Collaborative Research: Microbial associations in zooplankton: significance for the marine nitrogen cycle

合作研究：浮游动物中的微生物关联：对海洋氮循环的意义

• 批准号: 1130495
• 负责人: Pia Moisander
• 金额: $ 61.7万
• 依托单位: University of Massachusetts, Dartmouth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-15 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1130495&HistoricalAwards=false
• 关键词: Collaborative; Research; Microbial; associations; zooplankton

Intellectual merit Nitrogen (N2) fixation is a key biogeochemical process providing new N for the marine ecosystem. Current estimates of the global rates suggest that the inputs and outputs of N are not in balance, leaving an apparent deficiency in N2 fixation in the oceanic N budget. Based on recovery of N2 fixation gene fragments, however, numerous potential N2-fixing microbes are present in the euphotic layer and below, yet evidence for their contribution to N2-fixation is lacking. The goal of this study is to identify and determine the importance of potentially diazotrophic, heterotrophic prokaryotes occupying a previously unstudied niche in the upper ocean.This project PIs hypothesize that N2 fixation in zooplankton-associated microbial communities is an important source of new N in the open ocean contributing to the oceanic N budget. In oligotrophic, N-limited open ocean waters, zooplankton are faced with the same low N availability in their diets that limits growth of primary producers and heterotrophic microbes in the open ocean. Zooplankton guts would be a particularly suitable environment for heterotrophic N2-fixers as the nitrogenase enzyme is inhibited by oxygen. In many terrestrial insects, N2 fixation by gut microbes serves as a source of N. The aim of this study is to investigate whether similar associations occur in marine zooplankton that live on N-limited phytoplankton. The PIs will investigate specific associations between copepods from N-limited and non-N limited oceanic waters with microorganisms that are potentially or actively fixing N. They will also investigate the fate of this N to study whether the new N is incorporated into the zooplankton host. The main research objectives are to determine whether:1. diazotrophic microflora exist in copepods and what is their seasonal and spatial variability, 2. microbial communities associated with copepods are actively fixing N2, 3. diazotroph communities contribute to the N nutrition of their zooplankton hosts. Monthly samples will be collected in the oligotrophic Sargasso Sea, in association with BATS sampling cruises. In addition, experiments and field studies will be conducted in Bermuda during the summer. For comparison to a site that is not severely N limited, and for methods development, additional studies will be carried out in coastal Gulf of Maine waters. Selected copepod species and their fecal pellets will be analyzed for the presence of nifH genes and their expression using cloning and sequencing and Reverse Transcriptase-PCR. Quantitative PCR will be employed to investigate the seasonal distributions of dominant phylotypes. Anaerobic cultivation will be used for the enrichment of the gut microflora. Zooplankton will be incubated with 15N2 to quantify microbial N2 fixation activity and its fate of N through zooplankton overall 15N content and nanoSIMS determination of 15N localization. Products of this study will include novel microbial isolates or consortia, evidence regarding taxa-specific expression of N2 fixation in these microhabitats, and a first estimate for the importance of this process for the oceanic N budget.Broader impactsThis project addresses fundamental issues regarding the sources of oceanic nitrogen and will test hypotheses regarding previously overlooked diazotrophic niches. As open ocean productivity is frequently N limited, characterization of new sources of N will have global impacts. The PIs will engage students from K-12 to graduate levels in this research. Graduate student at the UMD will develop their dissertation research within the framework of the study, and several undergraduate students will participate in field and lab components at UMD. Marine microbiology course content will be built into the K-12 science curriculum of the Ocean Explorium of the city of New Bedford, Massachusetts. Part of the work will be performed as a collaborative project with L. Riemann, Univ. of Copenhagen, thus strengthening international connections.

氮素固定是一种关键的生物地球化学过程，为海洋生态系统提供新的氮素。目前对全球速率的估计表明，N的输入和输出不平衡，这使得海洋N预算在固定N方面存在明显不足。然而，基于对固氮基因片段的回收，在真光层及其下方存在着大量潜在的固氮微生物，但缺乏它们对固氮的贡献的证据。这项研究的目的是确定和确定潜在的重氮性、异养性原核生物在上层海洋中占据一个以前未被研究的生态位的重要性。该项目PI假设与浮游动物相关的微生物群落中的氮固定是开放海洋中新氮的一个重要来源，对海洋氮收支有贡献。在低营养、N有限的开放海洋水域，浮游动物在其饲料中面临着同样的低N有效性，这限制了初级生产者和异养微生物在开放海洋中的生长。浮游动物肠道特别适合异养固氮菌，因为固氮酶受到氧气的抑制。在许多陆生昆虫中，肠道微生物对氮的固定是氮的一个来源。本研究的目的是调查在以氮限制的浮游植物为生的海洋浮游动物中是否也存在类似的联系。PIS将调查来自N限制和非N限制的海洋中的桡足类与潜在或积极固定N的微生物之间的特定联系。他们还将调查这种N的命运，以研究新的N是否被合并到浮游动物宿主中。主要研究目标是确定：1.桡足类中是否存在固氮微生物区系及其季节和空间变异性；2.与桡足类相关的微生物群落正在积极地固定N_2；3.固氮微生物群落对其浮游动物宿主的N营养有贡献。每月将在营养稀少的马尾藻海采集样品，并与BATS采样邮轮一起进行。此外，夏季还将在百慕大进行实验和实地研究。为了与不受严格北界限制的地点进行比较，并为了开发方法，将在缅因湾沿海水域进行额外的研究。将使用克隆和测序以及逆转录酶-PCR来分析选定的桡足类物种及其粪便颗粒中是否存在nifH基因及其表达。定量聚合酶链式反应将被用来调查优势种系的季节分布。将采用厌氧培养来丰富肠道微生物区系。浮游动物将与15N孵育，通过浮游动物总的15N含量和纳米SIMS对15N定位的测定，来量化微生物的固氮活性及其N的去向。这项研究的产品将包括新的微生物分离物或联合体，关于这些微生境中氮固定的分类群特异性表达的证据，以及对这一过程对海洋氮预算的重要性的初步估计。广泛的影响本项目解决了关于海洋氮的来源的基本问题，并将检验关于以前被忽视的重氮营养生态位的假设。由于公海生产力往往受到N的限制，表征新的N来源将对全球产生影响。PIS将邀请从K-12到研究生的学生参与这项研究。UMD的研究生将在该研究的框架内开展他们的论文研究，几名本科生将参与UMD的现场和实验室组件。海洋微生物学课程内容将被纳入马萨诸塞州新贝德福德市海洋探索中心的K-12科学课程。部分工作将作为与L.Riemann大学的合作项目进行。哥本哈根，从而加强了国际联系。