Electrical Conductivity as a Determinant of Nanoparticle Impact on Iron Reduction by Shewanella oneidensis

The increasing environmental prevalence of inorganic nanoparticles (NPs) necessitates a deeper understanding of their impacts on microbial iron reduction. However， a knowledge gap exists regarding how NP electrical conductivity influences metal-reducing bacteria under anaerobic conditions. This study tested the specific hypothesis that NP conductivity is a primary determinant of its effect on the growth and Fe(III)-reduction capacity of Shewanella oneidensis MR-1. An integrated approach combining geochemical analysis， transmission electron microscopy， and gene expression quantification was employed to investigate the effects of conductive (gold， laponite) and insulating (silica) NPs. The results demonstrated a clear dichotomy: conductive NPs enhanced the reduction of hydrous ferric oxide (HFO)， which correlated with significant upregulation of the outer membrane cytochrome gene mtrC， while insulating silica NPs severely inhibited reduction in both HFO and the clay mineral nontronite (NAu-2)， concomitantly with a loss of cell viability and suppressed mtrC expression. The effects were further modulated by surface charge interactions between the NPs and the mineral substrates. This study provides evidence that the electrical conductivity of nanoparticles is a pivotal property governing their environmental impact on microbial iron reduction， offering a crucial framework for predicting the ecological consequences of nanomaterial releases.