The Structure, Functions and Potential Medicinal Effects of Chlorophylls Derived from Microalgae.

Microalgae are considered to be natural producers of bioactive pigments, with the production of pigments from microalgae being a sustainable and economical strategy that promises to alleviate growing demand. Chlorophyll, as the main pigment of photosynthesis, has been widely studied, but its medicinal applications as an antioxidant, antibacterial, and antitumor reagent are still poorly understood. Chlorophyll is the most important pigment in plants and algae, which not only provides food for organisms throughout the biosphere, but also plays an important role in a variety of human and man-made applications. The biological activity of chlorophyll is closely related to its chemical structure; its specific structure offers the possibility for its medicinal applications. This paper reviews the structural and functional roles of microalgal chlorophylls, commonly used extraction methods, and recent advances in medicine, to provide a theoretical basis for the standardization and commercial production and application of chlorophylls.

Mediator subunit MED8 interacts with heat shock transcription factor HSF3 to promote fucoxanthin synthesis in the diatom Phaeodactylum tricornutum.

Fucoxanthin, a natural carotenoid that has substantial pharmaceutical value due to its anticancer, antioxidant, antiobesity, and antidiabetic properties, is biosynthesized from glyceraldehyde-3-phosphate (G3P) via a series of enzymatic reactions. However, our understanding of the transcriptional mechanisms involved in fucoxanthin biosynthesis remains limited. Using reverse genetics, the med8 mutant was identified based on its phenotype of reduced fucoxanthin content, and the biological functions of MED8 in fucoxanthin synthesis were characterized using approaches such as gene expression, protein subcellular localization, protein-protein interaction and chromatin immunoprecipitation assay. Gene-editing mutants of MED8 exhibited decreased fucoxanthin content as well as reduced expression levels of six key genes involved in fucoxanthin synthesis, namely DXS, PSY1, ZDS-like, CRTISO5, ZEP1, and ZEP3, when compared to the wild-type (WT) strain. Furthermore, we showed that MED8 interacts with HSF3, and genetic analysis revealed their shared involvement in the genetic pathway governing fucoxanthin synthesis. Additionally, HSF3 was required for MED8 association with the promoters of the six fucoxanthin synthesis genes. In conclusion, MED8 and HSF3 are involved in fucoxanthin synthesis by modulating the expression of the fucoxanthin synthesis genes. Our results increase the understanding of the molecular regulation mechanisms underlying fucoxanthin synthesis in the diatom P. tricornutum.

Alteration in Community Dynamics of Chaetoceros curvisetus and Bacterioplankton Communities in Response to Surfactin Exposure.

The use of surfactin is a promising method to mitigate algal blooms. However, little is known about surfactin toxicity to algae and bacterioplankton. Here, we treated Chaetoceros curvisetus, the dominant species of algal blooms in the East China Sea, with 0, 0.5, 1, 2, 3, and 4 mg/L of surfactin for 96 h to investigate temporal variability. Our results showed that low concentrations of surfactin (<2 mg/L) changed the cell morphology of C. curvisetus, and higher concentrations (>3 mg/L) had lethal effects. Meanwhile, we examined the community dynamics of the free-living (FL, 0.22-5 µm) and particle-attached (PA, >5 µm) bacterioplankton of C. curvisetus in response to different surfactin concentrations and cultivation periods. Both PA and FL bacterioplankton were mainly composed of Proteobacteria, Actinobacteria, and Bacteroidetes, while FL bacterioplankton were more diverse than PA bacterioplankton. The variations of FL and PA bacterioplankton were significantly constrained by the surfactin concentration. Surfactin changed the lifestyle of some bacterioplankton from FL to PA, which mainly belonged to abundant bacterioplankton. Furthermore, we identified some surfactin-sensitive species/taxa. Our study will help enhance the ability to predict marine microbial responses under the effect of surfactin, providing a research foundation for this new harmful algal bloom mitigation method.

Mixotrophic culture of Chaetoceros sp. and the synergistic carbon and energy metabolism.

This research studied the metabolic mechanism of the mixotrophic Chaetoceros sp. The results showed this alga had the highest cell density and growth rate of 47.72 × 105 cells mL-1 and 0.41 d-1, respectively, with a maximum dry weight of 2.90 g/L, when compared to photoautotrophic and photoheterotrophic modes. Compared to photoheterotrophy, transcriptomics results showed the Rubisco, PGK, and GAPDH related genes were separately up-regulated by 1.03, 2.36, and 1.36 times in CBB cycle in mixotrophic mode, suggesting intermediate metabolites of EMP and PPP can enter the chloroplast via transporter proteins, or membrane permeation, and feedback inhibition regulates the reduction of multiple reactions in CBB cycle. Chaetoceros sp. achieves high biomass by utilizing ATP and carbon structures from EMP and PPP pathways, and the addition of NaHCO3 leads to an up-regulation of CBB cycle for the mixotrophic alga, resulting in higher biomass compared to the photoheterotrophic mode.

The Influence of Authoritarian-Benevolent Leadership on Subordinates' Work Engagement: A Social Information Processing Perspective.

Purpose: The dynamic and complex external environment calls for leaders to be both benevolent and authoritarian to cope with the mutually exclusive demands in the management process. But few research paid attention to the dark side of leaders' inconsistent behaviors on employees' work outcomes. Based on social information processing theory, this study investigated the impact of authoritarian-benevolent leadership on subordinates' work engagement and explored the mediating role of leader-member exchange ambivalence and the moderating role of trait mindfulness. Methods: A two-wave time-lagged survey approach was employed and data from 309 employees from three Chinese companies were collected. R 4.2.1 and SPSS 26.0 were used to test our hypotheses. Results: The findings demonstrated how subordinates were influenced in their work engagement by authoritarian-benevolent leadership and leader-member exchange ambivalence and emphasized the value of maintaining a high level of trait mindfulness. This study indicated that (1) authoritarian-benevolent leadership was negatively associated with work engagement, which was mediated by leader-member exchange ambivalence; (2) subordinates' trait mindfulness moderated the relationship between leader-member exchange ambivalence and work engagement; (3) the indirect effect of authoritarian-benevolent leadership on subordinates' work engagement through leader-member exchange ambivalence was moderated by subordinates' trait mindfulness. Conclusion: This study reveals the dark side of authoritarian-benevolent leadership and deepens our understanding of the mechanism underlying the effect of authoritarian-benevolent leadership on subordinates' work engagement from a new theoretical perspective. Practical implications are provided for managers to effectively develop authoritarian-benevolent leadership skills and improve subordinates' work engagement.

Enhancement of hemostatic properties of Cyclotella cryptica frustule through genetic manipulation.

BACKGROUND: The silicified cell wall of diatoms, also known as frustule, shows huge potential as an outstanding bio-nanomaterial for hemostatic applications due to its high hemostatic efficiency, good biocompatibility, and ready availability. As the architectural features of the frustule determine its hemostatic performance, it is of great interest to develop an effective method to modify the frustule morphology into desired patterns to further improve hemostatic efficiency. RESULTS: In this study, the gene encoding Silicalemma Associated Protein 2 (a silicalemma-spanning protein) of Cyclotella cryptica (CcSAP2) was identified as a key gene in frustule morphogenesis. Thus, it was overexpressed and knocked down, respectively. The frustule of the overexpress lines showed no obvious alteration in morphology compared to the wild type (WT), while the size, specific surface area (BET), pore volume, and pore diameter of the knockdown strains changed greatly. Particularly, the knockdown frustules achieved a more pronounced coagulation effect and in vivo hemostatic performance than the WT strains. Such observations suggested that silicalemma proteins are ideal genetic encoding targets for manipulating frustule morphology associated hemostatic properties. Furthermore, the Mantel test was adopted to identify the key morphologies associated with C. cryptica bleeding control. Finally, based on our results and recent advances, the mechanism of frustule morphogenesis was discussed. CONCLUSION: This study explores a new strategy for enhancing the hemostatic efficiency of the frustule based on genetic morphology modification and may provide insights into a better understanding of the frustule morphogenesis mechanism.

The influence of spermidine on the build-up of fucoxanthin in Isochrysis sp. Acclimated to varying light intensities.

Spermidine is a type of important growth regulator, which involved in the biosynthesis of photosynthetic pigments, and has the function of promoting cell proliferation. In this study, Isochrysis sp. was selected as the research object to explore the effects of spermidine supplementation on the growth of algal cells and fucoxanthin synthesis under different light intensities. The results showed that the cell density (5.40 × 106 cells/mL) of algae were the highest at 11 days under the light intensity of 200 µmol·m-2·s-1 and spermidine content of 150 µM. The contents of diadinoxanthin (1.09 mg/g) and fucoxanthin (6.11 mg/g) were the highest when spermidine was added under low light intensity, and the growth of algal cells and fucoxanthin metabolism were the most significant. In the carotenoid synthesis pathway, PDS (phytoene desaturase) was up-regulated by 1.96 times and VDE (violaxanthin de-epoxidase) was down-regulated by 0.95 times, which may promote fucoxanthin accumulation.

Integrated Biogeography and Assembly Mechanisms of Microeukaryotic Communities in Coastal Waters Near Shellfish Cultivation.

The Lianjiang coast in the East China Sea is a typical subtropical marine ecosystem, and shellfish cultivation occupies almost all of the available tidal flats. Many studies have investigated the effects of shellfish cultivation on benthic organisms and sediments, while the impact of shellfish cultivation on plankton ecosystems is still poorly understood. This study investigated the biogeographical patterns of microeukaryotic communities from Lianjiang coastal waters in four seasons using 18S ribosomal RNA gene amplicon sequencing. Microeukaryotes were mainly comprised of Dinoflagellata, Diatomea, Arthropoda, Ciliophora, Chlorophyta, Protalveolata, Cryptophyceae, and Ochrophyta, and presented significant differences in three habitats (the aquaculture area, confluent area, and offshore area) and four seasons. Similarity percentage analysis revealed that Paracalanus parvus, Heterocapsa rotundata, Bestiolina similis, and five additional key taxa contributed to spatio-temporal differences. Seasonal environmental and spatial factors explained 27.47% of microeukaryotic community variation on average, with 11.11% of the variation shared. Environmental variables, particularly depth, pH, and nitrite concentration, were strongly associated with the microeukaryotic community compositions. The neutral community model further demonstrated that stochastic processes were sufficient in shaping substantial variation in microeukaryotic communities across four seasons, which may reveal the remaining unexplained microeukaryotic community variation. We further divided four seasons into the aquaculture stages and non-aquaculture stages, and speculated that aquaculture activities may increase the dispersal limitation of microeukaryotes in coastal waters, especially for the big bodied-microbes like Arthropoda. The results provide a better understanding of the biogeographical patterns, processes, and mechanisms of microeukaryotic communities near shellfish cultivation.

Mixotrophy, a more promising culture mode: Multi-faceted elaboration of carbon and energy metabolism mechanisms to optimize microalgae culture.

Some mixotrophic microalgae appear to exceed the sum of photoautotrophy and heterotrophy in terms of biomass production. This paper mainly reviews the carbon and energy metabolism of microalgae to reveal the synergistic mechanisms of the mixotrophic mode from multiple aspects. It explains the shortcomings of photoautotrophic and heterotrophic growth, highlighting that the mixotrophic mode is not simply the sum of photoautotrophy and heterotrophy. Specifically, microalgae in mixotrophic mode can be divided into separate parts of photoautotrophic and heterotrophic cultures, and the synergistic parts of photoautotrophic culture enhance aerobic respiration and heterotrophic culture enhance the Calvin cycle. Additionally, this review argues that current deficiencies in mixotrophic culture can be improved by uncovering the synergistic mechanism of the mixotrophic mode, aiming to increase biomass growth and improve quality. This approach will enable the full utilization of advantagesin various fields, and provide research directions for future microalgal culture.

Valorization of Phaeodactylum tricornutum for integrated preparation of diadinoxanthin and fucoxanthin.

Integrated preparation of high-purity carotenoids from marine microalgae using green and efficient methods still faces enormous challenges. In this study, valorization of the economic Phaeodactylum tricornutum using integrated preparation of diadinoxanthin (Ddx) and fucoxanthin (Fx) was explored containing four steps including algae cultivation, solvent extraction, ODS open-column chromatography, and ethanol precipitation for the first time. Several essential key factors were optimized for simultaneously extracting Ddx and Fx from P. tricornutum. ODS open-column chromatography was used to isolate Ddx and Fx. Purification of Ddx and Fx was accomplished using ethanol precipitation. After optimization, the purity of Ddx and Fx was more than 95%, and the total recovery rates of Ddx and Fx were approximately 55% and 85%, respectively. The purified Ddx and Fx were identified as all-trans-diadinoxanthin and all-trans-fucoxanthin, respectively. The antioxidant capacity of the purified Ddx and Fx was assessed using two tests in vitro: DPPH and ABTS radical assays.

Screening of antibiotics to obtain axenic cell cultures of a marine microalga Chrysotila roscoffensis.

Due to high growth rate, outstanding abiotic stress tolerance, and rich value-added substances, Chrysotila roscoffensis, belonging to the phylum of Haptophyta, can be considered as a versatile resource for industrial exploitation of bioactive compounds. However, the application potential of C. roscoffensis has drawn attention until just recently, and the understanding related to the biological properties of this species is still scarce. For example, the sensitivities of C. roscoffensis to antibiotics, which is essential for the verification of heterotrophic capacity and the establishment of efficient genetic manipulation system is still unavailable. Aiming to provide fundamental information for future exploitation, the sensitivities of C. roscoffensis to nine types of antibiotics were tested in this study. The results demonstrated that C. roscoffensis exhibited relatively high resistances to ampicillin, kanamycin, streptomycin, gentamicin, and geneticin, while was sensitive to bleomycin, hygromycin B, paromomycin, and chloramphenicol. Using the former five types of antibiotics, a bacteria removal strategy was established tentatively. Finally, the axenicity of treated C. roscoffensis was confirmed based on a multi-strategy method including solid plate, 16S rDNA amplification, and nuclear acid staining. This report can provide valuable information for the development of optimal selection markers, which are meaningful for more extensive transgenic studies in C. roscoffensis. Moreover, our study also paves the way for the establishment of heterotrophic/mixotrophic cultivation modes of C. roscoffensis.

Changes in biochemical metabolites in manila clam after a temporary culture with high-quality microalgal feed mixed with the dinoflagellate species Karlodinium veneficum and K. zhouanum.

Phytoplankton composition is an important factor affecting the growth and physiological biochemical characteristics of filter-feeding bivalves. With the increasing trend in dinoflagellate biomass and blooms in mariculture areas, how the physio-biochemical traits and seafood quality of the mariculture organism are affected by the dinoflagellates, especially those at nonfatal levels, is not well understood. Different densities of two Karlodinium species, namely K. veneficum (KV) and K. zhouanum (KZ), mixed with high quality microalgal food Isochrysis galbana was applied in feeding manila clam Ruditapes philippinarum in a 14-day temporary culture, to comparatively study how the critical biochemical metabolites such as glycogen, free amino acids (FAAs), fatty acids (FAs), volatile organic compounds (VOCs) in the clam were affected. The survival rate of the clam showed dinoflagellate density and species specificity. The high-density KV group inhibited survival to 32% lower than that of the pure I. galbana control, respectively, while KZ at low concentrations did not significantly affect the survival compared with the control. In the high-density KV group, the glycogen and FAA contents decreased (p < 0.05), indicating that energy and protein metabolism were significantly affected. Amount of carnosine (49.91 ± 14.64 to 84.74 ± 8.59 µg/g of muscle wet weight) was detected in all the dinoflagellate-mixed groups, while it was not present in the field samples or in the pure I. galbana control, showing that carnosine participated in the anti-stress activities when the clam was exposed to the dinoflagellates. The global composition of FAs did not significantly vary among the groups. However, contents of the endogenous C18 PUFA precursors linoleic acid and α-linolenic acid significantly decreased in the high-density KV group compared to all the other groups, indicating that high density of KV affected the metabolisms of fatty acids. From the results of the changed VOC composition, oxidation of fatty acids and degradation of free amino acids might occur in the clams exposed to dinoflagellates. The increased VOCs, such as aldehydes, and decreased 1-octen-3-ol probably produced a more fishy taste and reduced food flavor quality when the clam was exposed to the dinoflagellates. This present study demonstrated that the biochemical metabolism and seafood qulity of the clam were affected. However, KZ with moderate density in the feed seemed to be beneficial in aquaculture for increasing the content of carnosine, a high-valued substance with multiple bioactivities.

Diversity, Biosynthesis and Bioactivity of Aeruginosins, a Family of Cyanobacteria-Derived Nonribosomal Linear Tetrapeptides.

Aeruginosins, a family of nonribosomal linear tetrapeptides discovered from cyanobacteria and sponges, exhibit in vitro inhibitory activity on various types of serine proteases. This family is characterized by the existence of the 2-carboxy-6-hydroxy-octahydroindole (Choi) moiety occupied at the central position of the tetrapeptide. Aeruginosins have attracted much attention due to their special structures and unique bioactivities. Although many studies on aeruginosins have been published, there has not yet been a comprehensive review that summarizes the diverse research ranging from biogenesis, structural characterization and biosynthesis to bioactivity. In this review, we provide an overview of the source, chemical structure as well as spectrum of bioactivities of aeruginosins. Furthermore, possible opportunities for future research and development of aeruginosins were discussed.

The use of surfactin in inhibiting Botrytis cinerea and in protecting winter jujube from the gray mold.

Surfactin has the potential to be used as a food preservative. However, efficiency and action mechanism in various applications need more assessments and research. In this study, the antifungal effects and the mechanism of action of surfactin on the fungus Botrytis cinerea were investigated. The effects of applying surfactin for the removal of gray mold on the quality of winter jujube were investigated based on the changes in fruit fatty acids. The results showed that (1) surfactin significantly inhibited the growth of B. cinerea, the EC50 at 5 d was 46.42 mg/L. (2) Surfactin significantly reduced the disease incidence and diameter of gray mold-inoculated winter jujube in a concentration-dependent manner. For that treated with surfactin at the EC50, the incidence decreased by 38.89%. (3) For B. cinerea under surfactin treatment, the mycelial morphology changed, the levels of total lipids and ergosterol decreased, the reactive oxygen species levels increased, and the cell integrity was completely damaged. (4) For winter jujube inoculated by B. cinerea, the contents of saturated fatty acids decreased and unsaturated fatty acids increased. For those under the surfactin treatments, winter jujube maintained the fatty acid composition at the level of non-inoculated groups. Mechanical injury significantly changed the fatty acid composition of winter jujube; however, surfactin not only was able to inhibit the growth of gray mold but also mitigated the adverse effects from mechanical injury. The present study demonstrated the potential applications of surfactin in the preservation of postharvest fruit quality.

The Heat Shock Transcription Factor PtHSF1 Mediates Triacylglycerol and Fucoxanthin Synthesis by Regulating the Expression of GPAT3 and DXS in Phaeodactylum tricornutum.

In addition to being important primary productive forces in marine ecosystems, diatoms are also rich in bioactive substances such as triacylglycerol and fucoxanthin. However, little is known about the transcriptional mechanisms underlying the biosynthesis of these substances. In this study, we found that the heat shock transcription factor PtHSF1 positively regulated the synthesis of triacylglycerol and fucoxanthin in Phaeodactylum tricornutum. Overexpression of PtHSF1 could increase the contents of triacylglycerol and fucoxanthin and upregulate key enzyme genes involved in the triacylglycerol and fucoxanthin biosynthesis pathways. On the other hand, gene silencing of PtHSF1 reduced the contents of triacylglycerol and fucoxanthin and the expression of the key enzyme genes involved in the triacylglycerol and fucoxanthin biosynthesis pathways. Further biochemical analysis revealed that PtHSF1 upregulated glycerol-2-phosphate acyltransferase 3 (GPAT3) and 1-deoxy-d-xylulose 5-phosphate synthase (DXS) by directly binding to their promoters, while genetic analysis demonstrated that PtHSF1 acted upstream of GPAT3 and DXS to regulate triacylglycerol and fucoxanthin synthesis. Therefore, in addition to elucidating the regulation mechanisms underlying PtHSF1-mediated triacylglycerol and fucoxanthin synthesis, this study also provided a candidate target for metabolic engineering of triacylglycerol and fucoxanthin in P. tricornutum.

Comparative metabarcoding analysis of phytoplankton community composition and diversity in aquaculture water and the stomach contents of Tegillarca granosa during months of growth.

Filter-feeder bivalves and phytoplankton are interdependent. Their interaction plays important role in estuarine and coastal ecosystem. The correlation between bivalve feeding and phytoplankton is highly species specificity and environment dependent. In the background of miniature and nondiatom trend of phytoplankton in coastal seawaters, how bivalve respond and how the response play roles in the phytoplankton community are poorly known. In the present study, by applying DNA metabarcoding approach based on plastid 23S rDNA, this question was addressed by comparing the phytoplankton composition in the seston and the stomach content of blood clam Tegillarca granosa sampled during the growth period from March to November 2020 in an experimental farm on tidal flat in Xiangshan Bay, East China Sea. The result showed that, a total of seven phyla, 55 genera and 73 species of phytoplankton were identified for all samples. Chlorophyta, Bacillariophyta, and Cyanobacteria were found to be three dominant phyla both in the stomach contents and seston. High diversity of pico-sized phytoplankton, which was easy overlooked by microscopy, was revealed both in seston and stomach contents. This result indicated that the clam was able to feed on the pico-sized algae. At the genus level, the most abundant genera were the pico-sized green alga Ostreococcus (6.12 %-67.88 %) in seston and Picochlorum (4.07 %-35.33 %) in the stomach contents. In addition, microalgae of high nutritional value showed trend of higher proportion in stomach contents than that in seston, especially in July and September when significant growth of T. granosa was observed during this period (the body size increased 155 %). Biodiversity of phytoplankton in the seston was totally higher than that in stomach content, however, the changes among the months showed respective trend. Especially in July when the biodiversity was the lowest in seston, that in the stomach content showed the highest. The results indicated that blood clam farming might influence the phytoplankton composition, including those of pico-sized level, although the particular species in seston were mainly correlating with the dominant environmental factors such as temperature, salinity, pH respectively. These results extend the understanding of roles that bivalve aquaculture may play in the changing of coastal phytoplankton community.

Mixotrophic culture of bait microalgae for biomass and nutrients accumulation and their synergistic carbon metabolism.

Microalgae cannot meet the bait demand for aquaculture due to light intensity limitation and other disadvantageous conditions. This research selected 6 mixotrophic microalgae, and the optimal strains and organic carbon were screened. The results showed that Thalassiosira pseudonana and Chlorella sp. are suitable for mixotrophic culture. The maximum cell density of Thalassiosira pseudonana was found to be 1.67 times than that of the photoautotrophic group when glycerol was added. The maximum cell density of Chlorella sp. with acetic acid was 1.69 times than that of the photoautotrophic group. When the concentration of acetic acid was 5.0 g·L-1 and the concentration of KNO3 was 0.2 g·L-1, the maximum biomass of Chlorella sp. could reach 3.54 × 107 cells·mL-1; the maximum biomass of Thalassiosira pseudonana was 5.53 × 106 cells·mL-1 with 10.0 g·L-1 glycerol and 0.2 g·L-1 KNO3. Metabolomic analysis further revealed that mixotrophic bait microalgae could promote the accumulation of lipids and amino acids.

Macroalgae-Derived Multifunctional Bioactive Substances: The Potential Applications for Food and Pharmaceuticals.

Macroalgae, as one of the important photosynthetic organisms in the marine environment are widely used in various fields, particularly in the production of food and pharmaceuticals. Given their wide distribution, easy accessibility and high efficiency in fixing carbon dioxide through the carbon concentrating mechanism, they can produce abundant nutriments or metabolites. Moreover, macroalgae can assimilate nitrogen and phosphorus bases on the purification of wastewater, and thus further accumulate high levels of bioactive substances. This review mainly introduces the distribution characteristics of macroalgae and their unique bioactive applications in food, medicine and environmental remediation. Their functional ingredients and bioactive substances are beneficial in food production and/or medicine development. Resource utilization of macroalgae coupled with wastewater and waste gas treatment would provide a sustainable path for bioactive substances production.

Enhancement of violaxanthin accumulation in Nannochloropsis oceanica by overexpressing a carotenoid isomerase gene from Phaeodactylum tricornutum.

Nannochloropsis has been considered as a promising feedstock for the industrial production of violaxanthin. However, a rational breeding strategy for the enhancement of violaxanthin content in this microalga is still vacant, thereby limiting its industrial application. All-trans-lycopene locates in the first branch point of carotenogenesis. The carotenoid isomerase (CRTISO), catalyzing the lycopene formation, is thus regarded as a key enzyme for carotenogenesis. Phaeodactylum tricornutum can accumulate high-level carotenoids under optimal conditions. Therefore, it is feasible to improve violaxanthin level in Nannochloropsis by overexpression of PtCRTISO. Protein targeting analysis of seven PtCRTISO candidates (PtCRTISO1-6 and PtCRTISO-like) demonstrated that PtCRTISO4 was most likely the carotenoid isomerase of P. tricornutum. Moreover, the transcriptional pattern of PtCRTISO4 at different cultivation periods was quite similar to other known carotenogenesis genes. Thus, PtCRTISO4 was transformed into N. oceanica. Compared to the wild type (WT), all three transgenic lines (T1-T3) of N. oceanica exhibited higher levels of total carotenoid and violaxanthin. Notably, T3 exhibited the peak violaxanthin content of 4.48 mg g-1 dry cell weight (DCW), which was 1.68-folds higher than WT. Interestingly, qRT-polymerase chain reaction (PCR) results demonstrated that phytoene synthase (NoPSY) rather than ζ-carotene desaturase (NoZDS) and lycopene ß-cyclase (NoLCYB) exhibited the highest upregulation, suggesting that PtCRTISO4 played an additional regulatory role in terms of carotenoid accumulation. Moreover, PtCRTISO4 overexpression increased C18:1n-9 but decreased C16:1n-7, implying that C18:1 may serve as a main feedstock for xanthophyll esterification in Nannochloropsis. Our results will provide valuable information for the violaxanthin production from Nannochloropsis.