Cellulose Reshapes Microbial C–S–Fe Coupling to Suppress Direct and Fe(III)-Mediated Pyrite Oxidation
Min Zhang, Yu Liu, Guoping Jiang, Jing Wen, Ling Xia, Ibrahim Ahmed Ibrahim, Fenliang Fan, Zhenghua Liu, Xueduan Liu, Qingyun Yan, Delong Meng, Huaqun YinAbstract
Pyrite oxidation generates sulfate and acidity in sulfide-bearing mine soils, but how structural carbon suppresses this process remains unresolved. We combined a 56-day pyrite-amended soil microcosm with geochemical measurements, qPCR, metagenomics, DNA stable isotope probing (DNA-SIP), genome-resolved analysis, and apparent kinetic modeling. Cellulose decreased NaOH-extractable sulfate by 72.71% and HCl-extractable Fe(III) by 55.13% at day 56. DNA-SIP showed that cellulose-derived carbon entered a phylogenetically distributed assimilating guild with genomic potential for oxidative-hydrolytic cellulose deconstruction, Fe(III) reduction, sulfate uptake, and assimilatory sulfate reduction. Enriched metagenome-assembled genomes collocated these C, Fe, and S functions within individual populations, whereas time-series metagenomes showed sustained cellulose-deconstruction and sulfur-assimilation potential without broad enrichment of Fe-reduction genes. Thus, functionally important assimilators could reshape Fe–S cycling without consistently dominating bulk community abundance. Consistent with these genomic and geochemical patterns, the apparent model indicated weaker O2-driven direct oxidation, Fe(II) oxidation/Fe(III) regeneration, and effective reactivity of extractable Fe(III). These results identify a microbial mechanism whereby cellulose utilization redirects C–S–Fe coupling toward more reductive and assimilatory transformations, suppressing pyrite oxidation without detectable mineral-surface coating.