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

California State University-Chico, Chico CA

Investigators

Abstract

ABSTRACT OCE-0350409 / OCE-0350359 Emiliania 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.