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Role of extracellular electron transfer in the nitrogen cycleExtracellular electron transfer impacts the nitrogen cycle by enhancing microbial processes and connecting to other biogeochemical cycles. Understanding EET mechanisms provides insights into ecosystem functioning and potential advancements; Arpita Bose and Zhecheng (Robert) Zhang explain. Nitrogen is a fundamental element required by all living species. It can be found in amino acids, proteins, and nucleic acids. The nitrogen cycle promotes nitrogen transformation and transit across the environment, making it available for biological activity. Key steps in the cycle include nitrogen fixation (conversion of atmospheric nitrogen to ammonia), nitrification (oxidation of ammonia to nitrate), denitrification (reduction of nitrate to nitrogen gas), and anaerobic ammonium oxidation (anammox), which then converts ammonium and nitrite directly to nitrogen gas. Extracellular electron transfer (EET) is the mechanism by which microorganisms transmit electrons from their cells to accept electrons from external donors. This ability allows microorganisms to interact with insoluble substrates, which, in turn, influences a variety of biogeochemical cycles, including the nitrogen cycle. Understanding EET’s function sheds light on microbial ecology and environmental processes.
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This content will become publicly available on October 1, 2026
Interfacial extracellular electron uptake is linked to nitrate respiration in the marine heterotroph, Thalassospira xiamenensis SN3
Thalassospira species are ubiquitous marine bacteria with poorly understood ecology, and some have been implicated in iron corrosion. To better elucidate the mechanisms and ecological implications of extracellular electron transfer (EET) in oxidative processes, we conducted genomic and bioelectrochemical characterization of Thalassospira xiamenensis strain SN3, an obligate heterotroph isolated from coastal marine sediment cathode- oxidizing enrichments. Physiologic and genomic analyses indicate that SN3 lacks the capacity for lithoautotrophic growth and lacks homologs to genes canonically involved in EET. Bioelectrochemical characterization of SN3 cells shows that inward EET requires a terminal electron acceptor (respiration). Deletion of nitrate reductase catalytic subunit napA abolished current consumption and catalytic activity under nitrate-reducing conditions. Media exchange experiments demonstrate that inward EET in SN3 is facilitated by direct contact with the electrode, with a formal midpoint potential of 153 ± 16 mV vs. SHE. Through deletion of the formate dehydrogenase fdhABCD and electrochemical characterization of mutant cells, we show that inward EET is not a function of Fdh enzyme sorption to the electrode, as has been demonstrated for other organisms. This provides further evidence of a cell-mediated and contact-dependent EET mechanism. This work provides a foundation for investigating this metabolically versatile organism’s yet uncharacterized mechanism of EET.
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- Award ID(s):
- 2239052
- PAR ID:
- 10592106
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Bioelectrochemistry
- Volume:
- 165
- Issue:
- C
- ISSN:
- 1567-5394
- Page Range / eLocation ID:
- 108976
- Subject(s) / Keyword(s):
- Cathode oxidation Biocorrosion Electromicrobiology Extracellular Electron Transfer Weak Electrotroph
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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