Abstract
Extracellular electron transfer (EET) is a microbial metabolism that enables efficient electron transfer between microbial cells and extracellular solid materials. Microorganisms harbouring EET abilities have received considerable attention for their various biotechnological applications, including bioleaching and bioelectrochemical systems. On the other hand, recent research revealed that microbial EET potentially induces corrosion of iron structures. It has been well known that corrosion of iron occurring under anoxic conditions is mostly caused by microbial activities, which is termed as microbiologically influenced corrosion (MIC). Among diverse MIC mechanisms, microbial EET activity that enhances corrosion via direct uptake of electrons from metallic iron, specifically termed as electrical MIC (EMIC), has been regarded as one of the major causative factors. The EMIC-inducing microorganisms initially identified were certain sulfate-reducing bacteria and methanogenic archaea isolated from marine environments. Subsequently, abilities to induce EMIC were also demonstrated in diverse anaerobic microorganisms in freshwater environments and oil fields, including acetogenic bacteria and nitrate-reducing bacteria. Abilities of EET and EMIC are now regarded as microbial traits more widespread among diverse microbial clades than was thought previously. In this review, basic understandings of microbial EET and recent progresses in the EMIC research are introduced.
Highlights
Acquisition of energy is an indispensable activity for all living organisms
This review introduces the basic knowledge in microbial electron transfer (EET) metabolisms and the recent research progresses on the relevance of microbial EET to iron corrosion
The studies on microbiologically influenced corrosion (MIC) in the last decades have demonstrated that physiologically and phylogenetically diverse microorganisms, including sulfate-reducing bacteria (SRB) (Proteobacteria), methanogens (Euryarchaeota), acetogens (Firmicutes) and Nitrate-reducing bacteria (NRB) (Firmicutes and Bacteroidetes), stimulate iron corrosion via their EET metabolisms. Further investigation on these microorganisms, especially on their EET mechanisms, and identification of novel electrical MIC (EMIC)-causing microorganisms will lead to technological development for MIC mitigation
Summary
Extracellular electron transfer (EET) is a microbial metabolism that enables efficient electron transfer between microbial cells and extracellular solid materials. Recent research revealed that microbial EET potentially induces corrosion of iron structures. Among diverse MIC mechanisms, microbial EET activity that enhances corrosion via direct uptake of electrons from metallic iron, termed as electrical MIC (EMIC), has been regarded as one of the major causative factors. The EMIC-inducing microorganisms initially identified were certain sulfate-reducing bacteria and methanogenic archaea isolated from marine environments. Abilities to induce EMIC were demonstrated in diverse anaerobic microorganisms in freshwater environments and oil fields, including acetogenic bacteria and nitrate-reducing bacteria. Abilities of EET and EMIC are regarded as microbial traits more widespread among diverse microbial clades than was thought previously. Basic understandings of microbial EET and recent progresses in the EMIC research are introduced
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