Nitrogen Fixing Prokaryotes in Corals: Is Nitrogen Fixation a Core Function of the Coral Microbiome?

珊瑚中的固氮原核生物：固氮是珊瑚微生物组的核心功能吗？

• 批准号: 1437054
• 负责人: Michael Lesser
• 金额: $ 78.35万
• 依托单位: University of New Hampshire
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1437054&HistoricalAwards=false
• 关键词: Nitrogen; Fixing; Prokaryotes; Corals; Fixation

Coral reefs provide crucial services for people and are becoming increasingly threatened by climate change. But many important questions about coral reefs remain unanswered, such as how their incredibly high biodiversity has developed and is maintained. It is well known that reef-forming corals consist of many different groups of bacteria and algae that live in the tissues of corals, but the function of most of these microbes remain unknown. One of the reported microbial functions is the process called nitrogen fixation. Nitrogen fixation is better known as a very important process on land. For example, alfalfa in agricultural fields has microbes associated with its roots that can capture nitrogen from the air and replace nitrogen lost from soils in water. The nitrogen cycle in the oceans is less well known, especially in tropical waters where nitrogen levels are low, although nitrogen in coral reef systems is known to derive mainly from nitrogen fixation. Recently nitrogen-fixing bacteria have been discovered in the tissues of corals, which begs the overarching question of this project: how important is the contribution of this fixed nitrogen to corals and to the surrounding environment? This research will integrate with an educational program that fosters critical thinking and cooperative learning among participants by involving undergraduate students who will work closely with the scientists. Students from underrepresented backgrounds will be recruited; the undergraduates will become part of an existing undergraduate research opportunities program where they receive mentoring, financial support, and intensive writing support while conducting original research projects of their own. Also a new program will be developed with the university's veterans office to attract and transition veterans into science fields across campus. Finally, outreach activities will be organized at local public high schools, and some public environmental education lectures about the ecology and biology of coral reefs are planned.Significant gaps in understanding exist about the role of prokaryotes in the physiology, biochemistry and ecology of reef-forming corals. This project will assess how different prokaryotic communities affect the biogeochemistry of nitrogen, specifically nitrogen fixation, within the coral holobiont and how nitrogen fixation contributes to the dissolved organic nitrogen (DON) content of excreted mucus. The introduction of "new nitrogen" though nitrogen fixation and release of DON could have significant impacts on the biogeochemistry of nitrogen in the adjacent benthic communities surrounding corals. High throughput sequencing tools will be used to quantify the taxonomic and functional diversity of these symbioses in corals from the Pacific and Caribbean, as well as the taxonomic diversity of nifH genes in the tissues of corals. Rates of nitrogen fixation on several coral species from Australia, Hawaii and Curacao will be measured, along with the translocation of fixed nitrogen to all compartments of the coral holobiont, and the contribution of "new nitrogen" to the DON of mucus released to the environment determined. The results will increase our understanding of the taxonomic and functional biodiversity of symbiotic prokaryotes in corals. This project will also help guide future studies on the biogeochemical cycling of coral-derived nitrogen on coral reefs.

珊瑚礁为人类提供重要服务，但正日益受到气候变化的威胁。但有关珊瑚礁的许多重要问题仍未得到解答，例如它们令人难以置信的高度生物多样性是如何发展和维持的。众所周知，形成珊瑚礁的珊瑚由生活在珊瑚组织中的许多不同的细菌和藻类组成，但大多数这些微生物的功能仍然未知。已报道的微生物功能之一是固氮过程。众所周知，固氮是陆地上一个非常重要的过程。例如，农田中的苜蓿的根部有微生物，可以捕获空气中的氮，并补充水中土壤中流失的氮。海洋中的氮循环鲜为人知，尤其是在氮含量较低的热带水域，尽管已知珊瑚礁系统中的氮主要来自固氮。最近在珊瑚组织中发现了固氮细菌，这引出了该项目的首要问题：这种固定氮对珊瑚和周围环境的贡献有多重要？这项研究将与一项教育计划相结合，通过让本科生与科学家密切合作，培养参与者之间的批判性思维和合作学习。将招募来自代表性不足背景的学生；本科生将成为现有本科生研究机会计划的一部分，在该计划中，他们在开展自己的原创研究项目的同时，将获得指导、财政支持和深入的写作支持。此外，该大学还将与退伍军人办公室共同制定一项新计划，以吸引退伍军人并将其转入校园内的科学领域。最后，将在当地公立高中组织推广活动，并计划举办一些有关珊瑚礁生态和生物学的公共环境教育讲座。人们对原核生物在造礁珊瑚的生理、生物化学和生态中的作用存在重大认识差距。该项目将评估不同的原核生物群落如何影响珊瑚全生物体内氮的生物地球化学，特别是固氮作用，以及固氮作用如何影响分泌粘液的溶解有机氮（DON）含量。通过固氮和释放 DON 引入“新氮”可能会对珊瑚周围邻近底栖群落的氮生物地球化学产生重大影响。高通量测序工具将用于量化太平洋和加勒比珊瑚中这些共生体的分类和功能多样性，以及珊瑚组织中 nifH 基因的分类多样性。将测量来自澳大利亚、夏威夷和库拉索岛的几种珊瑚物种的固氮率，以及固定氮向珊瑚全生物体所有区室的转移，并确定“新氮”对释放到环境中的粘液中的呕吐毒素的贡献。这些结果将增加我们对珊瑚共生原核生物的分类学和功能生物多样性的理解。该项目还将有助于指导未来关于珊瑚礁上珊瑚源氮的生物地球化学循环的研究。