High redox potential promotes oxidation of pyrite under neutral conditions: Implications for optimizing pyrite autotrophic denitrification

Pyrite autotrophic denitrification (PAD) represents an important natural attenuation process of nitrate pollution and plays a pivotal role in linking nitrogen, sulfur, and iron cycles in a variety of anoxic environments. However, there are knowledge gaps about the oxidation mechanism of pyrite under anaerobic neutral conditions. This study explored the performance of PAD in the presence of EDTA and revealed the mechanism of anaerobic pyrite oxidation and microbial mineral transformation. It was demonstrated that similar to 200 mV was the electrochemical threshold for converting pyrite into bioavailable forms in PAD conditions, and accelerated pyrite oxidation by Fe3+-EDTA complexes can improve the performance of PAD effectively. Furthermore, genus related to sulfur and nitrogen cycle (Sulfurimonas, Denitrobacter) were found at higher abundances in cultures containing EDTA. The analysis of metagenomic binning showed that the microbial community in PAD culture with EDTA addition exhibited higher levels of functional diversity and redundancy. These results will further the understanding of the oxidation mechanism of pyrite under anaerobic neutral conditions and the corresponding microbial activities, and provide insights into the practical application of PAD.

Automated summary

This study investigated the performance of pyrite autotrophic denitrification (PAD) in the presence of EDTA and uncovered the mechanism of anaerobic pyrite oxidation and microbial mineral transformation. The electrochemical threshold for converting pyrite into bioavailable forms in PAD conditions was found to be around 200 mV, and the presence of Fe3+-EDTA complexes accelerated pyrite oxidation. Higher abundances of sulfur- and nitrogen-cycling genera were observed in cultures containing EDTA, indicating increased functional diversity and redundancy in the microbial community. These findings contribute to a better understanding of pyrite oxidation under anaerobic neutral conditions and suggest practical applications for PAD.