Culturing of the first 37:4 predominant lacustrine haptophyte: Geochemical, biochemical, and genetic implications

Abstract

Long chain alkenones (LCAs) are potential biomarkers for quantitative paleotemperature reconstructions from lacustrine environments. However, progress in this area has been hindered, because the conditions necessary for the growth of haptophytes responsible for alkenone distributions in lake sediments: the predominance of C 37:4 LCA are not known. Here we report the first enrichment culturing of a novel haptophyte phylotype (Hap-A) from Lake George, ND that produces predominantly C 37:4-LCA. Hap-A was enriched from its resting phase collected from deep sediments rather than from water column samples. In contrast, enrichments from near surface water yielded a different haptophyte phylotype (Hap-B), closely related to Chrysotila lamellosa and Pseudoisochrysis paradoxa, which does not display C 37:4-LCA predominance (similar enrichments have been reported previously). The LCA profile in sediments resembles that of enrichments containing Hap-A, suggesting that Hap-A is the dominant alkenone producer of the sedimentary LCAs. In enrichments, increased lighting appeared to be crucial for triggering alkenone production. Both U 37 K and U 38 K indices show a promising, positive relationship with temperature for Hap-A in enrichments, but the offset from the environmental calibration suggests that other factors (e.g., the growth stage or nutrients) may influence the absolute U 37 K value. Based on 18S rRNA gene analyses, several lakes from the Northern Great Plains, as well as Pyramid Lake, NV and Tso Ur, Tibetan Plateau, China contain the same two haptophyte phylotypes. Analysis of surface sediment from the Great Plains lakes show the Hap-A-type LCA distribution, whereas Pyramid and Tso Ur show the Hap-B type distribution. Waters of the Great Plain lakes are dominated by sulfate ions, whereas those Pyramid and Tso Ur are dominated by carbonate ions, suggesting that the sulfate to carbonate ratio may be a determining factor for the dominance of the Hap-A and Hap-B phylotypes in natural settings.