Collaborative Research--Investigation of the Phsysiological Function of Alkenones in the Coccolithophore Emiliania Huxleyi

摘要-0350409/OCE-0350359虎纹伊蚊(Ehux)是一种世界性的球虫类物种，可以形成壮观的水华，有时会对食物链产生深远的影响。Ehux在海洋碳和硫的生物地球化学中起着核心作用，其在海洋沉积物中保存的长链、不饱和甲基酮(烯酮)异构体的比例现在被广泛用作古温度指标(UK‘37)。然而，这些水华的机制仍然知之甚少，这些事件对沉积记录的影响以及这些不寻常的脂类在Ehux生态中的作用也是如此。Ehux的初步分批培养工作显示，在目前所检测的所有菌株中，在光照良好、营养耗竭的固定生长条件下，烷基化合物和相关脂类(统称为‘PULCA’)的主要细胞积聚。而且，在菌株CCMP1742中，其UK‘37对生长温度的响应与在长期、连续黑暗中观察到的全球UK’37相同。在15摄氏度，这是唯一被广泛研究的生长温度，这种对UK‘37的非热生理影响对应于古温度估计中可能相当重要的3摄氏度不确定性。在这项研究中，来自俄勒冈州立大学和加州州立大学-CHICO的研究人员将调查这些数量占主导地位的中性脂质在Ehux中所起的具体生理作用，并提供对UK‘37的非热影响的进一步了解。具体地说，CCMP1742将在其生长温度范围的极端情况下进行检查，以测试营养耗竭和黑暗施加的生理压力是否对Ehux设定的UK‘37有定量影响，即取决于生长温度。此外，科学家团队将使用CCMP1742进行批量培养实验，以检验在硝酸盐充足的条件下，健康、指数级增长的Ehux细胞暴露在长期、连续的黑暗中是否会导致氨基酸的生物合成，这些氨基酸来自外部通过硝酸盐吸收获得的氮和从储存的PULCA储备中获得的碳。这些实验的样本将在全面的生化基础上进行PULCA、有机碳和TN的检测，以及总可水解性氨基酸和碳水化合物的检测，以及详细的氨基酸组成。作为这项工作的组成部分，将使用协调一致的13C和15N示踪剂进行创新的批量培养实验，以明确定义PULCA碳和硝酸盐-N的细胞命运。将与其他Ehux菌株进行相同执行的比较实验，以确定CCMP1742在多大程度上是一种从今天的海洋中产生PULCA的生理上独特的分离物。最后，科学家团队将通过几种类型的显微镜研究PULCA的细胞位置(S)。

ABSTRACTOCE-0350409 / OCE-0350359Emiliania huxleyi (Ehux) is a cosmopolitan coccolithophorid species that can form spectacular blooms, sometimes with profound food-web impacts. Ehux plays a central role in the ocean's carbon and sulfur biogeochemistry, and ratios of its long-chain, unsaturated methyl ketone (alkenone) isomers preserved in marine sediments are now used widely as paleotemperature proxies (UK'37). However, the mechanism of these blooms is still poorly understood, as is the consequence of such events on the sedimentary record and the role of these unusual lipids in Ehux ecology. The preliminary batch culture work with Ehux shows major cellular buildup of alkenones and related lipids (collectively termed 'PULCA') under well-illuminated, nutrient-depleted stationary growth conditions in all strains examined so far. And, in strain CCMP1742 whose UK'37 versus growth temperature response is identical with the global UK'37 observed in cells exposed to prolonged, continuous darkness. At 15'C, the only growth temperature yet studied extensively, such non-thermal physiological impacts on UK'37 correspond to a possibly quite significant 3'C uncertainty in paleotemperature estimates. In this study, researchers from Oregon State University and California State University - Chico will investigate the specific physiological role that these quantitatively dominant neutral lipids play in Ehux, as well as to provide additional understanding of non-thermal impacts on UK'37. Specifically, CCMP1742 will be examined at the extremes of its growth temperature range to test whether or not the physiological stress imposed by the nutrient depletion and darkness has a quantitative impact on the UK'37 set by Ehux that is growth temperature dependent. In addition, the team of scientists will conduct batch culture experiments with CCMP1742 to examine whether or not the exposure of healthy, exponentially-growing Ehux cells to prolonged, continuous darkness under nitrate-replete conditions will result in biosynthesis of amino acids from nitrogen obtained externally by nitrate uptake and carbon obtained from stored PULCA reserves. Samples from these experiments will be examined on a comprehensive biochemical basis for PULCA, organic carbon and TN, as well as total hydrolysable amino acids and carbohydrates and a detailed amino acid composition. As an integral part of this work, innovative batch culture experiments will be conducted using concerted 13C and 15N tracers to define unequivocally the cellular fate of PULCA carbon and nitrate-N. Identically executed comparative experiments will be conducted with other Ehux strains to determine the extent that CCMP1742 is a physiologically unique PULCA-producing isolate from today's ocean. Finally, the team of scientists will investigate the cellular location(s) of PULCA by several types of microscopy.