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

Emiliania huxleyi（Ehux）是一种世界性的球石藻类物种，可以形成壮观的花朵，有时会产生深刻的食物网影响。 Ehux在海洋的碳和硫地球化学中起着核心作用，保存在海洋沉积物中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代用指标（UK'37）。 然而，这些水华的机制仍然知之甚少，因为这类事件对沉积记录的后果以及这些不寻常的脂质在Ehux生态中的作用。 Ehux的初步分批培养工作显示，在迄今为止检查的所有菌株中，在良好照明、营养物耗尽的静止生长条件下，烯酮和相关脂质（统称为“PULCA”）的主要细胞积累。 而且，在菌株CCMP 1742中，其UK'37对生长温度的响应与在暴露于长时间连续黑暗的细胞中观察到的总体UK'37相同。 在15 'C，唯一的生长温度尚未广泛研究，这种非热生理影响英国'37对应于一个可能相当显着的3 'C的不确定性在古温度估计。在这项研究中，来自俄勒冈州州立大学和加州州立大学-奇科的研究人员将调查这些数量上占主导地位的中性脂质在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，将在其生长温度范围的极端条件下检查CCMP 1742，以检测营养耗尽和黑暗施加的生理应激是否对Ehux设定的UK'37（生长温度依赖性）产生定量影响。 此外，科学家团队将使用CCMP 1742进行批量培养实验，以检查健康，指数生长的Ehux细胞在充满硝酸盐的条件下暴露于长时间，连续的黑暗中是否会导致从外部获得的氮中生物合成氨基酸通过硝酸盐吸收和从储存的PULCA储备中获得的碳。 从这些实验的样品将进行全面的生化基础上的PULCA，有机碳和TN，以及总水解氨基酸和碳水化合物和详细的氨基酸组成的检查。 作为这项工作的一个组成部分，创新的分批培养实验将使用协调一致的13 C和15 N示踪剂进行明确定义的细胞命运的PULCA碳和硝酸盐-N。 将使用其他Ehux菌株进行相同的比较实验，以确定CCMP 1742在当今海洋中是一种生理学上独特的产生PULCA的分离株的程度。 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.