Short Steven M, Zehr Jonathan P
Department of Biological Sciences, University of Denver, Denver, CO 80208, USA.
Environ Microbiol. 2007 Jun;9(6):1591-6. doi: 10.1111/j.1462-2920.2007.01258.x.
Like many estuaries, the Chesapeake Bay has pronounced gradients in salinity and nutrients. Previous studies have shown that there is a high diversity of nitrogenase (nifH) genes in the estuary, and that there are specific distributions of individual nifH phylotypes. In contrast to previous work that revealed the remarkable diversity of nifH phylotypes in the Chesapeake estuary, in this study of nifH expression we only detected two phylotypes, and both were phylogenetically related to cyanobacterial nifH genes. One of the phylotypes was closely related to a nifH sequence from the filamentous, heterocystous cyanobacterium Anabaena cylindrica, and was found at the head of the estuary. The other phylotype was found in a sample collected near the mouth of the estuary and was closely related to nifH sequences from Group A unicellular cyanobacteria, which has previously been reported in oceanic waters only. These nifH phylotypes had distinct patterns of expression that were restricted to different regions of the Chesapeake Bay. This study provides the first evidence of nifH expression in the Chesapeake Bay, and suggests that diazotrophic unicellular cyanobacteria have a broader distribution and activity than previously recognized.
与许多河口一样，切萨皮克湾在盐度和养分方面有明显的梯度变化。先前的研究表明，该河口的固氮酶（nifH）基因具有高度多样性，且各个nifH系统发育型具有特定的分布。与之前揭示切萨皮克河口nifH系统发育型显著多样性的研究不同，在这项关于nifH表达的研究中，我们仅检测到两种系统发育型，且两者在系统发育上均与蓝细菌nifH基因相关。其中一种系统发育型与丝状、异形胞蓝细菌圆柱鱼腥藻的nifH序列密切相关，且在河口源头被发现。另一种系统发育型在河口入海口附近采集的样本中被发现，并且与仅在海洋水域中报道过的A组单细胞蓝细菌的nifH序列密切相关。这些nifH系统发育型具有独特的表达模式，且局限于切萨皮克湾的不同区域。本研究提供了切萨皮克湾nifH表达的首个证据，并表明固氮单细胞蓝细菌的分布和活性比之前认为的更广泛。
