Unsilent partners: Constraining the contribution of methanogen-protist symbioses to total methane production in anoxic marine habitats

沉默的伙伴：限制产甲烷菌-原生生物共生体对缺氧海洋生境甲烷总产量的贡献

• 批准号: 1322928
• 金额: $ 17万
• 依托单位: Beinart Roxanne A
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1322928&HistoricalAwards=false
• 关键词: Unsilent; partners; Constraining; contribution; methanogen

Overview: There is a growing appreciation for the ubiquity of microbial symbioses on earth, yet in most habitats we have only a basic understanding of their physiology and ecology. Many eukaryotes have evolved specific associations with prokaryotes that capitalize on the relative diversity of prokaryotic metabolisms. In terms of numbers, symbiont populations often rival or exceed free-living prokaryotes in their environment, therefore, through their metabolism, symbionts may have a significant effect on their biotic and abiotic environment. Despite this, there is limited knowledge of the symbiotic function and metabolic activity of most symbiotic taxa.Symbioses between anaerobic protists and intracellular, methanogenic archaea have been found in many anoxic habitats, however the contribution of symbiont-produced methane (CH4) to the marine CH4 cycle is yet unconstrained. In non-marine environments, like rice paddies and lakes, they have been found to significantly contribute to the production of CH4, suggesting that these symbioses may be important to the biogeochemical cycling of this climate-active gas. However, though taxa known to host methanogens have been detected in general surveys of protists in oxygen (O2) -poor and anoxic marine water columns, to date, they have never been specifically surveyed, and no studies have quantified their contribution to CH4 production in these habitats. Additionally, outside of their methanogenic function, nothing is known about the physiological capacity of their symbionts. To develop an understanding of the details of these partnerships and to address the contribution of microbial symbionts to the CH4 cycle, the fellow will examine the ecology and physiology of methanogen-protist symbioses in Saanich Inlet (SI), a seasonally anoxic fjord off the coast of British Columbia, Canada that accumulates CH4 (greater than 1 micrometer) in its deep water from a yet unconstrained source. With sponsor Dr. Virginia Edgcomb at Woods Hole Oceanographic Institution (WHOI), the fellow will combine a) fluorescence-activated cell sorting based surveys of the abundance and diversity of methanogen-hosting protists, with assessment of their metabolism through b) the experimental measurement of CH4 production by natural populations and c) analysis of total symbiont gene content (i.e., genomics). This robust combination of observational and experimental approaches will provide valuable insight into distribution, physiology and activity of these symbioses, allowing the first estimation of the contribution of protist-associated methanogens to CH4 production in an anoxic marine water column. Intellectual merit: Anoxic and low-O2 marine water columns are thought to contribute 50-60% of the global oceanic emission of CH4, a climate-active gas. It is typically assumed that the CH4 in these habitats originates from the underlying sediment, where methanogenesis is known to occur. Water column production is presumed to be unimportant in these areas, as free-living methanogens cannot compete successfully with sulfate-reducing bacteria for common substrates (e.g, Hydrogen) in sulfate-replete seawater. However, symbiotic methanogens are protected from competition with sulfate-reducing bacteria since substrates are host provided. Consequently, methanogenesis by the symbionts of protists in the water column may account for a significant fraction of the CH4 budget in these areas. Thus, the proposed effort will substantially advance our understanding of the underlying source of CH4 in O2-deficient and anoxic marine habitats. Since rising temperatures are predicted to cause the expansion of oxygen-depleted habitats, better insight into CH4 cycling in these areas will become increasingly important to our understanding and modeling of global oceanic CH4 emissions. Broader Impacts: The broader impacts of the proposed effort include disseminating the findings to the scientific and wider community through public lectures, and supporting participation of underrepresented groups in ocean sciences research through mentorship of 1-2 undergraduates in the WHOI Summer Student and Minority Fellowship programs. Additionally, funds from the annual fellowship allowance have been budgeted to develop an educational unit about marine symbioses with a local non-profit marine education foundation. This unit will be presented by the fellow to K-12 students from disadvantaged communities from the southern New England area.

概述：越来越多的人认识到微生物共生体在地球上的普遍性，但在大多数栖息地，我们对它们的生理和生态只有基本的了解。许多真核生物已经进化出与原核生物的特定关联，从而利用原核生物代谢的相对多样性。在数量上，共生体的数量往往可以与原核生物相媲美，甚至超过原核生物，因此，共生体可以通过代谢对生物和非生物环境产生重要影响。尽管如此，目前对大多数共生类群的共生功能和代谢活性的了解有限，厌氧原生生物和细胞内的产甲烷古菌之间的共生体已被发现在许多缺氧的栖息地，但共生体产生的甲烷（CH 4）的海洋CH 4循环的贡献尚未受到限制。在非海洋环境中，如稻田和湖泊，它们被发现对甲烷的产生有显著贡献，这表明这些共生体可能对这种气候活性气体的生物地球化学循环很重要。然而，虽然已知的宿主产甲烷菌的类群已被发现在一般调查原生生物在氧气（O2）-穷人和缺氧的海洋水柱，到目前为止，他们从来没有被专门调查，也没有研究量化的CH 4生产在这些栖息地的贡献。此外，除了它们的产甲烷功能之外，对其共生体的生理能力一无所知。为了了解这些伙伴关系的细节，并解决微生物共生体对甲烷循环的贡献，该研究员将研究Saanich Inlet（SI）的产甲烷生物-原生生物共生体的生态学和生理学，Saanich Inlet是加拿大不列颠哥伦比亚省海岸外的季节性缺氧峡湾，它从一个尚未受约束的来源在深水中积累甲烷（大于1微米）。该研究员将与伍兹霍尔海洋研究所（WHOI）的Virginia Edgcomb博士合作，将联合收割机a）基于荧光激活细胞分选的对产甲烷菌宿主原生生物丰度和多样性的调查与通过B）自然种群甲烷产量的实验测量和c）共生体总基因含量（即，基因组学）。这种强大的观测和实验方法的结合将提供有价值的洞察这些共生体的分布，生理和活动，允许第一次估计的贡献原生生物相关的产甲烷菌在缺氧的海洋水体中的甲烷生产。智力优点：缺氧和低氧海洋水柱被认为贡献了全球海洋排放的50-60%的甲烷，这是一种气候活性气体。通常认为，这些生境中的甲烷来自底层沉积物，已知甲烷生成发生在那里。据推测，在这些地区，水柱的产生并不重要，因为自由生活的产甲烷菌不能成功地与硫酸盐还原菌竞争硫酸盐丰富的海水中的常见底物（如氢）。然而，共生产甲烷菌的保护竞争与硫酸盐还原菌，因为基板提供主机。因此，甲烷的共生体的原生生物在水柱中可能占一个显着的一部分，在这些地区的CH 4预算。因此，拟议的努力将大大提高我们的理解的基本来源的甲烷在O2缺乏和缺氧的海洋栖息地。由于预计气温上升将导致缺氧栖息地的扩张，因此更好地了解这些地区的CH 4循环对于我们理解和模拟全球海洋CH 4排放将变得越来越重要。更广泛的影响：拟议努力的更广泛影响包括通过公开讲座向科学界和更广泛的社区传播研究结果，并通过在WHOI暑期学生和少数民族奖学金计划中指导1-2名本科生来支持代表性不足的群体参与海洋科学研究。此外，年度研究金津贴的资金已编入预算，用于与当地一个非营利海洋教育基金会建立一个关于海洋共生的教育单位。本单元将由研究员介绍给来自南部新英格兰地区弱势社区的K-12学生。