Suitability of Phytosterols Alongside Fatty Acids as Chemotaxonomic Biomarkers for Phytoplankton

Abstract

The composition and abundance of phytoplankton is an important factor defining ecological status of marine and freshwater ecosystems. Chemotaxonomic markers (e.g., pigments and fatty acids) are needed for monitoring changes in a phytoplankton community and to know the nutritional quality of seston for herbivorous zooplankton. Here we investigated the suitability of sterols along with fatty acids as chemotaxonomic markers using multivariate statistics, by analyzing the sterol and fatty acid composition of 10 different phytoplankton classes including altogether 37 strains isolated from freshwater lakes. We were able to detect a total of 47 fatty acids and 29 sterols in our phytoplankton samples, which both differed statistically significantly between phytoplankton classes. Due to the high variation of fatty acid composition among Cyanophyceae, taxonomical differentiation increased when Cyanophyceae were excluded from statistical analysis. Sterol composition was more heterogeneous within class than fatty acids and did not improve separation of phytoplankton classes when used alongside fatty acids. However, we conclude that sterols can provide additional information on the abundance of specific genera within a class which can be generated by using fatty acids. For example, whereas high C16 ω-3 PUFA (polyunsaturated fatty acid) indicates the presence of Chlorophyceae, a simultaneous high amount of ergosterol could specify the presence of Chlamydomonas spp. (Chlorophyceae). Additionally, we found specific 4α-methyl sterols for distinct Dinophyceae genera, suggesting that 4α-methyl sterols can potentially separate freshwater dinoflagellates from each other.

The Importance of Phytoplankton Biomolecule Availability for Secondary Production

“…The study of Taipale et al (2016a) describes sterol profiles for several freshwater phytoplankton strains and concludes that in contrary to FA synthesis, their sterol synthesis is in general less related to phylogeny. However, the study of Taipale et al (2016a) does not evaluate the nutritional quality of sterols for zooplankton, but that is reported by MartinCreuzburg et al (2009MartinCreuzburg et al ( , 2014 and Martin-Creuzburg and Von Elert (2004).…”

“…Herbivorous zooplankton diet consists of various phytoplankton species, which differ in their grazing resistance (e.g., size, shape, armor, and toxins) and nutritional quality (Taipale et al, 2013(Taipale et al, , 2016aJonasdottir, 2015). The relative carbon (C) and nitrogen (N) contents are more or less the same in phytoplankton and zooplankton, and therefore are not often considered as limiting nutrients for zooplankton (Hessen et al, 2013).…”

Trophic Transfer of Macroalgal Fatty Acids in Two Urchin Species: Digestion, Egestion, and Tissue Building

“…The following heating program, based on Taipale et al (2013), was used: 50 • C was maintained for 1 min, then the temperature was increased at a rate of 10 • C min −1 to 140 • C, after which the warming rate was adjusted to 1.40 • C min −1 to 190 • C and held for 3 min, followed by 5 • C min −1 to 220 • C, and finally heated at 13 • C min −1 to 240 and held for 2 min. The FA were identified from relative retention times and specific ions and then quantified using peaks of the major ions (Taipale et al, 2016). Concentrations of FAs were calculated based on calibration curves (Pearson correlation coefficient ≥ 0.99) of serial dilutions of known standard FAME mixtures (GLC standard mixture 566C, Nu-Chek Prep, Elysian, MN, USA).…”

Interplay of community dynamics, temperature, and productivity on the hydrogen isotope signatures of lipid biomarkers

“…Phytol and short-chain fatty acids are produced by all photoautotrophs and may be dominated by phytoplankton that are optimized to grow under the nutrient regimes of each system, while relatively more of the brassicasterol may come from taxa that are nutrientstressed and relying more on the pentose phosphate pathway than photosystem I. Alternatively, the difference in α brassicasterol-water values between the two lakes could be due to variable contributions of brassicasterol from different phytoplankton sources. Even though brassicasterol is produced by fewer organisms than short-chain fatty acids and phytol, it still has multiple sources (Volkman et al, 1998;Volkman, 2003;Rampen et al, 2010;Taipale et al, 2016). Species-specific differences in hydrogen isotope fractionation have not been observed for sterols but have been reported for fatty acids and alkenones (Schouten et al, 2006;Zhang and Sachs, 2007), making this an unconstrained possibility that could be responsible for the difference in α brassicasterol-water between the oligotrophic and eutrophic lake.…”

“…Brassicasterol is a sterol that is commonly used as a biomarker for diatoms, although it has also been detected in some non-diatom eukaryotic phytoplankton (Volkman et al, 1998;Volkman, 2003;Rampen et al, 2010;Taipale et al, 2016) and occasionally in plant oils (Zarrouk et al, 2009). Since brassicasterol is not produced by bacterial sources, it seems improbable that the 25 ‰ (Greifen) and 19 ‰ (Lucerne) decreases in its δ 2 H values from April to May could be due to proportionately greater heterotrophic contributions during the winter, as suggested for fatty acids.…”