Omoregie Enoma O, Crumbliss Lori L, Bebout Brad M, Zehr Jonathan P
Department of Ocean Sciences and Institute of Marine Sciences, University of California, Santa Cruz, California 95064, USA.
Appl Environ Microbiol. 2004 Apr;70(4):2119-28. doi: 10.1128/AEM.70.4.2119-2128.2004.
In many environments, biological nitrogen fixation can alleviate nitrogen limitation. The high rates of N(2) fixation often observed in cyanobacterial mats suggest that N(2) fixation may be an important source of N. In this study, organisms expressing nifH were identified in a Lyngbya sp.- and two Microcoleus chthonoplastes-dominated cyanobacterial mats. The pattern of nitrogenase activity was determined for the Lyngbya sp. mat and a Microcoleus chthonoplastes mat sampled directly in Guerrero Negro, Mexico. Their maximum rates were 23 and 15 micro mol of C(2)H(4) m(-2) h(-1), respectively. The second Microcoleus mat, which was maintained in a greenhouse facility, had a maximum rate of 40 micro mol of C(2)H(4) m(-2) h(-1). The overall diel pattern of nitrogenase activity in the three mats was similar, with the highest rates of activity occurring during the dark period. Analysis of nifH transcripts by reverse transcription-PCR revealed that several different organisms were expressing nifH during the dark period. nifH phylotypes recovered from these mats were similar to sequences from the unicellular cyanobacterial genera Halothece, Myxosarcina, and Synechocystis, the filamentous cyanobacterial genera Plectonema and Phormidium, and several bacterial nifH groups. The results of this study indicate that several different organisms, some of which were not previously known to fix nitrogen, are likely to be responsible for the observed dark-period nitrogenase activity in these cyanobacterial mats.
在许多环境中，生物固氮作用可以缓解氮限制。在蓝藻席中经常观察到的高固氮率表明，固氮作用可能是氮的一个重要来源。在本研究中，在以席藻属和两种嗜盐微鞘藻为主的蓝藻席中鉴定出了表达nifH的生物。测定了直接采自墨西哥格雷罗内格罗的席藻属蓝藻席和嗜盐微鞘藻蓝藻席的固氮酶活性模式。它们的最大速率分别为23和15微摩尔乙烯每平方米每小时。保存在温室设施中的第二个嗜盐微鞘藻蓝藻席，其最大速率为40微摩尔乙烯每平方米每小时。这三个蓝藻席中固氮酶活性的总体昼夜模式相似，最高活性速率出现在黑暗期。通过逆转录-聚合酶链反应对nifH转录本进行分析，结果显示在黑暗期有几种不同的生物在表达nifH。从这些蓝藻席中回收的nifH系统型与单细胞蓝藻属盐生蓝藻属、粘囊藻属和集胞藻属、丝状蓝藻属织线藻属和席藻属以及几个细菌nifH组的序列相似。本研究结果表明，几种不同的生物，其中一些以前未知具有固氮能力，可能是这些蓝藻席中观察到的黑暗期固氮酶活性的原因。
