Collaborative Research: Autotrophic carbon fixation at a shallow-water hydrothermal system: Constraining microbial activity, isotopic and geochemical regimes

合作研究：浅水热液系统的自养碳固定：限制微生物活动、同位素和地球化学状况

• 批准号: 1124141
• 负责人: Costantino Vetriani
• 金额: $ 19.67万
• 依托单位: Rutgers University New Brunswick
• 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: 2011-10-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1124141&HistoricalAwards=false
• 关键词: Collaborative; Research; Autotrophic; carbon; fixation

Currently, there is only limited information on the identity and activity of the microorganisms carrying out CO2-fixation in situ, despite the fact that these organisms form the basis of their respective ecosystems. Representatives that are able to grow autotrophically are known to exist in almost all major groups of prokaryotes, and these organisms play essential roles in ecosystems by providing a continuous supply of organic carbon for heterotrophs. Microorganisms present in extreme environments utilize CO2- fixation pathways other than the Calvin-Benson-Bassham (CBB) cycle. At present, five alternative autotrophic CO2 fixation pathways are known. Different carbon fixation pathways result in distinct isotopic signatures of the produced biomass due to the isotopic discrimination between light (12C) and heavy (13C) carbon by the carboxylating enzymes. Thus, inferences about the carbon fixation pathway predominantly utilized by the microbial community can also be made based on the stable carbon isotopic composition of the organic matter, in extant systems as well as in the geological record. However, at present little is known about the systematics and extents of fractionation during carbon fixation by prokaryotic organisms, and to our knowledge no studies exist that have systematically studied the relationship between the operation of different carbon fixation pathways and how this is reflected in the stable carbon isotopic composition in a natural system. This is a 2-year interdisciplinary, international research program that employs a powerful combination of cutting-edge research tools aiming to improve our understanding of autotrophic carbon fixation and its chemical and isotopic signature along environmental gradients in a natural hydrothermal system. The following hypotheses are addressed: 1. The diversity of microorganisms present along a thermal and redox gradient, and rates of CO2 fixation, will reflect adaptation to in situ temperatures and geochemical conditions 2. Microorganisms utilizing the CBB cycle for autotrophic CO2-fixation will represent a smaller percentage of the chemolithoautotrophic community at higher temperatures, where microorganisms utilizing alternative CO2-fixation pathways dominate 3. Isotopic values of biomass and specific biomarker molecules will vary along a thermal and redox gradient from zones characterized by a higher hydrothermal fluid flux and thus higher temperatures to the surrounding, cooler areas, corresponding to the physiology of the microorganisms utilizing different pathways for carbon fixationThe PIs will use a multidisciplinary approach to delineate the relative contribution of the different carbon fixation pathways along an environmental gradient by combining metagenomic analyses coupled with: 1) an assessment of the frequency and the expression of specific key genes involved in carbon fixation, and 2) with the measurement of carbon fixation rates. These data will be integrated with the determination of stable C isotopic composition of biomass, DIC, and specific hydrocarbons/lipids. Due to its easy accessibility, well-established environmental gradients, and extensive background information, the shallow-water vents off Milos (Greece) will be used as a natural laboratory to perform these studies. Intellectual Merit. The data generated in this study will allow constraints on the relationship between autotrophic carbon fixation and the resulting isotopic signatures of biomass and specific biomarker molecules (e.g. CH4, C2+ alkanes, lipids) in a natural system.. This has implications for assessing the importance of carbon fixation in extant ecosystems, and it will also provide a tool to improve the interpretation of isotopic values in the geological record.Broader Impacts. This is an interdisciplinary and collaborative effort between US and foreign institutions, creating unique opportunities for networking and to foster international collaborations. This will also benefit the involved students (1 graduate, several undergraduates) and a postdoc. The PIs have been involved in several educational and public outreach activities over the years that have reached literally millions of individuals. Finally, the project fits with the focus of a number of multi-disciplinary and international initiatives, in which PIs are active members (e.g. SCOR working group on Hydrothermal energy and the ocean carbon cycle;and Deep Carbon Observatory at CIW).

目前，尽管这些微生物构成了各自生态系统的基础，但关于在原地进行二氧化碳固定的微生物的特性和活性的信息有限。在几乎所有主要的原核生物群体中都存在能够自养生长的代表，这些生物通过为异养生物提供持续的有机碳供应，在生态系统中发挥着重要作用。在极端环境中存在的微生物利用二氧化碳固定途径而不是卡尔文-本森-巴萨姆（CBB）循环。目前已知的自养型CO2固定途径有5种。由于羧化酶对轻碳（12C）和重碳（13C）的同位素区分，不同的碳固定途径导致产生的生物质具有不同的同位素特征。因此，微生物群落主要利用的固碳途径也可以根据现存系统和地质记录中有机质的稳定碳同位素组成来推断。然而，目前对原核生物固碳过程中分馏的分类学和程度知之甚少，据我们所知，目前还没有研究系统地研究不同固碳途径的运行之间的关系以及这种关系如何反映在自然系统的稳定碳同位素组成中。这是一个为期两年的跨学科国际研究项目，采用尖端研究工具的强大组合，旨在提高我们对天然热液系统中自养碳固定及其沿环境梯度的化学和同位素特征的理解。本文提出了以下假设：沿着热还原梯度和氧化还原梯度存在的微生物多样性以及二氧化碳固定速率将反映对原位温度和地球化学条件的适应2。在较高温度下，利用CBB循环进行自养二氧化碳固定的微生物在趋化石自养群落中所占比例较小，而利用其他二氧化碳固定途径的微生物占主导地位。生物量和特定生物标志物分子的同位素值将沿着热液通量较高、温度较高的区域到周围温度较低的区域的热还原梯度变化。pi将使用多学科方法，通过结合宏基因组分析，以及：1)评估参与碳固定的特定关键基因的频率和表达，以及2)碳固定率的测量，来描绘不同碳固定途径在环境梯度上的相对贡献。这些数据将与生物量、DIC和特定碳氢化合物/脂质的稳定碳同位素组成的测定相结合。由于其易于接近，良好的环境梯度和广泛的背景信息，米洛斯（希腊）的浅水喷口将被用作进行这些研究的天然实验室。知识价值。本研究中产生的数据将限制自然系统中自养碳固定与生物量和特定生物标志物分子（例如CH4， C2+烷烃，脂类）的同位素特征之间的关系。这对评估现有生态系统中碳固定的重要性具有重要意义，并且还将提供一种工具来改进对地质记录中同位素值的解释。更广泛的影响。这是美国和外国机构之间的跨学科合作努力，为建立网络和促进国际合作创造了独特的机会。参与的学生（1名研究生，几名本科生）和一名博士后也将受益。多年来，pi参与了几次教育和公共宣传活动，接触了数百万人。最后，该项目符合许多多学科和国际倡议的重点，其中pi是积极成员（例如SCOR热液能和海洋碳循环工作组；以及CIW的深层碳观测站）。