Extracellular enzymes in aggregates and contributions of free enzymes to hydrolytic activities: Consequences for organic mater remineralizations in marine systems

聚集体在海洋有机质动态中发挥着核心作用，拥有多种微生物群落，这些微生物群落调节胶体、颗粒和溶解有机物的转化和运输。由于这些聚集体可能是碳再矿化的热点，聚集体中的微生物动力学一直是密集研究的焦点。已经在聚集体中测量到高比率的酶活性，但仅有有限范围的底物代用品被用于评估这些活性。然而，微生物胞外酶的结构特性是至关重要的，因为它们决定了可被异养群落代谢的有机大分子的性质。在这个项目中，北卡罗来纳大学教堂山分校的研究人员将探索聚集相关微生物群落的酶能力，并使用浮游植物提取物、溶解有机碳和多糖作为底物，将它们与非聚集相关群落进行比较。将同时比较微生物群落的组成，以确定酶活性谱的差异是否与活跃微生物群落的组成差异有关。由于有机集合体，特别是作为下沉有机质的组成部分，在类云状层中，或从表层沉积物中重新悬浮，往往包括矿物颗粒和相关的有机质，他们将调查与表面相关的有机质可以被与集合体相关的微生物群落水解的程度。初步调查进一步表明，特定的酶被释放到水柱中，而其他酶仍然与细胞和/或聚集体相关，因此他们将在无聚集体的样品中测量游离酶的活性和结构特性。模型表明，当微生物获得合理回报时，游离酶的活跃释放应该发生。研究人员将评估影响酶寿命的因素，这是关键的实验数据，可用于测试关于微生物胞外酶的相互矛盾的模型预测。更广泛的影响：这个项目将有助于教和学，两名本科生，一名研究生和一名博士后作为研究团队的组成部分。该项目的成果将在国家会议上提出，并将在科学文献中发表。这个项目的结果将被纳入到PI在研究生和本科生层面上教授的课程中。目前的本科生研究助理中有两名是女性。

Aggregates play a central role in organic matter dynamics in the ocean, harboring diverse communities of microorganisms that mediate the transformations and transport of colloidal, particulate, and dissolved organic matter. Because these aggregates can be hot spots of carbon remineralization, microbial dynamics in aggregates have been a focus of intense investigation. High rates of enzymatic activities have been measured in aggregates, but only a limited range of substrate proxies have been used to assess these activities. The structural specificities of microbial extracellular enzymes are critical, however, since they determine the nature of organic macromolecules that can be metabolized by heterotrophic communities. In this project, investigators at the University of North Carolina at Chapel Hill will probe the enzymatic capabilities of aggregate-associated microbial communities and compare them with non-aggregate associated communities using phytoplankton extracts, dissolved organic carbon, and polysaccharides as substrates. The composition of the microbial communities will be compared in parallel to determine whether differences in the spectrum of enzyme activities are related to compositional differences in the active microbial communities. Since organic aggregates particularly as components of sinking organic matter, in the nepheloid layer, or resuspended from surface sediments often include mineral particles with associated organic matter, they will investigate the extent to which surface-associated organic matter can be hydrolyzed by aggregate-associated microbial communities. Preliminary investigations further suggest that specific enzymes are released into the water column while other enzymes remain associated with cells and/or aggregates, so they will measure the activities as well as the structural specificities of free enzymes in aggregate-free samples. Models suggest that active release of free enzymes should occur when microorganisms receive a reasonable return. The investigators will assess factors affecting enzyme lifetimes, critical experimental data that could be used to test conflicting model predictions about microbial extracellular enzymes. Broader Impacts: This project will contribute to teaching and learning, with two undergraduates, a graduate student, and a postdoc as integral members of the research team. Results of the project will be presented at national meetings and will be published in the scientific literature. Results of this project will be incorporated into classes the PI teaches at both graduate and undergraduate levels. Two of the current undergraduate research assistants are women.