Enhanced denitrification by sunlight-hematite: A neglected nitrogen flow pattern in red soil.

Mineral-microbe interactions in the Earth's Critical Zone significantly influence elemental biogeochemical cycling and energy flow processes. This study addresses the key scientific question of how semiconducting minerals drive microbial nitrogen cycling. In the red soil environment, the presence of semiconducting minerals enhances the denitrification process mediated by facultative microorganisms (Pseudomonas aeruginosa PAO1) with denitrifying activity. Compared to darkness, light significantly enhanced the synergistic denitrification kinetic process of red soil and Pseudomonas aeruginosa PAO1 (1.87 times). Cyclic voltammetry shows that the P. aeruginosa PAO1-red soil synergistic system exhibits distinct redox peaks under light. The constant potential current curve and electrochemical impedance spectroscopy measurements reveal a high photocurrent density (1.0 μA/cm) and minimal polarization resistance (102 Ω) under this condition. These findings confirm that the sunlight-red soil-P. aeruginosa PAO1 synergistic process has excellent electron generation and migration capacity, active redox reactions, and good electron compatibility. Additionally, the photoelectrons of semiconductive minerals in red soil profoundly impact the metabolic processes of microbial denitrification functional genes. Using real-time polymerase chain reaction (qPCR) gene array technology, the abundance of nitrogen metabolism functional genes in P. aeruginosa PAO1 increased by 200 % during the light-red soil synergistic process. Notably, denitrification-related genes (ureC, nirS1, gdhA, and nosZ2) were significantly upregulated. This study confirms that semiconducting minerals are involved in the nitrogen cycle pathway of microbial denitrification and supplements the theory of mineral-microbial synergistic element biogeochemical cycling in the natural environment.