Abstract
Owing to the hierarchical organization of biology, from genomes over transcriptomes and proteomes down to metabolomes, there is continuous debate about the extent to which data and interpretations derived from one level, e.g. the transcriptome, are in agreement with other levels, e.g. the metabolome. Here, we tested the effect of ocean acidification (OA; 400 vs. 1000 μatm CO2) and its modulation by light intensity (50 vs. 300 μmol photons m-2 s-1) on the biomass composition (represented by 75 key metabolites) of diploid and haploid life-cycle stages of the coccolithophore Emiliania huxleyi (RCC1216 and RCC1217) and compared these data with interpretations from previous physiological and gene expression screenings. The metabolite patterns showed minor responses to OA in both life-cycle stages. Whereas previous gene expression analyses suggested that the observed increased biomass buildup derived from lipid and carbohydrate storage, this dataset suggests that OA slightly increases overall biomass of cells, but does not significantly alter their metabolite composition. Generally, light was shown to be a more dominant driver of metabolite composition than OA, increasing the relative abundances of amino acids, mannitol and storage lipids, and shifting pigment contents to accommodate increased irradiance levels. The diploid stage was shown to contain vastly more osmolytes and mannitol than the haploid stage, which in turn had a higher relative content of amino acids, especially aromatic ones. Besides the differences between the investigated cell types and the general effects on biomass buildup, our analyses indicate that OA imposes only negligible effects on E. huxleyi´s biomass composition.
Highlights
The globally distributed coccolithophore Emiliania huxleyi is an intensively investigated microalga, especially because of its dual role in biogeochemistry
In the course of intensified research over the past decades, E. huxleyi has become a model organism for calcifying marine microalgae, because it is globally distributed with many ecotypes from different ocean provinces [5], or because many of these ecotypes were shown to be highly responsive to ocean acidification [6,7,8], and because its genome has been sequenced [5], enabling the exploitation of wider ‘omics’ approaches
We investigated the effects of Ocean Acidification’ (OA) on the metabolic composition of calcifying diploid and noncalcifying haploid E. huxleyi life-cycle stages and their modulation by light, i.e. cellular energization
Summary
The globally distributed coccolithophore Emiliania huxleyi is an intensively investigated microalga, especially because of its dual role in biogeochemistry. Besides being photosynthetic phytoplankton that contributes to the so-called ‘organic carbon pump’ of the oceans, it is able to produce elaborately shaped CaCO3 shells. The heavy calcite material aggregates with various other marine particles, and enhances their export to depth In this way, marine calcifiers strongly influence the relative strengths of the oceanic carbon pumps [2]. In the course of intensified research over the past decades, E. huxleyi has become a model organism for calcifying marine microalgae, because it is globally distributed with many ecotypes from different ocean provinces [5], or because many of these ecotypes were shown to be highly responsive to ocean acidification [6,7,8], and because its genome has been sequenced [5], enabling the exploitation of wider ‘omics’ approaches. RNA- and protein-based approaches have since delivered insights into the ecophysiology of the life-cycle stages of E. huxleyi [9,10] and the responses of this microalga towards a set of diverse environmental triggers and stimuli, like prolonged darkness [11], increased light intensity [12], nutrient starvation [13,14,15,16,17] and OA [18,19,20,21,22,23]
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