Fermentative iron reduction buffers acidification and promotes microbial metabolism in marine sediments

Microbial iron reduction is a crucial process in natural ecosystems, contributing to the cycling of elements and supporting the biological activities of organisms. However, the significance of fermentative iron reduction in marine environments and microbial metabolism remains understudied compared with iron reduction coupled with respiration. The main objective of our study was to investigate the influence of fermentative iron reduction on microbial populations and marine sediment. Our findings revealed a robust iron-reducing activity in the enriched marine sediment, demonstrating a maximum ferrihydrite-reducing rate of 0.063 mmol/h. Remarkably, ferrihydrite reduction exhibited an intriguing pH-buffering effect through the release of OH+ and Fe2+ ions, distinct from fermentation alone. This effect resulted in substantial improvements in glucose consumption (71.4%), bacterial growth (48.1%), and metabolite production (80.8%). To further validate the acidification-buffering and metabolism-promoting effects of ferrihydrite reduction, we conducted iron-reducing experiments using a pure strain, Clostridium pasteurianum DMS525. The observed pH-buffering effect resulted from microbial iron reduction in marine sediment and has potential environmental implications by reducing CO2 emissions, mitigating acidification, and preserving the delicate balance of marine ecosystems.