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Long-chain alkenones (LCAs) produced by phylogenetically classified Groups 1 and 3 Isochrysidales are increasingly used for paleotemperature and/or paleosalinity reconstructions in oligohaline lakes and marine environments. However, there are considerable difficulties in the paleoenvironmental interpretation of LCAs from Group 2 Isochrysidales thriving in saline lakes. The biggest challenge lies in our poor understanding of the complexity and ecological niches of individual Group 2 subclades in saline lakes. Here, we perform comprehensive analysis of haptophyte-specific 18S rRNA sequences and distributions of LCAs, and long-chain alkenoates (LCEs) in surface sediments and suspended particulate matter (SPM) from 37 saline lakes in northern China. These lakes span a large salinity gradient from 0.5 to 308‰. Combined with published genomic data of Group 2 Isochrysidales, our phylogenetic analysis reveals three Group 2 subclades occupying distinct ecological niches: one ice-related bloomer Group 2i and two warm-season bloomers Groups 2w1 and 2w2. Group 2i, the earliest seasonal bloomer, frequently co-occurs with Group 2w1 in sediments from saline lakes with relatively low to intermediate salinity waters, whereas Group 2w2 blooms in hypersaline waters. Based on existing data, C39:4 methyl alkenone is a chemotaxonomic biomarker for Group 2i. %C37:4 (relative abundance of C37:4 to the total C37 alkenones) values in the three Group subclades follow the order: Group 2i > Group 2w2 > Group 2w1. The %C37:4 in sediment cores of saline lakes does not directly record past salinity changes, but instead reflects variable contributions in production by these three subclades. This could indirectly and partially reflect overall salinity changes in some lakes dominated by Groups 2i and 2w1, but can be more complicated in lakes dominated by other assemblages. For our sites, we also demonstrate that direct use of C37 alkenone unsaturation indices ( U 37 K , U 37 K ' , and U 37 K ' ' ) for paleotemperature reconstructions in saline lakes is generally not feasible, except for cases where alkenone-producing Isochrysidales are dominated by one single species/subclade and seasonal production effects can be circumvented. We propose two possible alternative proxies for paleotemperature reconstructions in saline lakes: 1) unsaturation ratios of C41 and C42 alkenones, as these compounds are predominantly produced by a limited number of Group 2 species, such as Isochrysis nuda ( Liao et al., 2020 ); 2) C38Et/C36OEt ratio (ratio of C38 ethyl alkenones and C36 ethyl alkenoates), which appears to have similar temperature sensitivity for Groups 2w1 and 2w2, in lakes with no Group 2i inputs. Our study provides new insights into the phylogenetic classifications of Group 2 Isochrysidales and their ecological/environmental niches, which are fundamental for more quantitative and rigorous applications of LCAs and LCEs in saline lakes as paleosalinity and paleotemperature proxies.

The study examined different types of organic manure on the culture of marine plankton as a potential source of food for rabbitfish, Siganus stellatus, larvae. Cow dung showed significantly higher species abundance and diversity of cultured marine plankton followed by chicken and finally mixed media manure (p

Novel nutritional/functional applications of Isochrysis strains are mostly based on their diversified lipid classes. The content of these lipids is modulated by different factors, among which salinity has been comparatively understudied. Since managing salinity is key for optimal microalgae outdoor mass production and most studied Isochrysis strains are marine, the lipid response to nearly extreme hypo and hyper salinity in a new estuarine strain is here described. Total lipids in exponentially grown Isochrysis galbana VLP gradually decreased from 334 ± 36.6 mg g-1 at a salinity of 5 psu to 164.3 ± 24.4 mg g-1 at 50 psu. Present is the first report on lipid class (LC) remodeling in response to salinity in any Isochrysis strain. Two main storage lipids, steryl esters (SE) and triacylglycerol (TAG), underwent the fastest absolute decrease as salinity increased during both active and halted growth in the estuarine strain I. galbana VLP. Alkenones also decreased with salinity although less markedly. Among photosynthetic lipids, galactolipids were more affected by salinity than the anionic lipids. Salinity had minor influence on the relative sterol and betaine lipid proportions. Salinity explained more of total LC variation (34.6%) than culture stage (30.3%), whereas the opposite occurred with fatty acid (FA) variation. The main FA affected by salinity were 20:5n-3, 18:3n-3, 18:5n-3 and 18:2n-6. Nutritional value of I. galbana VLP from 5 psu exponential cultures was 1.5-fold to 2-fold higher than under all other conditions. Isochrysis production in low salinity waters can be a sustainable procedure compatible with its optimized nutritional value.

In the quest of finding local strains of marine ciliates that can be easily cultured under a broad range of salinity and fed with microalgae, Fabrea salina Henneguy, 1890 and Condylostoma sp. Bory de St. Vincent, 1826 were cultured for 22 days in small volumes at a temperature of 16–18 °C and fed with flagellated microalgae. F. salina presented a clear preference for the salinity of 40 ppt and Condylostoma. sp. for 20 ppt. Rhodomonas salina Hill and Wetherbee, 1989 were the most efficient feeds, resulting in 30 ind./mL in F. salina and 73 ind./mL in Condylostoma. Dunaliella salina Teodoresco, 1905 and Nephroselmis sp. F. Stein, 1878 also resulted in considerable ciliate densities while Isochrysis galbana Parke, 1949 came last with the highest density in Condylostoma. The strain of Tetraselmis sp. F. Stein, 1878 (var. red pappas) which is transformed in immobilized palmelloid cells and the dinoflagellate Amphidinium carterae Hulburt, 1957, which is suspected of toxin production, were inappropriate for both ciliates. These ciliates can be easily cultured and can serve as useful organisms in bioassays and probably as live food in marine fish hatcheries.

The paracalanid copepod,Bestiolina amoyensis, is a widely distributed species occurring in subtropical inshore waters across the Pacific Ocean. Its small size, herbivorous feeding habit, and high adaptability make the species one of the most promising candidates as potential live feed for hatchery larval rearing. This study investigated effects of different feeding density of microalgaeIsochrysisspp. (1 × 105, 2 × 105, 3 × 105, 4 × 105, and 5 × 105cells ml–1) and photoperiod (8L:16D, 12L:12D, and 16L:8D) on productivity-related parameters, including egg production, female life expectancy and population dynamics ofB. amoyensis. Results showed that total egg output over female lifespan, final population size and intrinsic rate of population of 12L:12D photoperiod treatments were always the highest among three photoperiod conditions, especially at the food concentration of 4 × 105cells ml–1, indicatingB. amoyensishad high reproductive performance and the population was in a more stable status. The number of nauplii from 4 × 105cells ml–1algal concentration treatment accounted for 75% of the population, and the ratio of females to males approaching 1:1 when photoperiod was 12L:12D; female life expectancy was 10.5 ± 0.6 days. In conclusion, our results showed thatIsochrysisspp. is a suitable feed forB. amoyensiswith an optimal concentration at 4 × 105cells mL–1; the optimal photoperiod forB. amoyensisrearing is 12L:12D. The relatively long reproductive lifespan and high intrinsic population increase rate makeB. amoyensisa good candidate to develop culture techniques for hatchery larval rearing.

International audience; Shellfish farming, a key sector of French aquaculture activity, allows the production of oyster spat in a controlled environment. Their production in commercial hatcheries requires control over the quality of the seawater used to sustain crossbreeding, breeding, and the production of fodder microalgae. Therefore, improving the filtration conditions of incoming water is crucial in ensuring the sustainability of production. An ultrafiltration pilot plant was therefore installed at Vendee Naissain. This ultrafiltration pilot plant allows filtration at 0.02 mu m; it is used upstream of hatcheries to eliminate pathogens and parasites that can influence the development of cultivated species and downstream to remove oyster gametes in hatchery effluents. The objectives of this work were: (i) to use ultrafiltered seawater for the culture of the microalga Isochrysis lutea (T-Iso) to determine whether better growth than that observed with borehole water, historically used by the producer, can be achieved; and (ii) to determine whether the use of ultrafiltered water results in better fertilization rates of the cupped oyster Crassostrea gigas compared to filtered and UV-treated seawater. Ultrafiltered water has shown definite efficiency for culturing T-Iso with rapid growth and significant reduction in contamination compared to cultivation in well water. The contribution of ultrafiltered water in hatching is more nuanced; ultrafiltered water does not stabilize hatch rates, and its quality is highly dependent on the quality of the seawater used.

Aim This study investigated the effect of several metabolic enhancers on the expression of fatty acid biosynthetic genes and their influence on the production of high-value PUFA in the marine microalgae Isochrysis sp., CASA CC 101. Methods and Results The effect of the presence of iron (Fe), nicotinic acid (NIC), methyl jasmonate (MJ) and thidiazuron (TDZ) on the expression of the fatty acid desaturase genes Δ6Des, Δ5Des and Δ4Des was studied in cultures of the marine microalga Isochrysis sp., CASA CC 101. The production of high-value PUFA like γ-linolenic acid (GLA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was correlated with these gene expressions. The results showed that MJ, Fe and TDZ significantly increased the lipid content than the control. MJ specifically up-regulated ∆6Des gene expression and thereby increased GLA production. Whereas Fe specifically increased ∆5Des gene expression and thereby increased EPA production. However, Fe and TDZ-treated cells effectively upregulated the expression of ∆4Des and increased the production of DHA when compared with control cells. Conclusions Our findings suggest that addition of Fe and MJ in the culture medium triggers the expression of PUFA biosynthetic genes, especially ∆6Des and ∆4Des, in marine microalga Isochrysis sp., CASA CC 101 their presence resulted in increased production of the PUFAs GLA, EPA and DHA. Significance and Impact of the Study This study shows that the addition of Fe and MJ to the culture media of Isochrysis sp., CASA CC 101 results in up-regulation of its genes Δ4Des, Δ6Des and Δ5Des, and improves the production of PUFA. Therefore, the addition of Fe and MJ to the culture medium is useful to increase the production of high-value PUFA in Isochrysis sp., CASA CC 101 and also to the other micro algal species.

Upwelling is known to affect the ecology and life history of temperate nearshore organisms, and these effects are thought to be mediated by changes in temperature and food supply. However, little information is available for tropical systems. To understand how changes in the intensity of upwelling might impact marine invertebrates, we tested how factorial combinations of temperature, salinity, and phytoplankton availability affected growth and reproduction of a common intertidal snail, Crepidula cf. marginalis. We used temperatures typical of nonupwelling (29°C), moderate (26°C) and severe (23°C) upwelling, salinities typical of nonupwelling (30 ppt) and upwelling (34 ppt) and a good diet (Isochrysis) and a better diet (Isochrysis and Tetraselmis) as a proxy for increased productivity during upwelling. Overall, temperature and diet had consistent effects on body size, with better food and lower temperatures promoting larger size, as well as promoting shorter time to first reproduction. Diet had the largest effects on clutch size, with clutch size increasing with better diet. Temperature had the largest effect on offspring size and the frequency of discarded broods; offspring size decreased with increasing temperature and the frequency of discarded broods also decreased with increasing temperatures. We found no significant 3rd order interactions and few significant strong 2nd order interactions, which have often been found in similar experimental studies using stressful treatments. For this tropical slipper limpet, the effect of higher food and cooler temperatures during upwelling appears to be positive, promoting higher growth rates, larger clutch sizes, and larger offspring size suggesting that both factors likely play an important role underlying reproductive responses to upwelling. Climatic changes, like El Niño, which suppress upwelling in the Bay of Panama, appear likely to negatively impact this species., To understand how they interact to effect life histories, we raised tropical snails (Crepidula cf. marginalis) under a factorial combination of diet, temperature, and salinity. The results show that a combination of lower temperatures and higher food availability results in increased growth, larger broods, and larger hatching sizes. C. cf. marginalis, therefore, performs better under conditions similar to upwelling compared to those similar to nonupwelling conditions experienced in the Bay of Panama. This effect is largely mediated through the increased body size under higher food and cooler temperatures.

El presente estudio evaluó el uso de las microalgas Arthrospira sp., Chlorella sp., Isochrysis sp. y Nannochloropsis sp. como constituyentes parciales del alimento balanceado para tilapia del Nilo (Oreochromis niloticus) bajo condiciones de cultivo estático en un estudio de 53 días de duración. Un alimento balanceado comercial con contenido de proteína cruda de 45% se utilizó como dieta control, mismo que se molió finamente y se reconstituyó incorporando, a un nivel de inclusión de 25% de la dieta, las harinas de las cuatro especies de microalgas mencionadas. Se analizaron parámetros de producción de tilapia, incluyendo índices de crecimiento y supervivencia, mediante análisis de varianza. Los índices de crecimiento, tales como peso final, peso ganado y porcentaje de peso ganado de los peces alimentados con las microalgas Arthrospira sp. y Chlorella sp., así como la supervivencia, fueron similares a los de aquellos que recibieron la dieta control, mientras que el crecimiento de peces alimentados con las microalgas Isochrysis sp. y Nannochloropsis sp. fue inferior estadísticamente. Estos resultados indican que Arthrospira sp. y Chlorella sp. pueden ser incorporadas a un nivel de 25% del alimento balanceado sin afectar significativamente el crecimiento o la supervivencia de O. niloticus.ABSTRACTIn the present study, the use of the microalgae Arthrospira sp., Chlorella sp., Isochrysis sp., and Nannochloropsis sp., as partial constituents in diets for Nile tilapia (Oreochromis niloticus), was evaluated in static tanks in a 53-day study, with a commercial diet containing 45% crude protein as a control treatment. Then, we replaced 25% of this diet with meals derived from each of the four microalgae species. Analysis of variance was employed to evaluate fish growth performance. Fish fed the diets with the microalgae Arthrospira sp. and Chlorella sp. had growth performance comparable to that of fish fed the control diet, as evaluated by growth parameters, such as final weight, weight gain, and percent weight gain, among others. In contrast, growth of fish receiving the microalgae Isochrysis sp. and Nannochloropsis sp. was significantly lower. Results of the present study indicate that the use of 25% of Arthrospira sp. and Chlorella sp. meals incorporated into the diet of O. niloticus does not compromise fish development, although there seems to be an opportunity for a further increment of the replacement level.

The purpose of this work was to investigate the viability of a microalgae catalytic pyrolysis/hydrotreating plant to kerosene, diesel and gasoline using Aspen Plus. A series of 2000 dry tonne per day scenarios were simulated with the final goal of determine the price in USD per litre of the drop-in fuels produced and the economic feasibility of the technique at a large-scale. Different scenarios (mechanical, solar and thermal drying), microalgae (Nannochloropsis and Isochrysis) and catalysts (Li-LSX zeolite, Ni-Ce/Al2O3, Ni-Ce/ZrO2). For this work, a systematic design approach by Douglas was considered and the whole process was actualised with the Marshall and Swift Cost Index of 2016. The lowest minimum fuel selling price (1.418 $/L) was found for Isochrysis and Li-LSX-zeolite. Finally, the sensitivity analysis showed that the bio-oil yield was the most influent factor, leading to a variation of the fuel price between 1.158 $/L to 1.751 $/L assuming a 20% of variation. The techno-economic assessment and sensitivity analysis indicated that Isochrysis and Li-LSX-zeolites are promising for the production of drop-in fuels, but further research is required to further reduce the price of the feedstock production and drying to be competitive with lignocellulosic materials.

DEVELOPMENT of Nitzschia sp. AS SEDIMENT TEST ORGANISM. Sediment bioassay requires a test organism which suitable with the test material, for example sediment. However, benthic phytoplankton as the test organism has not been widely applied in Indonesia. Recently, bioassay test still uses phytoplankton which lives in water column such as Chaetoceros gracilis, Tetraselmis sp., Isochrysis sp., or uses another test organism like mussel, sea urchin larvae and amphipod. In addition, Nitszchia sp. is one of culture collection at Research Centre for Oceanography so it could be added value of culture collection. Therefore, this paper aims to describe the potential use of phytoplankton benthic, Nitzschia sp. as sediment test organism.

Unique algal lipids known as alkenones were evaluated as potential phase change materials (PCMs). Alkenones were isolated and purified from commercial Isochrysis algal biomass and their thermal properties evaluated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Alkenone crystallinity appears to impact latent heat of fusion (ΔHfus), however both the ΔHfus and melting temperature (∼65 °C) of two different alkenone compositions obtained from separate commercial Isochrysis suppliers were nearly identical. Compared to a synthetic bis-fatty acid PCM, alkenones showed improved thermal stability by TGA and comparable ΔHfus (up to 275 J/g) by DSC. Overall the results demonstrate competitive properties for alkenones to other renewable and non-renewable PCMs such that alkenones represent a promising and potentially superior alternative for various ‘green’ PCM technologies.

Phytoplankton occupies a key trophic level in aquatic ecosystems. Chemical impacts on these primary producers can disrupt the integrity of an entire ecosystem. Two freshwater (Pseudokirchneriella subcapitata-Ps and Scenedesmus obliquus-S) and three marine (Phaeodactylum tricornutum-P, Isochrysis galbana-I, Tetraselmis suecica-T) microalgae species were exposed to dilutions of four chemicals: nanoparticles (n-TiO2, n-ZnO), amoxicillin (antibiotic), and white musk (personal care fragrance) to determine the half maximal effective concentration (EC50) after 72 h of exposure under standardized and controlled environmental conditions. Cell cultures were exposed to EC50 to determine sublethal effects (72 h) based on biochemical (chlorophylls a, b, c), molecular (changes in outer cell wall structure), and morphological alterations. We report for the first time EC50 values for nanoparticles in not standardized species (S, I and T) and for amoxicillin and white musk in all tested species. Standardized species (Ps and P) were less sensitive than non-standardized in some cases. Fourier-transformed infrared spectroscopy showed a marked spectral alteration (from 10.44% to 90.93%) of treated cultures compared to negative controls; however, principal component analysis disclosed no differences in molecular alteration between the five microalgae species or the two aquatic habitats considered. There was a significant decrease in chlorophylls content in all species exposed to EC50 compared to controls (Kruskal Wallis test; p < 0.05). There was a significant increase in cell-size (Mann–Whitney U test; p < 0.05) in I, P and T exposed to white musk and S exposed to amoxicillin. Findings highlight ecotoxicological risks from new generation pollutants for primary producers in aquatic ecosystems.

Marine and freshwater algae and their products are in growing demand worldwide because of their nutritional and functional properties. Microalgae (unicellular algae) will constitute one of the major foods of the future for nutritional and environmental reasons. They are sources of high-quality protein and bioactive molecules with potential application in the modern epidemics of obesity and diabetes. They may also contribute decisively to sustainability through carbon dioxide fixation and minimization of agricultural land use. This paper reviews current knowledge of the effects of consuming edible microalgae on the metabolic alterations known as metabolic syndrome (MS). These microalgae include Chlorella, Spirulina (Arthrospira) and Tetraselmis as well as Isochrysis and Nannochloropsis as candidates for human consumption. Chlorella biomass has shown antioxidant, antidiabetic, immunomodulatory, antihypertensive, and antihyperlipidemic effects in humans and other mammals. The components of microalgae reviewed suggest that they may be effective against MS at two levels: in the early stages, to work against the development of insulin resistance (IR), and later, when pancreatic -cell function is already compromised. The active components at both stages are antioxidant scavengers and anti-inflammatory lipid mediators such as carotenoids and -3 PUFAs (eicosapentaenoic acid/docosahexaenoic acid; EPA/DHA), prebiotic polysaccharides, phenolics, antihypertensive peptides, several pigments such as phycobilins and phycocyanin, and some vitamins, such as folate. As a source of high-quality protein, including an array of bioactive molecules with potential activity against the modern epidemics of obesity and diabetes, microalgae are proposed as excellent foods for the future. Moreover, their incorporation into the human diet would decisively contribute to a more sustainable world because of their roles in carbon dioxide fixation and reducing the use of land for agricultural purposes., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (grant numbers AGL2017-83599-R).

To develop greener extraction alternatives for microalgae biomass, ultrasound assisted extraction (UAE) and pressurized liquid extraction (PLE) with different biobased solvents were investigated, demonstrating that both techniques are useful alternatives for algal lipid extraction. Specifically, Nannochloropsis gaditana lipids were extracted by UAE and PLE at different temperatures and extraction times with sustainable solvents like 2-Methyltetrahydrofuran (2-MeTHF) and its mixtures with ethanol and other alcohols. The best oil yields for both PLE and UAE of N. gaditana were achieved with the mixture of 2-MeTHF:ethanol (1:3), reaching yields of up to 16.3%, for UAE at 50 °C and up to 46.1% for PLE at 120 °C. Lipid composition of the extracts was analyzed by HPLC-ELSD and by GC-MS to determine lipid species and fatty acid profile, respectively. Different fractionation of lipid species was achieved with PLE and solvent mixtures of different polarity. Thus, for the extraction of glycolipids, ethanolic extracts contained higher amounts of glycolipids and EPA, probably due to the higher polarity of the solvent. The optimized method was applied to microalgae Isochrysis galbana and Tetraselmis chuii showing the potential of mixtures of biobased solvents like 2-methyl-THF and ethanol in different proportions to efficiently extract and fractionate lipids from microalgal biomass.

Microalgal biomass is a sustainable and valuable source of lipids with omega-3 fatty acids. The efficient extraction of lipids from microalgae requires fast and alternative extraction methods, frequently combined with biomass pre-treatment by different procedures. In this work, Pressurized liquid extraction (PLE) was optimized and compared with traditional lipid extraction methods, Folch and Bligh and Dyer, and with a new Ultrasound Assisted Extraction (UAE) method for lipids from microalgae Isochrysis galbana. To further optimize PLE and UAE, enzymatic pre-treatment of microalga Isochrysis galbana was studied with commercial enzymes Viscozyme and Celluclast. No significant differences were found for lipid yields among different extraction techniques used. However, advanced extraction techniques with or without pre-treatment are a green, fast, and toxic solvent free alternative to traditional techniques. Lipid composition of Isochrysis was determined by HPLC-ELSD and included neutral and polar lipids, showing that each fraction comprised different contents in omega-3 polyunsaturated fatty acids (PUFA). The highest polar lipids content was achieved with UAE (50 &deg, C and 15 min) and PLE (100 &deg, C) techniques. Moreover, the highest omega-3 PUFA (33.2%), eicosapentaenoic acid (EPA) (3.3%) and docosahexaenoic acid (DHA) (12.0%) contents were achieved with the advanced technique UAE, showing the optimized method as a practical alternative to produce valuable lipids for food and nutraceutical applications.

Microalgae are renewable and valuable natural sources of triacylglycerol (TAG) for nutritional application or specific purposes. The aim of this study was to evaluate the TAGs produced by twelve microalgae species for production of human milk fat substitutes (HMFs). The investigated species were Chlorella vulgaris (CV-15 and CV-395), Chlorella zofingiensis, Chlorella pyrenoidosa, Scenedesmus sp., Chlorococcum sp., Nitzschia laevis, Phaeodactylum tricornutum, Isochrysis sp., Isochrysis galbana, Nannochloropsis oceanica and Nannochloropsis salina. The total fatty acids (TFAs) contents of these species varied from 15.9 to 31.1%. TAG was the main lipid class (65.1–91.0%). Based on the evaluation model in view of the fatty acid composition and positional distribution of TAGs by GC–MS and 13C NMR, among the tested species, Isochrysis-derived TAGs mimicking human milk TAGs (HMTs) gave the highest G values (deducting score) that were close to that of lard. The G value (69.2) of Isochrysis sp. TAG was within the range of G value for local infant formulas; whereas, the G value (61.2) of I. galbana TAG was a bit lower than the lower limit of local infant formulas. Moreover, the melting and crystallization properties of TAGs from Isochrysis sp. and I. galbana were similar to those of HMTs. These results showed that Isochrysis TAGs could be promising candidates for HMFs feedstock.

The effects of mono- and bi-microalgal diets on shell length, organic tissue, and survival of Spondylus limbatus juveniles were tested in two separate feeding experiments. The first examined nine single species of microalgae: Chaetoceros gracilis, C. muelleri, Isochrysis aff. galbana (T-ISO), Tetraselmis chuii, T. maculata, Pavlova lutheri, Dunaliella salina, Rhodomonas sp., and Nannochloropsis sp. An extra treatment maintaining the juveniles in a long line culture was at Ayangue Bay, Province of Santa Elena, Ecuador. Single diets of P. lutheri, C. muelleri, and C. gracilis showed the best combined growth of survival performance in juveniles, and were therefore selected for the bi-algal diet experiment design with the inclusion of I. galbana T-ISO due to its recommended use in bivalve culture. A second experiment consisted in selecting the best three microalgae species that resulted from the first experiment and combined each other in binary treatments at 1:1 ratio. All bi-algal diets in combination with P. lutheri showed good result in growth (shell and biomass), yield, and survival. However, single P. lutheri mono-algal diet showed equal or better performance index than the other bi-algal combined diets, demonstrating the pertinence in using this microalga as food for S. limbatus juveniles.

The chlorophyll fluorescence parameters of Isochrysis. galbana at different nitrogen levels were determined by using chlorophyll fluorescence with the aim of better understanding the operative status of photosynthetic system II (PSII) and electron transport chain in oleaginous microalgae. In this experiment, the growth and photosynthetic efficiency were restricted in N-deprived I. galbana, which were mainly presented in significant decrease of cell numbers and chlorophyll content, the dramatic decline of Fv/Fm, P.I., ΦPSII and rETR, and commensurate increase of NPQ and Wk. The growth of algal cells gradually increased with rising nitrogen concentration, especially reached the top in N-1.76 mM L1 medium, but were inhibited in N-3.52 mM L1 medium. The results suggested that N-deprivation and N-deficiency could inhibit the growth and photosynthesis of I. galbana, but excessive nitrogen could also restrict the growth of algal cells. The nitrogen concentration plays an important role in the algal growth and photosynthesis.

In this exploratory study, eight types of microalgae from different phyla (Chlamydomonas reinhardtii, Chlorella species, Haematococcus pluvialis, Porphyridium purpureum, Porphyridium cruentum, Isochrysis species, Isochrysis galbana, and Pavlova lutheri) were tested for their antibacterial activities against eight target pathogenic bacterial strains. The agar well diffusion method and broth micro dilution assay were conducted to estimate the antibacterial activity. Microalgae cell-free supernatants, exopolysaccharides (EPS), water, and organic solvent extracts were used for inhibition analysis. EPS extracted from P. lutheri showed activity against Bacillus subtilis and Pseudomonas aeruginosa. Inhibition zone diameters of 14- 20 mm were recorded on agar plates, while the minimum inhibitory concentrations in the broth micro dilution assay were 0.39-25 mg ml-1. During this study, haptophyte microalgae, Isochrysis species, and P. lutheri extracts showed the highest activity against most of the tested pathogenic bacterial strains, while most of the extracts were active against the important foodborne pathogen P. aeruginosa. This study showed promising results regarding important microalgae phyla, which will further aid research related to extracts and exploitation of bioactive metabolic compounds in the food and pharmaceutical industries.

We report 1900-year long records of alknone concentration, C38/C37 ratio, and U 37 k , U 37 k ' and a newly-developed alkenone unsaturation index U 37 k ' ' -based temperatures in a sediment core retrieved from Kusai Lake in the northern Qinghai-Tibetan Plateau. The predominance of C37 and C38 alkenones with minor presence of C39 and C40 alkenones, and the absence of C38 methyl alkenones are indicative of alkneones produced by Isochrysis, which is consistent with the results of sedimentary haptophyte DNA analyses. The interval from 400 to 1200 AD is characterized by higher alkenone concentrations and C38/C37 ratios than the other intervals, which can be attributed to the predominant production of Isochrysis during the entire phytoplankton blooms. With the assistance of information on gene abundance, we attributed this phenomenon to drastic ecological changes in Kusai Lake around 1200 AD in response to climatic changes from warm and wet to cold and dry conditions, and resultant decreased riverine inflow but increased nutrient concentration. The U 37 k ' ' -based temperatures with U 37 k ' ' substituting U 37 k ' in a equation concluded based on studies on lakes from high latitude areas in Germany are the most reliable reconstructed summer surface water temperatures for Kusai Lake since they are close to the current summer monthly mean temperature of Wudaoliang Meteorological Station, approximately 50 km to the south of Kusai Lake, and exhibit variations that are generally in accordance with those of the 51-year moving average summer temperatures reconstructed from thicknesses of varve light layers in Kusai Lake sediments. Besides, variations showed by this U 37 k ' ' -based summer surface water temperatures are also generally consistent with those showed by reconstructed temperatures in China.

Microalgae could be of importance for future biodiesel production as an alternative for a third generation of biofuels. To select the most appropriate strain for biodiesel production, three microalgae species, namely Isochrysis sp., Nannochloropsis maritima and Tetraselmis sp., isolated from Tunisian coast, were biochemically characterized. Initially, gas chromatography analysis showed that Isochrysis sp. and N. maritima contained 5- and 10-fold total fatty acids, respectively, more than Tetraselmis sp. Then, the two microalgae Isochrysis sp. and N. maritima were subject to random mutagenesis using ultraviolet-C radiation. Subsequently, a total of 18 mutants were obtained from both species. The neutral lipid evaluation on said 18 mutants allowed the retention of only 7 to further fatty acid characterization. Finally, gas chromatography revealed that the mutant 5c Isochrysis sp. was characterized by a high level of saturated fatty acids (52.3%), higher amount of monounsaturated fatty acids (29.3%), lower level of polyunsaturated fatty acids (18.4%) and a significant 1.3-fold increase in its C16-C18 content compared to the wild-type strain, which would make it an interesting candidate for biofuel production.

The aim of this study is to produce new medium-long-medium structured triacylglycerols (MLM-STAGs) containing caprylic acid (CA) at the sn-1,3 positions, and long chain saturated fatty acids (LCSFAs) and bioactive fatty acids at the sn-2 position via two-step enzymatic process by Lipozyme TL-IM, using autotrophic microalgae (Isochrysis galbana) TAGs. In the first step, the ethanolysis of microalgae oil TAGs for 2-monoacylglycerols (2-MAGs) production are performed in the presence of water content of 5 wt% at ethanol/oil mole ratio of 24:1 with Lipozyme TL-IM at 25 °C for 12 h. In the larger-scale production of 2-MAGs, the 2-MAGs yield and the purity of the purified MAGs attained are 31.44-36.08 wt% and 91.57 mol%, respectively. In the second reaction, these 2-MAGs are esterified with caprylic acid (CA) in n-hexane system to synthesize almost pure MLM-STAGs with the recycled Lipozyme TL-IM under the optimized conditions. The final MLM-STAGs contain 64.28% CA and 13.35% ω-3 polyunsaturated fatty acids. The CA-LCSFAs-CA (43.01%) and novel CA-stearidonic acid (SDA, C18:4ω-3)-CA (23.88%) are the major MLM-STAGs present. In all, Isochrysis galbana-derived oil containing SDA is a promising source for producing high-value microalgal bioproducts by two-step enzymatic process in a cost-effective manner.