Denitrification versus respiratory ammonification: environmental controls of two competing dissimilatory NO3−/NO2− reduction pathways in Shewanella loihica strain PV-4
Denitrification versus respiratory ammonification: environmental controls of two competing dissimilatory NO3−/NO2− reduction pathways in Shewanella loihica strain PV-4
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DOI：
10.1038/ismej.2014.201
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发表时间：
2014-10
期刊：
影响因子：
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通讯作者：
Sukhwan Yoon;C. Cruz-García;R. Sanford;K. Ritalahti;F. Löffler
中科院分区：
文献类型：
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作者：
Sukhwan Yoon;C. Cruz-García;R. Sanford;K. Ritalahti;F. Löffler
反硝化作用和呼吸氨化作用是两个相互竞争、节能的NO_3-−/NO_2-−还原途径，它们对氮的滞留、植物生长和气候有重要的生物地球化学影响。对同时具有反硝化和呼吸氨化途径的细小希瓦氏杆菌PV-4进行了分批和连续培养实验，揭示了决定N03−/NO2−去向的因素。在低碳氮比(即电子给体限制生长条件)下，反硝化作用占主导地位，而在高C/N比(即电子受体限制生长条件)下，氨氮是主要产物。PH和温度对NO_3-−/NO_2-−的去向也有影响，pH值高于7.0，温度为30 °C时，有利于铵的生成。逆转录酶实时定量PCR分析将表型观察与nirKandnosZ转录本丰度相关联，在有利于呼吸氨化的条件下，nirKandnosZ转录本丰度分别减少了1600倍和27倍。在PV-4株基因组上编码的两个rfA4基因中，nrfA0844只有在恒化器接受最低C/N比1.5时转录减少，而nrfA0505在所有生长条件下都在低水平(≤3.4×10−2转录本/细胞)转录。在中等C/N比时，反硝化和呼吸氨化同时发生，nrfA0844(5.5个转录子/细胞)和nirK(0.88个转录子/细胞)都被转录。最近的研究结果表明，同时具有反硝化和呼吸氨化途径的生物在土壤和沉积物生态系统中并不少见，而菌株PV-4提供了一个易于操作的实验系统来探索异化的NO3−/NO2−还原途径的调节。
Denitrification and respiratory ammonification are two competing, energy-conserving NO3−/NO2−reduction pathways that have major biogeochemical consequences for N retention, plant growth and climate. Batch and continuous culture experiments usingShewanella loihicastrain PV-4, a bacterium possessing both the denitrification and respiratory ammonification pathways, revealed factors that determine NO3−/NO2−fate. Denitrification dominated at low carbon-to-nitrogen (C/N) ratios (that is, electron donor-limiting growth conditions), whereas ammonium was the predominant product at high C/N ratios (that is, electron acceptor-limiting growth conditions). pH and temperature also affected NO3−/NO2−fate, and incubation above pH 7.0 and temperatures of 30 °C favored ammonium formation. Reverse-transcriptase real-time quantitative PCR analyses correlated the phenotypic observations withnirKandnosZtranscript abundances that decreased up to 1600-fold and 27-fold, respectively, under conditions favoring respiratory ammonification. Of the twonrfAgenes encoded on the strain PV-4 genome,nrfA0844transcription decreased only when the chemostat reactor received medium with the lowest C/N ratio of 1.5, whereasnrfA0505transcription occurred at low levels (≤3.4 × 10−2transcripts per cell) under all growth conditions. At intermediate C/N ratios, denitrification and respiratory ammonification occurred concomitantly, and bothnrfA0844(5.5 transcripts per cell) andnirK(0.88 transcripts per cell) were transcribed. Recent findings suggest that organisms with both the denitrification and respiratory ammonification pathways are not uncommon in soil and sediment ecosystems, and strain PV-4 offers a tractable experimental system to explore regulation of dissimilatory NO3−/NO2−reduction pathways.