Langlois Rebecca J, LaRoche Julie, Raab Philipp A
IFM-GEOMAR, Leibniz-Institut fuer Meereswissenschaften, Duesternbrooker Weg 20, 24105 Kiel, Germany.
Appl Environ Microbiol. 2005 Dec;71(12):7910-9. doi: 10.1128/AEM.71.12.7910-7919.2005.
To understand the structure of marine diazotrophic communities in the tropical and subtropical Atlantic Ocean, the molecular diversity of the nifH gene was studied by nested PCR amplification using degenerate primers, followed by cloning and sequencing. Sequences of nifH genes were amplified from environmental DNA samples collected during three cruises (November-December 2000, March 2002, and October-November 2002) covering an area between 0 to 28.3 degrees N and 56.6 to 18.5 degrees W. A total of 170 unique sequences were recovered from 18 stations and 23 depths. Samples from the November-December 2000 cruise contained both unicellular and filamentous cyanobacterial nifH phylotypes, as well as gamma-proteobacterial and cluster III sequences, so far only reported in the Pacific Ocean. In contrast, samples from the March 2002 cruise contained only phylotypes related to the uncultured group A unicellular cyanobacteria. The October-November 2002 cruise contained both filamentous and unicellular cyanobacterial and gamma-proteobacterial sequences. Several sequences were identical at the nucleotide level to previously described environmental sequences from the Pacific Ocean, including group A sequences. The data suggest a community shift from filamentous cyanobacteria in surface waters to unicellular cyanobacteria and/or heterotrophic bacteria in deeper waters. With one exception, filamentous cyanobacterial nifH sequences were present within temperatures ranging between 26.5 and 30 degrees C and where nitrate was undetectable. In contrast, nonfilamentous nifH sequences were found throughout a broader temperature range, 15 to 30 degrees C, more often in waters with temperature of <26 degrees C, and were sometimes recovered from waters with detectable nitrate concentrations.
为了解热带和亚热带大西洋海洋固氮群落的结构，利用简并引物通过巢式PCR扩增研究了nifH基因的分子多样性，随后进行克隆和测序。从2000年11月至12月、2002年3月以及2002年10月至11月三次航次采集的环境DNA样本中扩增出nifH基因序列，这些样本覆盖了北纬0至28.3度、西经56.6至18.5度的区域。从18个站点和23个深度共获得了170个独特序列。2000年11月至12月航次的样本中包含单细胞和丝状蓝藻的nifH系统发育型，以及γ-变形杆菌和III类群序列，后者目前仅在太平洋有报道。相比之下，2002年3月航次的样本仅包含与未培养的A组单细胞蓝藻相关的系统发育型。2002年10月至11月航次的样本包含丝状和单细胞蓝藻以及γ-变形杆菌序列。有几个序列在核苷酸水平上与先前描述的来自太平洋的环境序列相同，包括A组序列。数据表明群落从表层水中的丝状蓝藻转变为深层水中的单细胞蓝藻和/或异养细菌。除了一个例外，丝状蓝藻的nifH序列出现在26.5至30摄氏度之间且未检测到硝酸盐的温度范围内。相比之下，非丝状nifH序列在更广泛的温度范围（15至30摄氏度）内被发现，更多出现在温度<26摄氏度的水域，并且有时从可检测到硝酸盐浓度的水域中获得。
