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In natural environments, the surfaces of corroded metals are often covered with biofilms, which provide protection for microorganisms to survive, grow, and reproduce. At different depths within the biofilm, the concentrations of dissolved oxygen, organic matter, inorganic salts, etc., vary, which results in differences among the microbial species present in various layers (Figure 1). At the surface layer of the biofilm that is close to the fluid phase, the dissolved oxygen level is high and nutrients are readily available; the microorganisms in this layer carry out aerobic metabolism, breaking down organic matter to produce simple polymers and organic acids. Nitrifying bacteria, manganese-oxidizing bacteria, iron-oxidizing bacteria (IOB), sulfur-oxidizing bacteria (SOB), and others can all be found in this layer. As the depth of the biofilm increases, the dissolved oxygen concentration decreases, allowing facultative anaerobes that can utilize metabolic products from surface microbes to survive, such as certain microorganisms engaged in fermentation and denitrification processes. At the bottom layer of the biofilm near the metal substrate, the dissolved oxygen concentration is very low, resulting in an anaerobic environment that is favorable for the survival of anaerobic microorganisms, including methanogens, SRB, and iron-reducing bacteria (IRB). Among the corrosion-related microorganisms mentioned above, the impact of SRB, SOB, IOB, and IRB on corrosion has attracted considerable attention; as research progresses, their mechanisms of corrosion are also continually being elucidated. Figure 1