Collaborative Research: Marine priming effect - molecular mechanisms for the biomineralization of terrigenous dissolved organic matter in the ocean

概述：每年有大量看似难处理的陆源溶解有机物(t-DOM)通过河流输送到海岸，但海洋中的t-DOM含量却低得惊人。T-DOM的去除是全球碳循环的核心，但驱动去除的机制仍然知之甚少。在土壤中，不稳定的有机化合物的存在会增强顽固性化合物的再矿化，这一现象被称为启动效应(PE)。在土壤系统中，PE在数量上是重要的，但在水生系统中却很少受到关注，尽管它有可能解释陆地-海洋界面上的碳矿化模式。这个项目调查了沿海海洋中PE的大小以及产生它的代谢和生态机制。它专注于美国大西洋沿岸沼泽的微生物群落。在这些系统中，河流上的t-DOM为评估PE的大小提供了一个特别有价值和易于处理的模型。这项研究利用从乔治亚河收集的具有良好特征的DOM标准作为t-DOM的模型材料，在与自然沿海微生物群落和异养海洋细菌的培养的一系列实验室实验中，玫瑰杆菌谱系。玫瑰杆菌是这项工作特别合适的生物模型，因为它们在美国东南部沿海地区大量存在，并已知能分解木质素和其他植物衍生的芳香化合物。长期(60天)的孵化实验将跟踪由于添加不同化学复杂性的不稳定DOM而产生的PE。木质素酚的变化将是PE对t-DOM降解影响的主要衡量标准，但该研究还监测了由光学性质代表并由高分辨率质谱学鉴定的更广泛的芳香族化合物。通过胞外酶活性、细菌产量、群落组成和基因转录分析来测量微生物对添加的活性有机物的反应，将揭示PE的生物学机制。使用玫瑰杆菌菌株的实验将允许在一个定义明确的实验系统中详细研究代谢途径、特定细菌和有机碳矿化之间的关系。来自实验室实验的基因表达、微生物活性和DOM转化的数据将被整合起来，以阐明作为PE的一部分而被调用的特定代谢途径，并指导分子工具的开发，以在项目的最后一年沿着河流到沿海海洋样带追踪遗传特征。智力优势：异养微生物在陆地-海洋界面重新矿化t-DOM中的作用是生物海洋学中的一个中心问题。T-DOM的成分，主要是木质素，在某种意义上是难降解的，因为相对于其他生物分子，降解速度通常很慢，但木质素可以有效地从陆地和开阔海洋之间的某个地方移除。该项目将确定引发剂是否在沿海海洋中t-DOM的快速去除中发挥作用，提供作为引发剂最有效的活性有机物类型的证据，并试图发现PE被介导的代谢途径。这些研究有可能揭示保守和可预测的代谢反应，这些反应可能有助于调节海洋环境中自然产生的半不稳定/难降解DOM的转化和周转。由于气候变化可能会影响陆源碳和营养物质向沿海海洋的通量，因此有必要了解PE的大小和机制，以预测这些变化通量的地球化学后果。广泛的影响：该项目将直接支持两名研究生和几名本科生的跨学科和多机构培训。UTK最近资助的本科生研究体验(REU)计划下的培训机会将被利用并扩展到参与该项目的当地UTK本科生。该项目的资金还将为研究人员继续在新泽西州纽瓦克的一所主要是少数族裔的高中发展外展项目提供支持。最后，所有私人投资机构将继续以演示文稿、论文和其他形式及时传播其研究成果。

Overview: Large fluxes of apparently refractory terrigenous dissolved organic matter (t-DOM) are transported through rivers to the coast each year, yet there are vanishingly low traces of t-DOM in the oceans. The removal of t-DOM is central to the global carbon cycle, yet the mechanisms that drive removal remain poorly understood. In soils, the presence of labile organic compounds is known to enhance the remineralization of recalcitrant compounds, a phenomenon known as the priming effect (PE). The PE is quantitatively important in soil systems, but has received little attention in aquatic systems despite its potential to explain C mineralization patterns at the land-sea interface. This project investigates the magnitude of PE in the coastal ocean and the metabolic and ecological mechanisms that give rise to it. It focuses on the microbial communities of US Atlantic Ocean coastal marshes. In these systems, river-borne t-DOM provides a particularly valuable and tractable model for evaluating the magnitude of the PE. The study utilizes a well-characterized DOM standard collected from a Georgia river as the model t-DOM material in a series of laboratory experiments with natural coastal microbial communities and cultures of heterotrophic marine bacteria of the Roseobacter lineage. Roseobacters are particularly appropriate biological models for this work as they are abundant in southeastern US coastal zones and are known to catabolize lignin and other plant-derived aromatic compounds. Long-term (60 day) incubation experiments will track the PE resulting from addition of labile DOM of differing chemical complexity. Changes in lignin phenols will be the primary measure of the influence of PE on t-DOM degradation, but the research also monitors a broader suite of aromatic compounds represented by optical properties and identified by high-resolution mass spectrometry. Measurements of the microbial response to added labile organic matter, via extracellular enzyme activities, bacterial production, community composition and gene transcript analysis, will reveal the biological mechanisms responsible for the PE. Experiments using Roseobacter strains will allow detailed investigation of the relationship between metabolic pathways, specific bacteria, and organic carbon mineralization in a well-defined experimental system. Data on gene expression, microbial activity, and DOM transformations from the lab experiments will be integrated to elucidate the specific metabolic pathways invoked as part of the PE and guide development of molecular tools to track genetic signatures along a river to coastal ocean transect in the final year of the project.Intellectual Merit: The role of heterotrophic microorganisms in remineralizing t-DOM at the land-sea interface is a central question in biological oceanography. Components of t-DOM, principally lignin, are refractory in the sense that degradation rates are typically slow relative to other biomolecules, and yet lignin is effectively removed somewhere between land and the open ocean. The project will determine whether priming plays a role in the rapid removal of t-DOM in the coastal ocean, provide evidence for the types of labile organic matter most effective as priming agents, and attempt to discover the metabolic pathways by which the PE is mediated. These studies have the potential to reveal conserved and predictable metabolic responses that may contribute to regulation of the transformation and turnover of naturally occurring semi-labile/refractory DOM in marine environments. As climate change is likely to affect fluxes of both terrigenous carbon and nutrients to the coastal ocean, understanding the magnitude and mechanisms of PE will be necessary to predict the geochemical consequences of these changing fluxes.Broader Impacts: The project will directly support the interdisciplinary and multi-institutional training of two graduate students and several undergraduate students. Training opportunities under a recently funded Research Experiences for Undergraduates (REU) program at UTK will be leveraged and extended to local UTK undergraduates participating in the project. Funding of this project will also provide support for research faculty to continue to develop an outreach program at a primarily minority high school in Newark NJ. Finally, all PIs will continue to disseminate their research results in presentations, papers and other forms on a timely basis.