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首页> 外文期刊>Applied Microbiology >Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria
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Potential Role of Nitrite for Abiotic Fe(II) Oxidation and Cell Encrustation during Nitrate Reduction by Denitrifying Bacteria

机译：亚硝酸盐在反硝化细菌还原硝酸盐过程中对非生物Fe（II）氧化和结壳的潜在作用

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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 ～8 mM 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.
机译：已观察到微生物在缺氧和微氧条件下，在中性pH下会氧化Fe（II）。虽然大多数降低混合营养型硝酸盐的Fe（II）氧化细菌都被富含Fe（III）的矿物包裹着，但光养养性和微需氧的Fe（II）氧化剂避免了细胞结壳。 Fe（II）的氧化机理及其结壳的原因至今仍未解决。在这里，我们使用基于培养的方法和电子显微镜，比较了两种先前描述的硝酸盐还原型Fe（II）氧化剂（Acidovorax sp。菌株BoFeN1和Pseudogulbenkiania sp。菌株2002）和两种异养硝酸盐还原剂（Paracoccus denitrificans ATCC 19367和P. denitrificans）。 （Pd 1222）。在存在5 mM乙酸盐的情况下，所有4个菌株在5天内氧化了约8 mM Fe（II），并在培养基中积累了亚硝酸盐（最大浓度为0.8至1.0 mM）。铁（III）矿物（主要是针铁矿）在细胞表面附近形成并沉淀在细胞外。有趣的是，在周质和细胞质中也观察到了矿物质的形成。预期细胞内矿化在生理上是不利的，但是即使在Fe（II）氧化的晚期，乙酸盐的消耗仍被观察到。通过凝集素染色用荧光显微镜检测到细胞外聚合物（EPS），特别是在Fe（II）存在的情况下，这表明EPS的产生是对Fe（II）毒性的反应或减少结壳的策略。根据此处提供的数据，我们提出了亚硝酸盐驱动的细胞结壳的间接机制，即亚硝酸盐在异养反硝化过程中形成并非生物氧化Fe（II）。这项工作增加了自然界中已知的Fe（II）氧化细菌的集合，并使我们在地质记录中保存为化石的古代微生物中描述微生物Fe（II）氧化的能力变得复杂。

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