Novel alkenone-producing strains of genus Isochrysis (Haptophyta) isolated from Canadian saline lakes show temperature sensitivity of alkenones and alkenoates

Abstract

Alkenone-producing species have been recently found in diverse lacustrine environments, albeit with taxonomic information derived indirectly from environmental genomic techniques. In this study, we isolated alkenone-producing algal species from Canadian saline lakes and established unialgal cultures of individual strains to identify their taxonomical and molecular biological characteristics. Water and sediments collected from the lakes were first enriched in artificial seawater medium over a range of salinities (5-40‰) to cultivate taxa in vitro. Unialgal cultures of seven haptophyte strains were isolated and categorized in the Isochrysis clade using SSU and LSU rRNA gene analysis. The alkenone distributions within isolated strains were determined to be novel compared with other previously-reported alkenone-producing haptophytes. While all strains produced the typical C37 and C38 range of isomers, one strain isolated from Canadian salt lakes also produced novel C41 and C42 alkenones that are temperature sensitive. In addition, we showed that all alkenone unsaturation indices (e.g., and) are temperature dependent in culture experiments, and that alkenoate indices (e.g., , , RIA38 and A37/A38) provide alternative options for temperature calibration based on these new lacustrine algal strains. Importantly, these indices show temperature dependence in culture experiments at temperatures below 4 10 ˚C, where traditional alkenone proxies were not as sensitive. We hypothesize that this suite of calibrations may be used for reconstructions of past water temperature in a broad range of lakes in the Canadian prairies.

Next‐Generation Sequencing to Identify Lacustrine Haptophytes in the Canadian Prairies: Significance for Temperature Proxy Applications

“…Interestingly, when comparing different in situ calibrations from lakes containing Group I (D'Andrea et al, , ; Longo et al, ; Zink et al, ) and Group II haptophytes (Toney et al, ; Wang & Liu, ), the slopes converge on a smaller range (0.02‐0.028), suggesting that the temperature dependency is likely more consistent in the natural environment and among different taxa from Group I and Group II haptophyte species. Differences in temperature dependency in cultures versus the natural environment have been observed for both marine and non‐marine haptophyte taxa, which may be linked to differences in physiological conditions/status (e.g., Araie et al, ; Ono et al, ; Sun et al, ; Theroux et al, ). In addition, the y ‐intercept varies between culture and environmental calibrations (Figure ).…”

“…In the present study, we sought to identify these additional LCA-producing haptophyte species via genomic analyses targeting the haptophyte 18S rRNA gene. Although Sanger sequencing is commonly used in environmental genomic studies to identify haptophyte species in lacustrine environments (e.g., Araie et al, 2018;Coolen et al, 2004;D'Andrea et al, 2016;Theroux et al, 2010), we opted for next-generation sequencing (NGS). NGS has been previously employed when studying haptophytes, providing many novel insights into the taxonomy, phylogeny, diversity, and ecology of these algae (Egge et al, 2015;Endo et al, 2018;Gran-Stadniczeñko et al, 2017;Shalchian-Tabrizi et al, 2011;Theroux et al, 2012).…”

Abrupt Freshening Since the Early Little Ice Age in Lake Sayram of Arid Central Asia Inferred From an Alkenone Isomer Proxy

“…(a) Abundance of Group I Isochrysidales (relative to Group II) versus salinity and logistic probability for the presence of Group I and II Isochrysidales (Isochrysidales DNA data of lakes are from Araie et al, 2018; D'Andrea et al, 2016; Kaiser et al, 2019; Plancq et al, 2018, 2019; Richter et al, 2019; Theroux et al, 2010; K. J. Wang, O'Donnell, et al, 2019; Y. Yao et al, 2019; Table S2). (b) Three‐dimensional diagram showing the published LCA indices (RIK 37 , RIK 38E , and C 38 Me/C 38 Et) between Groups I (Longo et al, 2016, 2018; K. J. Wang, O'Donnell, et al, 2019; Y. Yao et al, 2019) and II ( R. lamellosa , I. galbana , and T. lutea ; Zheng et al, 2019).…”

Alkenone Distributions and Hydrogen Isotope Ratios Show Changes in Haptophyte Species and Source Water in the Holocene Baltic Sea

“…Haptophytes are extremely diverse, with over 300 documented species (Jordan & Chamberlain, 1997). Certain species of the order Isochrysidales are the only known producers of long-chain alkenones and polyunsaturated methyl and ethyl ketones with chain lengths between 35 and 42 carbon atoms (de Leeuw et al, 1980;Volkman et al, 1980;Theroux et al, 2010;Araie et al, 2018). These long-chain alkenones are often well preserved in sediments and provide highly useful proxies to understand past changes in global climate, in particular the U K′ 37 index, a proxy for sea surface temperature (Brassell et al, 1986;Müller et al, 1998;Prahl & Wakeham, 1987;Tierney & Tingley, 2018).…”