Dinoflagellate Amphiesmal Dynamics: Cell Wall Deposition with Ecdysis and Cellular Growth

Multifaceted Dinoflagellates and the Marine Model Prorocentrum cordatum

BACKGROUND

Dinoflagellates are a monophyletic group within the taxon Alveolata, which comprises unicellular eukaryotes. Dinoflagellates have long been studied for their organismic and morphologic diversity as well as striking cellular features. They have a main size range of 10-100 µm, a complex "cell covering", exceptionally large genomes (∼1-250 Gbp with a mean of 50,000 protein-encoding genes) spread over a variable number of highly condensed chromosomes, and perform a closed mitosis with extranuclear spindles (dinomitosis). Photosynthetic, marine, and free-living Prorocentrum cordatum is a ubiquitously occurring, bloom-forming dinoflagellate, and an emerging model system, particularly with respect to systems biology.

SUMMARY

Focused ion beam/scanning electron microscopy (FIB/SEM) analysis of P. cordatum recently revealed (i) a flattened nucleus with unusual structural features and a total of 62 tightly packed chromosomes, (ii) a single, barrel-shaped chloroplast devoid of grana and harboring multiple starch granules, (iii) a single, highly reticular mitochondrion, and (iv) multiple phosphate and lipid storage bodies. Comprehensive proteomics of subcellular fractions suggested (i) major basic nuclear proteins to participate in chromosome condensation, (ii) composition of nuclear pores to differ from standard knowledge, (iii) photosystems I and II, chloroplast complex I, and chlorophyll a-b binding light-harvesting complex to form a large megacomplex (>1.5 MDa), and (iv) an extraordinary richness in pigment-binding proteins. Systems biology-level investigation of heat stress response demonstrated a concerted down-regulation of CO2-concentrating mechanisms, CO2-fixation, central metabolism, and monomer biosynthesis, which agrees with reduced growth yields.

KEY MESSAGES

FIB/SEM analysis revealed new insights into the remarkable subcellular architecture of P. cordatum, complemented by proteogenomic unraveling of novel nuclear structures and a photosynthetic megacomplex. These recent findings are put in the wider context of current understanding of dinoflagellates.

Cellulose from dinoflagellates as a versatile and environmentally friendly platform for the production of functionalised cellulose nanofibres

Cellulose nanofibres (CNFs), also known as nano-fibrillated cellulose, have emerged as highly promising sustainable biomaterials owing to their numerous advantages, including high accessibility, long-term sustainability, low toxicity, and mechanical properties. Recently, marine organisms have been explored as novel and environmentally friendly sources of cellulose fibers (CFs) due to their easy cultivation, extraction and biocompatibility. Dinoflagellates, a group of marine phytoplankton, have gained particular attention due to their unique cellulosic morphology and lignin-free biomass. Previously, we showed that the unique amorphous nature of dinoflagellate-derived cellulose offers various benefits. This study further explores the potential of dinoflagellate-derived CFs as a sustainable and versatile CNF source. Extracted dinoflagellate cellulose is effectively converted into CNFs via one-step TEMPO oxidation without significant polymer degradation. In addition, the biological compatibility of the CNFs is improved by amine-grafting using putrescine and folic acid. The products are characterised by conductometric titration, zeta potential measurements, TGA, GPC, FTIR, SEM/TEM, XRD, and XPS. Finally, in a proof-of-principle study, the application of the functionalised CNFs in drug delivery is tested using methylene blue as a drug model. Our findings suggest that dinoflagellate-derived CNFs provide an eco-friendly platform that can be easily functionalised for various applications, including drug delivery.

Different biological responses of Skeletonema costatum and Prorocentrum donghaiense to polymetallic nodules from seawaters

The negative impacts of polymetallic nodules mining on deep-sea benthic organisms have been widely established, but there is still a lack of understanding of the environmental impact on the surface ocean scenario. Phytoplankton growth experiment was conducted to determine the biological effect of polymetallic nodules on Prorocentrum donghaiense and Skeletonema costatum. The results showed that regardless of concentration and particle size, polymetallic nodules show a promoting effect on P. donghaiense (p < 0.05), the cell density in the experimental group increased by 35.2%-46.5% compared to the control at the end of the experiment. While fine particles significantly inhibited the growth of S. costatum (p < 0.05), the maximum inhibition rate on cell density reached 63.1%. Polymetallic nodules significantly enhance the Fv/Fm and the maximum electron transport rate of photosystem II in P. donghaiense, thereby increasing its growth rate. However, polymetallic nodules particles stimulated the antioxidant activity and extracellular polymeric substances secretion of S. costatum, resulting in phytoplankton flocculation and sedimentation, which inhibits its growth. Thus, these discriminatory impacts may cause alterations in biomass and community structure, ultimately affecting the ecological function.

Electrophysiological techniques in marine microalgae study: A new perspective for harmful algal bloom (HAB) research

Electrophysiological techniques, by measuring bioelectrical signals and ion channel activities in tissues and cells, are now widely utilized to study ion channel-related physiological functions and their underlying mechanisms. Electrophysiological techniques have been extensively employed in the investigation of animals, plants, and microorganisms; however, their application in marine algae lags behind that in other organisms. In this paper, we present an overview of current electrophysiological techniques applicable to algae while reviewing the historical usage of such techniques in this field. Furthermore, we explore the potential specific applications of electrophysiological technology in harmful algal bloom (HAB) research. The application prospects in the studies of stress tolerance, competitive advantage, nutrient absorption, toxin synthesis and secretion by HAB microalgae are discussed and anticipated herein with the aim of providing novel perspectives on HAB investigations.

Genomic architecture constrains macromolecular allocation in dinoflagellates

Dinoflagellate genomes have a unique architecture that may constrain their physiological and biochemical responsiveness to environmental stressors. Here we quantified how nitrogen (N) starvation influenced macromolecular allocation and C:N:P of three photosynthetic marine dinoflagellates, representing different taxonomic classes and genome sizes. Dinoflagellates respond to nitrogen starvation by decreasing cellular nitrogen, protein and RNA content, but unlike many other eukaryotic phytoplankton examined RNA:protein is invariant. Additionally, 2 of the 3 species exhibit increases in cellular phosphorus and very little change in cellular carbon with N-starvation. As a consequence, N starvation induces moderate increases in C:N, but extreme decreases in N:P and C:P, relative to diatoms. Dinoflagellate DNA content relative to total C, N and P is much higher than similar sized diatoms, but similar to very small photosynthetic picoeukaryotes such as Ostreococcus. In aggregate these results indicate the accumulation of phosphate stores may be an important strategy employed by dinoflagellates to meet P requirements associated with the maintenance and replication of their large genomes.

Environmental pH signals the release of monosaccharides from cell wall in coral symbiotic alga

Reef-building corals thrive in oligotrophic environments due to their possession of endosymbiotic algae. Confined to the low pH interior of the symbiosome within the cell, the algal symbiont provides the coral host with photosynthetically fixed carbon. However, it remains unknown how carbon is released from the algal symbiont for uptake by the host. Here we show, using cultured symbiotic dinoflagellate, Breviolum sp., that decreases in pH directly accelerates the release of monosaccharides, that is, glucose and galactose, into the ambient environment. Under low pH conditions, the cell surface structures were deformed and genes related to cellulase were significantly upregulated in Breviolum. Importantly, the release of monosaccharides was suppressed by the cellulase inhibitor, glucopyranoside, linking the release of carbon to degradation of the agal cell wall. Our results suggest that the low pH signals the cellulase-mediated release of monosaccharides from the algal cell wall as an environmental response in coral reef ecosystems.

Dinoflagellates as sustainable cellulose source: Cultivation, extraction, and characterization

The global demand for manufacturing and consuming biodegradable materials from natural sources has created a great interest in microalgae, such as dinoflagellates. Photosynthetic dinoflagellates are a sustainable source of natural materials such as cellulose as they grow using only sunlight and CO₂ at near-neutral pH without any fertilizers. In this paper, the cultivation of two species of dinoflagellates (Peridinium sp. and Prorocentrum micans) is established under lab conditions (up to 20 l), cellulose extraction is optimized, and the resulting material is thoroughly characterized. Dinoflagellate cellulose was extracted at room temperature by sequential treatment with highly concentrated 30 % NaOH and 6 M HCl, followed by bleaching with 10 % H₂O₂. The overall yield of cellulose is around 73 % (w/w), and roughly 85 % of the original dinoflagellate cellulosic morphology remains intact. Chemical purity, morphology, and porosity of the dinoflagellate-derived cellulose are analysed by different characterization techniques (ICP-OES, SEM, XRD, ATR-FTIR, Raman, NMR, TGA, BET, and GPC). XRD characterization of the extracted cellulose shows characteristic reflexes corresponding to a cellulose II allomorph which is mainly amorphous. This result is further supported by ATR-FTIR, Raman, and NMR spectroscopy. Overall, these results show that the extracted cellulose is a highly porous, lignin-free material that is thermally stable up to 260 °C. Its high degree of purity and porosity make dinoflagellate-derived cellulose a promising, sustainable candidate for the development of functional hybrid materials for biomedical applications.

Oleaginous Heterotrophic Dinoflagellates—Crypthecodiniaceae

The heterotrophic Crypthecodinium cohnii is a major model for dinoflagellate cell biology, and a major industrial producer of docosahexaenoic acid, a key nutraceutical and added pharmaceutical compound. Despite these factors, the family Crypthecodiniaceae is not fully described, which is partly attributable to their degenerative thecal plates, as well as the lack of ribotype-referred morphological description in many taxons. We report here significant genetic distances and phylogenetic cladding that support inter-specific variations within the Crypthecodiniaceae. We describe Crypthecodinium croucheri sp. nov. Kwok, Law and Wong, that have different genome sizes, ribotypes, and amplification fragment length polymorphism profiles when compared to the C. cohnii. The interspecific ribotypes were supported by distinctive truncation-insertion at the ITS regions that were conserved at intraspecific level. The long genetic distances between Crypthecodiniaceae and other dinoflagellate orders support the separation of the group, which includes related taxons with high oil content and degenerative thecal plates, to be ratified to the order level. The current study provides the basis for future specific demarcation-differentiation, which is an important facet in food safety, biosecurity, sustainable agriculture feeds, and biotechnology licensing of new oleaginous models.