Microscale zero-valent iron enhances light-dependent inorganic carbon assimilation in a Shewanella oneidensis-Rhodopseudomonas palustris coculture.

Authors

Zhengyang Lu, Yanwen Shen, Xiaohong Guan

Published in

Bioresource technology. Pages 136120. Oct 25, 2026. Epub Oct 25, 2026.

Abstract

Microbial carbon dioxide (CO₂) fixation driven by solid electron donors is often constrained by interfacial electron transfer. Here, we evaluated microscale zero-valent iron (mZVI) in an illuminated, anoxic coculture of Shewanella oneidensis and Rhodopseudomonas palustris using physiological, isotopic, electrochemical and metatranscriptomic analyses. Under photoautotrophic conditions, 200 mg L^-1 mZVI increased the peak optical density at 600  nm (OD₆₀₀) from 0.36 to 0.80 and mixed-biomass δ¹³C from 3038.60 ‰ to 3503.65‰. Bulk OD₆₀₀ increased in nanoscale zero-valent iron cultures, although extracellular lactate dehydrogenase release was 37.4% higher than with mZVI, consistent with greater membrane damage. With 10  mM succinate, mZVI increased the coculture peak OD₆₀₀ from 0.682 to 0.927. Ferrozine lowered the mZVI-associated biomass response by 13-31% but did not abolish it, indicating that soluble Fe(II) contributed without fully accounting for the phenotype. Microscale magnetite produced a comparable peak OD₆₀₀ (0.813), although its reversible Fe(II)/Fe(III) cycling precluded attribution to solid-state conduction alone. A lactate-nitrate diagnostic assay showed that the additional coculture growth was not reproduced by cell-free spent medium or membrane separation, indicating a requirement for close association. Extracellular appendages, enhanced anodic currents, increased expression of S. oneidensis electron-transfer genes and R. palustris carbon-assimilation genes, and lower pioABC expression were consistent with mineral-associated interspecies electron transfer beyond soluble Fe(II) shuttling. However, the relative contributions of direct contact, flavins and surface iron cycling remain unresolved. The response required illumination. Microscale iron minerals may therefore provide a biocompatible electron-transfer interface for CO₂-fixing consortia at illuminated anoxic biointerfaces.

PMID:
42927836
Bibliographic data and abstract were imported from PubMed on 26 Oct 2026.

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