Yoon Sukhwan, Nissen Silke, Park Doyoung, Sanford Robert A, Löffler Frank E
Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee, USA Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA University of Tennessee and Oak Ridge National Laboratory (UT-ORNL) Joint Institute for Biological Sciences (JIBS) and Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.
Appl Environ Microbiol. 2016 Jun 13;82(13):3793-800. doi: 10.1128/AEM.00409-16. Print 2016 Jul 1.
Bacteria capable of reduction of nitrous oxide (N2O) to N2 separate into clade I and clade II organisms on the basis of nos operon structures and nosZ sequence features. To explore the possible ecological consequences of distinct nos clusters, the growth of bacterial isolates with either clade I (Pseudomonas stutzeri strain DCP-Ps1, Shewanella loihica strain PV-4) or clade II (Dechloromonas aromatica strain RCB, Anaeromyxobacter dehalogenans strain 2CP-C) nosZ with N2O was examined. Growth curves did not reveal trends distinguishing the clade I and clade II organisms tested; however, the growth yields of clade II organisms exceeded those of clade I organisms by 1.5- to 1.8-fold. Further, whole-cell half-saturation constants (Kss) for N2O distinguished clade I from clade II organisms. The apparent Ks values of 0.324 ± 0.078 μM for D. aromatica and 1.34 ± 0.35 μM for A. dehalogenans were significantly lower than the values measured for P. stutzeri (35.5 ± 9.3 μM) and S. loihica (7.07 ± 1.13 μM). Genome sequencing demonstrated that Dechloromonas denitrificans possessed a clade II nosZ gene, and a measured Ks of 1.01 ± 0.18 μM for N2O was consistent with the values determined for the other clade II organisms tested. These observations provide a plausible mechanistic basis for why the relative activity of bacteria with clade I nos operons compared to that of bacteria with clade II nos operons may control N2O emissions and determine a soil's N2O sink capacity.
Anthropogenic activities, in particular fertilizer application for agricultural production, increase N2O emissions to the atmosphere. N2O is a strong greenhouse gas with ozone destruction potential, and there is concern that nitrogen may become the major driver of climate change. Microbial N2O reductase (NosZ) catalyzes N2O reduction to environmentally benign dinitrogen gas and represents the major N2O sink process. The observation that bacterial groups with clade I nosZ versus those with clade II nosZ exhibit distinct affinities to N2O has implications for N2O flux models, and these distinct characteristics may provide opportunities to curb N2O emissions from relevant soil ecosystems.
能够将一氧化二氮（N₂O）还原为氮气（N₂）的细菌根据nos操纵子结构和nosZ序列特征分为进化枝I和进化枝II生物。为了探究不同nos簇可能产生的生态后果，研究了具有进化枝I（施氏假单胞菌菌株DCP - Ps1、洛伊希瓦希瓦氏菌菌株PV - 4）或进化枝II（芳香脱氯单胞菌菌株RCB、脱卤厌氧粘细菌菌株2CP - C）nosZ的细菌分离株利用N₂O的生长情况。生长曲线未显示出区分所测试的进化枝I和进化枝II生物的趋势；然而，进化枝II生物的生长产量比进化枝I生物高出1.5至1.8倍。此外，N₂O的全细胞半饱和常数（Kss）区分了进化枝I和进化枝II生物。芳香脱氯单胞菌的表观Ks值为0.324±0.078μM，脱卤厌氧粘细菌的表观Ks值为1.34±0.35μM，显著低于施氏假单胞菌（35.5±9.3μM）和洛伊希瓦希瓦氏菌（7.07±1.13μM）测得的值。基因组测序表明反硝化脱氯单胞菌拥有进化枝II的nosZ基因，测得的N₂O的Ks值为1.01±0.18μM，与其他测试的进化枝II生物测定的值一致。这些观察结果为为什么与具有进化枝II nos操纵子的细菌相比，具有进化枝I nos操纵子的细菌的相对活性可能控制N₂O排放并决定土壤的N₂O汇容量提供了一个合理的机制基础。
人为活动，特别是农业生产中的肥料施用，增加了向大气中的N₂O排放。N₂O是一种强大的温室气体，具有破坏臭氧层的潜力，人们担心氮可能成为气候变化的主要驱动因素。微生物N₂O还原酶（NosZ）催化将N₂O还原为对环境无害的氮气，是主要的N₂O汇过程。具有进化枝I nosZ的细菌群体与具有进化枝II nosZ的细菌群体对N₂O表现出不同亲和力这一观察结果对N₂O通量模型有影响，并且这些不同特征可能为抑制相关土壤生态系统中的N₂O排放提供机会。
