Abstract
Diatoms are very efficient in their use of available nutrients. Changes in nutrient availability influence the metabolism and the composition of the cell constituents. Since diatoms are valuable candidates to search for oil producing algae, measurements of diatom-produced compounds can be very useful for biotechnology. In order to explore the diversity of lipophilic compounds produced by diatoms, we describe the results from an analysis of 13 diatom strains. With the help of a lipidomics platform, which combines an UPLC separation with a high resolution/high mass accuracy mass spectrometer, we were able to measure and annotate 142 lipid species. Out of these, 32 were present in all 13 cultures. The annotated lipid features belong to six classes of glycerolipids. The data obtained from the measurements were used to create lipidomic profiles. The metabolomic overview of analysed cultures is amended by the measurement of 96 polar compounds. To further increase the lipid diversity and gain insight into metabolomic adaptation to nitrogen limitation, diatoms were cultured in media with high and low concentrations of nitrate. The growth in nitrogen-deplete or nitrogen-replete conditions affects metabolite accumulation but has no major influence on the species-specific metabolomic profile. Thus, the genetic component is stronger in determining metabolic patterns than nitrogen levels. Therefore, lipid profiling is powerful enough to be used as a molecular fingerprint for diatom cultures. Furthermore, an increase of triacylglycerol (TAG) accumulation was observed in low nitrogen samples, although this trend was not consistent across all 13 diatom strains. Overall, our results expand the current understanding of metabolomics diversity in diatoms and confirm their potential value for producing lipids for either bioenergy or as feed stock.
Highlights
Diatoms are eukaryotic phototrophs and are able to very efficiently sequester water-dissolved carbon dioxide
Diatom starter cultures were obtained from National Center for Marine Algae and Microbiota in Bigelow, USA (Thalassiosira pseudonana CCMP1335, T. pseudonana CCMP1007 and T. weissflogii CCMP1587, T. weissflogii CCMP1336, Chaetoceros simplex CCMP200) and from a collection at University of Texas at Austin (Amphitetras antediluviana, ECT3627; Biddulphia biddulphiana, ECT3902; Cerataulina daemon, AP8; Eunotogramma sp., AP8Eunoto; Hemiaulus sinensis, 24I10-1AHemi; Leptocylindrus danicus, ECT3929araphid3; Rhizosolenia setigera, 25VI12-2ARhizo; Thalassionema frauenfeldii, ECT3929ThalXL)
To induce changes in lipid metabolism of diatoms, they were cultivated in standard f/2 medium [24] as well as in this medium containing only 20% of the f/2-medium’s nitrate (176 μM)
Summary
Diatoms are eukaryotic phototrophs and are able to very efficiently sequester water-dissolved carbon dioxide. Diatoms are very efficient at nutrient utilization and successful organisms in various environments [8] but can be readily adapted into prolific cultures; in these artificial conditions they often outcompete other algae in mixed cultures [9,10]. They are relatively resistant to various pathogens [11,12]. The genetic transformation of diatoms was initiated with the aim of improving oil production [14] This approach might be very promising especially with the development of genomics tools for diatoms [15,16,17,18,19]. Marine algae synthesize diverse lipids, such as phosphatidylcholine, which might be important for food or feed production [20]
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