Constraining the role of microbes in the structural iron (Fe) reduction of iron-bearing minerals improves our understanding of sediments and ice sheets as a source of dissolved Fe (dFe) to the oceans. However, bio-mediated structural Fe-reduction has yet to be studied in cryospheric environments. Here, we show that the Fe reducing psychrophile bacterium isolated from sea ice in Antarctica, reduced structural Fe in nontronite (NAu-2) and maghemite (γ-FeO), common mineral phases in glacial ice, and marine sediments in Antarctica, during two freeze–thaw cycles (−10 °C to +15 °C), resulting in the release of dFe. The modification of turbostratically disordered nontronite (ferric iron dominant phase) to discrete ordered illite-like structure (ferrous iron dominant phase), and the aggregation of altered small maghemite particles with neoformation of vivianite (Fe(PO)·nHO) indicated the microbially induced reductive dissolution of nontronite and maghemite, respectively. The biotic Fe-reduction gradually decreased and ceased as the temperature approached freezing (−8 °C), however the rection reactivated in the thawing cycle (−7 to +15 °C). No discernable biotic Fe-reduction was measured for either mineral under freezing conditions, suggesting that temperature limits the activity of the microbes. Further, and regardless of temperatures during two freeze–thaw cycles, Fe-reduction was not observed in abiotic control. Overall, these results highlight the importance of microbially induced Fe reduction during seasonal freeze–thaw cycles of ice and sediments in continuous supplying bioavailable dFe to cryospheric environments and the often Fe-limited polar oceans.

中文翻译：

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冻融循环过程中微生物介导的含铁矿物还原溶解


限制微生物在含铁矿物结构铁 (Fe) 还原中的作用，可以提高我们对沉积物和冰盖作为海洋溶解铁 (dFe) 来源的认识。然而，生物介导的结构铁还原尚未在冰冻圈环境中进行研究。在这里，我们展示了从南极洲海冰中分离出的铁还原嗜冷细菌，在两个过程中还原了绿脱石（NAu-2）和磁赤铁矿（γ-FeO）中的结构铁，冰川冰中的常见矿物相以及南极洲的海洋沉积物。冻融循环（−10 °C 至 +15 °C），导致 dFe 的释放。乱层无序绿脱石（三价铁主要相）向离散有序伊利石状结构（二价铁主要相）的改性，以及改变的小磁赤铁矿颗粒与新形成的六铁矿（Fe(PO)·nH2O）的聚集表明微生物诱导的分别还原溶解绿脱石和磁赤铁矿。当温度接近冰点（-8°C）时，生物铁还原逐渐减少并停止，但在解冻周期（-7至+15°C）中反应重新激活。在冷冻条件下，这两种矿物质都没有测量到明显的生物铁还原作用，这表明温度限制了微生物的活动。此外，无论两次冻融循环期间的温度如何，在非生物控制中都没有观察到铁还原。总体而言，这些结果强调了冰和沉积物季节性冻融循环期间微生物诱导的铁还原对于向冰冻圈环境和通常铁含量有限的极地海洋持续供应生物可利用的铁的重要性。