铁还原细菌Shewanella oneidensis MR-4诱导水合氧化铁形成蓝铁矿的过程

Ferrihydrite reduction and vivianite biomineralization mediated by iron reducing bacterium Shewanella oneidensis MR-4

摘要:

[目的]研究铁还原细菌Shewanella oneidensis MR-4在细胞外诱导形成含铁矿物的矿物相、化学成分和形貌结构等特性及其变化，深化对铁还原细菌细胞外诱导矿化过程的认识。[方法]在以30 mmol/L乳酸钠为电子供体，10 mmol/L水合氧化铁为电子受体，[HCO₃^-]为30 mmol/L，[PO₄^3-]为5 mmol/L条件下，30恒温下厌氧培养，进行细菌生长和细胞外诱导矿化实验，定期采样测量反应体系的pH、生物量、Fe（II）浓度；采用激光拉曼光谱（Raman）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）和X-射线衍射（XRD）等方法对不同时间点的矿化产物进行分析。[结果]MR-4在还原Fe（III）的过程中，细胞快速生长，表明MR-4的Fe（III）还原和乳酸氧化过程相互耦合，从而进行细胞生长，并在细胞外诱导矿物形成。对不同阶段矿化产物的综合分析表明，反应进行到约8 d时，无定形-弱结晶的水合氧化铁部分地转化为纳米尺寸的磁铁矿晶体颗粒；约16 d时，反应体系中开始出现蓝铁矿晶体颗粒；约20 d后，几乎所有矿物转化为纤维状或者叶片状的蓝铁矿。[结论]铁还原细菌Shewanella oneidensis MR-4细胞外诱导矿化过程受环境条件控制，当以乳酸钠和水合氧化铁分别作为电子供体和受体，相对高的[PO₄^3-]/[HCO₃^-]（1：6）时，水合氧化铁先转化为磁铁矿，最后大量转化为蓝铁矿。本研究为全面认识铁还原细菌的生物诱导矿化过程和评估其参与铁元素地球化学循环提供了新的数据。

Abstract:

[Objective] To explore the mineralogical, chemical and microscopic properties of extracellular vivianite formation induced by iron-reducing bacteria Shewanella oneidensis MR-4. [Methods] MR-4 cells grown with 30 mmol/L of lactate and 10 mmol/L of amorphous ferrihydrite, which were used as electron donor and electron acceptor, respectively. The medium was buffered with 30 mmol/L[HCO₃^-] and 5 mmol/L[PO₄^3-], and the culture was incubated at 30℃. The headspace of serum bottle flushed with N₂/CO₂(V/V, 80/20). The pH, biomass and[Fe(Ⅱ)] of the culture were measured by sampling at different time points. Meanwhile, the combination of X-ray diffraction, scanning electron microscope, laser Raman and transmission electron microscope approaches were applied to characterize the mineralogical, chemical and morphological properties of products produced within the culture. [Results] MR-4 could couple the reduction of Fe(Ⅲ) with the oxidation of lactate for their cell growth and mineral transformation of Ferrihydrite. Specifically, ferrihydrite was initially transformed to nanometer-sized magnetite particles and majorly to micrometer-sized vivianite with bladed and fibrous morphologies finally. [Conclusion] The biomineralization process and products by MR-4 were strongly affected by environmental conditions such as the types and concentration of anions. In this case with relatively high[PO₄^3-] within the culture, ferrihydrite was initially converted to nanometer-sized magnetite, and was transformed into vivianite dominantly at the end of the culture. The result of this paper provides a new insight for comprehensive understanding of the microbial induced biomineralization of iron-reducing bacteria and its role in the iron element biogeochemical cycle.