Department of Natural Sciences, University of Kalmar, SE - 39182 Kalmar, Sweden.
Environ Microbiol Rep. 2009 Apr;1(2):145-54. doi: 10.1111/j.1758-2229.2009.00021.x. Epub 2009 Feb 25.
Heterocystous filamentous cyanobacteria are regarded as the main N2 -fixing organisms (diazotrophs) in the Baltic Sea. However, some studies indicate that picoplankton may also be important. The aim of this study was to examine the composition of putative diazotrophs in the picoplankton (< 3 µm) and to identify links to environmental factors. Nitrogenase (nifH) genes were amplified from community DNA by nested PCR, followed by cloning and sequencing. Clone libraries from nine environmental samples collected from the central Baltic Sea (April-October 2003, 3 m depth) and a negative control yielded a total of 433 sequences with an average clone library coverage of 92%. The sequences fell within nifH Clusters I, II and III and formed 15 distinct groups (> 96% amino acid similarity). Most of the sequences (77%) fell into nifH Cluster I (cyanobacteria and α-, β- and γ-Proteobacteria). However, only 26 sequences were related to cyanobacteria (e.g. Pseudanabaena) and among these no unicellular phylotypes were found. Sequences clustering with alternative nitrogenases (anfH) and Archaea were found in one sample while sequences related to anaerobic phylotypes were found in six samples distributed throughout the season. The identified phylogenetic groups showed covariance with several environmental factors but no strong links could be established. This suggests a variable and complex regulation of diazotrophic groups within Baltic Sea picoplankton.
异形胞丝状蓝藻被认为是波罗的海的主要固氮生物（固氮菌）。然而，一些研究表明微微型浮游生物也可能很重要。本研究的目的是检测微微型浮游生物（<3μm）中假定固氮菌的组成，并确定与环境因素的联系。通过巢式 PCR 从群落 DNA 中扩增氮酶（nifH）基因，然后进行克隆和测序。从波罗的海中部（2003 年 4 月至 10 月，3 米深）采集的九个环境样本和一个阴性对照的克隆文库共获得了 433 个序列，平均克隆文库覆盖率为 92%。这些序列属于 nifH 聚类 I、II 和 III，形成了 15 个不同的组（>96%的氨基酸相似性）。大多数序列（77%）属于 nifH 聚类 I（蓝藻和α-、β-和γ-变形菌）。然而，只有 26 个序列与蓝藻（如 Pseudanabaena）有关，而在这些序列中没有发现单细胞的类群。在一个样本中发现了与替代氮酶（anfH）和古菌聚类的序列，而在六个分布在整个季节的样本中发现了与厌氧类群有关的序列。鉴定出的系统发育群与几个环境因素存在协方差，但没有建立起很强的联系。这表明波罗的海微微型浮游生物中的固氮菌群体的调控具有可变性和复杂性。
