Molecular and cellular mechanisms of neutral lipid accumulation in diatom following nitrogen deprivation

Metabolic response to a heterologous poly-3-hydroxybutyrate (PHB) pathway in Phaeodactylum tricornutum

The marine diatom Phaeodactylum tricornutum is an emerging host for metabolic engineering, but little is known about how introduced pathways are integrated into the existing metabolic framework of the host or influence transgene expression. In this study, we expressed the heterologous poly-3-hydroxybutyrate (PHB) pathway using episomal expression, which draws on the precursor acetyl coenzyme-A (AcCoA). By experimentally perturbing cultivation conditions, we gained insight into the regulation of the endogenous metabolism in transgenic lines under various environmental scenarios, as well as on alterations in AcCoA flux within the host cell. Biosynthesis of PHB led to distinct shifts in the metabolome of the host, and further analysis revealed a condition-dependent relationship between endogenous and transgenic metabolic pathways. Under N limitation, which induced a significant increase in neutral lipid content, both metabolic and transcriptomic data suggest that AcCoA was preferably shunted into the endogenous pathway for lipid biosynthesis over the transgenic PHB pathway. In contrast, supply of organic carbon in the form of glycerol supported both fatty acid and PHB biosynthesis, suggesting cross-talk between cytosolic and plastidial AcCoA precursors. This is the first study to investigate the transcriptomic and metabolomic response of diatom cell lines expressing a heterologous multi-gene pathway under different environmental conditions, providing useful insights for future engineering attempts for pathways based on the precursor AcCoA. KEY POINTS: • PHB expression had minimal effects on transcription of adjacent pathways. • N limitation favoured native lipid rather than transgenic PHB synthesis. • Glycerol addition allowed simultaneous lipid and PHB accumulation.

Transcriptomic analysis of Chaetoceros muelleri in response to different nitrogen concentrations reveals the activation of pathways to enable efficient nitrogen uptake

Nitrogen is the principal nutrient deficiency that increases lipids and carbohydrate content in diatoms but negatively affects biomass production. Marine diatom Chaetoceros muelleri is characterized by lipid and carbohydrate accumulation under low nitrogen concentration without affecting biomass. To elucidate the molecular effects of nitrogen concentrations, we performed an RNA-seq analysis of C. muelleri grown under four nitrogen concentrations (3.53 mM, 1.76 mM, 0.44 mM, and 0.18 mM of NaNO3). This research revealed that changes in global transcription in C. muelleri are differentially expressed by nitrogen concentration. "Energetic metabolism", "Carbohydrate metabolism" and "Lipid metabolism" pathways were identified as the most upregulated by N deficiency. Due to N limitation, alternative pathways to self-supply nitrogen employed by microalgal cells were identified. Additionally, nitrogen limitation decreased chlorophyll content and caused a greater response at the transcriptional level with a higher number of unigenes differentially expressed. By contrast, the highest N concentration (3.53 mM) recorded the lowest number of differentially expressed genes. Amt1, Nrt2, Fad2, Skn7, Wrky19, and Dgat2 genes were evaluated by RT-qPCR. In conclusion, C. muelleri modify their metabolic pathways to optimize nitrogen utilization and minimize nitrogen losses. On the other hand, the assembled transcriptome serves as the basis for metabolic engineering focused on improving the quantity and quality of the diatom for biotechnological applications. However, proteomic and metabolomic analysis is also required to compare gene expression, protein, and metabolite accumulation.

Lipidomic and Metabolomic Analyses Reveal Changes of Lipid and Metabolite Profiles in Rapeseed during Nitrogen Deficiency

Nitrogen is one of the most essential macronutrients for plant growth and its availability in soil is vital for agricultural sustainability and productivity. However, excessive nitrogen application could reduce the nitrogen use efficiency and produce environmental pollution. Here, we systematically determined the response in lipidome and metabolome in rapeseed during nitrogen starvation. Plant growth was severely retarded during nitrogen deficiency, while the levels of most amino acids were significantly decreased. The level of monogalactosyldiacyglycerol (MGDG) in leaves and roots was significantly decreased, while the level of digalactosyldiacylglycerol (DGDG) was significantly decreased in roots, resulting in a significant reduction of the MGDG/DGDG ratio during nitrogen starvation. Meanwhile, the levels of sulfoquinovosyl diacylglycerol, phosphatidylglycerol and glucuronosyl diacylglycerol were reduced to varying extents. Moreover, the levels of metabolites in the tricarboxylic acid cycle, Calvin cycle and energy metabolism were changed during nitrogen deficiency. These findings show that nitrogen deprivation alters the membrane lipid metabolism and carbon metabolism, and our study provides valuable information to further understand the response of rapeseed to nitrogen deficiency at the metabolism level.

Physiological Functions of Phospholipid:Diacylglycerol Acyltransferases

Triacylglycerol (TAG) is among the most energy dense storage forms of reduced carbon in living systems. TAG metabolism plays critical roles in cellular energy balance, lipid homeostasis, cell growth and stress responses. In higher plants, microalgae and fungi, TAG is assembled by acyl-CoA-dependent and acyl-CoA-independent pathways catalyzed by diacylglycerol (DAG) acyltransferase and phospholipid:DAG acyltransferase (PDAT), respectively. This review contains a summary of the current understanding of the physiological functions of PDATs. Emphasis is placed on their role in lipid remodeling and lipid homeostasis in response to abiotic stress or perturbations in lipid metabolism.

Exploring the dichotomy: Shotgun metagenomics reveals diversity of beneficial and pathogenic protist community in arid wetlands of northeastern South Africa

Arid regions harbor seasonal and permanent wetlands, as biodiversity hotspots crucial for ecosystem services despite harsh conditions. These wetlands, typically dependent on episodic intense rainfall, are understudied compared to their humid counterparts. While the diversity of plants and animals in these wetlands is well-known, the microbial communities remain largely unexplored. To address this knowledge gap, we employed metagenome sequencing technologies to profile protist communities, including pathogenic protozoa, and their associated functional pathways, in sediment of permanent and seasonal arid freshwater wetlands across northern South Africa. Results revealed a core community of protists dominated by phylum Apicomplexa (66.73 %), Euglenazoa (19.03 %), Bacillariophyta (5.44 %), Metamonada (4.65 %), Cryptophyta (1.90 %), and Amoebazoa (1.21 %). Seasonal wetlands showed significantly higher protist diversity compared to permanent wetlands (Shannon index, p = 0.019; Chao1, p = 0.0095). A high abundance and diversity of human and zoonotic pathogenic protists (87.67 %) was observed, with lower levels of photoautotrophs (6.69 %) and limited diversity of phagotrophs (5.64 %). Key photoautotrophs identified included diatoms (Thalassiosiraceae and Phaeodactylaceae) and cryptophytes (genus Hemiselmis and Cryptophyta), with consumers/phagotrophs exhibited a correlation with the bacterial community abundance (r2 = 0.218, p < 0.001). Pathogenic protozoans identified, include malaria-causing Plasmodium, kinetoplastids (genus Besnoita, Theilleria, Neospora, Toxoplasma, Encephalitozoon, and Babesia) and waterborne protozoans of public health importance (such as Cryptosporidium parvum and Giardia lamblia). Furthermore, the enrichment of pathogenesis-associated pathways (amino acid biosynthesis, peptidoglycan maturation, heme biosynthesis and degradation, and the Calvin-Benson-Bassham cycle), along with virulence gene families identified, highlighted these wetlands as potential reservoirs for infectious diseases. Our results unveil a baseline protist taxonomic and functional composition within arid wetlands, including beneficial and pathogenic protozoa. The close proximity of these wetlands to human activity raises concern for local and transboundary spread of these pathogens. Thus, continued monitoring is vital for disease control and preserving these unique ecosystems.

Membranes that make fat: roles of membrane lipids as acyl donors for triglyceride synthesis and organelle function

Triglycerides constitute an inert storage form for fatty acids deposited in lipid droplets and are mobilized to provide metabolic energy or membrane building blocks. The biosynthesis of triglycerides is highly conserved within eukaryotes and normally involves the sequential esterification of activated fatty acids with a glycerol backbone. Some eukaryotes, however, can also use cellular membrane lipids as direct fatty acid donors for triglyceride synthesis. The biological significance of a pathway that generates triglycerides at the expense of organelle membranes has remained elusive. Here we review current knowledge on how cells use membrane lipids as fatty acid donors for triglyceride synthesis and discuss the hypothesis that a primary function of this pathway is to regulate membrane lipid remodeling and organelle function.

The identification of a correlation between lipid content in the model diatom Phaeodactylum tricornutum and pH treatment strategies

pH treatment promotes single-cell lipid accumulation and significantly affects microalgae growth. This study investigates the correlation between lipid content and environmental pH using the model diatom Phaeodactylum tricornutum (P. tricornutum). We compared three distinct pH treatment strategies-continuous, intermittent, and a two-phase culture-in P. tricornutum. Rigorous analysis of chlorophyll content, cell density, and lipid content indicated that ongoing pH treatment at pH 9.5 (CHES) emerged as the most effective approach for lipid accumulation in P. tricornutum. The CHES buffer treatment significantly boosted total lipid yield and led to a reduction in protein content. Carbohydrate content experienced a slight decline under CHES buffer treatment, but changes were observed in the activities of key enzymes. Specifically, [acyl-carrier-protein] S-malonyltransferase (MAT) activity decreased after 3 days in the control treatment, while no significant change was noted under the CHES buffer treatment. In contrast, diacylglycerol O-acyltransferase (DGAT) activity showed upregulation 2 and 3 days post-CHES buffer treatment. Moreover, the study identified differentially expressed genes enriched in Gene Ontology (GO) terms associated with protein biosynthesis, photosynthesis, nucleoside metabolism, and transferase activity. These outcomes underscore the pivotal role of CHES buffer in orchestrating primary metabolism, potentially steering carbon flux towards lipogenesis. As a result, the potential of microalgae as a sustainable source of biofuels contributes significantly to the transition towards a more environmentally friendly energy landscape.

Biomass productivity and characterization of Tetradesmus obliquus grown in a hybrid photobioreactor

In this study, the effects of CO2 addition on the growth performance and biochemical composition of the green microalga Tetradesmus obliquus cultured in a hybrid algal production system (HAPS) were investigated. The HAPS combines the characteristics of tubular photobioreactors (towards a better carbon dioxide dissolution coefficient) with thin-layer cascade system (with a higher surface-to-volume ratio). Experimental batches were conducted with and without CO2 addition, and evaluated in terms of productivity and biomass characteristics (elemental composition, protein and lipid contents, pigments and fatty acids profiles). CO2 enrichment positively influenced productivity, and proteins, lipids, pigments and unsaturated fatty acids contents in biomass. The HAPS herein presented contributes to the optimization of microalgae cultures in open systems, since it allows, with a simple adaptation-a transit of the cultivation through a tubular portion where injection and dissolution of CO2 is efficient-to obtain in TLC systems, greater productivity and better-quality biomass.

NADP+-dependent isocitrate dehydrogenase as a novel target for altering carbon flux to lipid accumulation and enhancing antioxidant capacity in Tetradesmus obliquus

Regulatory complexities in lipogenesis hinder the harmonization of metabolic carbon precursors towards lipid synthesis. Exploring regulatory complexities in lipogenesis, this study identifies NADP+-dependent isocitrate dehydrogenase (IDH) in Tetradesmus obliquus as a key factor. Overexpression IDH in strains ToIDH-1 and ToIDH-2 resulted in a 1.69 and 1.64-fold increase in neutral lipids, respectively, compared to the wild type, with lipid yield reaching 234.56 and 227.17 mg/L. Notably, despite slower growth, the cellular biomass augmented to 790.67 mg/L. Metabolite analysis indicated a shift in carbon precursors from protein to lipid and carbohydrate synthesis. Morphological observations revealed increases in the volume and number of lipid droplets, alongside a change in the fatty acid profile favoring monounsaturated and saturated fatty acids. Furthermore, IDH overexpression enhanced NADPH production and antioxidant activity, thereby further boosting lipid accumulation when combined with salt stress. This study suggests a pathway for improved lipogenesis and algal growth via metabolic engineering.

Assessment of heavy metals and environmental stress conditions on the production potential of polyunsaturated fatty acids (PUFAs) in indigenous microalgae isolated from the Gulf of Mannar coastal waters

The present study evaluated the effects of heavy metals, viz., lead, mercury, and cadmium, on growth, chlorophyll a, b, c, carotenoids, and PUFA content of marine microalgae Chlorella sp. and Cylindrotheca fusiformis. At 96-h exposure, the IC50 values for Hg2+, Pb2+, and Cd2+ were 0.85 mg/L, 2.4 mg/L, and 5.3 mg/L respectively, in Chlorella sp. In C. fusiformis, IC50 values for Hg2+, Pb2+, and Cd2+ were 0.5 mg/L, 1.2 mg/L, and 3 mg/L respectively. The pigment contents of both microalgae were significantly affected upon heavy metal exposure. In Chlorella sp. and C. fusiformis, the exposed concentrations of Hg2+ averagely decreased the PUFA content by 76.34% and 78.68%, respectively. Similarly, Pb2+-exposed concentrations resulted in 54.50% and 82.64% average reductions in PUFA content of Chlorella sp. and C. fusiformis, respectively. Cd2+-exposed concentrations showed 32.58% and 40.54% average reduction in PUFA content of Chlorella sp. and C. fusiformis, respectively. Among the environmental stress conditions, the dark treatment has increased total PUFA content by 6.63% in Chlorella sp. and 3.92% in C. fusiformis. It was observed that the 50% nitrogen starvation (two-stage) significantly improved the PUFA production from 26.47 ± 6.55% to 40.92 ± 10.74% in Chlorella sp. and from 11.23 ± 5.01 to 32.8 ± 14.17% in C. fusiformis. The toxicity for both microalgae was followed in the order Hg2+ > Pb2+ > Cd2+. Among the two species, Chlorella sp. has shown a high tolerance to heavy metals and can be effectively utilized in PUFA production.

Understanding the Impact of Nitrogen Availability: A Limiting Factor for Enhancing Fucoxanthin Productivity in Microalgae Cultivation

This study aimed to investigate the regulation of fucoxanthin (FX) biosynthesis under various nitrogen conditions to optimize FX productivity in Phaeodactylum tricornutum. Apart from light, nitrogen availability significantly affects the FX production of microalgae; however, the underlying mechanism remains unclear. In batch culture, P. tricornutum was cultivated with normal (NN, 0.882 mM sodium nitrate), limited (LN, 0.22 mM), and high (HN, 8.82 mM) initial nitrogen concentrations in f/2 medium. Microalgal growth and photosynthetic pigment production were examined, and day 5 samples were subjected to fucoxanthin-chlorophyll a/c-binding protein (FCP) proteomic and transcriptomic analyses. The result demonstrated that HN promoted FX productivity by extending the exponential growth phase for higher biomass and FX accumulation stage (P1), showing a continuous increase in FX accumulation on day 6. Augmented FX biosynthesis via the upregulation of carotenogenesis could be primarily attributed to enhanced FCP formation in the thylakoid membrane. Key proteins, such as LHC3/4, LHCF8, LHCF5, and LHCF10, and key genes, such as PtPSY, PtPDS, and PtVDE, were upregulated under nitrogen repletion. Finally, the combination of low light and HN prolonged the P1 stage to day 10, resulting in maximal FX productivity to 9.82 ± 0.56 mg/L/day, demonstrating an effective strategy for enhancing FX production in microalgae cultivation.

Chemical constituents from the heterotrophic marine microalgae Aurantiochytrium sp. SC145 and their antimicrobial activities

One new indol, N-methoxymethyltryptophol (1), one new phenolic, (2 R)-2-(4-hydroxyphenyl)ethyl 2-hydroxy-3-phenylpropanoate (2) and fifteen known compounds (3-17) were isolated from the methanol extract of the fermentation of marine microalgae Aurantiochytrium sp. SC145. Their structures were elucidated by 1D-, 2D-NMR spectroscopic analysis, HR-ESI-MS, quantum chemical calculation methods and by comparing their NMR data with those reported in the literature. All compounds were evaluated for their antimicrobial activities against microorganisms. Compounds 2, 3 and 11 significantly exhibited antimicrobial activities on all tested Gram-(+), Gram-(-) bacteria and the yeast C. albicans with MIC values ranging from 32 to 256 µg/mL.

Triazine herbicide reduced the toxicity of the harmful dinoflagellate Karenia mikimotoi by impairing its photosynthetic systems

Triazine herbicides are common contaminants in coastal waters, and they are recognized as inhibitors of photosystem II, causing significant hinderance to the growth and reproduction of phytoplankton. However, the influence of these herbicides on microalgal toxin production remains unclear. This study aimed to examine this relationship by conducting a comprehensive physiological and 4D label-free quantitative proteomic analysis on the harmful dinoflagellate Karenia mikimotoi in the presence of the triazine herbicide dipropetryn. The findings demonstrated a significant decrease in photosynthetic activity and pigment content, as well as reduced levels of unsaturated fatty acids, reactive oxygen species (ROS), and hemolytic toxins in K. mikimotoi when exposed to dipropetryn. The proteomic analysis revealed a down-regulation in proteins associated with photosynthesis, ROS response, and energy metabolism, such as fatty acid biosynthesis, chlorophyll metabolism, and nitrogen metabolism. In contrast, an up-regulation of proteins related to energy-producing processes, such as fatty acid β-oxidation, glycolysis, and the tricarboxylic acid cycle, was observed. This study demonstrated that dipropetryn disrupts the photosynthetic systems of K. mikimotoi, resulting in a notable decrease in algal toxin production. These findings provide valuable insights into the underlying mechanisms of toxin production in toxigenic microalgae and explore the potential effect of herbicide pollution on harmful algal blooms in coastal environments.

Lipid accumulation mechanism of Amphora coffeaeformis under nitrogen deprivation and its application as a feed additive in Carassius auratus aquaculture

BACKGROUND

Amphora coffeaeformis, a unicellular diatom, can significantly accumulate lipids under nitrogen (N) limitation. However, the molecular mechanism underlying lipid accumulation in A. coffeaeformis remains unknown and its application development is lagging.

RESULTS

This work analyzed the lipid composition of A. coffeaeformis under N deprivation and investigated its mechanism underlying lipid accumulation using RNA-seq. The results showed that the total lipid content of A. coffeaeformis increased from 28.22 to 44.05% after 5 days of N deprivation, while the neutral lipid triacylglycerol (TAG) content increased from 10.41 to 25.21%. The transcriptional profile showed that N deprivation induced wide-ranging reprogramming of regulation and that most physiological activities were repressed, while the upregulation of glycerol-3-phosphate acyltransferase directly determined TAG accumulation. Moreover, we explored the effect of A. coffeaeformis as a food additive on the lipid composition of crucian carp. The results showed that the contents of unsaturated fatty acids in the meat of fish supplemented with A. coffeaeformis were significantly increased, indicating its potential application in animal nutrition for improving meat quality indicators.

CONCLUSION

The findings shed light on the molecular mechanisms of neutral lipid accumulation and revealed the key genes involved in lipid metabolism in A. coffeaeformis. Moreover, we also confirmed that A. coffeaeformis can be used as feed additive for improving the lipid composition of crucian carp meat, which provided evidence for the biotechnology application of this high-oil microalgae.

Ferulago bernardii as a New Source of α-Pinene Binds to ctDNA: In Silico and in Vitro Studies

Ferulago bernardii Tomk & M. Pimen belongs to Apiaceae family. Various species of the Ferulago genus have antioxidant, anticholinesterase, cytotoxic, and antiproliferative effects. In this study, the essential oil of F. bernardii was extracted using the Clevenger apparatus. The essential oil compounds were identified using GC-MS/FID. The interaction between the essential oil and DNA strands was evaluated through spectrophotometric titration. The molecular mechanism of the interaction between the main components of the essential oil and different DNA strands was assessed using molecular dynamics simulation. Based on the results, 92.03±1.20 % of the essential oil consisted of α-pinene. Therefore, the essential oil could serve as a suitable source of α-pinene. α-pinene is a monoterpene hydrocarbon that has various effects, including anti-inflammatory, antioxidant, antimicrobial, and antitumor properties. The binding constant of the essential oil to DNA strands (Ka ) was determined to be 5.40±0.47×10-3  M-1 . Molecular dynamics simulation demonstrated that α-pinene could interact with AT and CG rich DNA strands and indirectly stabilize G-Quadruplex. Given the different applications for α-pinene and its high percentage in the essential oil, it is suggested that researchers pay more attention to F. bernardii in the pharmaceutical, cosmetic, and food industries.

Strategies of NaCl Tolerance in Saline-Alkali-Tolerant Green Microalga Monoraphidium dybowskii LB50

Studying how freshwater cells modify metabolism and membrane lipids in response to salt stress is important for understanding how freshwater organisms adapt to salt stress and investigating new osmoregulatory ways. Physiological, biochemical, metabolic, and proteomic analyses were applied in a novel saline-alkali-tolerant microalga Monoraphidium dybowskii LB50 under different NaCl concentrations. Cells adopt a variety of strategies to adapt to salt stress, including increasing ion transport and osmolytes, regulating cell cycle and life history, and accumulating triacylglycerol (TAG). A large number of metabolic activities point to TAG accumulation. With increasing NaCl concentration, the C resource for TAG accumulation went from photosynthetically fixed C and a small amount of lipid remodeling to macromolecule degradation and a mass of lipid remodeling, respectively. The energy for TAG accumulation went from linear electron transfer and oxidative phosphate pentose pathway to cyclic electron flow, substrate phosphorylation, oxidation phosphorylation, and FA oxidation. Additionally, digalacturonic acid and amino acids of the N-acetyl group, which usually were the osmotica for marine organisms, were important for M. dybowskii LB50. Freshwater organisms evolved many biological ways to adapt to salt stress. This insight enriches our understanding of the adaptation mechanisms underlying abiotic stress.

UDP-glucose pyrophosphorylase as a target for regulating carbon flux distribution and antioxidant capacity in Phaeodactylum tricornutum

UDP-glucose pyrophosphorylase (UGPase) is a key enzyme for polysaccharide synthesis, and its role in plants and bacteria is well established; however, its functions in unicellular microalgae remain ill-defined. Here, we perform bioinformatics, subcellular localization as well as in vitro and in vivo analyses to elucidate the functions of two UGPs (UGP1 and UGP2) in the model microalga Phaeodactylum tricornutum. Despite differences in amino acid sequence, substrate specificity, and subcellular localization between UGP1 and UGP2, both enzymes can efficiently increase the production of chrysolaminarin (Chrl) or lipids by regulating carbon flux distribution without impairing growth and photosynthesis in transgenic strains. Productivity evaluation indicate that UGP1 play a bigger role in regulating Chrl and lipid production than UGP2. In addition, UGP1 enhance antioxidant capacity, whereas UGP2 is involved in sulfoquinovosyldiacylglycerol (SQDG) synthesis in P. tricornutum. Taken together, the present results suggest that ideal microalgal strains can be developed for the industrial production of Chrl or lipids and lay the foundation for the development of methods to improve oxidative stress tolerance in diatoms.

The molecular mechanisms and environmental effects of modified clay control algal blooms in aquacultural water

Modified clay (MC) technology is an effective method for controlling harmful algal blooms (HABs). Based on field experience, a bloom does not continue after treatment with MC, even though the residual HAB biomass accounts for 20-30% of the initial biomass. Laboratory studies using unialgal cultures have found that MC could inhibit the growth of the residual algal cells to prevent HABs. Nevertheless, the phytoplankton in field waters is diverse. Therefore, unclassified complex mechanisms may exist. To illustrate the molecular mechanisms through which MC controls HABs in the field and verify the previous laboratory findings, a series of experiments and bioinformatics analyses were conducted using bloom waters from aquacultural ponds. The results showed that a 72.29% removal efficiency of algal biomass could effectively control blooms. The metatranscriptomic results revealed that the number of downregulated genes (131,546) was greater than that of upregulated genes (24,318) at 3 h after MC addition. Among these genes, several genes related to DNA replication were downregulated; however, genes involved in DNA repair were upregulated. Metabolism-related pathways were the most significantly upregulated (q < 0.05), including photosynthesis and oxidative phosphorylation. The results also showed that MC reduced most of the biomass of the dominant phytoplankton species, likely by removing apical dominance, which increased the diversity and stability of the phytoplankton community. In addition to reducing the pathogenic bacterial density, MC reduced the concentrations of PO₄^3- (96.22%) and SiO₃^2- (66.77%), thus improving the aquaculture water quality, altering the phytoplankton community structure (the proportion of Diatomea decreased, and that of Chlorophyta increased), and inhibiting phytoplankton growth. These effects hindered the rapid development of large phytoplankton biomasses and allowed the community structure to remain stable, reducing HAB threats. This study illustrates the molecular mechanisms through which MC controls HABs in the field and provides a scientific method for removing HABs in aquacultural waters.

Physiochemical and molecular responses of the diatom Phaeodactylum tricornutum to illumination transitions

BACKGROUND

Light is a key regulatory factor for photosynthesis and metabolism of microalgae. The diatom Phaeodactylum tricornutum is capable of exhibiting metabolic flexibility in response to light fluctuations. However, the metabolic switching and underlying molecular mechanisms upon illumination transitions remain poorly understood for this industrially relevant marine alga. To address these, the physiochemical and molecular responses of P. tricornutum upon high light (HL) and recovery (HLR) were probed.

RESULTS

Upon HL, P. tricornutum exhibited quick responses, including decreases in cell division, major light harvesting pigments (e.g., chlorophyll a, β-carotene, and fucoxanthin), chloroplastidic membrane lipids (e.g., monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol), and long-chain polyunsaturated fatty acids (e.g., C20:5), as well as increases in carbohydrates and neutral lipids particularly triacylglycerol. During HLR stage when the stress was removed, these physiochemical phenotypes were generally recovered, indicative of a rapid and reversible changes of P. tricornutum to cope with illumination transitions for survival and growth. Through the integrated analysis with time-resolved transcriptomics, we revealed the transcriptional control of photosynthesis and carbon metabolism in P. tricornutum responding to HL, which could be reversed more or less during the HLR stage. Furthermore, we highlighted key enzymes involved in carotenoid biosynthesis and lipid metabolism of P. tricornutum and identified monooxygenases putatively responsible for catalyzing the ketolation step towards fucoxanthin synthesis from neoxanthin.

CONCLUSIONS

The detailed profiling of physiochemical and transcriptional responses of P. tricornutum to HL-HLR treatments advances our understanding on the adaption of the alga to illumination transitions and provides new insights into engineering of the alga for improved production of value-added carotenoids and lipids.

An attempt to simultaneously quantify the polysaccharide, total lipid, protein and pigment in single Cyclotella cryptica cell by Raman spectroscopy

BACKGROUND

At present, the conventional methods for determining photosynthetic products of microalgae are usually based on a large number of cell mass to reach the measurement baseline, and the result can only reveal the average state at the population level, which is not feasible for large-scale and rapid screening of specific phenotypes from a large number of potential microalgae mutants. In recent years, single-cell Raman spectra (SCRS) has been proved to be able to rapidly and simultaneously quantify the biochemical components of microalgae. However, this method has not been reported to analyze the biochemical components of Cyclotella cryptica (C. cryptica). Thus, SCRS was first attempt to determine these four biochemical components in this diatom.

RESULTS

The method based on SCRS was established to simultaneously quantify the contents of polysaccharide, total lipids, protein and Chl-a in C. cryptica, with thirteen Raman bands were found to be the main marker bands for the diatom components. Moreover, Partial Least Square Regression (PLSR) models based on full spectrum can reliably predict these four cellular components, with Pearson correlation coefficient for these components reached 0.949, 0.904, 0.801 and 0.917, respectively. Finally, based on SCRS data of one isogenic sample, the pairwise correlation and dynamic transformation process of these components can be analyzed by Intra-ramanome Correlation Analysis (IRCA), and the results showed silicon starvation could promote the carbon in C. cryptica cells to flow from protein and pigment metabolism to polysaccharide and lipid metabolism.

CONCLUSIONS

First, method for the simultaneous quantification of the polysaccharide, total lipid, protein and pigment in single C. cryptica cell are established. Second, the instant interconversion of intracellular components was constructed through IRCA, which is based on data set of one isogenic population and more precision and timeliness. Finally, total results indicated that silicon deficiency could promote the carbon in C. cryptica cells to flow from protein and pigment metabolism to polysaccharide and lipid metabolism.

Identification and Functional Analysis of Acyl-Acyl Carrier Protein Δ9 Desaturase from Nannochloropsis oceanica

The oleaginous marine microalga Nannochloropsis oceanica strain IMET1 has attracted increasing attention as a promising photosynthetic cell factory due to its unique excellent capacity to accumulate large amounts of triacylglycerols and eicosapentaenoic acid. To complete the genomic annotation for genes in the fatty acid biosynthesis pathway of N. oceanica, we conducted the present study to identify a novel candidate gene encoding the archetypical chloroplast stromal acyl-acyl carrier protein Δ⁹ desaturase. The full-length cDNA was generated using rapid-amplification of cDNA ends, and the structure of the coding region interrupted by four introns was determined. The RT-qPCR results demonstrated the upregulated transcriptional abundance of this gene under nitrogen starvation condition. Fluorescence localization studies using EGFP-fused protein revealed that the translated protein was localized in chloroplast stroma. The catalytic activity of the translated protein was characterized by inducible expression in Escherichia coli and a mutant yeast strain BY4389, indicating its potential desaturated capacity for palmitoyl-ACP (C16:0-ACP) and stearoyl-ACP (C18:0-ACP). Further functional complementation assay using BY4839 on plate demonstrated that the expressed enzyme restored the biosynthesis of oleic acid. These results support the desaturated activity of the expressed protein in chloroplast stroma to fulfill the biosynthesis and accumulation of monounsaturated fatty acids in N. oceanica strain IMET1.

Flashing lights affect the photophysiology and expression of carotenoid and lipid synthesis genes in Nannochloropsis gaditana

Nannochloropsis gaditana is a promising microalga for biotechnology. One of the strategies to stimulate its full potential in metabolite production is exposure to flashing lights. Here, we report how N. gaditana adapts to different flashing light regimes (5, 50, and 500 Hz) by changing its cellular physiology and the relative expression of genes related to critical cellular functions. We analyzed the differential mRNA abundance of genes related to photosynthesis, nitrogen assimilation and biosynthesis of chlorophyll, carotenoids, lipids, fatty acids and starch. Analysis of photosynthetic efficiency and high mRNA abundance of photoprotection genes supported the inference that excess excitation energy provided by light absorbance during photosynthesis was produced under low frequency flashing lights and was dissipated by photopigments via the xanthophyll-cycle. Increased relative expression levels of genes related to the synthesis of carotenoids and chlorophyll confirmed the accumulation of photopigments previously observed at low frequency flashing lights. Higher differential mRNA abundance of genes related to the triacylglycerol biosynthesis were observed at lower frequency flashing lights, possibly triggered by a poor nitrogen assimilation caused by low mRNA abundance of a nitrate reductase gene. This study advances a new understanding of algal physiology and metabolism leading to improved cellular performance and metabolite production.

Composition identification and UV-C irradiation growth inhibition effect of green shading on the greenhouse cover

Greenhouse cover pollution with green shading composed of dust, microalgae and bacteria is a severe problem in tropical areas. The shading results in lower greenhouse indoor light intensity reducing the yield and quality of protected horticulture crops. However, few studies have focused on environmentally efficient ways to remove green shading to increase greenhouse production. In this study, five purified microalgae were isolated from the green shading of three greenhouse roofs and were identified using morphological and molecular assessments. The effects of Ultraviolet-C irradiation (UV-C, 254 nm) at doses of 100, 200 and 300 mJ cm^-2 on the growth of GLY-1 microalgae were investigated. The results indicated that five purified microalgae all appeared to belong to the genus of Jaagichlorella. The purified microalgae cell density and chlorophyll content decreased respectively by 26.89-74.44 % and 42.02-77.31 % at 1-3 d after UV-C treatment with doses ranging from 100 to 300 mJ cm^-2. The inhibition of the growth rate of microalgae was significantly positively correlated with the UV-C irradiation dose and significantly negatively correlated with treatment time. In summary, UV-C irradiation treatment at 300 mJ cm^-2 and 3 d could substantially inhibit microalgae growth in green shading on greenhouse covers. UV-C irradiation could be an effective method for solving the problem of greenhouse cover pollution with microalgae.

Nitrogen Starvation Enhances the Production of Saturated and Unsaturated Fatty Acids in Aurantiochytrium sp. PKU#SW8 by Regulating Key Biosynthetic Genes

Nitrogen deprivation is known to improve lipid accumulation in microalgae and thraustochytrids. However, the patterns of fatty acid production and the molecular mechanisms underlying the accumulation of unsaturated and saturated fatty acids (SFAs) under nitrogen starvation remain largely unknown for thraustochytrids. In this study, batch culture experiments under nitrogen replete and nitrogen starvation conditions were performed, and the changes in the transcriptome of Aurantiochytrium sp. PKU#SW8 strain between these conditions were investigated. Our results showed improved yields of total fatty acids (TFAs), total unsaturated fatty acids, and total SFAs under nitrogen starvation, which suggested that nitrogen starvation favors the accumulation of both unsaturated and saturated fatty acids in PKU#SW8. However, nitrogen starvation resulted in a more than 2.36-fold increase of SFAs whereas a 1.7-fold increase of unsaturated fatty acids was observed, indicating a disproportionate increase in these groups of fatty acids. The fabD and enoyl-CoA hydratase genes were significantly upregulated under nitrogen starvation, supporting the observed increase in the yield of TFAs from 2.63 ± 0.22 g/L to 3.64 ± 0.16 g/L. Furthermore, the pfaB gene involved in the polyketide synthase (PKS) pathway was significantly upregulated under nitrogen starvation. This suggested that the increased expression of the pfaB gene under nitrogen starvation may be one of the explanations for the increased yield of docosahexaenoic acid by 1.58-fold. Overall, our study advances the current understanding of the molecular mechanisms that underlie the response of thraustochytrids to nitrogen deprivation and their fatty acid biosynthesis.

RNA-seq analysis reveals genes related to photosynthetic carbon partitioning and lipid production in Phaeodactylum tricornutum under alkaline conditions

Alkaline pH can induce triacylglyceride accumulation in microalgae, however its molecular mechanism remains elusive. Here, we investigated the effect of 2-[N-cyclohexylamino]-ethane-sulfonic acid (CHES) -induced intracellular alkalization on the lipid production in Phaeodactylum tricornutum. Intracellular pH was increased upon CHES treatment, displaying a high BCECF fluorescence ratio. CHES treatment significantly induced lipid accumulation but had no change in cell density and biomass. The expression of genes involved in photoreaction, carbon fixation, glycolysis, pentose phosphate pathway, amino acid catabolism, GS/GOGAT cycle, TCA cycle, triacylglyceride assembly, de novo fatty acid synthesis were up-regulated, while that in amino acid biosynthesis were down-regulated under CHES conditions. Correspondingly, the activity of phosphoribulokinase, carbonic anhydrase, pyruvate dehydrogenase and acetaldehyde dehydrogenase were enhanced by CHES treatment. Chloroplast-specific biological processes were activated by CHES treatment in P. tricornutum, which redirects the flux of carbon into lipid biosynthesis, meanwhile stimulates de novo fatty acid biosynthesis, leading to lipid accumulation under CHES conditions. These indicate an enhancement of intermediate metabolism, resulting in lipid accumulation by CHES.

Evidence of 2,4-diaminobutyric acid (DAB) production as a defense mechanism in diatom Thalassiosira pseudonana

The neurotoxic secondary metabolite β-N-methylamino-L-alanine (BMAA) and its structural isomer 2,4-diaminobutyric acid (DAB) are known to be produced by various phytoplankton groups. Despite the worldwide spread of these toxin producers, no obvious role and function of BMAA and DAB in diatoms have been identified. Here, we investigated the effects of biotic factors, i.e., predators and competitors, as possible causes of BMAA and/or DAB regulation in the two diatom species Phaeodactylum tricornutum and Thalassiosira pseudonana. DAB was specifically regulated in T. pseudonana by the presence of predators and competitors. The effects of DAB on both diatoms as competitors and on the copepod Tigriopus sp. as predator at individual and at population levels were examined. The toxic effects of DAB on the growth of T. pseudonana and the population of Tigriopus sp. were significant. The effect of DAB as a defensive secondary metabolite is assumed to be environmentally relevant depending on the number of the copepods. The results show a potential function of DAB that can play an important role in defense mechanisms of T. pseudonana.

Effect and function of β-N-methylamino-L-alanine in the diatom Phaeodactylum tricornutum

The neurotoxin β-N-methylamino-L-alanine (BMAA) is an environmental factor connected to neurodegenerative diseases. BMAA can be produced by various microorganisms (e.g. bacteria, cyanobacteria, dinoflagellates and diatoms) present in diverse ecosystems. No previous study has revealed the function of BMAA in diatoms. In the present study, we combined physiological data with metabolomic and transcriptional data in order to investigate the effect and function of BMAA in the diatom Phaeodactylum tricornutum. P. tricornutum, exposed to different concentrations of exogenous BMAA, showed concentration dependent responses. When the concentration of supplemented BMAA was sufficient to arrest the growth of P. tricornutum, oxidative stress and obstructed carbon fixation were obtained from the specific metabolite and transcriptional data. Results also indicated increased concentration of intracellular chlorophyll a and alterations in the GS-GOGAT cycle, whereas the urea cycle was suppressed. We therefore conclude that BMAA represents a toxic metabolite able to control the growth of P. tricornutum by triggering oxidative stress, and further influencing photosynthesis and nitrogen metabolisms.

Metabolomic, proteomic and lactylated proteomic analyses indicate lactate plays important roles in maintaining energy and C:N homeostasis in Phaeodactylum tricornutum

Background

Phaeodactylum tricornutum accumulates lipids while the growth also increases under high CO₂, shedding light on its potential application in the reduction of CO₂ emissions and at the same time acquiring biodiesel raw materials. However, the sensing and transducing of high C:N signals and the related response mechanism(s) remained unknown.

Results

In this study, a multiple omics analysis was performed with P. tricornutum under low nitrogen (LN) and high CO₂ (HC) conditions. The results indicated that 2-oxoglutarate was significantly increased under both LN and HC. Meanwhile, proteins involved in carbon concentration mechanism decreased, indicated that 2-oxoglutarate might regulate C:N balance through suppressing carbon fixation. Lactate, which acts in energy metabolism, signal transduction and ‘LactoylLys’ modification on proteins, was the most upregulated metabolite under both LN and HC conditions. Meanwhile, proteins involved in carbon, nitrogen and energy metabolisms were significantly regulated. Western blotting analysis suggested that non-histone L-lactylation modification was enhanced under LN and HC. Moreover, lactylated proteins were enriched in photosynthesis, central carbon metabolism, nitrogen metabolism, fatty acid synthesis and oxidative phosphorylation.

Conclusion

It is suggested that lactate might play important roles in energy homeostatic maintenance and C:N balance regulation in P. tricornutum through protein lactylation modification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02152-8.

Natural Polymers and Their Nanocomposites Used for Environmental Applications

The aim of this review is to bring together the main natural polymer applications for environmental remediation, as a class of nexus materials with advanced properties that offer the opportunity of integration in single or simultaneous decontamination processes. By identifying the main natural polymers derived from agro-industrial sources or monomers converted by biotechnology into sustainable polymers, the paper offers the main performances identified in the literature for: (i) the treatment of water contaminated with heavy metals and emerging pollutants such as dyes and organics, (ii) the decontamination and remediation of soils, and (iii) the reduction in the number of suspended solids of a particulate matter (PM) type in the atmosphere. Because nanotechnology offers new horizons in materials science, nanocomposite tunable polymers are also studied and presented as promising materials in the context of developing sustainable and integrated products in society to ensure quality of life. As a class of future smart materials, the natural polymers and their nanocomposites are obtained from renewable resources, which are inexpensive materials with high surface area, porosity, and high adsorption properties due to their various functional groups. The information gathered in this review paper is based on the publications in the field from the last two decades. The future perspectives of these fascinating materials should take into account the scale-up, the toxicity of nanoparticles, and the competition with food production, as well as the environmental regulations.

Mixotrophic Cultivation of Microalgae Using Biogas as the Substrate

Biogas utilization through biotechnology represents a potential and novel technology. We propose the microalgal mixotrophic cultivation to convert biogas to microalgae-based biodiesel, in which methanotroph was co-cultured to convert CH₄ to organic intermediate (and CO₂) for microalgal mixotrophic growth. This study constructed a co-culture of Methylocystis bryophila (methanotroph) and Scenedesmus obliquus (microalgae) with biogas feeding. Compared with the single culture of S. obliquus, higher microalgal biomass but a lower chlorophyll concentration was observed. The organic metabolism-related genes were upregulated, verifying microalgal mixotrophic growth. The stoichiometric calculation of M. bryophila culture shows that M. bryophila tends to release organic matter rather than grow under a low O₂ content. M. bryophila rarely grew under five different light intensities, indicating that M. bryophila acts as a biocatalyst in the co-culture. The organic intermediate released by methanotroph increased the maximum biomass of microalgal culture, accelerated nitrogen absorption, accumulated more monounsaturated fatty acids, and improved the adaptation to light. The co-culture of microalgae and methanotroph may provide new opportunities for microalgae-based biodiesel production using biogas as a substrate.

Effects of Structural and Compositional Changes of Nanochloropsis oceania after Enzyme Treatment on EPA-Rich Lipids Extraction

Improved methods for the extraction of eicosapentaenoic acid (EPA), an essential and economically important polyunsaturated fatty acid, are urgently required. However, lipid extraction rates using food-grade solvents such as ethanol are usually low. To improve the ethanol-based extraction rate, and to elucidate the relevant mechanisms, we used cellulase and laccase to treat powdered Nannochloropsis, one of the most promising microalgal sources of EPA. Cellulase and laccase synergistically increased lipid yields by 69.31% and lipid EPA content by 42.63%, by degrading the amorphous hemicellulose and cellulose, improving crystallinity, and promoting the release and extraction of lysodiacylglyceryltrimethylhomoserine. Scanning electron microscopy showed that cell morphology was substantially altered, with cell-wall rupture, loss of cell boundaries, and the release of intracellular substances. In conclusion, Nannochloropsis lipid yields may be directly linked to cell-wall hemicellulose structure, and enzymatic treatment to alter this may improve lipid yields.

Combined effect of CO2 concentration and low-cost urea repletion/starvation in Chlorella vulgaris for ameliorating growth metrics, total and non-polar lipid accumulation and fatty acid composition

Different CO₂ concentration such as 0.03, 5, 10 and 15% and low-cost urea repletion/starvation in Chlorella vulgaris on growth, total and non-polar lipid content and fatty acid composition was studied. Chlorella vulgaris grown at 0.03% CO₂ apparently revealed inferior biomass yield 0.55 g/L on 14th day compared to CO₂ supplemented cells. In the case of CO₂ supply, 15% CO₂ has unveiled higher biomass yield at about 1.83 g/L on day 12 whereas biomass yield for 5 and 10% CO₂ supplemented cells was 1.61 and 1.73 g/L, respectively on 12th day of cultivation. The biomass productivity (g) per liter per day was 32 mg in control condition whereas it was 125, 134 and 144 mg/L/d in 5, 10 and 15% CO₂ supplied cells, respectively. Lipid content of the strain grown at control, 5, 10 and 15% CO₂ was 21.2, 22.1, 23.4 and 24.6%, respectively and however, without CO₂ addition in low-cost urea repleted and urea depleted medium grown cells revealed 21.2 and 24.2%, respectively. Interestingly, strain grown at 15% CO₂ supply in urea deplete medium yielded 28.7% lipid and contribution of non-polar lipids in total lipids is 69.7%. Further, the fatty acid composition of the strain grown in 15% CO₂ supply in urea depleted medium showed C16:0, C16:1, C18:1 and C18:3 in the level of 30.12, 9.98, 23.43, and 11.97%, respectively compared to control and urea amended condition.

Culture Conditions Affect Antioxidant Production, Metabolism and Related Biomarkers of the Microalgae Phaeodactylum tricornutum

Phaeodactylum tricornutum (Bacillariophyta) is a worldwide-distributed diatom with the ability to adapt and survive in different environmental habitats and nutrient-limited conditions. In this research, we investigated the growth performance, the total lipids productivity, the major categories of fatty acids, and the antioxidant content in P. tricornutum subjected for 15 days to nitrogen deprivation (N-) compared to standard culture conditions (N+). Furthermore, genes and pathways related to lipid biosynthesis (i.e., glucose-6-phosphate dehydrogenase, acetyl-coenzyme A carboxylase, citrate synthase, and isocitrate dehydrogenase) and photosynthetic activity (i.e., ribulose-1,5-bisphospate carboxylase/oxygenase and fucoxanthin-chlorophyll a/c binding protein B) were investigated through molecular approaches. P. tricornutum grown under starvation condition (N-) increased lipids production (42.5 ± 0.19 g/100 g) and decreased secondary metabolites productivity (phenolic content: 3.071 ± 0.17 mg GAE g-1; carotenoids: 0.35 ± 0.01 mg g−1) when compared to standard culture conditions (N+). Moreover, N deprivation led to an increase in the expression of genes involved in fatty acid biosynthesis and a decrease in genes related to photosynthesis. These results could be used as indicators of nitrogen limitation for environmental or industrial monitoring of P. tricornutum.

MYB gene family in the diatom Phaeodactylum tricornutum revealing their potential functions in the adaption to nitrogen deficiency and diurnal cycle

The MYB transcription factor (TF) family is one of the largest and most important TF families, regulating the growth and response of microalgae to stress. However, the gene structure and characteristics of Phaeodactylum tricornutum MYB TFs, and their functions under nitrogen deficiency, have not been explored yet. To identify all P. tricornutum MYB (PtMYB) genes, the MYB gene family was analyzed at the genome-wide level in this study. A total ofm26 PtMYB genes were identified from the genome of P. tricornutum. These PtMYB genes were divided into 5 subfamilies: 5R-MYB, 4R-MYB, R2R3-MYB, R1R2R3-MYB, and MYB-related proteins. Phylogenetical motif and gene structure analyses of MYB genes indicated that the number and proportion of MYB TFs were species-specific, and MYB genes exhibited a lot of duplication events from microalgae to higher plants. Furthermore, the differentially expressed patterns of all 26 PtMYB TFs implied that PtMYB genes might have functional specificity under nitrogen deficiency. Homology analysis of MYB genes revealed that PtMYB3, PtMYB15, and PtMYB21 might play important roles in the regulation of the diurnal cycle and response to nitrogen stress in P. tricornutum. PtMYB3, PtMYB15, and PtMYB21 genes might be used as potential candidate genes for further studying the regulatory mechanisms of P. tricornutum under nitrogen deficiency. This work provides an important foundation for the future research of the potential functions of PtMYB genes and its diurnal regulatory mechanisms under nitrogen deficiency.

The Transition Toward Nitrogen Deprivation in Diatoms Requires Chloroplast Stand-By and Deep Metabolic Reshuffling

Microalgae have adapted to face abiotic stresses by accumulating energy storage molecules such as lipids, which are also of interest to industries. Unfortunately, the impairment in cell division during the accumulation of these molecules constitutes a major bottleneck for the development of efficient microalgae-based biotechnology processes. To address the bottleneck, a multidisciplinary approach was used to study the mechanisms involved in the transition from nitrogen repletion to nitrogen starvation conditions in the marine diatom Phaeodactylum tricornutum that was cultured in a turbidostat. Combining data demonstrate that the different steps of nitrogen deficiency clustered together in a single state in which cells are in equilibrium with their environment. The switch between the nitrogen-replete and the nitrogen-deficient equilibrium is driven by intracellular nitrogen availability. The switch induces a major gene expression change, which is reflected in the reorientation of the carbon metabolism toward an energy storage mode while still operating as a metabolic flywheel. Although the photosynthetic activity is reduced, the chloroplast is kept in a stand-by mode allowing a fast resuming upon nitrogen repletion. Altogether, these results contribute to the understanding of the intricate response of diatoms under stress.

Transcriptomic responses to phosphorus in an invasive cyanobacterium, Raphidiopsis raciborskii: Implications for nutrient management

Phosphorus (P) is a vital macronutrient associated with the growth and proliferation of Raphidiopsis raciborskii, an invasive and notorious bloom-forming cyanobacterium. However, the molecular mechanisms involved in P acclimation remain largely unexplored for Raphidiopsis raciborskii. Here, transcriptome sequencing of Raphidiopsis raciborskii was conducted to reveal multifaceted mechanisms involved in mimicking dipotassium phosphate (DIP), β-glycerol phosphate (Gly), 2-aminoethylphosphonic acid (AEP), and P-free conditions (NP). Chlorophyll a fluorescence parameters showed significant differences in the NP and AEP groups compared with the DIP and Gly-groups. Expression levels of genes related to phosphate transportation and uptake, organic P utilization, nitrogen metabolism, urea cycling, carbon fixation, amino acid metabolism, environmental information, the ATP-synthesis process in glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway were remarkably upregulated, while those related to photosynthesis, phycobiliproteins, respiration, oxidative phosphorylation, sulfur metabolism, and genetic information were markedly downregulated in the NP group relative to the DIP group. However, the expression of genes involved in organic P utilization, the urea cycle, and genetic information in the Gly-group, and carbon-phosphorus lyase, genetic information and environmental information in the AEP group were significantly increased compared to the DIP group. Together, these results indicate that Raphidiopsis raciborskii exhibits the evolution of coordination of multiple metabolic pathways and certain key genes to adapt to ambient P changes, which implies that if P is reduced to control Raphidiopsis raciborskii bloom, there is a risk that external nutrients (such as nitrogen, amino acids, and urea) will stimulate the growth or metabolism of Raphidiopsis.

Development of the "Applied Proteomics" Concept for Biotechnology Applications in Microalgae: Example of the Proteome Data in Nannochloropsis gaditana

Most of the marine ecosystems on our planet are still unknown. Among these ecosystems, microalgae act as a baseline due to their role as primary producers. The estimated millions of species of these microorganisms represent an almost infinite source of potentially active biocomponents offering unlimited biotechnology applications. This review considers current research in microalgae using the "omics" approach, which today is probably the most important biotechnology tool. These techniques enable us to obtain a large volume of data from a single experiment. The specific focus of this review is proteomics as a technique capable of generating a large volume of interesting information in a single proteomics assay, and particularly the concept of applied proteomics. As an example, this concept has been applied to the study of Nannochloropsis gaditana, in which proteomics data generated are transformed into information of high commercial value by identifying proteins with direct applications in the biomedical and agri-food fields, such as the protein designated UCA01 which presents antitumor activity, obtained from N. gaditana.

Hyperaccumulation of fucoxanthin by enhancing methylerythritol phosphate pathway in Phaeodactylum tricornutum

The established human health benefits of carotenoids along with the contemporary consumption of natural carotenoids bring the necessity to sustainable production of carotenoids. Among, marine diatoms have emerged as the potential biological resources for carotenoid production; however, their relatively lower yield in native strains provides the impetus to genetically improve the diatoms to cope with the burgeoning demand. In this study, we genetically improved the diatom Phaeodactylum tricornutum by overexpressing key carotenogenic genes involved in methylerythritol phosphate (MEP) pathway. The genes with lower relative transcript level under optimum conditions such as CMK and CMS were selected and overexpressed in P. tricornutum individually. Both CMK and CMS overexpressing lines exhibited elevated growth and photosynthesis. The expression of key carotenogenic genes such as PSY, PDS, ZDS, CRT, and LCYB was significantly upregulated. Furthermore, total carotenoid content was significantly increased; particularly, fucoxanthin content was increased by 1.83- and 1.82-fold in engineered lines CMK and CMS, respectively. Together, the results identify the potential metabolic targets and also uncover the crucial role of MEP pathway in redirecting metabolic precursors towards carotenogenesis. KEY POINTS: • Low abundant genes CMS and CMK of MEP pathway were overexpressed in the diatom • Total carotenoid content was increased, particularly fucoxanthin • Critical metabolic nodes were uncovered to accelerate fucoxanthin biosynthesis.

Toxicity evaluation of butyl acrylate on the photosynthetic pigments, chlorophyll fluorescence parameters, and oxygen evolution activity of Phaeodactylum tricornutum and Platymonas subcordiformis

Butyl acrylate is a hazardous and noxious substance (HNS) listed in the top 50 chemicals that is most likely to be involved in HNS spilling incident. At present, information about toxicity effect of butyl acrylate on marine organisms was insufficient, especially on marine microalgae. Phaeodactylum tricornutum (P. tricornutum) and Platymonas subcordiformis (P. subcordiformis) were used as test organism to evaluate the toxic effect of butyl acrylate on their photosynthetic system. Results showed that chlorophyll a (Chl-a) content, the net photosynthetic oxygen evolution rate (NOR), and chlorophyll fluorescence parameters including maximal photochemical efficiency (Fv/Fm), electron transfer rate (ETR), photochemical quenching (qP), and non-photochemical quenching (NPQ) were all stimulated in the toxic dose of 5,10, and 25 mg/L while those were significantly inhibited in the highest concentration of 25 mg/L groups after 96 h. Meanwhile, it was also found that Fv/Fm would be a suitable indicator for evaluating the toxicity of butyl acrylate on the photosynthetic system of two marine microalgae according to the analysis of Pearson correlation coefficient and integrated biomarker response (IBR). Once butyl acrylate enters the marine ecosystem, the toxicity data obtained in this study could be used as a reference for evaluating the effect of butyl acrylate on the photosynthetic capacity of marine microalgae.

Fatty Acids Derivatives From Eukaryotic Microalgae, Pathways and Potential Applications

The exploitation of petrochemical hydrocarbons is compromising ecosystem and human health and biotechnological research is increasingly focusing on sustainable materials from plants and, to a lesser extent, microalgae. Fatty acid derivatives include, among others, oxylipins, hydroxy fatty acids, diols, alkenones, and wax esters. They can occur as storage lipids or cell wall components and possess, in some cases, striking cosmeceutical, pharmaceutical, and nutraceutical properties. In addition, long chain (>20) fatty acid derivatives mostly contain highly reduced methylenic carbons and exhibit a combustion enthalpy higher than that of C_14–20 fatty acids, being potentially suitable as biofuel candidates. Finally, being the building blocks of cell wall components, some fatty acid derivatives might also be used as starters for the industrial synthesis of different polymers. Within this context, microalgae can be a promising source of fatty acid derivatives and, in contrast with terrestrial plants, do not require arable land neither clean water for their growth. Microalgal mass culturing for the extraction and the exploitation of fatty acid derivatives, along with products that are relevant in nutraceutics (e.g., polyunsaturated fatty acids), might contribute in increasing the viability of microalgal biotechnologies. This review explores fatty acids derivatives from microalgae with applications in the field of renewable energies, biomaterials and pharmaceuticals. Nannochloropsis spp. (Eustigmatophyceae, Heterokontophyta) are particularly interesting for biotechnological applications since they grow at faster rates than many other species and possess hydroxy fatty acids and aliphatic cell wall polymers.

CO2 supply modulates lipid remodelling, photosynthetic and respiratory activities in Chlorella species

Microalgae represent a potential solution to reduce CO2 emission exploiting their photosynthetic activity. Here, the physiologic and metabolic responses at the base of CO2 assimilation were investigated in conditions of high or low CO2 availability in two of the most promising algae species for industrial cultivation, Chlorella sorokiniana and Chlorella vulgaris. In both species, high CO2 availability increased biomass accumulation with specific increase of triacylglycerols in C. vulgaris and polar lipids and proteins in C. sorokiniana. Moreover, high CO2 availability caused only in C. vulgaris a reduced NAD(P)H/NADP+ ratio and reduced mitochondrial respiration, suggesting a CO2 dependent increase of reducing power consumption in the chloroplast, which in turn influences the redox state of the mitochondria. Several rearrangements of the photosynthetic machinery were observed in both species, differing from those described for the model organism Chlamydomonas reinhardtii, where adaptation to carbon availability is mainly controlled by the translational repressor NAB1. NAB1 homologous protein could be identified only in C. vulgaris but lacked the regulation mechanisms previously described in C. reinhardtii. Acclimation strategies to cope with a fluctuating inorganic carbon supply are thus diverse among green microalgae, and these results suggest new biotechnological strategies to boost CO2 fixation.