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Metabolic profiling identifies trehalose as an abundant and diurnally fluctuating metabolite in the microalga Ostreococcus tauri

View Article: PubMed Central - PubMed

ABSTRACT

Introduction: The picoeukaryotic alga Ostreococcus tauri (Chlorophyta) belongs to the widespread group of marine prasinophytes. Despite its ecological importance, little is known about the metabolism of this alga.

Objectives: In this work, changes in the metabolome were quantified when O. tauri was grown under alternating cycles of 12 h light and 12 h darkness.

Methods: Algal metabolism was analyzed by gas chromatography-mass spectrometry. Using fluorescence-activated cell sorting, the bacteria associated with O. tauri were depleted to below 0.1% of total cells at the time of metabolic profiling.

Results: Of 111 metabolites quantified over light–dark cycles, 20 (18%) showed clear diurnal variations. The strongest fluctuations were found for trehalose. With an intracellular concentration of 1.6 mM in the dark, this disaccharide was six times more abundant at night than during the day. This fluctuation pattern of trehalose may be a consequence of starch degradation or of the synchronized cell cycle. On the other hand, maltose (and also sucrose) was below the detection limit (~10 μM). Accumulation of glycine in the light is in agreement with the presence of a classical glycolate pathway of photorespiration. We also provide evidence for the presence of fatty acid methyl and ethyl esters in O. tauri.

Conclusions: This study shows how the metabolism of O. tauri adapts to day and night and gives new insights into the configuration of the carbon metabolism. In addition, several less common metabolites were identified.

Electronic supplementary material: The online version of this article (doi:10.1007/s11306-017-1203-1) contains supplementary material, which is available to authorized users.

No MeSH data available.


Quantification of cell density and bacterial content of O. tauri cultures by flow cytometry. a Example of a flow cytogram of an O. tauri culture (density plot). For illustration, a sample with a significant portion of bacteria (20%) is shown. b Cell densities obtained by flow cytometry compared to cell densities obtained by hemocytometer counting of different dilutions of 16-day old O. tauri cultures. In both cases, total cells were counted. For the flow-cytometric measurements, samples with the indicated cell densities were prepared with ASWO medium, and two technical replicates were counted. For hemocytometry, three independent biological samples with a cell density of ~7 × 106 cells ml−1 were counted (using five technical replicates per biological replicate), and the cell densities of the remaining samples were calculated. Mean ± standard deviation is shown
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Fig1: Quantification of cell density and bacterial content of O. tauri cultures by flow cytometry. a Example of a flow cytogram of an O. tauri culture (density plot). For illustration, a sample with a significant portion of bacteria (20%) is shown. b Cell densities obtained by flow cytometry compared to cell densities obtained by hemocytometer counting of different dilutions of 16-day old O. tauri cultures. In both cases, total cells were counted. For the flow-cytometric measurements, samples with the indicated cell densities were prepared with ASWO medium, and two technical replicates were counted. For hemocytometry, three independent biological samples with a cell density of ~7 × 106 cells ml−1 were counted (using five technical replicates per biological replicate), and the cell densities of the remaining samples were calculated. Mean ± standard deviation is shown

Mentions: As a first step towards the metabolic profiling of the marine microalga O. tauri, we used flow cytometry to simultaneously quantify the cell densities of algae and bacteria present in the same culture. For this purpose, cells were fixed with glutaraldehyde and stained with the DNA-binding dye SYBR Green I (see Sect. 2 for details). Samples were then analyzed by flow cytometry using one channel that detects SYBR Green I fluorescence, and one channel that detects chlorophyll fluorescence (Fig. 1a). In the resulting flow cytogram, O. tauri cells are represented by events that show high levels of both chlorophyll and bound SYBR Green I, while non-photosynthetic cells (mostly bacteria) only show a high amount of SYBR Green I (Fig. 1a).


Metabolic profiling identifies trehalose as an abundant and diurnally fluctuating metabolite in the microalga Ostreococcus tauri
Quantification of cell density and bacterial content of O. tauri cultures by flow cytometry. a Example of a flow cytogram of an O. tauri culture (density plot). For illustration, a sample with a significant portion of bacteria (20%) is shown. b Cell densities obtained by flow cytometry compared to cell densities obtained by hemocytometer counting of different dilutions of 16-day old O. tauri cultures. In both cases, total cells were counted. For the flow-cytometric measurements, samples with the indicated cell densities were prepared with ASWO medium, and two technical replicates were counted. For hemocytometry, three independent biological samples with a cell density of ~7 × 106 cells ml−1 were counted (using five technical replicates per biological replicate), and the cell densities of the remaining samples were calculated. Mean ± standard deviation is shown
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5392535&req=5

Fig1: Quantification of cell density and bacterial content of O. tauri cultures by flow cytometry. a Example of a flow cytogram of an O. tauri culture (density plot). For illustration, a sample with a significant portion of bacteria (20%) is shown. b Cell densities obtained by flow cytometry compared to cell densities obtained by hemocytometer counting of different dilutions of 16-day old O. tauri cultures. In both cases, total cells were counted. For the flow-cytometric measurements, samples with the indicated cell densities were prepared with ASWO medium, and two technical replicates were counted. For hemocytometry, three independent biological samples with a cell density of ~7 × 106 cells ml−1 were counted (using five technical replicates per biological replicate), and the cell densities of the remaining samples were calculated. Mean ± standard deviation is shown
Mentions: As a first step towards the metabolic profiling of the marine microalga O. tauri, we used flow cytometry to simultaneously quantify the cell densities of algae and bacteria present in the same culture. For this purpose, cells were fixed with glutaraldehyde and stained with the DNA-binding dye SYBR Green I (see Sect. 2 for details). Samples were then analyzed by flow cytometry using one channel that detects SYBR Green I fluorescence, and one channel that detects chlorophyll fluorescence (Fig. 1a). In the resulting flow cytogram, O. tauri cells are represented by events that show high levels of both chlorophyll and bound SYBR Green I, while non-photosynthetic cells (mostly bacteria) only show a high amount of SYBR Green I (Fig. 1a).

View Article: PubMed Central - PubMed

ABSTRACT

Introduction: The picoeukaryotic alga Ostreococcus tauri (Chlorophyta) belongs to the widespread group of marine prasinophytes. Despite its ecological importance, little is known about the metabolism of this alga.

Objectives: In this work, changes in the metabolome were quantified when O. tauri was grown under alternating cycles of 12 h light and 12 h darkness.

Methods: Algal metabolism was analyzed by gas chromatography-mass spectrometry. Using fluorescence-activated cell sorting, the bacteria associated with O. tauri were depleted to below 0.1% of total cells at the time of metabolic profiling.

Results: Of 111 metabolites quantified over light–dark cycles, 20 (18%) showed clear diurnal variations. The strongest fluctuations were found for trehalose. With an intracellular concentration of 1.6 mM in the dark, this disaccharide was six times more abundant at night than during the day. This fluctuation pattern of trehalose may be a consequence of starch degradation or of the synchronized cell cycle. On the other hand, maltose (and also sucrose) was below the detection limit (~10 μM). Accumulation of glycine in the light is in agreement with the presence of a classical glycolate pathway of photorespiration. We also provide evidence for the presence of fatty acid methyl and ethyl esters in O. tauri.

Conclusions: This study shows how the metabolism of O. tauri adapts to day and night and gives new insights into the configuration of the carbon metabolism. In addition, several less common metabolites were identified.

Electronic supplementary material: The online version of this article (doi:10.1007/s11306-017-1203-1) contains supplementary material, which is available to authorized users.

No MeSH data available.