Substrate structural complexity and abundance control distinct mechanisms of microbially-driven carbon cycling in the ocean

海洋中微生物驱动的碳循环的独特机制海洋中产生的有机碳几乎有一半是由细菌处理的。细菌使用细胞外（细胞外）酶将大的有机分子分解为可以运输到细胞中的小分子。最近发现，细菌以两种方式使用胞外酶：“自私摄取”和“外部水解”。外部水解将低分子量产物释放到环境中，在那里它们可以被其他生物体利用。“自私的摄取”释放很少或没有产品。这项研究将确定海洋沃茨中“自私吸收”的程度和位置。这一过程影响海洋中有机碳的分布、有机小分子为更广泛的细菌提供食物的流动以及细菌群落的组成和动态。最近的研究结果表明，“自私”的细菌在深海沃茨中很活跃，它们在那里吸收不会被外部水解的复杂多糖（糖）。这些结果启发了一个新的模型，将“自私吸收”和外部水解与细菌使用的有机物质的数量和复杂性联系起来。该项目将通过描述海洋有机物的多糖部分，并研究有机物丰度、结构复杂性和胞外酶使用之间的关系来测试该模型。研究生和本科生将作为现场和实验室研究小组的成员参与该项目。该研究将验证多糖加工机制与细胞产生水解所需酶的成本有关的假设，以及细胞获得足够投资回报的可能性。将要测试的概念模型表明，当有机物丰富时，或者当酶的生产成本可以分摊时（例如，在颗粒上，在生物膜中）;当高分子量（HMW）有机物稀缺时，特别是当HMW有机物非常复杂时，自私摄取将是更好的策略。本研究将通过表征从海洋收集的溶解有机物（DOM）和颗粒有机物（POM）的含多糖组分的结构，通过确定来自表面和深海的天然微生物群落对不同多糖的自私摄取程度和外部水解速率，以及通过控制不同结构复杂性的多糖的丰度的孵育实验。该项目将与马克斯·普朗克海洋微生物学研究所的同事合作开展，该研究所在碳水化合物化学和结构分析以及先进显微镜和复杂微生物群落分析方面的专业知识是该项目的核心。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Substrate Structural Complexity and Abundance Control Distinct Mechanisms of Microbially-Driven Carbon Cycling in the OceanAlmost half of the organic carbon produced in the ocean is processed by bacteria. Bacteria use extracellular (outside the cell) enzymes to break down large organic molecules to small sizes that can be transported into their cells. It has recently been discovered that bacteria use extracellular enzymes in two ways: ‘selfish uptake’ and ‘external hydrolysis’. External hydrolysis releases low molecular weight products to the environment where they can be used by other organisms. ‘Selfish uptake’ releases little or no products. This research will determine the extent and location of ‘selfish uptake’ in ocean waters. This process affects the distribution of organic carbon in the ocean, the flow of small organic molecules to feed a wider range of bacteria, and the composition and dynamics of the bacterial community. Recent results show that ‘selfish’ bacteria are active in deep ocean waters, where they take up complex polysaccharides (sugars) that are not hydrolyzed externally. These results inspired a new model that links ‘selfish uptake’ and external hydrolysis to the amount and complexity of the organic matter that is used by bacteria. This project will test the model by describing the polysaccharide fraction of marine organic matter, and studying the relationships between organic matter abundance, structural complexity, and extracellular enzyme use. Graduate and undergraduate students will participate in the project as members of the research team in the field and in the laboratory.This research will test the hypothesis that the mechanism of polysaccharide processing is related to the cost to a cell of producing the enzymes required for its hydrolysis, and the probability that a cell will receive sufficient return on investment for producing the enzymes. The conceptual model that will be tested suggests that external hydrolysis is favored when organic matter is abundant, or when enzyme production costs can be shared (e.g., on particles, in biofilms); selfish uptake would be a better strategy when high molecular weight (HMW) organic matter is scarce, and particularly when the HMW organic matter is very complex. This study will test this model by characterizing the structure of polysaccharide-containing components of dissolved organic matter (DOM) and particulate organic matter (POM) collected from the ocean, by determining the extent of selfish uptake and rates of external hydrolysis of different polysaccharides by natural microbial communities from the surface and the deep ocean, and by incubation experiments that control for the abundance of polysaccharides of different structural complexity. This project will be carried out in collaboration with colleagues at the Max Planck Institute for Marine Microbiology, whose expertise in carbohydrate chemistry and structural analyses, and in advanced microscopy and analysis of complex microbial communities, are central to the project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.