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.

Zehr 9977460和Montoya 9977528营养物质（主要是磷，氮和铁）的可用性限制了海洋的生产力。氮通常被认为是贫营养海洋中的养分。氮是二氮气气体的形式，是地球大气中的主要组成部分，在海水中作为溶解气体丰富。但是，大多数生物体可以以硝酸盐，铵或有机氮的形式使用氮，但不能直接使用二氮。这种形式的氮只能通过重18zotrophs来使用，该氮可以通过酶氮酶的作用将氮固定到铵中。多样化的原核生物分类群具有固定氮，包括异养细菌，蓝细菌和古细菌。尽管可以固定氮的微生物类型多种多样，但以前很少有氮 - 固定分类群是从开阔的海洋中报道的。 在大西洋和太平洋地区的最新研究表明，氮固定在氮动力学中比以前认为的更重要，并且可能存在大型的，不计入氮气到混合层中的通量，这可能是由于氮固定。通过已知的重18zotrophs，TrichodeSmium和内共生菌richelia对氮固定的估计，无法解释这种估计的N通量。使用分子方法，最近已经证明，在开放式环境中存在多种微生物，在开放式环境中具有多种固定能力的固定能力。 在该项目中，将使用分子方法，培养工作，氮固定速率测量和稳定的同位素测量来检查这些微生物的生态和生物学意义。 RNA技术的最新发展（NIFH逆转录酶聚合酶链反应，RT-PCR）使得在季节性研究和实验操作中检查了独特的氮酶系统型的表达。这些研究将集中在热地位置，以识别和表征新颖的固氮蓝细菌，确定控制其生长和活性的因素，并使用稳定的同位素技术量化其对局部氮预算的贡献。同时，将通过N-15示踪剂测量和RT-PCR研究与无脊椎动物相关的氮固定活性的实验，以识别负责观察到的氮固定活性的氮固化微生物的类型。最后，新型重氮营养物将通过检查氮固定设备（NIFH以外的氮基因基因）来确定这些生物体的氮固定设备是否不寻常，这可能具有生物技术应用以及进化含义。 在开阔的海洋中，这些新颖的固氮微生物的鉴定和表征对于评估海洋的氮预算至关重要。