Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments
Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments
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DOI：
10.1128/aem.02013-17
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发表时间：
2018-01-01
影响因子：
4.4
通讯作者：
Schmidt, Caroline
中科院分区：
文献类型：
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作者：
Schaedler, Franziska;Lockwood, Cindy;Schmidt, Caroline
硝酸盐还原铁（II）氧化细菌已被发现约20年。关于硝酸盐还原和亚铁氧化在多大程度上是通过酶途径或通过异养反硝化形成的亚硝酸盐诱导的非生物过程耦合的，一直存在很大争议。本研究的目的是评估耦合硝酸盐还原和铁（II）氧化监测底物浓度的变化，以及在硝酸盐还原菌的活性在自然沿岸的淡水沉积物中，在响应与硝酸盐和铁（II）的刺激。在基质修正的微宇宙中，我们发现，亚铁的生物氧化依赖于同时微生物还原硝酸盐。此外，灭菌沉积物中亚硝酸盐对二价铁的非生物氧化速度还不足以解释在微生物活性沉积物中观察到的铁氧化速率。此外，在某些情况下，编码对硝酸盐还原至关重要的酶的基因的表达水平受到二价铁的存在的刺激。这些结果表明亚铁对细菌反硝化有直接影响，并支持微生物硝酸盐还原受生物铁（II）氧化刺激的假设。通过Fe（III）矿物质的形成改变土壤中的养分或重金属的流动性，以及在全球范围内，例如，主要温室气体一氧化二氮的形成虽然硝酸盐还原和Fe（II）氧化的耦合在20年前就有报道，并从那时起进行了深入研究，但其潜在机制仍然未知。主要的知识差距之一是酶促Fe（II）氧化与硝酸盐还原的程度，这在文献中经常受到质疑。在本研究中，我们提供的证据微生物介导的硝酸盐还原铁（II）氧化淡水沉积物。这一证据是基于硝酸盐还原和铁（II）氧化的速率确定在微宇宙培养和铁对反硝化所需的基因的表达的影响。
Nitrate-reducing iron(II)-oxidizing bacteria have been known for approximately 20 years. There has been much debate as to what extent the reduction of nitrate and the oxidation of ferrous iron are coupled via enzymatic pathways or via abiotic processes induced by nitrite formed by heterotrophic denitrification. The aim of the present study was to assess the coupling of nitrate reduction and iron(II) oxidation by monitoring changes in substrate concentrations, as well as in the activity of nitrate-reducing bacteria in natural littoral freshwater sediment, in response to stimulation with nitrate and iron(II). In substrate-amended microcosms, we found that the biotic oxidation of ferrous iron depended on the simultaneous microbial reduction of nitrate. Additionally, the abiotic oxidation of ferrous iron by nitrite in sterilized sediment was not fast enough to explain the iron oxidation rates observed in microbially active sediment. Furthermore, the expression levels of genes coding for enzymes crucial for nitrate reduction were in some setups stimulated by the presence of ferrous iron. These results indicate that there is a direct influence of ferrous iron on bacterial denitrification and support the hypothesis that microbial nitrate reduction is stimulated by biotic iron(II) oxidation.IMPORTANCE The coupling of nitrate reduction and Fe(II) oxidation affects the environment at a local scale, e.g., by changing nutrient or heavy metal mobility in soils due to the formation of Fe(III) minerals, as well as at a global scale, e.g., by the formation of the primary greenhouse gas nitrous oxide. Although the coupling of nitrate reduction and Fe(II) oxidation was reported 20 years ago and has been studied intensively since then, the underlying mechanisms still remain unknown. One of the main knowledge gaps is the extent of enzymatic Fe(II) oxidation coupled to nitrate reduction, which has frequently been questioned in the literature. In the present study, we provide evidence for microbially mediated nitrate-reducing Fe(II) oxidation in freshwater sediments. This evidence is based on the rates of nitrate reduction and Fe(II) oxidation determined in microcosm incubations and on the effect of iron on the expression of genes required for denitrification.