Nitrogen Fixation in the Open Ocean: Assessing the Role of Recently Discovered Diazotrophs

公海固氮：评估最近发现的固氮生物的作用

• 批准号: 9977460
• 负责人: Jonathan Zehr
• 金额: $ 45万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-12-15 至 2004-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9977460&HistoricalAwards=false
• 关键词: Nitrogen; Fixation; Open; Ocean; Assessing

Zehr 9977460 and Montoya 9977528The availability of nutrients, primarily phosphorus, nitrogen and iron, limits the productivity of the oceans. Nitrogen is often believed to be an important, if not limiting, nutrient in oligotrophic oceans. Nitrogen, in the form of dinitrogen gas, is a major component of the Earth's atmosphere and is abundant in seawater as dissolved gas. However, most organisms can use nitrogen in the form of nitrate, ammonium, or organic nitrogen, but cannot directly use dinitrogen. This form of nitrogen can be used only by diazotrophs, which can "fix" nitrogen into ammonium through the action of the enzyme nitrogenase. Diverse prokaryotic taxa have the ability to fix nitrogen, including heterotrophic bacteria, cyanobacteria and Archaea. Despite the diversity of types of microorganisms that can fix nitrogen, very few nitrogen--fixing taxa have previously been reported from the open ocean. Recent studies in the Atlantic and Pacific Oceans indicate that nitrogen fixation is more important in nitrogen dynamics than previously believed, and that there may be a large, unaccounted for flux of nitrogen into the mixed layer, which may be due to nitrogen fixation. Estimates of the nitrogen fixation by known diazotrophs, the cyanobacterium Trichodesmium and endosymbiont Richelia, cannot account for this estimated N flux.Using a molecular approach, it has very recently been shown that there are diverse microorganisms in the open ocean environment, which have the genetic capacity for nitrogen fixation. In this project, the ecological and biological significance of these microorganisms will be examined using molecular approaches, cultivation efforts, nitrogen fixation rate measurements, and stable isotope measurements. Recent developments in RNA technology (nifH reverse-transcriptase polymerase chain reaction, RT-PCR) make it possible to examine the expression of the unique nitrogenase phylotypes in seasonal studies, and in experimental manipulations. These studies will focus at the HOT site in order to identify and characterize the novel nitrogen-fixing cyanobacterium, to determine the factors controlling its growth and activity, and to quantify its contribution to the local nitrogen budget using stable isotope techniques. In parallel, experiments on nitrogen-fixation activity associated with invertebrates will be investigated by N-15 tracer measurements and RT-PCR to identify the types of nitrogen-fixing microorganisms responsible for observed nitrogen fixation activity. Finally, the novel diazotroph will be characterized by examining the nitrogen fixation apparatus (nitrogenase genes other than nifH) to determine whether the nitrogen fixation apparatus of these organisms is unusual, which may have biotechnological applications as well as evolutionary implications. The identification and characterization of these novel nitrogen-fixing microorganisms in the open ocean is timely and potentially important for evaluating the nitrogen budget of the sea.

泽尔9977460和蒙托亚9977528营养物质的可获得性，主要是磷、氮和铁，限制了海洋的生产力。在营养稀少的海洋中，氮通常被认为是一种重要的营养物质，如果不是限制的话。氮气以氮气的形式存在，是地球大气的主要成分，在海水中以溶解气体的形式大量存在。然而，大多数生物可以利用硝酸盐、铵或有机氮的形式，但不能直接利用氮素。这种形式的氮只能被重氮菌利用，重氮菌可以通过酶固氮酶的作用将氮固定到铵中。不同的原核生物具有固氮能力，包括异养细菌、蓝藻和古生菌。尽管有多种类型的微生物可以固定氮素，但以前从公开海洋中报道的固定氮素的分类群很少。最近在大西洋和太平洋的研究表明，固氮在氮素动力学中比以前认为的更重要，可能有大量的、无法解释的氮通量进入混合层，这可能是由于固氮。对已知的重氮菌--蓝藻、毛霉菌和内共生菌--的固氮能力的估计不能解释这一估计的氮通量。最近用分子方法证明，在公海环境中存在多种微生物，它们具有固氮的遗传能力。在这个项目中，将使用分子方法、培养努力、固氮率测量和稳定同位素测量来检查这些微生物的生态和生物学意义。RNA技术(nifH逆转录聚合酶链式反应，RT-PCR)的最新发展使得在季节性研究和实验操作中检测独特的固氮酶系统型的表达成为可能。这些研究将集中在热点地区，以鉴定和表征新型固氮蓝藻，确定控制其生长和活性的因素，并利用稳定同位素技术量化其对当地氮素收支的贡献。同时，将通过N-15示踪剂测量和RT-PCR来调查与无脊椎动物相关的固氮活性实验，以确定负责观察到的固氮活性的固氮微生物的类型。最后，新的固氮菌将通过检测固氮器(除nifH以外的固氮酶基因)来确定这些生物的固氮器是否不寻常，这可能具有生物技术应用和进化意义。公海中这些新的固氮微生物的鉴定和特征对于评估海洋的氮收支是及时的和潜在的重要的。