Abiotic oxidation of Fe(II) by reactive nitrogen species in cultures of the nitrate-reducing Fe(II) oxidizer Acidovorax sp BoFeN1 - questioning the existence of enzymatic Fe(II) oxidation
Abiotic oxidation of Fe(II) by reactive nitrogen species in cultures of the nitrate-reducing Fe(II) oxidizer Acidovorax sp BoFeN1 - questioning the existence of enzymatic Fe(II) oxidation
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DOI：
10.1111/gbi.12019
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发表时间：
2013-03-01
期刊：
影响因子：
3.7
通讯作者：
Kappler, A.
中科院分区：
文献类型：
--
作者：
Klueglein, N.;Kappler, A.
硝酸盐还原、Fe(II)氧化菌与酶催化Fe(II)氧化反应耦合为硝酸盐还原。反硝化通过中间体(NO2，NO)进行，这些中间体可以在中性，特别是在酸性pH下非生物地氧化Fe(II)。在这里，我们提出了一个改进的Fe(II)定量方案，以防止酸性铁提取过程中的人工现象，并评估了非生物Fe(II)氧化与酶催化Fe(II)氧化在硝酸盐还原Fe(II)氧化剂Acidovorax sp.培养中的作用。BoFeN1。在提铁过程中，用氨基磺酸代替盐酸与亚硝酸盐反应，防止非生物氧化Fe(II)。无氨基酸的非生物实验表明，氧化态Fe(II)亚硝酸盐样品的酸化导致的Fe(II)氧化量是缺氧样品的5.6倍，这是因为生成的NO被O2迅速再氧化，从而导致非生物氧化和对Fe(II)的低估。通过我们使用氨基磺酸的修订方案，我们量化了BoFeN1在4天内氧化了大约7 mM的Fe(II)。在没有添加氨基磺酸的情况下，仅在2天内就检测到了同样的氧化。此外，在针铁矿作为表面催化剂的情况下，Fe(II)与亚硝酸盐的非生物孵育导致了与正在生长的BoFeN1培养物中观察到的相似的非生物Fe(II)氧化速率。在以N2O为电子受体的乙酸酯上观察到了BoFeN1的生长。当添加Fe(II)时，没有观察到Fe(II)的氧化，这表明活性N中间体(NO2，NO)的缺乏阻碍了Fe(II)的氧化。在醋酸盐/硝酸盐BoFeN1培养物中添加亚铁水合物[Fe(OH)3]，可产生与添加Fe(II)对生长的影响相当的生长刺激作用。这表明，铁浓度升高可能是一种营养效应，而不是产生能量的Fe(II)氧化。因此，我们的发现表明，虽然不能完全排除反硝化菌对Fe(II)的酶催化氧化，但它对微生物培养中观察到的Fe(II)氧化的贡献可能比先前提出的要低，在确定酶机制介导的Fe(II)氧化之前，总体上必须受到质疑。
Nitrate-reducing, Fe(II)-oxidizing bacteria were suggested to couple with enzymatic Fe(II) oxidation to nitrate reduction. Denitrification proceeds via intermediates (NO2 , NO) that can oxidize Fe(II) abiotically at neutral and particularly at acidic pH. Here, we present a revised Fe(II) quantification protocol preventing artifacts during acidic Fe extraction and evaluate the contribution of abiotic vs. enzymatic Fe(II) oxidation in cultures of the nitrate-reducing, Fe(II) oxidizer Acidovorax sp. BoFeN1. Sulfamic acid used instead of HCl reacts with nitrite and prevents abiotic Fe(II) oxidation during Fe extraction. Abiotic experiments without sulfamic acid showed that acidification of oxic Fe(II) nitrite samples leads to 5.6-fold more Fe(II) oxidation than in anoxic samples because the formed NO becomes rapidly reoxidized by O2, therefore leading to abiotic oxidation and underestimation of Fe(II). With our revised protocol using sulfamic acid, we quantified oxidation of approximately 7mm of Fe(II) by BoFeN1 within 4days. Without addition of sulfamic acid, the same oxidation was detected within only 2days. Additionally, abiotic incubation of Fe(II) with nitrite in the presence of goethite as surface catalyst led to similar abiotic Fe(II) oxidation rates as observed in growing BoFeN1 cultures. BoFeN1 growth was observed on acetate with N2O as electron acceptor. When adding Fe(II), no Fe(II) oxidation was observed, suggesting that the absence of reactive N intermediates (NO2 , NO) precludes Fe(II) oxidation. The addition of ferrihydrite [Fe(OH)3] to acetate/nitrate BoFeN1 cultures led to growth stimulation equivalent to previously described effects on growth by adding Fe(II). This suggests that elevated iron concentrations might provide a nutritional effect rather than energy-yielding Fe(II) oxidation. Our findings therefore suggest that although enzymatic Fe(II) oxidation by denitrifiers cannot be fully ruled out, its contribution to the observed Fe(II) oxidation in microbial cultures is probably lower than previously suggested and has to be questioned in general until the enzymatic machinery-mediating Fe(II) oxidation is identified.