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

碳循环中的减速：海洋系统中的酶水解和碳流

• 批准号: 0323975
• 负责人: Carol Arnosti
• 金额: --
• 依托单位: University of North Carolina at Chapel Hill
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-09-01 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0323975&HistoricalAwards=false
• 关键词: Speed; Bumps; Carbon; Cycle; Enzymatic; Speed; Bumps; Carbon; Cycle; Enzymatic

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.

Abstractoce-0323975海洋系统中的最有机碳源自浮游植物，生物合成细胞大分子，例如蛋白质，脂质复合物和CO2的多糖。这些浮游植物大分子被依次转化，并且在大部分时，当碳通过海洋食品网时，大部分回忆起回到二氧化碳。微生物在这些回想起的过程中起着关键作用，骑自行车。海洋初级生产力的50％（Azam 1998）。尽管它们的重要性很明显，但微生物将浮游植物衍生的碳转换为CO2的特定速率和手段在很大程度上没有探索。因此，微生物活性及其催化的碳转化通常被降级为黑匣子。北卡罗来纳大学教堂山分校的研究人员在这个项目中，其内部运作是未知的。已经提出了细胞外酶水解的断言。碳循环的速率限制步骤（例如Arrieta和Herndl 2002）先前的工作（Arnosti等，1994）表明，这种断言不是先验的：需要更加差异的观点。在某些情况下，水柱中给定的大分子底物的水解非常迅速，而在其他位置的海水中未发现相同的底物（Arnosti等人提交）。也有证据表明，海水和沉积物异养微生物的细胞外酶活性的性质和速率有系统的差异（Arnosti，2000）。哪些因素控制了这些差异？拟议的工作旨在检查系统的因素，以控制海水和沉积微生物群落之间细胞外酶的模式和活动。为了识别和限制一些速度颠簸。在碳周期中，酶水解也将与随后的碳转化步骤进行定量联系，其中碳流的空间和时间连接的了解尤其稀疏。为实现这些目标，酶水解速率和模式的现场测量可能会与特定因素的实验室研究相结合，从而影响了eNEBOT的互联网。由于酶活性的测量受到了有限数量的市售底物和底物代理的限制，因此该项目还将扩大特征良好的浮游植物大分子的范围，其水解和后续转换可以详细研究。这些新的底物将用于现场实验以及实验室研究中，以通过微生物群落在缺氧沉积物中进行的转化来定量测量碳流量。