Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria
Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria
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DOI：
10.1128/aem.03277-13
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发表时间：
2014-02-01
影响因子：
4.4
通讯作者：
Obst, Martin
中科院分区：
文献类型：
--
作者：
Klueglein, Nicole;Zeitvogel, Fabian;Obst, Martin
已经观察到微生物在中性pH下在缺氧和微氧条件下氧化Fe（II）。虽然大多数兼养硝酸盐还原Fe（II）氧化细菌被富含Fe（III）的矿物质结壳，但光自养和微需氧Fe（II）氧化剂避免了细胞结壳。铁（II）的氧化机制和结壳的原因在很大程度上仍然没有得到解决。在这里，我们使用基于培养的方法和电子显微镜比较两个先前描述的硝酸盐还原Fe（II）氧化剂（Acidovorax sp.菌株BoFeN1和Pseudogulbenkiania sp.菌株2002）和两个异养硝酸盐还原剂（Paracoccus spermicans ATCC 19367和P. spermicans Pd 1222）。所有四种菌株氧化类似于8mM的Fe（II）在5天内，在5 mM的乙酸和积累的亚硝酸盐（最大浓度为0.8至1.0 mM）的存在下，在培养基中。铁（III）矿物，主要是针铁矿，形成和沉淀细胞外在细胞表面附近。有趣的是，矿物质的形成也观察到周质和细胞质内，细胞内矿化预计是生理上不利的，但乙酸消耗继续观察，即使在先进的阶段Fe（II）氧化。胞外聚合物（EPS）的检测凝集素染色与荧光显微镜，特别是在铁（II）的存在下，这表明，EPS生产是一个响应铁（II）的毒性或减少结壳的策略。基于这里提出的数据，我们提出了一个亚硝酸盐驱动的，间接的细胞结壳机制，亚硝酸盐的形式在异养反硝化和非生物氧化Fe（II）。这项工作增加了已知的Fe（II）氧化细菌在自然界中的组合，并使我们的能力，以描绘微生物的Fe（II）氧化保存在地质记录中的化石古微生物。
Microorganisms have been observed to oxidize Fe(II) at neutral pH under anoxic and microoxic conditions. While most of the mixotrophic nitrate-reducing Fe(II)-oxidizing bacteria become encrusted with Fe(III)-rich minerals, photoautotrophic and microaerophilic Fe(II) oxidizers avoid cell encrustation. The Fe(II) oxidation mechanisms and the reasons for encrustation remain largely unresolved. Here we used cultivation-based methods and electron microscopy to compare two previously described nitrate-reducing Fe(II) oxidizers (Acidovorax sp. strain BoFeN1 and Pseudogulbenkiania sp. strain 2002) and two heterotrophic nitrate reducers (Paracoccus denitrificans ATCC 19367 and P. denitrificans Pd 1222). All four strains oxidized similar to 8mM Fe(II) within 5 days in the presence of 5 mM acetate and accumulated nitrite (maximum concentrations of 0.8 to 1.0 mM) in the culture media. Iron(III) minerals, mainly goethite, formed and precipitated extracellularly in close proximity to the cell surface. Interestingly, mineral formation was also observed within the periplasm and cytoplasm; intracellular mineralization is expected to be physiologically disadvantageous, yet acetate consumption continued to be observed even at an advanced stage of Fe(II) oxidation. Extracellular polymeric substances (EPS) were detected by lectin staining with fluorescence microscopy, particularly in the presence of Fe(II), suggesting that EPS production is a response to Fe(II) toxicity or a strategy to decrease encrustation. Based on the data presented here, we propose a nitrite-driven, indirect mechanism of cell encrustation whereby nitrite forms during heterotrophic denitrification and abiotically oxidizes Fe(II). This work adds to the known assemblage of Fe(II)-oxidizing bacteria in nature and complicates our ability to delineate microbial Fe(II) oxidation in ancient microbes preserved as fossils in the geological record.