Diacylglyceryltrimethylhomoserine Research Articles

Effects of ultra-high pressure processing on microstructure, water distribution and lipidomics variances of Arabica coffee beans

The emerging non-thermal technique of ultra-high pressure (UHP) processing technology has seen significant advancements in food processing in recent years. The present study aimed to analyze the impact of UHP (100–300 MPa) processing on the color, microstructure, water distribution, and lipidomics variations of wet-processed Arabica coffee beans. The results indicated that the brightness and chromatic aberration of coffee beans were significantly altered by UHP processing, while other color parameters remained relatively unaffected. Scanning electron microscope examinations showed that UHP processing caused compression, compaction, and even collapse of the pore structure within coffee beans. Compared to wet-processed Arabica coffee beans, UHP processing promoted a more even water distribution and facilitated the conversion of bound and immobilized water into free water, with the maximum effect observed during UHP-200 treatment. Lipidomics analysis indicated that triacylglycerol (TAG, 24.75 %) and diacylglyceryl trimethylhomoserine (DGTS, 11.23 %). Notably, UHP-100, UHP-200, and UHP-300 samples exhibited 238, 191, and 788 differentially expressed lipids. The carbon chain length and degree of unsaturation of all differentially expressed lipids exhibited a pressure-dependent decrease with intricate interrelationships.

Comprehensive characterization of extracellular vesicles produced by environmental (Neff) and clinical (T4) strains of Acanthamoeba castellanii.

We conducted a comprehensive comparative analysis of extracellular vesicles (EVs) from two Acanthamoeba castellanii strains, Neff (environmental) and T4 (clinical). Morphological analysis via transmission electron microscopy revealed slightly larger Neff EVs (average = 194.5 nm) compared to more polydisperse T4 EVs (average = 168.4 nm). Nanoparticle tracking analysis (NTA) and dynamic light scattering validated these differences. Proteomic analysis of the EVs identified 1,352 proteins, with 1,107 common, 161 exclusive in Neff, and 84 exclusively in T4 EVs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) mapping revealed distinct molecular functions and biological processes and notably, the T4 EVs enrichment in serine proteases, aligned with its pathogenicity. Lipidomic analysis revealed a prevalence of unsaturated lipid species in Neff EVs, particularly triacylglycerols, phosphatidylethanolamines (PEs), and phosphatidylserine, while T4 EVs were enriched in diacylglycerols and diacylglyceryl trimethylhomoserine, phosphatidylcholine and less unsaturated PEs, suggesting differences in lipid metabolism and membrane permeability. Metabolomic analysis indicated Neff EVs enrichment in glycerolipid metabolism, glycolysis, and nucleotide synthesis, while T4 EVs, methionine metabolism. Furthermore, RNA-seq of EVs revealed differential transcript between the strains, with Neff EVs enriched in transcripts related to gluconeogenesis and translation, suggesting gene regulation and metabolic shift, while in the T4 EVs transcripts were associated with signal transduction and protein kinase activity, indicating rapid responses to environmental changes. In this novel study, data integration highlighted the differences in enzyme profiles, metabolic processes, and potential origins of EVs in the two strains shedding light on the diversity and complexity of A. castellanii EVs and having implications for understanding host-pathogen interactions and developing targeted interventions for Acanthamoeba-related diseases.IMPORTANCEA comprehensive and fully comparative analysis of extracellular vesicles (EVs) from two Acanthamoeba castellanii strains of distinct virulence, a Neff (environmental) and T4 (clinical), revealed striking differences in their morphology and protein, lipid, metabolites, and transcripts levels. Data integration highlighted the differences in enzyme profiles, metabolic processes, and potential distinct origin of EVs from both strains, shedding light on the diversity and complexity of A. castellanii EVs, with direct implications for understanding host-pathogen interactions, disease mechanisms, and developing new therapies for the clinical intervention of Acanthamoeba-related diseases.

Polar Lipids of Marine Microalgae Nannochloropsis oceanica and Chlorococcum amblystomatis Mitigate the LPS-Induced Pro-Inflammatory Response in Macrophages.

Microalgae are recognized as a relevant source of bioactive compounds. Among these bioactive products, lipids, mainly glycolipids, have been shown to present immunomodulatory properties with the potential to mitigate chronic inflammation. This study aimed to evaluate the anti-inflammatory effect of polar lipids isolated from Nannochloropsis oceanica and Chlorococcum amblystomatis. Three fractions enriched in (1) digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG), (2) monogalactosyldiacylglycerol (MGDG), and (3) diacylglyceryl-trimethylhomoserine (DGTS) and phospholipids (PL) were obtained from the total lipid extracts (TE) of N. oceanica and C. amblystomatis, and their anti-inflammatory effect was assessed by analyzing their capacity to counteract nitric oxide (NO) production and transcription of pro-inflammatory genes Nos2, Ptgs2, Tnfa, and Il1b in lipopolysaccharide (LPS)-activated macrophages. For both microalgae, TE and Fractions 1 and 3 strongly inhibited NO production, although to different extents. A strong reduction in the LPS-induced transcription of Nos2, Ptgs2, Tnfa, and Il1b was observed for N. oceanica and C. amblystomatis lipids. The most active fractions were the DGTS-and-PL-enriched fraction from N. oceanica and the DGDG-and-SQDG-enriched fraction from C. amblystomatis. Our results reveal that microalgae lipids have strong anti-inflammatory capacity and may be explored as functional ingredients or nutraceuticals, offering a natural solution to tackle chronic inflammation-associated diseases.

Differences in the lipid metabolism profile and clinical characteristics between eosinophilic and non-eosinophilic acute exacerbation of chronic obstructive pulmonary disease.

Objective: In this study, we aimed to investigate the differences in serum lipid metabolite profiles and their relationship with clinical characteristics between patients with eosinophilic and non-eosinophilic AECOPD. Methods: A total of 71 AECOPD patients were enrolled. Eosinophilic AECOPD was defined as blood EOS% ≥ 2% (n = 23), while non-eosinophilic AECOPD, as blood EOS< 2% (n = 48). Clinical data were collected, and serum lipid metabolism profiles were detected by liquid chromatography-mass spectrometry (LC-MS). The XCMS software package was used to pre-process the raw data, and then, lipid metabolite identification was achieved through a spectral match using LipidBlast library. Differences in lipid profiles and clinical features between eosinophilic and non-eosinophilic groups were analyzed by generalized linear regression. The least absolute shrinkage and selection operator (LASSO) was applied to screen the most characteristic lipid markers for the eosinophilic phenotype. Results: Eosinophilic AECOPD patients had less hypercapnic respiratory failures, less ICU admissions, a shorter length of stay in the hospital, and a lower fibrinogen level. In the lipid metabolism profiles, 32 significantly different lipid metabolites were screened through a t-test adjusted by using FDR (FDR-adjusted p < 0.05 and VIP> 1). Nine differential lipid metabolites were found to be associated with the three clinical features, namely, hypercapnia respiratory failure, ICU admission, and fibrinogen in further integration analysis. The species of triacylglycerol (TAG), phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and diacylglyceryl trimethylhomoserine (DGTS) were high in these eosinophilic AECOPD. The LASSO was applied, and three lipid metabolites were retained, namely, LPC (16:0), TAG (17:0/17:2/17:2), and LPC (20:2). The logistic regression model was fitted using these three markers, and the area under the ROC curve of the model was 0.834 (95% CI: 0.740-0.929). Conclusion: Patients with eosinophilic AECOPD had a unique lipid metabolism status. Species of TAGs and LPCs were significantly increased in this phenotype and were associated with better clinical outcomes.

Do betaine lipids replace phosphatidylcholine as fatty acid editing hubs in microalgae?

Acyl editing refers to a deacylation and reacylation cycle on a lipid, which allows for fatty acid desaturation and modification prior to being removed and incorporated into other pools. Acyl editing is an important determinant of glycerolipid synthesis and has been well-characterized in land plants, thus this review begins with an overview of acyl editing in plants. Much less is known about acyl editing in algae, including the extent to which acyl editing impacts lipid synthesis and on which lipid substrate(s) it occurs. This review compares what is known about acyl editing on its major hub phosphatidylcholine (PC) in land plants with the evidence for acyl editing of betaine lipids such as diacylglyceryltrimethylhomoserine (DGTS), the structural analog that replaces PC in several species of microalgae. In land plants, PC is also known to be a major source of fatty acids and diacylglycerol (DAG) for synthesis of the neutral lipid triacylglycerol (TAG). We review the evidence that DGTS contributes substantially to TAG accumulation in algae as a source of fatty acids, but not as a precursor to DAG. We conclude with evidence of acyl editing on other membrane lipid substrates in plants and algae apart from PC or DGTS, and discuss future analyses to elucidate the role of DGTS and other betaine lipids in acyl editing in microalgae.

13C-labeling reveals how membrane lipid components contribute to triacylglycerol accumulation in Chlamydomonas.

Lipid metabolism in microalgae has attracted much interest due to potential utilization of lipids as feedstocks for biofuels, nutraceuticals, and other high-value compounds. Chlamydomonas reinhardtii is a model organism for characterizing the synthesis of the neutral lipid triacylglycerol (TAG), from which biodiesel is made. While much of TAG accumulation under N-deprivation is the result of de novo fatty acid (FA) synthesis, recent work has revealed that approximately one-third of FAs, especially polyunsaturated FAs (PUFAs), come from preexisting membrane lipids. Here, we used 13C-isotopic labeling and mass spectrometry to analyze the turnover of glycerol backbones, headgroups, FAs, whole molecules, and molecular fragments of individual lipids. About one-third of the glyceryl backbones in TAG are derived from preexisting membrane lipids, as are approximately one-third of FAs. The different moieties of the major galactolipids turn over synchronously, while the FAs of diacylglyceryltrimethylhomoserine (DGTS), the most abundant extraplastidial lipid, turn over independently of the rest of the molecule. The major plastidic lipid monogalactosyldiacylglycerol (MGDG), whose predominant species is 18:3α/16:4, was previously shown to be a major source of PUFAs for TAG synthesis. This study reveals that MGDG turns over as whole molecules, the 18:3α/16:4 species is present in both DAG and TAG, and the positional distribution of these PUFAs is identical in MGDG, DAG, and TAG. We conclude that headgroup removal with subsequent acylation is the mechanism by which the major MGDG species is converted to TAG during N-deprivation. This has noteworthy implications for engineering the composition of microalgal TAG for food, fuel, and other applications.

Development of a lipid metabolism-related gene model to predict prognosis in patients with pancreatic cancer.

BACKGROUNDPancreatic cancer is a highly heterogeneous disease, making prognosis prediction challenging. Altered energy metabolism to satisfy uncontrolled proliferation and metastasis has become one of the most important markers of tumors. However, the specific regulatory mechanism and its effect on prognosis have not been fully elucidated.AIMTo construct a prognostic polygene signature of differentially expressed genes (DEGs) related to lipid metabolism.METHODSFirst, 9 tissue samples from patients with pancreatic cancer were collected and divided into a cancer group and a para-cancer group. All patient samples were subjected to metabolomics analysis based on liquid tandem chromatography quadrupole time of flight mass spectrometry. Then, mRNA expression profiles and corresponding clinical data of pancreatic cancer were downloaded from a public database. Least absolute shrinkage and selection operator Cox regression analysis was used to construct a multigene model for The Cancer Genome Atlas.RESULTSPrincipal component analysis and orthogonal projections to latent structures-discriminant analysis (OPLS-DA) based on lipid metabolomics analysis showed a clear distribution in different regions. A Euclidean distance matrix was used to calculate the quantitative value of differential metabolites. The permutation test of the OPLS-DA model for tumor tissue and paracancerous tissue indicated that the established model was consistent with the actual condition based on sample data. A bar plot showed significantly higher levels of the lipid metabolites phosphatidylcholine (PC), phosphatidyl ethanolamine (PE), phosphatidylethanol(PEtOH), phosphatidylmethanol (PMeOH), phosphatidylserine (PS) and diacylglyceryl trimethylhomoserine (DGTS) in tumor tissues than in paracancerous tissues. According to bubble plots, PC, PE, PEtOH, PMeOH, PS and DGTS were significantly higher in tumor tissues than in paracancerous tissues. In total, 12.3% (25/197) of genes related to lipid metabolism were differentially expressed between tumor tissues and adjacent paracancerous tissues. Six DEGs correlated with overall survival in univariate Cox regression analysis (P < 0.05), and a 4-gene signature model was developed to divide patients into two risk groups, with patients in the high-risk group having significantly lower overall survival than those in the low-risk group (P < 0.05). ROC curve analysis confirmed the predictive power of the model.CONCLUSIONThis novel model comprising 4 lipid metabolism-related genes might assist clinicians in the prognostic evaluation of patients with pancreatic cancer.

Characterization of the Bubblegum acyl-CoA synthetase of Microchloropsis gaditana.

The metabolic pathways of glycerolipids are well described in cells containing chloroplasts limited by a two-membrane envelope but not in cells containing plastids limited by four membranes, including heterokonts. Fatty acids (FAs) produced in the plastid, palmitic and palmitoleic acids (16:0 and 16:1), are used in the cytosol for the synthesis of glycerolipids via various routes, requiring multiple acyl-Coenzyme A (CoA) synthetases (ACS). Here, we characterized an ACS of the Bubblegum subfamily in the photosynthetic eukaryote Microchloropsis gaditana, an oleaginous heterokont used for the production of lipids for multiple applications. Genome engineering with TALE-N allowed the generation of MgACSBG point mutations, but no knockout was obtained. Point mutations triggered an overall decrease of 16:1 in lipids, a specific increase of unsaturated 18-carbon acyls in phosphatidylcholine and decrease of 20-carbon acyls in the betaine lipid diacylglyceryl-trimethyl-homoserine. The profile of acyl-CoAs highlighted a decrease in 16:1-CoA and 18:3-CoA. Structural modeling supported that mutations affect accessibility of FA to the MgACSBG reaction site. Expression in yeast defective in acyl-CoA biosynthesis further confirmed that point mutations affect ACSBG activity. Altogether, this study supports a critical role of heterokont MgACSBG in the production of 16:1-CoA and 18:3-CoA. In M. gaditana mutants, the excess saturated and monounsaturated FAs were diverted to triacylglycerol, thus suggesting strategies to improve the oil content in this microalga.

Lipidomics profiling of skin surface lipids in senile pruritus

BackgroundSenile pruritus is common, yet its etiology remains unknown. Aging-associated skin barrier defects and skin surface lipid (SSL) alterations have been postulated to play important roles in its occurrence. In the present study, the lipidomic profiles of SSLs in elderly patients were examined to better understand the potential causes of senile pruritus.MethodsTransepidermal water loss (TEWL) was evaluated to assess the skin barrier function. The Ameliorated Kawashima Itch Scale score was used to measure the pruritus severity. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and multivariate data analysis were employed to investigate SSL alterations.ResultsThe results showed that senile pruritus patients had higher TEWL values than control subjects (13.13 ± 4.28 versus 6.71 ± 2.45, p < 0.01). LC-MS/MS revealed significant differences in the lipidomic profiles and identified 81 species of SSLs that differed between the two groups. Compared with control subjects, senile pruritus patients had increased levels of ceramides (Cers), diacylglycerols, fatty acids, phosphatidylcholines, phosphatidylethanolamines, phytosphingosines, sphingosines, diacylceryl-3-O-carboxyhydroxymethylcholine, diacylglyceryl trimethylhomoserine, and unsaturated free fatty acids, but decreased levels of triacylglycerol. Cer-EOS, Cer-NDS, and Cer-NS were positively correlated with TEWL value (p < 0.05). Pruritus severity score was positively correlated with sphingomyelin, Cer-NP, Cer-AS, Cer-NDS, and Cer-NS, but negatively correlated with Cer-BS, Cer-EODS, Cer-EOS, and Cer-AP.ConclusionsThe present study indicated that patients with senile pruritus have impaired skin barrier function and altered SSL composition. Certain SSL species identified in this study may be potential targets for future studies on the pathogenesis of senile pruritus.Trial registrationPeking University International Hospital (Number: YN2018QN04; date: January 2019).

Comparative Primary Metabolic and Lipidomic Profiling of Freshwater and Marine Synechocystis Strains Using by GC-MS and NanoESI-MS Analyses

Synechocystis strains are considered as valuable resources for production of useful metabolites. Comparative primary metabolic and lipidomic profiling of freshwater and marine Synechocystis strains is needed to understand the physiological characteristics of each strain at molecular level. In this study, we performed comparative primary metabolic and lipidomic profiling of freshwater Synechocystis sp. PCC 6803 (hereafter Synechocystis 6803) and marine Synechocystis sp. PCC 7338 (hereafter Synechocystis 7338) by using gas chromatography-mass spectrometry and nano electrospray ionization-mass spectrometry. Neophytadiene, phytol, monogalactosyldiacylglycerol (MGDG), and digalactosyldiacylglycerol (DGDG) were significantly higher in Synechocystis 6803. Levels of alanine, aspartic acid, valine, linoleic acid, linolenic acid, oleic acid, plamitic acid, stearic acid, glucosylglycerol, sucrose, phosphatidylglycerol (PG), and diacylglyceryltrimethylhomoserine (DGTS) (only detected in Synechocystis 7338) were significantly higher in Synechocystis 7338. Our results provide basic information to choose Synechocystis strains for various industrial usages, and also provide fundamental information on the future development of novel Synechocystis strains to produce high levels of specific metabolites by metabolic pathway modulation.

Re-modeling of foliar membrane lipids in a seagrass allows for growth in phosphorus-deplete conditions.

In this study, we used liquid chromatography high-resolution tandem mass spectrometry to analyze the lipidome of turtlegrass (Thalassia testudinum) leaves with either extremely high phosphorus content or extremely low phosphorus content. Most species of phospholipids were significantly down-regulated in phosphorus-deplete leaves, whereas diacylglyceryltrimethylhomoserine (DGTS), triglycerides (TG), galactolipid digalactosyldiacylglycerol (DGDG), certain species of glucuronosyldiacylglycerols (GlcADG), and certain species of sulfoquinovosyl diacylglycerol (SQDG) were significantly upregulated, accounting for the change in phosphorus content, as well as structural differences in the leaves of plants growing across regions of varying elemental availability. These data suggest that seagrasses are able to modify the phosphorus content in leaf membranes dependent upon environmental availability.

Gains and losses of metabolic function inferred from a phylotranscriptomic analysis of algae

Hidden Markov models representing 167 protein sequence families were used to infer the presence or absence of homologs within the transcriptomes of 183 algal species/strains. Statistical analyses of the distribution of HMM hits across major clades of algae, or at branch points on the phylogenetic tree of 98 chlorophytes, confirmed and extended known cases of metabolic loss and gain, most notably the loss of the mevalonate pathway for terpenoid synthesis in green algae but not, as we show here, in the streptophyte algae. Evidence for novel events was found as well, most remarkably in the recurrent and coordinated gain or loss of enzymes for the glyoxylate shunt. We find, as well, a curious pattern of retention (or re-gain) of HMG-CoA synthase in chlorophytes that have otherwise lost the mevalonate pathway, suggesting a novel, co-opted function for this enzyme in select lineages. Finally, we find striking, phylogenetically linked distributions of coding sequences for three pathways that synthesize the major membrane lipid phosphatidylcholine, and a complementary phylogenetic distribution pattern for the non-phospholipid DGTS (diacyl-glyceryl-trimethylhomoserine). Mass spectrometric analysis of lipids from 25 species was used to validate the inference of DGTS synthesis from sequence data.

The bZIP1 Transcription Factor Regulates Lipid Remodeling and Contributes to ER Stress Management in Chlamydomonas reinhardtii.

Endoplasmic reticulum (ER) stress is caused by the stress-induced accumulation of unfolded proteins in the ER. Here, we identified proteins and lipids that function downstream of the ER stress sensor INOSITOL-REQUIRING ENZYME1 (CrIRE1) that contributes to ER stress tolerance in Chlamydomonas (Chlamydomonas reinhardtii). Treatment with the ER stress inducer tunicamycin resulted in the splicing of a 32-nucleotide fragment of a basic leucine zipper 1 (bZIP1) transcription factor (CrbZIP1) mRNA by CrIRE1 that, in turn, resulted in the loss of the transmembrane domain in CrbZIP1, and the translocation of CrbZIP1 from the ER to the nucleus. Mutants deficient in CrbZIP1 failed to induce the expression of the unfolded protein response genes and grew poorly under ER stress. Levels of diacylglyceryltrimethylhomoserine (DGTS) and pinolenic acid (18:3Δ5,9,12) increased in the parental strains but decreased in the crbzip1 mutants under ER stress. A yeast one-hybrid assay revealed that CrbZIP1 activated the expression of enzymes catalyzing the biosynthesis of DGTS and pinolenic acid. Moreover, two lines harboring independent mutant alleles of Chlamydomonas desaturase (CrDES) failed to synthesize pinolenic acid and were more sensitive to ER stress than were their parental lines. Together, these results indicate that CrbZIP1 is a critical component of the ER stress response mediated by CrIRE1 in Chlamydomonas that acts via lipid remodeling.

Heat shock‐induced metabolic conversion of membrane lipids, fatty acids and volatile organic compounds of Pyropia haitanensis under different heat shock time

SUMMARYLipid metabolites play an important role in understanding the stress physiology of Pyropia haitanensis, and can be used to facilitate development of stress‐resistant Pyropia cultivars. Therefore, in this study ultra performance liquid chromatography coupled with quadrupole time of flight mass spectrometry (UPLC‐Q‐TOF‐MS) and gas chromatography–mass spectrometry (GC–MS) based metabolomics approaches were developed to screen the responses of lipid metabolites such as phospholipids, glycolipids, fatty acids and volatile organic compounds (VOCs) to different heat shock times. A total of 26 potential lipid biomarkers including Lyso‐monogalactosyldiacylglycerol (Lyso‐MGDG), Lyso‐digalactosyldiacylglycerol (Lyso‐DGDG), sulfoquinovosylmonoacylglycerols (SQMG), sulfoquinovosyldiacylglycerol (SQDG), diacylglyceryltrimethylhomoserine (DGTS), triacylglycerol (TAG), Lyso‐phosphatidicacid (Lyso‐PA), Lyso‐phosphatidylcholine (Lyso‐PC), Lyso‐phosphatidylethanolamine (Lyso‐PE), Lyso‐phosphatidylglycerol (Lyso‐PG), phosphatidylglycerol (PG), phosphatidylinositol (PI), and phosphatidylinositol phosphate (PIP) were identified, most of which responded to high temperature by reducing or increasing levels after stimulation for 1 h or 6 h. After times longer than 6 h, the levels of most lipids gradually recovered to the control group levels. Moreover, the balance of lipids and fatty acids transformation was disrupted. Overall, 11 total fatty acids (TFAs), 13 free fatty acids (FFAs) and 29 VOCs were identified during 0–72 h of high temperature stress. The FFAs, especially polyunsaturated C 20 fatty acids and VOCs, showed opposing change trends, indicating the transformation between C 20 fatty acids and VOCs. Overall, this study provides important insights into the metabolic variations of P. haitanensis under different heat shock time and the relationship between the conversion of lipids, fatty acids, and VOCs. The information provided herein will facilitate efficient development and improvement of Pyropia quality by producing cultivars resistant to high temperature.

Using community metabolomics as a new approach to discriminate marine microbial particulate organic matter in the western English Channel

Metabolomics provides an unbiased assessment of a wide range of metabolites and is an emerging ‘omics technique in the marine sciences. We use ‘non-targeted’ community metabolomics to determine patterns in metabolite profiles associated with particulate organic matter (POM) at four locations from two long-term monitoring stations (L4 and E1) in the western English Channel. The polar metabolite fractions were measured using ultra-high performance liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (UHPLC-FT-ICR-MS), and the lipid fractions by direct infusion Fourier transform ion cyclotron resonance mass spectrometry (DI-FT-ICR-MS); these were then analysed to statistically compare the metabolite distributions. Results show significantly different profiles of metabolites across the four locations with the largest differences for both the polar and lipid fractions found between the two stations relative to the smaller differences associated with depth. We putatively annotate the most discriminant metabolites revealing a range of amino-acid derivatives, diacylglyceryltrimethylhomoserine (DGTS) lipids, oxidised fatty acids (oxylipins), glycosylated compounds, oligohexoses, phospholipids, triacylglycerides (TAGs) and oxidised TAGs. The majority of the polar metabolites were most abundant in the surface waters at L4 and least abundant in the deep waters at E1 (E1-70m). In contrast, the oxidised TAGs were more abundant at E1 and most abundant at E1-70m. The differentiated metabolites are discussed in relation to the health of the phytoplankton as indicated by nutrients, carbon and chlorophyll, and to the dominance (determined from metatranscript data) of the picoeukaryote Ostreococcus. Our results show proof of concept for community metabolomics in discriminating and characterising polar and lipid metabolite patterns associated with marine POM.

A Bifunctional Glycosyltransferase from Agrobacterium tumefaciens Synthesizes Monoglucosyl and Glucuronosyl Diacylglycerol under Phosphate Deprivation

Glycolipids are mainly found in phototrophic organisms (like plants and cyanobacteria), in Gram-positive bacteria, and a few other bacterial phyla. Besides the function as bulk membrane lipids, they often play a role under phosphate deprivation as surrogates for phospholipids. The Gram-negative Agrobacterium tumefaciens accumulates four different glycolipids under phosphate deficiency, including digalactosyl diacylglycerol and glucosylgalactosyl diacylglycerol synthesized by a processive glycosyltransferase. The other two glycolipids have now been identified by mass spectrometry and nuclear magnetic resonance spectroscopy as monoglucosyl diacylglycerol and glucuronosyl diacylglycerol. These two lipids are synthesized by a single promiscuous glycosyltransferase encoded by the ORF atu2297, with UDP-glucose or UDP-glucuronic acid as sugar donors. The transfer of sugars differing in their chemistry is a novel feature not observed before for lipid glycosyltransferases. Furthermore, this enzyme is the first glucuronosyl diacylglycerol synthase isolated. Deletion mutants of Agrobacterium lacking monoglucosyl diacylglycerol and glucuronosyl diacylglycerol or all glycolipids are not impaired in growth or virulence during infection of tobacco leaf discs. Our data suggest that the four glycolipids and the nonphospholipid diacylglyceryl trimethylhomoserine can mutually replace each other during phosphate deprivation. This redundancy of different nonphospholipids may represent an adaptation mechanism to enhance the competitiveness in nature.

Effects of Light Intensity and Nitrogen Starvation on Glycerolipid, Glycerophospholipid, and Carotenoid Composition in Dunaliella tertiolecta Culture

Time-course variation of lipid and carotenoid production under high light (300 μE/m2s) and nitrogen starvation conditions was determined in a Dunaliella tertiolecta strain. Nanoelectrospray (nanoESI) chip based direct infusion was used for lipid analysis and ultra-performance liquid chromatography (UPLC) coupled with a photodiode array (PDA) or atmospheric chemical ionization mass spectrometry (APCI-MS) was used for carotenoid analysis. A total of 29 lipids and 7 carotenoids were detected. Alterations to diacylglyceryltrimethylhomoserine (DGTS) and digalactosyldiacylglycerol (DGDG) species were significant observations under stress conditions. Their role in relation to the regulation of photosynthesis under stress condition is discussed in this study. The total carotenoid content was decreased under stress conditions, while ã-carotene was increased under nitrate-deficient cultivation. The highest productivity of carotenoid was attained under high light and nitrate sufficiency (HLNS) condition, which result from the highest level of biomass under HLNS. When stress was induced at stationary phase, the substantial changes to the lipid composition occurred, and the higher carotenoid content and productivity were exhibited. This is the first report to investigate the variation of lipids, including glycerolipid, glycerophospholipid, and carotenoid in D. tertiolecta in response to stress conditions using lipidomics tools.

New diacylglyceryltrimethylhomoserines from the marine microalga Nannochloropsis granulata and their nitric oxide inhibitory activity

Chemical investigation of polar lipids from the marine eustigmatophyte microalga Nannochloropsis granulata led to the isolation of six betaine lipid diacylglyceryltrimethylhomoserine (DGTS), namely, (2S)-1,2-bis-O-eicosapentaenoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (1), (2S)-1-O-eicosapentaenoyl-2-O-arachidonoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (2), (2S)-1-O-eicosapentaenoyl-2-O-myristoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (3), (2S)-1-O-eicosapentaenoyl-2-O-palmitoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (4), (2S)-1-O-eicosapentaenoyl-2-O-palmitoleoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (5), and (2S)-1-O-eicosapentaenoyl-2-O-linoleoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (6). Structures of the isolated DGTSs were elucidated based on both spectroscopic technique and degradation methods. This is the first report of isolation of 1 in pure state, and 2–6 are all new compounds. The isolated betaine lipids showed dose-dependent nitric oxide (NO) inhibitory activity against lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophage cells. Further study suggested that these betaine lipids (1–6) inhibit NO production in RAW264.7 macrophage cells through downregulation of inducible nitric oxide synthase expression, indicating the possible use as an anti-inflammatory agent. This is the first report of DGTS with anti-inflammatory activity.

Molecular Ion‐Independent Quantification of Polar Glycerolipid Classes in Marine Plankton Using Triple Quadrupole MS

Polar glycerolipids are a diverse family of lipid molecules that form the bulk of bacterial and eukaryotic microbial membranes. The earth and ocean sciences has a long history of using fatty acids as biomarkers for microbes, but have only recently begun to examine the intact polar lipids from which they are derived. Current analytical approaches rely on laboriously quantifying the molecular ions of each of these species independently. Thus, we saw a need for a method for quantifying polar glycerolipid classes that was: (i) selective for individual classes, (ii) inclusive of all species within a class, (iii) independent of foreknowledge of the molecular ions of the polar glycerolipid, and (iv) amenable to automated, high-throughput data analysis methods. Our new HPLC-electrospray-ionization triple-quadrupole MS (HPLC-ESI-TQMS) method can be applied to quantify the nine major classes of polar glycerolipid in planktonic communities: the phospholipids phosphatidylglycerol, phosphatidylethanolamine, and phosphatidylcholine; the glycolipids monoglycosyldiacylglycerol, diglycosyldiacylglycerol and sulfoquinovosyldiacylglycerol; and the betaine lipids diacylglyceryl trimethyl homoserine, diacylglyceryl hydroxymethyl trimethyl-β-alanine, and diacylglyceryl carboxyhydroxymethylcholine. The analyses rely on neutral loss and parent ion scan events that yield one chromatogram for each class of polar glycerolipid, simplifying downstream analysis and increasing sample throughput. The efficacy of the method was demonstrated by analyzing plankton community samples from a variety of marine environments.

Spatial distribution of intact polar lipids in North Sea surface waters: Relationship with environmental conditions and microbial community composition

We characterized and quantified the intact polar lipid (IPL) composition of the surface waters of the North Sea and investigated its relationships with environmental conditions, microbial abundances, and community composition. The total IPL pool comprised at least 600 different IPL species in seven main classes: the glycerophospholipids phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE); the sulfur‐bearing glycerolipid sulfoquinovosyldiacylglycerol (SQDG); and the nitrogen‐bearing betaine lipids diacylglyceryl‐trimethylhomoserine (DGTS), diacylglyceryl‐hydroxymethyltrimethylalanine (DGTA), and diacylglyceryl‐carboxyhydroxymethylcholine (DGCC). Although no significant relationships were found between the IPL composition and environmental parameters, such as nutrient concentrations, distance‐based ordination yielded distinct clusters of IPL species, which could in turn be tentatively correlated with the predominant microbial groups. SQDGs and PGs, as well as PC species containing saturated fatty acid moieties, were related to picoeukaryote abundances and PC species with polyunsaturated fatty acid (PUFA) moieties to nanoeukaryote abundances. The PEs were likely of mixed cyanobacterial–bacterial origin, whereas DGTA and DGCC species were mainly associated with cyanobacteria. DGTSs were likely derived from either pico‐ or nanoeukaryotes, although the DGTS species with PUFAs also showed some relationship with cyanobacterial abundances. Concentrations of the algal‐derived IPLs showed strong positive correlations with chlorophyll a concentrations, indicating they may be used as biomarkers for living photosynthetic microbes. However, direct relationships between the IPLs and microbial groups were relatively weak, implying that the predominant IPLs in marine surface waters are not derived from single microbial groups and that direct inferences of microbial community compositions from IPL compositions should be considered with care.