Functional evolution of elemental sulfur in Cr(VI) bioreduction during sulfidogenesis.

Adding 1 g/L elemental sulfur to a Shewanella oneidensis MR-1–lactate system increases Cr(VI) removal from 17.5% to 37.6%, with a 2.1-fold faster rate in stage I (0–6 h).

• Why it matters: The contribution of S0 itself to Cr(VI) reduction before sulfide forms is unclear, limiting mechanistic optimization of S0-driven sulfidogenic remediation.
• What they did: The authors ran Cr(VI) removal experiments with MR-1, lactate, and S0, then combined S K-edge XANES, Raman, electrochemistry, density functional theory, thermodynamic analysis, and comparisons of two S0 forms.
• The result: Stage I showed no detectable sulfide or reduced sulfur species, yet S0 structural changes and modeling support a transient electron-accepting S0 intermediate; later, sulfide production correlated with enhanced Cr(VI) reduction.

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