Dekas Anne E, Chadwick Grayson L, Bowles Marshall W, Joye Samantha B, Orphan Victoria J
California Institute of Technology, Pasadena, CA, 91106, USA.
Environ Microbiol. 2014 Oct;16(10):3012-29. doi: 10.1111/1462-2920.12247. Epub 2013 Sep 24.
Nitrogen (N2) fixation was investigated at Mound 12, Costa Rica, to determine its spatial distribution and biogeochemical controls in deep-sea methane seep sediment. Using (15)N2 tracer experiments and isotope ratio mass spectrometry analysis, we observed that seep N2 fixation is methane-dependent, and that N2 fixation rates peak in a narrow sediment depth horizon corresponding to increased abundance of aggregates of anaerobic methanotrophic archaea (ANME-2) and sulfate-reducing bacteria (SRB). Using fluorescence in situ hybridization coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS), we directly measured (15)N2 uptake by ANME-2/SRB aggregates (n = 26) and observed maximum (15)N incorporation within ANME-2-dominated areas of the aggregates, consistent with previous analyses. NanoSIMS analysis of single cells (n = 34) from the same microcosm experiment revealed no (15)N2 uptake. Together, these observations suggest that ANME-2, and possibly physically associated SRB, mediate the majority of new nitrogen production within the seep ecosystem. ANME-2 diazotrophy was observed while in association with members of two distinct orders of SRB: Desulfobacteraceae and Desulfobulbaceae. The rate of N2 fixation per unit volume biomass was independent of the identity of the associated SRB, aggregate size and morphology. Our results show that the distribution of seep N2 fixation is heterogeneous, laterally and with depth in the sediment, and is likely influenced by chemical gradients affecting the abundance and activity of ANME-2/SRB aggregates.
在哥斯达黎加的12号丘对氮（N₂）固定作用进行了研究，以确定其在深海甲烷渗漏沉积物中的空间分布和生物地球化学控制因素。通过¹⁵N₂示踪实验和同位素比率质谱分析，我们观察到渗漏处的N₂固定作用依赖于甲烷，且N₂固定率在一个狭窄的沉积物深度范围内达到峰值，该深度范围对应着厌氧甲烷氧化古菌（ANME - 2）和硫酸盐还原细菌（SRB）聚集体丰度的增加。利用与纳米级二次离子质谱联用的荧光原位杂交技术（FISH - NanoSIMS），我们直接测量了ANME - 2/SRB聚集体（n = 26）对¹⁵N₂的摄取，并在聚集体中以ANME - 2为主的区域观察到了最大的¹⁵N掺入量，这与之前的分析结果一致。对同一微观实验中的单细胞（n = 34）进行的纳米二次离子质谱分析显示没有¹⁵N₂摄取现象。综合这些观察结果表明，ANME - 2以及可能与之物理相关的SRB介导了渗漏生态系统中大部分新氮的产生。在与两个不同的SRB菌属（脱硫杆菌科和脱硫球菌科）的成员共生时，观察到了ANME - 2的固氮作用。单位体积生物量的N₂固定率与相关SRB的种类、聚集体大小和形态无关。我们的结果表明，渗漏处N₂固定作用的分布在沉积物的横向和深度方向上都是不均匀的，并且可能受到影响ANME - 2/SRB聚集体丰度和活性的化学梯度的影响。
