity, physiological functional traits, and biogeochemical roles. The establishment of a deep-sea microbial library related to corrosion still requires extensive corrosion coupon experiments. Based on a large amount of genomic data, species-corrosion patterns can be derived. Researchers have successfully discovered, isolated, and cultured microbial species from deep-sea hydrothermal vents, cold seeps, marine sediments, deep-sea water, and oceanic crust. These microorganisms primarily include marine bacteria, archaea, and viruses. Among them, sulfate-reducing prokaryotes (SRP) and iron-oxidizing prokaryotes (IOP) are the most commonly associated with corrosion processes (Barton and Northup, 2007). Guezennec et al. (1998) deployed various materials (such as 316 L stainless steel, titanium, copper-nickel alloy, etc.) in the deep-sea hydrothermal vent area of the Mid-Atlantic Ridge. After 4 days of exposure, a significant accumulation of biomass was observed on all material substrates, with the formation of thick but loosely attached biofilms on the surfaces. Analysis of their lipid extracts showed characteristics of SRP. Rajala et al. (2022a) reported an integrative study of the biofilms growing on the surface of corroding mooring chain links that had been deployed for 10 years at about 2 km depth. Wakai et al. (2024) collected slime-like precipitates composed of corrosion products and microbial communities from a geochemical reactor set on an artificial hydrothermal vent for 14.5 months, and conducted culture-dependent and -independent microbial community analyses with corrosive activity measurements, as shown in Figure 1C. The performance of sulfur-metabolizing microorganisms was prominent. Fe-S-driven element coupling has also become a fundamental basis for investigating corrosion mechanisms, as shown in Figure 1E. The methane cycle in marine sediments was closely linked with the sulfur cycle, as shown in Figure 1F (Friedrich and Finster, 2014). Microorganisms in hydrothermal vent systems are predominantly extremophilic bacteria or archaea, which utilize the abundant sulfides near hydrothermal vents to produce biomass. They form the foundation of the entire hydrothermal vent ecosystem. The deep-sea hydrothermal vent regions exhibit a high microbial diversity due to the chemical complexity and rapid environmental fluctuations in these habitats. In contrast, cold seep systems have higher biomass but lower biodiversity, with archaeal communities being the dominant microbial inhabitants. In deep-sea sediments, microbial abundance is influenced by the organic matter content and proximity to continental plates, with heterotrophic microorganisms prevailing in these regions. The oceanic crust, primarily composed of mafic and ultramafic rocks rich in minerals, hosts chemoautotrophic microorganisms that play a key role in biogeochemical cycles, such as those involving Fe, Mn, and S (Wang et al., 2013). For example, the Figure 1D illustrates a schematic of a microbial-dominated ecological function study in a deep-sea ferromanganese nodule deposition area (Zhang D. et al., 2023).

Deep-sea minerals encompass a variety of mineral resources located on the seafloor, primarily distributed across seamounts, ridges, and basins. Common deep-sea mineral deposits include manganese nodules, seafloor cobalt crusts, and hydrothermal deposits, which polymetallic resources formed naturally under deep-sea conditions. Interestingly, recent research suggests that metal nodules in deep sea may have the potential to produce oxygen (Sweetman et al., 2024). Oceanic ferromanganese nodules, a significant underwater metal resource, are widely distributed on the modern seafloor and are rich in Fe, Mn, Ni, Cu, Co, Mo, Li, and rare earth elements. These nodules generally have a core surrounded by concentric mineral layers and are typically found at depths greater than 4,000 m. The primary minerals include Fe-rich birnessite, amorphous ferrihydrite, and various detrital minerals like magnetite, hematite, quartz, calcite feldspar, clay minerals and mica (Hein et al., 2013).

Minerals influence many important microbial activities, including energy production, nutrient acquisition, cell adhesion, and biofilm formation (Hochella, 2002). For example FeMn crust and phosphorite substrates in the Southern California Borderland support enhanced trophic biodiversity and specific trophic niches (Pereira et al., 2024). Interestingly, a recent study found that minerals not only serve as a nutritional source for microorganisms but also act as signaling molecules that regulate microbial adaptation to the environment. Minerals function as “information transmitters” in ecosystems, and the rational use of mineral signals may become a new direction (Zhang et al., 2025).

Most organic carbon mineralization in marine sediments is associated with dissimilatory sulfate reduction (DSR), as shown in Figure 1D (Qian et al., 2019). A wide range of marine organisms and microorganisms have been identified for their role in mineralization. Examples include marine organisms such as sponges and tunicates as well as marine microorganisms that facilitate the mineralization of elements like Fe, S, Mg, Ca, Mn, and Cu, and U. Since these elements exist in multiple valence states, the mineralization layers formed under different environmental and biological conditions exhibit significant diversity.

BIM is a process in which organisms modify their local microenvironment through metabolic activities, creating physicochemical conditions that favor mineral precipitation. However, the resulting products often lack specific biological functions, as illustrated in Figures 2, 3A. BIM is widespread in nature. For example, microbial mineralization contributes to the formation of carbonates, moon milk, silicates, clays, iron and manganese oxides, sulfur, and saltpeter in caves (Northup and Lavoie, 2001). Some microorganisms can directly or indirectly induce the decomposition, hydration, dissolution, or formation of secondary minerals (Banfield et al., 1999). Biomineralization is a two-step process: initially, metal ions electrostatically bind to the anionic surfaces of the cell wall and the surrounding EPS, which then as nucleation sites for crystal growth (Konhauser, 1998). Induced mineralization involves interactions between bacterial surfaces and metal ions in colloidal ionic form. Specific organic and inorganic interactions allow biomineralization to play a potential role in forming high-grade mineral deposits (Leguey et al., 2010). Further studies by He et al. (2023) on deep-sea strains Alteromonas alteriprofundi HHU 13199^T and Alteromonas alterisediminis N102^T have provided insights into the primary mechanism underlying BIM.

Certain microorganisms, such as SRP, are well known for their role in biomineralization. SRP are among the primary strains studied in marine MIC and biomineralization research. For example, discovered study found that dissimilatory SRP, particularly those from the genera Desulfovibrio and Desulfotomaculum, could deposit electron dense FeS particles within their cells when cultured in an Fe rich medium (Jones et al., 1976). In modern sedimentary environments, SRP are the main producers of sulfides. The mineral composition resulting from SRP metabolic activity is highly dependent on the source of iron. Microorganisms play a key role in the formation of iron sulfides, particularly pyrite (FeS₂) (Duverger et al., 2020). The application of BIM in engineering, such as self-healing concrete and nanoparticle synthesis, has become a significant research focus.

Microbially-induced calcium carbonate precipitation (MICP) is a naturally occurring process that has gained considerable attention in recent decades (Li et al., 2024). BIM, primarily observed in various Bacillus strains, plays a key role in concrete self-healing. Among them, Bacillus pasteurii’s demonstrated excellent mineralization capability, making it a focal point of interest in geotechnical engineering (Debnath and Sen, 2024; Natalio and Maria, 2024). Recently, filamentous fungi have emerged as promising candidates for biomineralization-based self-healing concrete. Their hyphae networks form an interwoven three-dimensional structure, providing nucleation sites for CaCO₃ precipitation to repair cracks (Van Wylick et al., 2021). Recent advances in fungal-mediated self-healing concrete have further confirmed their potential in sustainable construction materials. Beyond construction applications, biomineralization has significant implications for nanoparticle synthesis. The interactions between proteins and nanoparticles at mineral interfaces have garnered significant attention in the development of novel biomaterial. However, the precise role of proteins in microbial transformation and BIM remains unclear (Liu et al., 2021). Park et al. (2022) described that periplasmic proteins, such as DegP-like proteins and heavy metal-binding proteins, may be involved in the biomineralization process. Additionally, Mn has recently been identified as an accelerator of nitrogen metabolism. Biomineralized MnOx is now believed to mediate ammonia oxidation, offering a potential alternative to conventional nitrogen removal processes (Liu et al., 2024).

BCM is a process in which biological macromolecules and cells actively regulate the reaction of ingested metal ions and anions through various physicochemical mechanisms, leading to the formations of biominerals with specific assembly forms and advanced structures (Weiner and Dove, 2003). The resulting mineralized products often provide organism with specific physiological functions. The BCM process can occur extracellularly, intercellularly, or intracellularly, with the mineralization sites depending on the specific cells involved in the process (Weiner and Dove, 2003). Figure 3B demonstrates an example of intracellular BCM. Almost all BCM processes take place within isolated microenvironment. During mineralization, vesicles often serve as confined microenvironment, guiding biominerals nucleation within microorganisms while controlling the composition and morphology of the resulting biominerals.

A typical representative of BCM is magnetotactic bacteria (MTB), which are Gram-negative bacteria capable of moving along magnetic field lines and oxygen concentration gradients. They are primarily isolated from hypoxic conditions in aquatic niches and rarely from soil (Mistry et al., 2024). MTB can synthesize intracellular nanoscale minerals of magnetite (Fe₃O₄) and/or greigite (Fe₃S₄), forming magnetosomes that enable magnetotactic orientation. As a result, they serve as an excellent model system for studying biomineralization (Lin et al., 2014). Magnetosomes are generally 20–120 nm in length, consist of highly pure magnetite or greigite and are arranged in chains within MTB. These structures have been regarded as magnetic fossils of life, serving as important clues for exploring early earth conditions and potential extraterrestrial life activities. In some marine protozoa, magnetotactic ability is acquired through the uptake of extracellular symbiotic bacteria, Wherein the protozoa ingest MTB along with their magnetosome chains, internalizing the bacteria (Mandal, 2023). Metal sulfides are a common type of extracellular bacterial biominerals, but intracellular biomineralization has also been observed, such as the formation of greigite in MTB (Park et al., 2022). Numerous MTBs may significantly influence the iron cycle in oxic-anoxic transition zones and anoxic zones, facilitating the deposition of fine-grained magnetite and greigite. Consequently, they enhance the remanent magnetization of sediments (Bazylizinki et al., 1993).

Biologically influenced mineralization is a passive process that does not directly result from microbial activities but rather from interactions between extracellular biopolymers and the geochemical environment (Decho, 2010). In biologically influenced mineralization, external, environmental factors, such as increased alkalinity, play a crucial role in creating conditions favorable for mineral precipitation, rather than microbial metabolism itself. However, an organic matrix is involved in biologically influenced mineralization, influencing the morphology and composition of the resulting crystals. This occurs through interactions between the forming mineral and the organic matter, which serves as a template for precipitation (Dupraz et al., 2009).

Knisz et al. (2023) described the primary mechanisms of MIC, including oxygen gradient corrosion under sediments, crevice corrosion, metabolite-induced corrosion, and electrochemical microbially influenced corrosion (EMIC). EMIC is classified into two types: direct and indirect. Direct EMIC occurs when microorganisms facilitate extracellular electron transfer (EET) by directly contacting metal surfaces leading to corrosion. Indirect EMIC involves the release of soluble electron mediators by microbes, which act as electron transfer shuttle, and accelerate corrosion of metals, as shown in Figures 4A,B. Biofilms further create additional crevices for various corrosion-related bacteria. Microbial activities within a biofilm can also enhance the influence of abiotic metallurgical conditions, promoting localized corrosion. During pipeline operations, factors such as pressure, stray currents, cathodic protection, and environmental variations can interact synergistically with microorganisms. These combined factors can lead to microbial-induced stress corrosion cracking (SCC), microbially-induced hydrogen-induced cracking (HIC), or crevice corrosion and under-deposit corrosion, where microbially-induced biomineralization occurs at specific locations. Such processes pose a severe risk to pipeline operational safety (Xiong et al., 2018).

Interfacial processes include early cell adhesion, biofilm development, and the formation of passive layers on mineral surfaces (Safar et al., 2020). For example, microorganisms can catalyze metal accumulation through microfossilization, which is induced by microbe-metal interactions (Henne et al., 2021). When materials are immersed in seawater, a conditioning film rapidly forms on their surface. This film is a surface coating formed by the adsorption of biomolecules from the surrounding environment, altering the material’s inherent surface properties and facilitating microbial attachment (Bhagwat et al., 2021). Subsequently, microorganisms undergo the biofilm development process, which includes adhesion, intercellular interactions, proliferation, maturation, and dispersion (Costerton et al., 1999), as illustrated in Figure 4C (Anusha and Mulky, 2023). A deeper understanding of the interactions between microorganisms and metallic minerals requires analytical tools with high chemical sensitivity and spatial resolution. In recent years, the growing application of X-ray techniques, ranging from nanoscale to microscale, as well as large-scale synchrotron accelerators has provided new insights into microbial growth, mineral dissolution, redox transformations, and biomineralization processes (Templeton and Knowles, 2009).

The process by which bacteria adhere to mineral surfaces is not yet fully understood. Some studies suggest a relationship between bacterial cells and mineral surfaces. For example, Pseudomonas aeruginosa PAO1 tends to adhere to mineral surfaces using its flagella and/or pili. Surface roughness is a critical factor that may hinder attachment (Han M. et al., 2024). To better understand the underlying molecular processes and mechanisms, Yan et al. (2016) analyzed the adhesion of Shewanella oneidensis MR-1 to goethite using flow-cell attenuated total reflection (ATR), Fourier-transform infrared (FTIR) spectroscopy, combined with two-dimensional correlation spectroscopy (2D-COS) analysis. Other studies have described that interactions between goethite and bacteria can damage bacterial cells by piercing the cell wall, causing bacterial aggregation at the liquid-air interface Ma et al. (2017). Analyzing the physical interfacial properties between cell envelopes, outer membrane cytochromes responsible for interfacial electron transfer, and complex mineral particles remains challenging. Models explaining how microorganisms acquire electrons from solid donors are multifaceted, and include electron transfer via redox mediators such as H₂ or direct contact through membrane proteins (Liu J. et al., 2016; Mei et al., 2024). In recent years, molecular mechanisms and gene regulation have also become key areas of interest in studying microbe-mineral interactions. For instance, studies have shown that extracellular DNA promotes EET via pyocyanin in P. aeruginosa biofilms (Xiao et al., 2014; Saunders et al., 2020).

Microorganisms utilize EET and external minerals during their growth, a process accompanied by the conversion of chemical energy (Tian et al., 2019). Electroactive microorganisms can establish electrical contacts with other cells and minerals on their outer-surface or reduce soluble extracellular redox-active molecules such as flavins and humic substances. Cytochromes, conductive protein filaments, soluble electron shuttles, and abiotic conductive materials can significantly extend the electronic reach of microorganisms beyond the cell surface (Lovley and Holmes, 2021). Enzymes such as hydrogenases, which catalyze the oxidation of molecular hydrogen, can mediate electron transfer to metals and may facilitate the formation of minerals at the bacteria-mineral interface. Additionally, research has shown that some methanogens are electrogenic and corrosion-causing microbes. Many methanogens involved in MIC can thrive extensively at abiotic-biotic interfaces (Mei et al., 2024). Scheller et al. (2016) studied EET between ANME and sulfate reduction, they lent support to the hypothesis that interspecies extracellular electron transfer is the syntrophic mechanism for ANME.

Due to the unique environmental characteristics of the deep sea, such as high hydrostatic pressure and oligotrophic conditions, corrosion of materials in deep-sea environments differs from that in shallow seawater. Rajala et al. (2022b) conducted a deep-sea hanging plate experiment and detected significant MIC on the material surface after 10 years. Numerous microorganisms adhered to and extensively colonized the mooring chain surface, greatly accelerating the metal’s corrosion rate. The corrosion mechanism of mooring chains in deep-sea environments is illustrated in Figure 5A.

Currently, due to the challenges in simulating the extreme conditions of the deep sea, research on the impact of deep-sea environmental factors on microbial corrosion remains limited. Laboratory simulations must account for factors such as high hydrostatic pressure, oligotrophic conditions, seawater flow dynamics, and temperature. Li J. et al. (2025) investigated the accelerated SCC mechanism of X80 steel under the combined influence of SRP and hydrostatic pressure in a high-pressure reactor. By varying the hydrostatic pressure to simulate deep-sea conditions, they observed that hydrostatic pressure promoted MIC, as shown in Figure 5B. In this case, hydrostatic pressure and iron sulfide facilitated the hydrogen evolution reaction, further accelerating corrosion.

Corrosion data are continuously collected across various industries, including petroleum, natural gas, shipping, and nuclear sectors, for risk assessment, component life prediction, and corrosion control (Li et al., 2015). Establishing and sharing corrosion data is an important topic at present. Multiple factors, such as material composition, microstructure, design parameters, as well as oxygen content, humidity, salinity, pH, temperature, and microbial communities, all influence the degradation of materials like pipelines. By integrating artificial intelligence, real-time corrosion monitoring can be achieved. For instance, Yao et al. (2019) proposed a method for detecting corrosion damage and other surface structural damages on hull structures based on convolutional neural networks. This method accelerates the application of artificial intelligence technologies in the field of shipbuilding and marine engineering, providing practical value for reasonably mitigating corrosion loss.

Currently, quantifiable data of MIC primarily manifest in corrosion weight loss and biofilm formation detection. Specifically, this includes corrosion rate, biofilm quantity, thickness, distribution, and the properties of corrosion products. Most theoretical and practical studies use methods such as SEM, CLSM, and electrochemical techniques to characterize biofilms and corrosion products. Additionally, many studies now employ various sensors, such as probes for the microenvironment within biofilms, to detect the microenvironment and determine their impact on biofilm-specific processes. For example, quantitative biofilm measurements and the detection of pH, polysaccharides, proteins, eDNA, and cytochrome C which is related to electron transfer mediators, are commonly used (Legner et al., 2020; Hunter Ryan and Beveridge Terry, 2005; Eddenden and Nitz, 2022; Jennings et al., 2015). The corrosion rate calculated using the formula shown below, where v_corr is the corrosion rate (mm/y), m₀ is the initial weight of the coupon before weight loss testing (g), m₁ is the weight of the coupon after testing and the corrosion products are removed (g). K is the unit constant (87,600), A is the working area of the coupon (cm²), t is the immersion period of the coupon (h), and ρ is the density of the coupon (g/cm³).

The structure of biomineralized films plays a crucial role in determining the corrosion behavior of metals (Liu et al., 2022). The critical transition from biofilm to a biomineralized film is essential for ensuring long-term anti-corrosion properties, as it addresses the inherent instability of biofilm protection against corrosion (Liu et al., 2018). Microorganisms can induce the formation of biomineralized films, which may possess properties such as super hydrophobicity to reduce biological adhesion or enhanced density to achieve corrosion inhibition. Given the complex competitive, symbiotic, and cooperative interactions among different microorganisms, the synergistic effects of various microbial communities in corrosion inhibition have garnered significant attention.

While the formation of biomineralized layers can inhibit uniform corrosion, it may also exacerbate localized corrosion processes such as pitting and crevice corrosion. For example, corrosion pits may form due to the presence of small anodes, and pitting corrosion can occur under the biomineralized films due to pigments secreted by microorganisms (Guo Z. et al., 2021; Liu et al., 2022). Interestingly, biomineralization can affect the visual appearance of corrosion by forming bubbles, these may create ecological niches for microorganisms that ultimately contribute to MIC (Martinez et al., 2022). Additionally, as described in Section 5, microbial-material interfacial interactions can lead to instability in mineral formation and their morphology, potentially promote corrosion.

Researchers can currently construct strains with enhanced mineralization and extracellular polymer secretion capabilities through microbial genetic engineering, thereby promoting the formation of denser, more uniform mineralized layers on metal surfaces to inhibit corrosion. Alternatively, through biofilm management technology, the porous, highly adhesive, and low-cost characteristics of EPS can be combined with existing corrosion inhibitors to develop multifunctional, versatile bio-coatings that sustainably enhance metal corrosion resistance. Li Z. et al. (2025) genetically engineered a mutant strain (Shewanella oneidensis PCA) capable of overproducing the electron shuttle phenazine-1-carboxylic acid (PCA). By integrating high-resolution passivation film characterization with molecular biology techniques, they systematically elucidated a novel microbial corrosion mechanism involving synergistic direct–indirect electron transfer that accelerates passive film dissolution. This work highlights the dual significance of microbial genetic engineering in both fundamental research and practical applications. Li X. et al. (2025) first utilized the biofilm formed by corrosion-protective microorganisms (Tenacibaculum mesophilum D-6) as a scaffold to construct a novel “smooth liquid-injected porous surface” (SLIPS) coating (TM@SLIPS). The biofilm’s high adhesion, flexibility, and porous structure provide an ideal framework for the uniform distribution of lubricants, thereby enhancing the coating’s durability. It is produced using bio-based materials through controlled cultivation, enabling scalable production at low cost and easy scalability.

Corrosion is not only related to economic losses, but its impact on the environment should also not be underestimated. Over 3,800 World War II sunken ships containing thousands of tons of oil are at risk of structural collapse due to continuous corrosion, posing a threat to the marine environment (Carter et al., 2021). As deep-sea engineering and exploration advance, the environmental consequences of MIC and biomineralization have become increasingly relevant. These microbial processes, while naturally occurring, can be exacerbated by anthropogenic materials and interventions, leading to long-term disruptions of fragile and poorly understood ecosystems. This section explores key areas of concern—including microbial biodiversity, toxic byproducts, long-term ecological consequences, mitigation strategies, and ethical considerations—and outlines approaches to reduce ecological impact while promoting sustainable deep-sea operations.