Haptophyte algae are recently credited as the most abundant and diverse primary producers in the world?s oceans, rendering their metabolic and carbon fixation pathways issues of utmost importance. Alkenone lipids produced by haptophyte algae of the order Isochrysidales occur ubiquitously in the world?s ocean and in numerous lakes and are an invaluable tool for paleotemperature reconstructions. However, the mismatch between cultured haptophytes and observed alkenone distributions in sediments has hindered the use of alkenones as a paleotemperature proxy in lakes. In order to confidently apply the alkenone unsaturation for paleotemperature reconstructions in lakes, it is necessary to fully understand the biology and biochemistry of the lacustrine alkenone-producing haptophytes using a consortium of techniques including culturing, lipid and molecular characterization. This proposal builds on our success in obtaining the first stable enrichment culture for a lacustrine haptophyte alga that produces predominantly C37:4 alkenones, the alkenone abundant in freshwater and brackish environments. Systematic sampling of lake water and plankton and in situ measurements of environmental parameters at Lake George, ND combined with extensive manipulation of our haptophyte culture will permit identification of the triggers for haptophyte algal blooms.

Our study will promote multidisciplinary collaboration (organic geochemistry, molecular biology, phycology, paleoclimatology, limnology) to studying important biological, geochemical and paleoclimatological problems, and allow cross-discipline training of graduate and undergraduate students. Close interaction with Brown University's existing NSF funded GK-12 program will bring high school teachers to participate in field trips and laboratory research, and lectures given at local schools, will broadly disseminate our research. Data generated from this research will also be incorporated into organic geochemistry and molecular biology courses targeted at the advanced undergraduate/graduate level and help support a full-time graduate student focusing on lacustrine haptophytes.

Project Report

Long chain alkenones are organic compounds produced by algae living in aquatic environments such as ocean and lakes. These compounds are unique in that the variations in their molecular structures can accurate reflect water temperature changes. Alkenones are also extremely recalcitrant organic molecules and have been found in ocean sediments over 100 million years old. In ocean environments, long chain alkenones have been used to reconstruct the sea surface temperature changes for time scales ranging from thousands to millions of years. So far alkenones represent one of best methods for deciphering the thermal history of the ocean surface. These long chain alkenones also exist in lake environments and have major potential for providing temperature reconstructions for continental regions. However, there are considerable challenges to apply alkenones for continental temperature reconstructions. Chief among these challenges is the species diversity: there are apparently multiple species of Haptophyte algae in lakes that produce similar alkenones and these different species may not have the same temperature senstivities. In order to successfully apply alkenones for continental temperature reconstructions, it is best to obtain pure cultures of these algae and perform laboratory experiments to identify the most robust alkenone - temperature relationships. Obtaining the pure cultures and performing laboratory experiments are among the main goals of this project. After extensive field campaigns at Lake George and collection of water fileter samples for DNA sequencing and extensive efforts to isolate individual alga, we have greatly advanced our understanding of the lacustrine haptophye algae and machanisms of alkenone productions. Our DNA sequencing throughout the haptophyte bloom season at Lake George revealed at least two different species of haptophytes (we called them Hap A and B respectively). We were able to isolate pure cultures of Hap B, and perform extensive laboratory experiments. We were able to obtain enrichment culture for Hap A and narrowed down it size range - it turns out Hap A is a very small organism with size smaller than 3 micron in diameter (called picoplankton). In the process of analyzing alkenones from Lake George and else where, we also made major technological stride by discovering a new type of gas chromatographic stationary phase capable of separating alkenones with unprecedented resolution. This project also support a female Ph.D. graduate student Susanna Theroux who successfully defended her PhD dissertation in November, 2012 and move on to the Joint Genome Institute of Department of Energy as a postdoctoral researcher. The project also supported two undergraduate students in participating in the multidisciplinary research. Partial support to graduate student William Longo lead to the discovery of new separation method for alkenones. Three peer-reviewed publications have been published and two are in the final stage of preparation.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Deborah Aruguete
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Brown University
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