Particulate organic matter triggers photoelectrotrophic denitrification: An overlooked biogeochemical reaction induced by sunlight
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PUBLIC SUMMARY
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Particulate organic matter (POM) can trigger photoelectrotrophic denitrification (PEDeN).
POM promotes PEDeN by acting as a bacterial photosensitizer, photoelectron shuttle and sacrifice agent.
POM with self-oxidation during triggering PEDeN may impact carbon turnover in ecosystems.
Highlights overlooked biogeochemical processes of elements/pollutants driven by POM-microbe systems.
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ABSTRACT
Particulate organic matter (POM) is a major carbon pool in terrestrial and aquatic ecosystems and its biogeochemical processes significantly affect the global carbon cycle and trophic levels of ecosystems. As a natural photosensitizer, there have been no reports on photoelectron transfer from POM to microorganisms, leading to the long-term neglect of POM biogeochemical processes. Using photoelectrotrophic denitrification (PEDeN) as a model system, this study is the first to demonstrate the POM-triggered PEDeN effect; that is, photoelectrons from POM were used to drive microbial denitrification. By constructing the Thiobacillus denitrificans-POM system, it was found that irradiation accelerated nitrate reduction with a kinetic constant of 0.03 ± 0.007 h−1. Irradiation resulted in a complete denitrification with nitrogen as the main product (56.3 ± 8.8%), compared to the dark system with nitrite as the main product. The significantly upregulated (p < 0.01) denitrifying genes support the idea that the conversion of nitrate to nitrogen is a microbial-mediated process. During this process, POM plays multiple roles: photosensitizing microorganisms, mediating photoelectron transfer, and acting as a sacrificial donor. The first two roles of POM have not been established previously, revealing a new electron-transfer mechanism between POM and microorganisms. The latter accelerated POM dissolution, representing a newly discovered POM photodissolution process involving microorganisms. The study highlights the previously overlooked photoelectrochemical reactions of POM with microorganism, emphasizing the need to explore the biogeochemical processes triggered by POM-microorganisms system and suggesting a strategy for promoting sunlight-driven denitrification in surface environments. -
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REFERENCES
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Chen M., Huang S., Luo J., et al. (2025). Particulate organic matter triggers photoelectrotrophic denitrification: An overlooked biogeochemical reaction induced by sunlight. The Innovation Geoscience 3:100129. https://doi.org/10.59717/j.xinn-geo.2024.100129
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Chen M., Huang S., Luo J., et al. (2025). Particulate organic matter triggers photoelectrotrophic denitrification: An overlooked biogeochemical reaction induced by sunlight. The Innovation Geoscience 3:100129. https://doi.org/10.59717/j.xinn-geo.2024.100129
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Figure 1.
Characterization of POM, T. denitrificans and T. denitrificans-POM system
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Figure 2.
PEDeN process by T. denitrificans-POM
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Figure 3.
Evidence lines of POM as bacterial photosensitizer
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Figure 4.
Evidence lines of POM as photoelectron shuttle during PEDeN process
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Figure 5.
Three-dimensional fluorescence spectra (EEM) of (A) Raw, (B) T. denitrificans-POM (light), (C) T. denitrificans-POM (dark) and (D) POM (light) after reaction
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