Metabolic trade-offs in : dose-dependent FeS nanoparticles modulate extracellular electron transfer and gene expression for mineral transformation.

Biogenic ferrous sulfide nanoparticles (FeS NPs) regulate sulfate (SO)-reducing bacteria (SRB)-driven iron/sulfur cycling in SO-rich anaerobic environments, yet their dose-dependent impacts on SRB metabolism remain unclear. This study revealed how FeS NPs dose modulates (a model SRB) in reducing schwertmannite (Sch). SRB preferentially reduced Fe(III) over SO in Sch FeS NPs-mediated extracellular electron transfer (EET). At low FeS doses (0-6 mM), the gene expression (sulfur metabolism) associated with mineral transformation increased despite a decline in SRB abundance, accompanied by a significant enhancement in Fe(III) reduction rate, yielding siderite and pyrite as dominant products. This enhancement was attributed to FeS NPs acting as electron conduits, as evidenced by a 4-9-fold surge in bio-current intensity. However, at high FeS doses (≥6 mM), nanoparticle aggregation formed a relatively thick mineral encrustation on cell surfaces, blocking EET pathways and leaving goethite as a residual phase. Strikingly, SRB exhibited a metabolic trade-off, suppressing population growth to amplify -driven electron flux under FeS stress. This adaptive strategy underscored SRB's resilience in FeS-rich environments while highlighting dose-dependent bifurcations in mineral transformation pathways. This study provided a new insight into manipulating SRB-dominated biogeochemical processes by controlling FeS NPs dose.