COLLABORATIVE RESEARCH: Investigation of the Physiological Function of Alkenones in the Coccolithophorid Emiliania Huxleyi

huxleyi （emiliania huxleyi, Ehux）是一种世界性的球石科植物，可以形成壮观的花，有时会对食物网产生深远的影响。Ehux在海洋的碳和硫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）异构体的比率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质在Ehux生态中的作用也是如此。Ehux的初步批量培养工作显示，在光照充足、营养耗尽的固定生长条件下，到目前为止所检查的所有菌株中，烯酮和相关脂质（统称为“PULCA”）的主要细胞积聚。并且，在CCMP1742菌株中，其UK'37对生长温度的反应与暴露于长时间连续黑暗的细胞中观察到的全球UK'37相同。在15'C，唯一被广泛研究的生长温度下，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显著的3'C的不确定性。在这项研究中，来自俄勒冈州立大学和加州州立大学奇科分校的研究人员将研究这些数量上占优势的中性脂在Ehux中发挥的特定生理作用，并提供对UK'37非热影响的额外理解。具体而言，CCMP1742将在其生长温度范围的极端情况下进行检查，以测试营养枯竭和黑暗所施加的生理应激是否对Ehux设定的生长温度依赖的UK'37产生定量影响。此外，科学家团队将用CCMP1742进行批量培养实验，以检验将健康的、呈指数增长的Ehux细胞暴露在充满硝酸盐的条件下，长期持续的黑暗中，是否会导致氨基酸的生物合成，这些氨基酸来源于硝酸盐吸收获得的外部氮和从储存的PULCA储备中获得的碳。这些实验样品将在综合生化基础上对PULCA、有机碳和TN、总水解氨基酸和碳水化合物以及详细的氨基酸组成进行检测。作为这项工作的一个组成部分，创新的批量培养实验将使用一致的13C和15N示踪剂进行，以明确定义PULCA碳和硝酸盐- n的细胞命运。将与其他Ehux菌株进行相同的比较实验，以确定CCMP1742是当今海洋中生理上独特的产pulca分离物的程度。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。

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.