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Yongsong Huang – One of the best experts on this subject based on the ideXlab platform.

  • C41 methyl and C42 ethyl Alkenones are biomarkers for Group II Isochrysidales
    Organic Geochemistry, 2020
    Co-Authors: Sian Liao, William M. Longo, Linda A. Amaral-zettler, Yuan Yao, Li Wang, Karen J. Wang, Yongsong Huang


    Abstract Alkenones are polyunsaturated long-chain methyl or ethyl ketones produced by species in the Isochrysidales, an order of haptophyte algae. Based on phylogenetic data, members of the Isochrysidales have been classified into three groups with each group showing significant differences in Alkenone profiles and preferred growth environments. Common carbon chain lengths of Alkenones range from 37 to 40. Extended C41 methyl (C41Me) and C42 ethyl (C42Et) Alkenones have been reported in hypersaline lakes in China (Lake Alahake and Lake Balikun), Canada (Lake Snakehole) and marine sediments (e.g., ∼95 Ma in Blake-Bahama Basin). It is unclear, however, if these extended Alkenones are produced by one or more groups of Isochrysidales. Here, we systematically examined Alkenones from cultures of Group II (Isochrysis nuda, Isochrysis litoralis, Ruttnera lamellosa, Isochrysis galbana and Tisochrysis lutea) and Group III (Emiliania huxleyi and Gephyrocapsa oceanica) Isochrysidales and environmental samples of Group I Isochysidales. C41Me and C42Et Alkenones were found in all Group II species with Isochrysis nuda producing the highest percentages, but not in Alkenones produced by Group I nor Group III Isochrysidales. Our results indicate that extended C41Me and C42Et Alkenones are specific biomarkers for Group II Isochrysidales. We also report the first temperature calibrations of Alkenones for Isochrysis nuda and Isochrysis litoralis using culture experiments, and find temperatures inferred from extended Alkenones in Balikun and Alahake surface sediments match warm-season temperatures based on Isochrysis nuda calibrations, which is further corroborated by genomic data indicating the dominance of Isochrysis nuda Isochrysidales.

  • Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for Alkenone production
    Geobiology, 2019
    Co-Authors: Nora Richter, Yongsong Huang, William M. Longo, Sarabeth George, Anna Shipunova, Linda Amaral-zettler


    Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of Alkenones, long-chain ketones that are commonly used for paleotemperature reconstructions. Alkenone-producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct Alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri-unsaturated Alkenone isomers (C37:3b Me, C38:3b Et, C38:3b Me, C39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small-subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high-throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well-supported clade separating the previously described “EV” clade from the “Greenland” clade. We infer the first partial large-subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well-supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of Alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri-unsaturated Alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on Alkenone biosynthesis.

  • systematic chemotaxonomic profiling and novel paleotemperature indices based on Alkenones and alkenoates potential for disentangling mixed species input
    Organic Geochemistry, 2019
    Co-Authors: Maureen H Conte, Yinsui Zheng, Patrick Heng, Richard S Vachula, Yongsong Huang


    Abstract The unsaturation indices ( U 37 K , U 37 K’ ) of long chain Alkenones are powerful paleotemperature proxies and have been widely applied for sea surface temperature (SST) reconstructions in the past three decades. However, these indices encounter major difficulties in systems harboring different Alkenone-producing haptophyte species, such as saline lakes and marginal ocean environments. All haptophytes produce C37 Alkenones, but different species often display large differences in temperature calibrations and may bloom in different seasons, hindering the use of U 37 K and U 37 K’ indices for reliable paleotemperature reconstructions in mixed systems. To overcome these problems, we have recently reported a new analytical method that allows comprehensive separation of up to 32 Alkenones, alkenoates and their double bond positional isomers in culture and sediment samples. Here we report a systematic analysis of Alkenones and alkenoates from six haptophyte cultures growing at a wide range of temperatures (4–25 °C). Together with a compilation of 230 previously published culture data sets, we present here systematic calibrations of temperature-sensitive indices based on all Alkenone and alkenoate homologues (including isomers). Using this dataset, we extract systematic chemotaxonomic criteria for differentiating individual haptophyte species and demonstrate such chemotaxonomic features can be encoded into a machine learning model for reliable species identifications. Specifically, we show that temperature calibrations based on C38 methyl ketones and C39 ethyl ketones are potentially useful for disentangling mixed inputs in estuarine systems where Group III (E. huxleyi) and Group II Alkenones mix, and that C36 ethyl alkenoate isomeric ratios display minimal species heterogeneity and are potentially more suited for reconstructing temperatures in mixed systems with different Group II haptophytes. Using the culture data as base profiles, we construct a mathematical model for estimating percentage inputs from Alkenones of different Isochrysidales groups in mixed systems, with potential implications for inferring past salinity changes. Overall, the results from this study demonstrate important new applications of Alkenone and alkenoate biomarkers in paleoclimate and paleoenvironmental research.

Naomi Harada – One of the best experts on this subject based on the ideXlab platform.

  • genomic and geochemical identification of the long chain Alkenone producers in the estuarine lake takahoko japan implications for temperature reconstructions
    Organic Geochemistry, 2020
    Co-Authors: Hiroto Kajita, Naomi Harada, Hodaka Kawahata, Miyako Sato, Hideto Nakamura, Naohiko Ohkouchi, Shun Tokioka


    Abstract Identifying the lacustrine haptophyte species that produce long-chain Alkenones (LCAs) is essential for using Alkenone unsaturation ratios to create lake water temperature reconstructions. We discovered LCAs in the brackish Lake Takahoko in northern Japan. The identity of LCA-producing species was investigated using 18S ribosomal DNA (rDNA) and organic geochemical analysis. Two distinct genetic groups, termed Tak-A and Tak-B, were identified within the Group II haptophyte phylotype. Tak-A was closely related to Hap-A, which was obtained from Lake George, USA; and Tak-B was identified as Isochrysis galbana. Because Hap-A and Isochrysis galbana have similar temperature calibrations, Tak-A and Tak-B were also expected to share similar calibrations. Therefore, the changes of their relative abundances in the lake should not significantly disturb paleotemperature reconstructions. The Alkenone temperature recorded in the surface sediment corresponded to the lake temperature in early to late summer. This is likely related to the haptophyte bloom season in Lake Takahoko suggesting that this lake may be a viable location for creating a lacustrine Alkenone paleotemperature record.

  • Alkenone production in the East Sea/Japan Sea
    Continental Shelf Research, 2014
    Co-Authors: Kyung Eun Lee, Sunghye Lee, Yonggi Park, Ho Jin Lee, Naomi Harada


    Abstract To test the applicability of Alkenones as a proxy for past sea surface temperature (SST) in the East Sea (Japan Sea), this study investigated the season and depth of Alkenone production in the area. Surface and subsurface seawater samples were collected from the East Sea during cruises carried out by the National Fisheries Research and Development Institute of Korea in 2008–2010. Surface samples were filtered for suspended material at two-month intervals. Subsurface samples were collected at water depths of 20, 50, 70 and 100 m by CTD bottle casts at two stations, one a coastal station and the other an offshore station. The results of Alkenone analysis show that the concentration of total C 37 Alkenones was generally high in the surface mixed layer and decreased with depth, indicating that Alkenones were most likely produced in or close to the surface mixed layer. Alkenone concentration varied seasonally: high in spring to fall and significantly reduced in winter. Comparisons of Alkenone-based temperatures with in situ seawater temperatures show that Alkenone temperatures measured from suspended particles in the surface waters were close to in situ SST in summer but were lower in winter. During winter, when Alkenone production is significantly reduced, Alkenones may be suspended for relatively long times and are likely to be advected from the north by eddies from Subpolar Front meanders. In summer when new production of Alkenones increases, the settling velocity of Alkenones appears to increase and residence time becomes shorter than in winter, suggesting that particles are less likely to be significantly advected at that time. Importantly, at the offshore station, coretop Alkenone temperature corresponds to annual-averaged SST, while at the coastal station it corresponds to summer-to-fall averaged SST.

  • Freshwater impacts recorded in tetraunsaturated Alkenones and Alkenone sea surface temperatures from the Okhotsk Sea across millennial-scale cycles
    Paleoceanography, 2008
    Co-Authors: Naomi Harada, Miyako Sato, Tatsuhiko Sakamoto


    [1] We present records of phytoplankton-produced Alkenones down a long piston core, which reveal changes of sea surface temperature (SST) and sea surface salinity (SSS) in the southwestern Okhotsk Sea over the past 120 ka. Between 20 and 60 ka B.P., Alkenone-derived temperatures typically increased by 6°C–8°C from periods corresponding, within a few hundred years, to stadials to those corresponding to interstadials recorded in Greenland ice cores. The abundance of C37:4 Alkenone relative to total C37 Alkenones (percent C37:4), a possible proxy for salinity, indicated that during most low SSS was associated with high SST. The warm freshwater events might be related to (1) a decline in the supply of saline water entering the Okhotsk Sea through the Soya Strait; (2) strengthening of the freshwater supply from the Amur River and precipitation over the Okhotsk Sea, associated mainly with increased Asian summer monsoon activity; and (3) the effect of melting sea ice. These findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the Pacific and the Atlantic sides of the Northern Hemisphere.

Yoshihiro Shiraiwa – One of the best experts on this subject based on the ideXlab platform.

  • Overexpression of Tisochrysis lutea Akd1 identifies a key cold-induced Alkenone desaturase enzyme.
    Scientific reports, 2018
    Co-Authors: Hirotoshi Endo, Iwane Suzuki, Hiroya Araie, Yutaka Hanawa, Yoshihiro Shiraiwa


    Alkenones are unusual long-chain neutral lipids that were first identified in oceanic sediments. Currently they are regarded as reliable palaeothermometers, since their unsaturation status changes depending on temperature. These molecules are synthesised by specific haptophyte algae and are stored in the lipid body as the main energy storage molecules. However, the molecular mechanisms that regulate the Alkenone biosynthetic pathway, especially the low temperature-dependent desaturation reaction, have not been elucidated. Here, using an Alkenone-producing haptophyte alga, Tisochrysis lutea, we show that the Alkenone desaturation reaction is catalysed by a newly identified desaturase. We first isolated two candidate desaturase genes and found that one of these genes was drastically upregulated in response to cold stress. Gas chromatographic analysis revealed that the overexpression of this gene, named as Akd1 finally, increased the conversion of di-unsaturated C37-Alkenone to tri-unsaturated molecule by Alkenone desaturation, even at a high temperature when endogenous desaturation is efficiently suppressed. We anticipate that the Akd1 gene will be of great help for elucidating more detailed mechanisms of temperature response of Alkenone desaturation, and identification of active species contributing Alkenone production in metagenomic and/or metatranscriptomic studies in the field of oceanic biogeochemistry.

  • Composition of long chain Alkenones and alkenoates as a function of growth temperature in marine haptophyte Tisochrysis lutea
    Organic Geochemistry, 2016
    Co-Authors: Hideto Nakamura, Ken Sawada, Hiroya Araie, Takashi Shiratori, Ken-ichiro Ishida, Iwane Suzuki, Yoshihiro Shiraiwa


    Abstract We investigated the compositions of long chain Alkenones and alkenoates in cultured strains of the marine haptophyte Tisochrysis lutea CCMP463 and T. lutea NIES-2590 (formerly classified as Isochrysis galbana). Both T. lutea strains grown at various temperatures of 15–35 °C could be characterized by the lack of tetraunsaturated Alkenones and alkenoates in comparison with strains in other genera Isochrysis and Ruttnera, which are classified in the same family Isochrysidaceae and order Isochrysidales that contain Alkenone-producing haptophytes. We found that T. lutea has a distinct Alkenone response to temperature, which is characterized by high U 37 K -temperature sensitivity at 15–30 °C and continuing sensitivity at warm-end temperatures over 30 °C, where the other species fail to adapt. Both strains showed similar trends in Alkenone compositions and Alkenone unsaturation index-temperature calibrations. In addition, both strains CCMP463 and NIES-2590 showed notably close phylogenetic relationships, even those that were collected from remote regions of the Atlantic Ocean, namely the Caribbean Sea and English Channel, where their habitats, particularly the sea surface temperature, are notably different. Considering previous published datasets, three genera, Isochrysis, Ruttnera and Tisochrysis, showed very different trends in the Alkenone unsaturation index-temperature calibration. These results suggest that the lack of tetraunsaturated Alkenones, warm-water oriented growth and the high sensitivity to growth temperature serve as distinct chemotaxonomic characteristics of T. lutea in the Isochrysidaceae family.

  • proteomic analysis of lipid body from the Alkenone producing marine haptophyte alga tisochrysis lutea
    Proteomics, 2015
    Co-Authors: Qing Shi, Hiroya Araie, Iwane Suzuki, Ranjith Kumar Bakku, Yoichiro Fukao, Randeep Rakwal, Yoshihiro Shiraiwa


    Lipid body (LB) is recognized as the cellular carbon and energy storage organelle in many organisms. LBs have been observed in the marine haptophyte alga Tisochrysis lutea that produces special lipids such as long-chain (C37-C40) ketones (Alkenones) with 2–4 trans-type double bonds. In this study, we succeeded in developing a modified method to isolate LB from T. lutea. Purity of isolated LBs was confirmed by the absence of chlorophyll auto-fluorescence and no contamination of the most abundant cellular protein ribulose-1,5-bisphosphate carboxylase/oxygenase. As Alkenones predominated in the LB by GC-MS analysis, the LB can be more appropriately named as “Alkenone body (AB).” Extracted AB-containing proteins were analyzed by the combination of 1DE (SDS-PAGE) and MS/MS for confident protein identification and annotated using BLAST tools at National Center for Biotechnology Information. Totally 514 proteins were identified at the maximum. The homology search identified three major proteins, V-ATPase, a hypothetical protein EMIHUDRAFT_465517 found in other Alkenone-producing haptophytes, and a lipid raft-associated SPFH domain-containing protein. Our data suggest that AB of T. lutera is surrounded by a lipid membrane originating from either the ER or the ER-derived four layer-envelopes chloroplast and function as the storage site of Alkenones and alkenes.