Metabolomic Profiling of 13 Diatom Cultures and Their Adaptation to Nitrate-Limited Growth Conditions

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.

Metabolome Analysis Reveals Betaine Lipids as Major Source for Triglyceride Formation, and the Accumulation of Sedoheptulose during Nitrogen-Starvation of Phaeodactylum tricornutum

“…We focused on this Phaeodactylum strain, because of its ability to grow in medium with low salinity and therefore being suited for wastewater cultivation strategies. Although the analysis of lipid remodeling triggered by stress conditions, especially N-starvation, is in focus of algae research [ 9 , 17 , 43 , 44 ], analysis of lipid molecular species under stress conditions, acyl-CoA profiling together with metabolome analysis are yet missing for most of the P . tricornutum strains.…”

“…Under N-depleted conditions, TAG was mainly composed of 16:0 and 16:1, just minor species with one 20:5(n-3) were determined and the main TAG species were 48:1, 48:2 and 48:3 ( Fig 2A ). TAG profiling of different marine microalgae also revealed a high amount of C16 FA [ 44 , 53 ]. In addition, in our study the precursor DAG primarily contained 16:0 and 16:1 and no 20:5(n-3) was detectable ( Fig 2A ).…”

Analytical considerations for (un)‐targeted metabolomic studies with special focus on forensic applications

“…There are different modified IS-based normalization strategies, which can be applied in metabolomics. Normalization of all analytes to the same IS, 46 to several IS based on chemical similarity and RT 17,47 or application of an IS-based normalization process. 48,49 Normalization of each metabolite to a single IS assumes that all compounds experience the same variations as the IS.…”

Exploring Valuable Lipids in Diatoms

“…It is advanced by the rapid development of sensitive and high resolution of mass spectrometry as well as lipid identification database, which allows for high-throughput analysis and accurate lipid profiling (Yamada et al, 2013). Processing of lipidomic data can also be achieved with the development of bioinformatics (Niemelä et al, 2009), and data could be visualized in multiple ways, such as principle component analysis plot and heat map, which enables sample classifications and a holistic overview (Bromke et al, 2015). However, the problem is the separation efficiency and ionization of various lipid classes, which could not be fully achieved by ultra-high performance liquid chromatography.…”