The Effect of Trophic Modes on Biomass and Lipid Production of Five Microalgal Strains

Five microalgae strains, namely Isochrysis galbana, Microchloropsis gaditana, Scenedesmus obliquus, Nannochloropsis oculata and Tetraselmis suecica, were selected as potential candidates for polyunsaturated fatty acids’ production, evaluating biomass productivity and their capacity to accumulate high lipid contents under different trophic modes. Microalgae strains were cultivated in the presence of 1% glucose using mixotrophic and heterotrophic conditions, while autotrophic cultures served as control experiments. The results demonstrate that S. obliquus performed the highest biomass productivity that reached 0.13 and 0.14 g L−1 d−1 under mixotrophic and heterotrophic conditions, respectively. I. galbana and S. obliquus utilized elevated contents of glucose in mixotrophy, removing 55.9% and 95.6% of the initial concentration of the carbohydrate, respectively, while glucose consumption by the aforementioned strains also remained high under heterotrophic cultivation. The production of lipids was maximal for I. galbana in mixotrophy and S. obliquus in heterotrophy, performing lipid productivities of 24.85 and 22.77 mg L−1 d−1, respectively. The most abundant saturated acid detected for all microalgae strains evaluated was palmitic acid (C16:0), while oleic and linolenic acids (C18:1n9c/C18:3n3) comprised the most abundant unsaturated fatty acids. I. galbana performed the highest linoleic acid (C18:2n6c) content under heterotrophic nutrition, which reached 87.9 mg g−1 of ash-free dry weight. Among the microalgae strains compared, the biomass and lipid production monitored for I. galbana and S. obliquus confirm that both strains could serve as efficient bioproducers for application in algal biorefineries.

PRUEBAS DE TOXICIDAD CON ELUTRIADOS DE SEDIMENTO MARINO DE LAS BAHÍAS LOS CHIMUS, TORTUGAS Y CASMA EN PERÚ EMPLEANDO LAS MICROALGAS Isochrysis galbana Y Nannochloropsis oceanica

Se realizaron pruebas de toxicidad con elutriados de sedimentos marinos provenientes de las bahías Los Chimus, Tortugas y Casma, en Perú, empleando las microalgas marinas Isochrysis galbana y Nannochloropsis oceanica. Las muestras de sedimento marino se colectaron en los meses de marzo y agosto de 2016. Estas pruebas de toxicidad se realizaron siguiendo los protocolos estandarizados, mediante pruebas estáticas a 96 h de exposición. Previamente, se determinó la sensibilidad de ambas cepas de microalgas al sulfato de cobre (CuSO4·5H2O) como sustancia de referencia. La Concentración de Inhibición media (CI50) obtenida en este ensayo demostró que I. galbana fue más sensible que N. oceanica. Los elutriados de los sedimentos marinos, provenientes de las zonas de estudio, presentaron diferentes niveles de toxicidad, tales como “no toxicidad” (CI50 = 90% - 100%), “moderada toxicidad” (CI50 = 59% - 81%) y “alta toxicidad” (CI50 < 59%) al emplear la microalga I. galbana; mientras que, para el caso de N. oceanica solo se presentó el de “no toxicidad” (CI50 = 90% - 100%) frente a las mismas muestras de elutriados de sedimentos. Estas pruebas de toxicidad demuestran que la microalga I. galbana detecta diferentes niveles de toxicidad, por lo que se podría emplear para evaluar ambientalmente muestras de sedimento marino como complemento a pruebas químicas, ya que no se discrimina el origen de la toxicidad.

Influence of Microalgae Diets on the Biological and Growth Parameters of Oithona nana (Copepoda: Cyclopoida)

Several species of the planktonic free-living genus Oithona have been successfully used in the larviculture of marine fish and shrimp. However, few studies have been published that allow us to estimate the potential of Oithona nana culture under controlled conditions. This work evaluated the effect of the microalgae Isochrysis galbana and Chaetoceros calcitrans as single (200,000 cells/mL) and mixed diets (100,000 + 100,000 cells/mL) on population and individual growth, ingestion rate, number of spawnings, fertility, development time by stage, and sex ratio of O. nana. We cultured this copepod at 28 ± 0.5 °C, 35 PSU salinity, 125 lux, and 12:12 photoperiod. Results showed that diet had no effect on the final population level (6273–7966 ind/L) or on individual growth, nor on sex ratio, with less males than females. With C. calcitrans, O. nana had a higher filtration rate (57 ng C/ind/day). On the other hand, a mixed diet induced a higher number of spawns (0.4 events/day) and nauplii per spawn (23 ind). Similarly, a single or mixed diet, containing I. galbana, accelerated the development rate by 6.33–7.00 days. We concluded that O. nana can be cultured with both microalgae, indicating its potential use in an intensive system for production. However, more research is required to improve the productivity of O. nana rearing.

Multi-omics Analyses Provides Insight into the Biosynthesis Pathways of Fucoxanthin in Isochrysis galbana

Isochrysis galbana is considered an ideal bait for functional foods and nutraceuticals in humans because of its high fucoxanthin (Fx) content. However, multi-omics analysis of the regulation networks for Fx biosynthesis in I. galbana has not been reported. In this study, we report a high-quality genome sequence of I. galbana LG007, which has a 92.73 Mb genome size, with a contig N50 of 6.99 Mb and 14,900 protein-coding genes. Phylogenomic inferences confirmed the monophyly of Haptophyta, with I. galbana sister to Emiliania huxleyi and Chrysochromulina tobinii. Evolutionary analysis revealed an estimated divergence time between I. galbana and E. huxleyi of ~ 133 million years ago (Mya). Gene family analysis indicated that lipid metabolism-related genes exhibited significant expansion, including IgPLMT, IgOAR1 and Δ-4 desaturase. Metabolome analysis showed that the content of carotenoid in I. galbana cultured under green light (7d-G) for 7 days was higher than that of white light (7d-W), and β-carotene was the main carotenoids, accounting for 79.09% of the total carotenoids. Comprehensive analysis of multi-omics analysis revealed that β-carotene, antheraxanthin, zeaxanthin and Fx content was increased by green light induction, which was significantly correlated with the expression of IgMYB98, IgZDS, IgPDS, IgLHCX2, IgZEP, IgLCYb, and IgNSY. These findings contribute to understanding Fx biosynthesis and its regulation, providing a valuable reference for food and pharmaceutical applications.

Efecto de la temperatura y concentración de microplásticos en la tasa de filtración del mejillón Semimytilus algosus (Mytiloida: Mytilidae)

Introducción: La presencia de microplásticos (MPs, partículas menores a 5 mm) y el incremento de la temperatura en los océanos, vienen generando perturbaciones en la vida marina, que se pueden relacionar con alteraciones en el metabolismo de organismos filtradores, como los mitílidos. Objetivo: Se evalúa el efecto de diferentes temperaturas y concentraciones de MPs sobre la tasa de filtración (TF) de Semimytilus algosus. Métodos: Una muestra de organismos (N = 72) fue expuesta a cuatro temperaturas (17, 20, 23 y 26 °C), y un testigo sin microplásticos (MPs0) y dos concentraciones de MPs (< 125 µm) de 0.125 mg/l (MPs1) y 0.250 mg/l (MPs2), todos en combinación con la microalga Isochrysis galbana (1x106 cel/ml/día) por 21 días. Resultados: A medida que aumentó la concentración de MPs, se redujo la TF de S. algosus. Respecto a la temperatura, durante el día 7 se observó una mayor TF a 23 °C en todos los tratamientos, y para los días 14 y 21 se obtuvieron los menores valores de TF a 23 y 26 °C. La acción conjunta del incremento de temperatura y MPs, afectó negativamente la TF de S. algosus, donde ambos factores ocasionaron el descenso de la TF para todos los tiempos de evaluación. No se registró mortalidad a 17 °C para ningún tratamiento, y en el caso de mitílidos expuestos a MPs1 y temperaturas de 20 y 26 °C se presentó la mayor mortalidad (67 %). Conclusiones: El estudio demuestra el efecto adverso del incremento de temperatura y MPs sobre la TF de S. algosus.

High Densities of a Prochlorophyte (Unresolved Species) Inhibit Grazing by the Herbivorous Copepod Parvocalanus crassirostris

Harmful algal blooms (HABs) are increasing in frequency and severity, underscoring the importance of understanding potential top-down controls of blooms. In the Indian River Lagoon (IRL), a shallow subtropical estuary, one harmful bloom was co-dominated by an unresolved prochlorophyte in the Family Prochlorothricaceae, which reached densities of &gt; 106 cells ml–1 engendering the term “Superbloom.” Experiments were conducted to evaluate grazing rates and the potential for top-down control by an abundant herbivorous copepod, Parvocalanus crassirostris, on the prochlorophyte. Those grazing rates were lower than the rates on a palatable alternative algal food, Isochrysis galbana, when both algal species were presented in monocultures with identical densities. Grazing on the prochlorophyte decreased or ceased at densities over 4.8 × 105 cells ml–1. When the prochlorophyte and the palatable alternative each comprised half of the total density, both species were consumed, but grazing on I. galbana was reduced compared to the grazing rates in a monoculture of this species, especially at higher cell densities. Copepod mortality was observed in treatments with high concentrations of the prochlorophyte, and these treatments contained mucilage. Experiments simulating viscosities produced by prochlorophyte mucilage yielded results consistent with the original grazing experiments (i.e., copepods showed lower grazing rates and higher mortality rates in higher viscosity treatments). Results reveal potential limitations of top-down controls by this grazer on prochlorophyte blooms and HABs that produce mucilage.

Antibacterial Activity of Microalgae Dunaliella salina, Tetraselmis chuii and Isochrysis galbana Against Aquatic Pathogens

Recently, expanded consideration has been paid to the business and potentiality of microalgae. Some microalgae are at present being studied for their capacity to find important metabolites for the drug industry or aquacultural applications. Concerning these biotechnological challenges, there is a consistent exertion accommodated in both finding and taking advantage of new microalgal assets and fostering their putative business results or modern valorizations. The crude methanol extracts of three microalgae, Dunaliella salina, Tetraselmis chuii, and Isochrysis galbana, have been investigated for antibacterial activity using the disk diffusion method against aquatic pathogens of fish, shrimp, and shellfish e.g. Pseudomonas fluorescence and Vibrio harveyi. This research aimed to analyze the antibacterial activity of crude extract of these microalgae against aquatic pathogens. The disk diffusion method was used to investigate the antibacterial activity. The result showed that only T. chuii has the inhibition zone for both tested bacteria P. fluorescence and V. harveyi with the inhibition zone of 3.0 ± 0.6 mm on 100 µg. g–1 of extract concentration and 4.20 ± 1.1 mm against P. fluorescence on 10000 µg. g–1 of extract concentration. While D. salina and I. galbana have inhibition zone only for V. harveyi with the inhibition zone of 4.4 ± 0.6 mm and 3.2 ± 0.7 mm on 10000 µg. g–1 of extract concentration. These three microalgae may have potential use in aquatic pathogens as antimicrobial agents. It would be possible to develop biologically active compounds of microalgae as a functional feed for aquaculture.

Fatty Acid Profiles of Selected Microalgae Used as Live Feeds for Shrimp Postlarvae in Vietnam

The importance of microalgal lipids for the survival and growth of shrimp postlarvae has been recognized in a range of studies. Microalgae with fast growth rates and high levels of polyunsaturated fatty acids (PUFA) are considered vital to maximise production and minimise cost in shrimp larviculture. The lipid content and fatty acid composition of microalgae used in shrimp production varies substantially between the algal classes and species being used in Vietnam. This study aims to characterise microalgal lipid and fatty acid (FA) profiles and evaluate the most promising species under growth conditions that are most suitable for shrimp aquaculture. Here, we report that the highest lipid contents were obtained in the Haptophyta microalgae, Tisochrysis lutea and Isochrysis galbana, at 90.3 and 61.1 mg/g, respectively. In contrast, two of the most popular diatom species being used for shrimp larval cultivation in Vietnam, Thalassiosira pseudonana and T. weissflogii, displayed the lowest lipid contents at 16.1 mg/g. Other microalgal species examined showed lipid contents ranging from 28.6 to 55 mg/g. Eicosapentaenoic acid (EPA, 20:5ω3) ranged from 0.6 to 29.9% across the species, with docosahexaenoic acid (DHA, 22:6ω3) present at 0.01 to 11.1%; the two omega (ω)–3 long-chain (LC, ≥C20) LC-PUFA varied between the microalgae groups. Polar lipids were the main lipid class, ranging from 87.2 to 97.3% of total lipids, and triacylglycerol was detected in the range of 0.01 to 2.5%. Saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) increased and PUFA decreased with increasing growth temperatures. This study demonstrated the differences in the lipid contents and FA profiles across 10 microalgal species and the effect of the higher temperature growing conditions encountered in Vietnam.

Feeding of a Scleractinian Coral, Goniopora columna, on Microalgae, Yeast, and Artificial Feed in Captivity

Nutritional requirements are critical in the process of coral aquaculture. In addition to energy from symbiotic algae, corals obtain sufficient nutrition through heterotrophic feeding. Microalgae and yeast are commonly used as nutritional supplements for many aquaculture organisms. In addition, if artificial feed can match or improve upon the nutritional supplementation provided by microalgae and yeast in the case of G. columna, then feeding this coral would be markedly easier. Hence, this article preliminarily discusses feeds suitable for G. columna. In this study, artificial PUFA rich in animal protein (R), Saccharomyces cerevisiae, Isochrysis galbana tml, and Nannochloropsis oculate were fed to G. columna at quantities of 5% and 10% of body weight. Growth, survival, body composition, and digestive enzymes were assessed. Regarding body composition, the coral’s protein content is higher than that of carbohydrate or fat; thus, evaluating the heterotrophic nutrition of G. columna by using protein absorption is appropriate. The protease content is also high in digestive enzymes. Protein content, protease activity, and specific growth rate were significantly higher in the R group than in other groups. The number of polyps in the groups fed R at 5% and 10% of body weight increased by 40.00 ± 2.43 and 47.33 ± 0.89 number, respectively, significantly greater increases than those achieved in the other groups (p < 0.05). Changes in body composition and digestive enzymes over a 24-h period were compared to determine the optimal feeding time. Protein content and protease activity increased markedly between 6:00 and 12:00. The experimental results suggest that R can improve the activity of G. columna digestive enzymes and their protein and lipid content in body tissue, shorten the cultivation time, and enhance the profitability of coral aquaculture.