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

概述：每年都有大量明显难降解的陆源溶解有机质（t-DOM）通过河流输送到海岸，但海洋中t-DOM的踪迹却越来越少。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被认为可以增强顽固性化合物的再矿化，这种现象被称为启动效应（PE）。PE在土壤系统中具有重要的定量意义，但在水生系统中却很少受到关注，尽管它有可能解释陆海界面的C矿化模式。该项目调查了沿海海洋中PE的大小以及产生PE的代谢和生态机制。它的重点是美国大西洋沿岸沼泽的微生物群落。在这些系统中，河流携带的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。该研究利用从乔治亚河收集的特征良好的DOM标准作为模型t-DOM材料，在一系列实验室实验中使用天然沿海微生物群落和玫瑰杆菌谱系异养海洋细菌培养。玫瑰杆菌是特别适合这项工作的生物模型，因为它们在美国东南部沿海地区大量存在，并且已知可以分解木质素和其他植物衍生的芳香族化合物。长期（60天）培养实验将跟踪添加不同化学复杂性的不稳定DOM所产生的PE。木质素酚的变化将是PE对t-DOM降解影响的主要测量指标，但该研究还监测了一系列更广泛的芳香族化合物，这些化合物由光学性质代表，并由高分辨率质谱法识别。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不稳定有机物的反应，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良好的实验系统中详细调查代谢途径，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转化数据将被整合，以阐明作为PE一部分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跟踪沿河到沿海海洋样带的遗传特征。智力价值：异养微生物在陆海界面t-DOM再矿化中的作用是生物海洋学的核心问题。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，木质素的降解速度通常很慢，但木质素可以在陆地和海洋之间的某个地方有效地去除。该项目将确定启动是否在沿海海洋中t-DOM的快速去除中发挥作用，为最有效的启动剂的不稳定有机物类型提供证据，并试图发现PE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，这些代谢反应可能有助于调节海洋环境中自然发生的半不稳定/难降解DOM的转化和周转。由于气候变化可能影响陆源碳和营养物质向沿海海洋的通量，因此了解PE的大小和机制对于预测这些通量变化的地球化学后果是必要的。更广泛的影响：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经验（REU）计划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提供支持，以继续在新泽西州纽瓦克的一所主要是少数民族的高中开展外展计划。最后，所有pi将继续以报告，论文和其他形式及时传播他们的研究成果。

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 attemp 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.