Speed Bumps in the Carbon Cycle: Enzymatic Hydrolysis and Carbon Flow in Marine Systems

海洋系统中的大多数有机碳来源于浮游植物，浮游植物从CO2中生物合成细胞大分子，如蛋白质、脂质复合物和多糖。这些浮游植物大分子被依次转化，并在大部分情况下，随着碳通过海洋食物网而被转化回二氧化碳。微生物在这些微生物化过程中起着关键作用，循环过程。海洋初级生产力的50%（Azam 1998）。虽然它们的重要性是显而易见的，但微生物将植物生长素衍生的碳转化为CO2的具体速率和方式在很大程度上尚未探索。因此，微生物活动及其催化的碳转化常常被置于黑盒子中。在这个项目中，位于查佩尔山的北卡罗来纳州大学的研究人员将进行调查，通过确定碳通过细胞外酶的活动启动循环的速率和方式来阐明黑匣子的工作原理。已经断言，胞外酶水解是。碳循环中的限速步骤（例如Arrieta和Herndl 2002）然而，先前的工作（Arnosti et al. 1994）表明，这一断言不是先验正确的：需要一个更有区别的视角。在某些情况下，特定大分子底物在水柱中的水解非常迅速，而在其他位置的海水中，相同底物的水解却无法检测到（Arnosti等人提交的）。还有证据表明，海水和沉积异养微生物的细胞外酶活性的性质和速率存在系统差异（Arnosti，2000年）。是什么因素控制了这些差异？拟议的工作是为了系统地研究可能控制海水和沉积物微生物群落中胞外酶的模式和活性的因素。为了找出并限制一些减速带。在碳循环中，酶水解也将与缺氧沉积物中随后的碳转化步骤定量联系起来，在缺氧沉积物中，碳流的空间和时间联系的知识特别稀少。为了实现这些目标，酶水解速率和模式的现场测量将与可能影响异养微生物群落中酶表达的特定因素的实验室研究相结合。由于酶活性的测量受到有限数量的商业可用的底物和底物代理的限制，本项目还将扩大其水解和随后的转化可以详细研究的良好表征的浮游植物大分子的光谱。这些新的基质将用于现场实验以及实验室调查，通过缺氧沉积物中微生物群落的转化来定量测量碳流。

ABSTRACTOCE-0323975Most organic carbon in marine systems originates from phytoplankton, which biosynthesize cellular macromolecules such as proteins, lipid complexes, and polysaccharides from CO2. These phytoplankton macromolecules are sequentially transformed and for the most part remineralized back to CO2 as carbon passes through the marine food web. Microbes play a key role in these remineralization processes, cycling ca. 50% of marine primary productivity (Azam 1998). Although their importance is clear, the specific rates and means by which microbes transform phytoplankton-derived carbon to CO2 are largely unexplored. Microbial activities and the carbon transformations they catalyze therefore are often relegated to the black box. of carbon cycling, whose inner workings are unknown.On this project, researchers at the University of North Carolina at Chapel Hill will conduct investigations to illuminate the workings of the black box by determining the rates and means by which carbon initiates cycling through the activities of extracellular enzymes. The assertion has been made that extracellular enzymatic hydrolysis is .the. rate-limiting step in carbon cycling (e.g. Arrieta and Herndl 2002) Previous work (Arnosti et al. 1994), however, demonstrates that this assertion is not a priori true: a more differentiated perspective is required. In some cases, hydrolysis of a given macromolecular substrate in the water column is extremely rapid, while the same substrate is not detectably hydrolyzed in seawater at other locations (Arnosti et al. submitted). There is also evidence for systematic differences in the nature and rates of extracellular enzymatic activities of seawater and of sedimentary heterotrophic microbes (Arnosti, 2000). What factors control these differences? The proposed work is intended to examine systematically factors that may control the patterns and activities of extracellular enzymes among seawater and sedimentary microbial communities. In an effort to identify and constrain some of the speed bumps. in the carbon cycle, enzymatic hydrolysis will also be linked quantitatively with subsequent carbon transformation steps in anoxic sediments, where knowledge of spatial and temporal connections of carbon flow is particularly sparse.To accomplish these goals, field measurements of enzymatic hydrolysis rates and patterns will be coupled with laboratory studies of specific factors that may affect enzyme expression in heterotrophic microbial communities. Since measurements of enzyme activities have been restricted by the limited number of commercially available substrates and substrate proxies, this project will also expand the spectrum of well-characterized phytoplankton macromolecules whose hydrolysis and subsequent transformations can be studied in detail. These new substrates will be used in field experiments as well as in laboratory investigations to quantitatively measure carbon flow via transformations carried out by microbial communities in anoxic sediments.