SLDP: a novel protein related to caleosin is associated with the endosymbiotic Symbiodinium lipid droplets from Euphyllia glabrescens

Investigation of organic contaminants in the blubber of a blue whale (Balaenoptera musculus) first stranded on the coast of Taiwan

This study presents a comprehensive assessment of persistent organic pollutants (POPs) in the blubber of a stranded blue whale found on the coast of Taiwan. The analysis included polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), Hexachlorobenzene (HCB), and polybrominated diphenyl ethers (PBDEs). The whale exhibited evident signs of emaciation, including low body weight, reduced blubber fat content, and thin blubber thickness. The dominant fatty acid type detected in the blubber was short-chain monounsaturated fatty acids (SC-MUFA), known to aid in thermoregulation. Stable isotope ratios indicated that the blue whale occupied a lower trophic position compared to a fin whale, suggesting its proximity to krill habitats in the Southern Ocean for feeding. The average concentrations of DDTs (1089.2 ± 4.7 ng/g lw; ΣDDT) and PCBs (1057.1 ± 49.8 ng/g lw) in the blubber were almost one order of magnitude higher than PAHs (41.7 ± 10.0 ng/g lw), HCB (70.6 ± 2. ng/g lw), and PBDEs (7.2 ± 1.2 ng/g lw). Pollutant concentrations in this individual blue whale were comparable to levels found in Norway, higher than those found in Chile, and notably lower than those found in Canada and Mexico. Calculating the biomagnification factor (BMF) for the POPs from krill (Euphausia superba) to the blue whale revealed significant bioaccumulation of pollutants in this particular whale. Additional research is imperative to achieve a thorough comprehension of bioaccumulation of POPs and their potential toxicological impacts on whale health.

Lipid Droplets in Endosymbiotic Symbiodiniaceae spp. Associated with Corals

Symbiodiniaceae species is a dinoflagellate that plays a crucial role in maintaining the symbiotic mutualism of reef-building corals in the ocean. Reef-building corals, as hosts, provide the nutrition and habitat to endosymbiotic Symbiodiniaceae species and Symbiodiniaceae species transfer the fixed carbon to the corals for growth. Environmental stress is one of the factors impacting the physiology and metabolism of the corals-dinoflagellate association. The environmental stress triggers the metabolic changes in Symbiodiniaceae species resulting in an increase in the production of survival organelles related to storage components such as lipid droplets (LD). LDs are found as unique organelles, mainly composed of triacylglycerols surrounded by phospholipids embedded with some proteins. To date, it has been reported that investigation of lipid droplets significantly present in animals and plants led to the understanding that lipid droplets play a key role in lipid storage and transport. The major challenge of investigating endosymbiotic Symbiodiniaceae species lies in overcoming the strategies in isolating lesser lipid droplets present in its intercellular cells. Here, we review the most recent highlights of LD research in endosymbiotic Symbiodiniaceae species particularly focusing on LD biogenesis, mechanism, and major lipid droplet proteins. Moreover, to comprehend potential novel ways of energy storage in the symbiotic interaction between endosymbiotic Symbiodiniaceae species and its host, we also emphasize recent emerging environmental factors such as temperature, ocean acidification, and nutrient impacting the accumulation of lipid droplets in endosymbiotic Symbiodiniaceae species.

Dynamic Regulation of Lipid Droplet Biogenesis in Plant Cells and Proteins Involved in the Process

Lipid droplets (LDs) are ubiquitous, dynamic organelles found in almost all organisms, including animals, protists, plants and prokaryotes. The cell biology of LDs, especially biogenesis, has attracted increasing attention in recent decades because of their important role in cellular lipid metabolism and other newly identified processes. Emerging evidence suggests that LD biogenesis is a highly coordinated and stepwise process in animals and yeasts, occurring at specific sites of the endoplasmic reticulum (ER) that are defined by both evolutionarily conserved and organism- and cell type-specific LD lipids and proteins. In plants, understanding of the mechanistic details of LD formation is elusive as many questions remain. In some ways LD biogenesis differs between plants and animals. Several homologous proteins involved in the regulation of animal LD formation in plants have been identified. We try to describe how these proteins are synthesized, transported to the ER and specifically targeted to LD, and how these proteins participate in the regulation of LD biogenesis. Here, we review current work on the molecular processes that control LD formation in plant cells and highlight the proteins that govern this process, hoping to provide useful clues for future research.

The Puzzling Conservation and Diversification of Lipid Droplets from Bacteria to Eukaryotes

Membrane compartments are amongst the most fascinating markers of cell evolution from prokaryotes to eukaryotes, some being conserved and the others having emerged via a series of primary and secondary endosymbiosis events. Membrane compartments comprise the system limiting cells (one or two membranes in bacteria, a unique plasma membrane in eukaryotes) and a variety of internal vesicular, subspherical, tubular, or reticulated organelles. In eukaryotes, the internal membranes comprise on the one hand the general endomembrane system, a dynamic network including organelles like the endoplasmic reticulum, the Golgi apparatus, the nuclear envelope, etc. and also the plasma membrane, which are linked via direct lateral connectivity (e.g. between the endoplasmic reticulum and the nuclear outer envelope membrane) or indirectly via vesicular trafficking. On the other hand, semi-autonomous organelles, i.e. mitochondria and chloroplasts, are disconnected from the endomembrane system and request vertical transmission following cell division. Membranes are organized as lipid bilayers in which proteins are embedded. The budding of some of these membranes, leading to the formation of the so-called lipid droplets (LDs) loaded with hydrophobic molecules, most notably triacylglycerol, is conserved in all clades. The evolution of eukaryotes is marked by the acquisition of mitochondria and simple plastids from Gram-positive bacteria by primary endosymbiosis events and the emergence of extremely complex plastids, collectively called secondary plastids, bounded by three to four membranes, following multiple and independent secondary endosymbiosis events. There is currently no consensus view of the evolution of LDs in the Tree of Life. Some features are conserved; others show a striking level of diversification. Here, we summarize the current knowledge on the architecture, dynamics, and multitude of functions of the lipid droplets in prokaryotes and in eukaryotes deriving from primary and secondary endosymbiosis events.

Identification of a Major Lipid Droplet Protein in a Marine Diatom Phaeodactylum tricornutum

Various kinds of organisms, including microalgae, accumulate neutral lipids in distinct intracellular compartments called lipid droplets. Generally, lipid droplets are generated from the endoplasmic reticulum, and particular proteins localize on their surface. Some of these proteins function as structural proteins to prevent fusion between the lipid droplets, and the others could have an enzymatic role or might be involved in intracellular membrane trafficking. However, information about lipid droplet proteins in microalgae is scarce as compared with that in animals and land plants. We focused on the oil-producing, marine, pennate diatom Phaeodactylum tricornutum that forms lipid droplets during nitrogen deprivation and we investigated the proteins located on the lipid droplets. After 6 d of cultivation in a nitrate-deficient medium, the mature lipid droplets were isolated by sucrose density gradient centrifugation. Proteomic analyses revealed five proteins, with Stramenopile-type lipid droplet protein (StLDP) being the most abundant protein in the lipid droplet fraction. Although the primary sequence of StLDP did not have homology to any known lipid droplet proteins, StLDP had a central hydrophobic domain. This structural feature is also detected in oleosin of land plants and in lipid droplet surface protein (LDSP) of Nannochloropsis species. As a proline knot motif of oleosin, conservative proline residues existed in the hydrophobic domain. StLDP was up-regulated during nitrate deprivation, and fluctuations of StLDP expression levels corresponded to the size of the lipid droplets.

Morphological Variability and Distinct Protein Profiles of Cultured and Endosymbiotic Symbiodinium cells Isolated from Exaiptasia pulchella

Symbiodinium is a dinoflagellate that plays an important role in the physiology of the symbiotic relationships of Cnidarians such as corals and sea anemones. However, it is very difficult to cultivate free-living dinoflagellates after being isolated from the host, as they are very sensitive to environmental changes. How these symbiont cells are supported by the host tissue is still unclear. This study investigated the characteristics of Symbiodinium cells, particularly with respect to the morphological variability and distinct protein profiles of both cultured and endosymbiotic Symbiodinium which were freshly isolated from Exaiptasia pulchella. The response of the cellular morphology of freshly isolated Symbiodinium cells kept under a 12 h L:12 h D cycle to different temperatures was measured. Cellular proliferation was investigated by measuring the growth pattern of Symbiodinium cells, the results of which indicated that the growth was significantly reduced in response to the extreme temperatures. Proteomic analysis of freshly isolated Symbiodinium cells revealed twelve novel proteins that putatively included transcription translation factors, photosystem proteins, and proteins associated with energy and lipid metabolism, as well as defense response. The results of this study will bring more understandings to the mechanisms governing the endosymbiotic relationship between the cnidarians and dinoflagellates.

A Compartmental Comparison of Major Lipid Species in a Coral-Symbiodinium Endosymbiosis: Evidence that the Coral Host Regulates Lipogenesis of Its Cytosolic Lipid Bodies

The lipid body (LB) formation in the host coral gastrodermal cell cytoplasm is a hallmark of the coral-Symbiodinium endosymbiosis, and such lipid-based entities are not found in endosymbiont-free cnidarian cells. Therefore, the elucidation of lipogenesis regulation in LBs and how it is related to the lipid metabolism of the host and endosymbiont could provide direct insight to understand the symbiosis mechanism. Herein, the lipid composition of host cells of the stony coral Euphyllia glabrescens, as well as that of their cytoplasmic LBs and in hospite Symbiodinium populations, was examined by high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS), and six major lipid species were identified: wax esters, sterol esters, triacylglycerols, cholesterols, free fatty acids, and phospholipids. Their concentrations differed significantly between host coral cells, LBs, and Symbiodinium, suggesting compartmental regulation. WE were only present in the host coral and were particularly highly concentrated in LBs. Amongst the four species of WE, the monoene R = C18:1/R = C16 was found to be LB-specific and was not present in the host gastrodermal cell cytoplasm. Furthermore, the acyl pool profiles of the individual LB lipid species were more similar, but not equal to, those of the host gastrodermal cells in which they were located, indicating partially autonomous lipid metabolism in these LBs. Nevertheless, given the overall similarity in the host gastrodermal cell and LB lipid profiles, these data suggest that a significant portion of the LB lipids may be of host coral origin. Finally, lipid profiles of the in hospite Symbiodinium populations were significantly distinct from those of the cultured Symbiodinium, potentially suggesting a host regulation effect that may be fundamental to lipid metabolism in endosymbiotic associations involving clade C Symbiodinium.

Nitrogen deprivation induces lipid droplet accumulation and alters fatty acid metabolism in symbiotic dinoflagellates isolated from Aiptasia pulchella

The stability of cnidarian-dinoflagellate (genus Symbiodinium spp.) endosymbioses depends on the regulation of nutrient transport between Symbiodinium populations and their hosts. Previously, we successfully induced the production of lipid droplets in the free-living cultured Symbiodinium (clade B) under the nitrogen-deprivation condition for 5 days. Therefore, the present study aimed at understanding the disruption of the endosymbiotic relationship between the cnidarians and dinoflagellates by nitrogen deprivation using Aiptasia pulchella as an example. Transmission electron micrographs revealed the formation of lipid droplets induced by nitrogen deprivation, and the lipid analyses further showed that polyunsaturated fatty acids were drastically enriched in Symbiodinium after 30 days of nitrogen deprivation, although these were unaffected after 5 days of nitrogen starvation. The present study also suggested that the host provided nitrogen to the symbiotic cells during short-term environmental stress. However, the relationship started to deteriorate after 30 days. These findings provide a more detailed understanding of the mechanisms of the symbiotic relationship between the symbiotic dinoflagellates in terms of the nitrogen source, which might provide more information for the explanation of the regulatory mechanism underlying endosymbiotic associations.