BIOCOMPOUNDS FOR AQUACULTURE FROM NEW MICROALGAE STRAINS Tetraselmis sp. IPM3 AND Skeletonema sp.

Microalgae are considered a potential source of nutrient in aquaculture and food industries, due  to their high content and quality of lipids, proteins and vitamins. They also  can have antifungal and antibacterial activities. Focusing on their nutritional value and therapeutic activities, they can play an important role in aquaculture, especially in fish larvae production. In this work, we describe the culture conditions for the recently isolated microalgae: Tetraselmis sp. IMP3 and Skeletonema sp. Tetraselmis sp. IMP3 was cultured indoors, in 70-L plastic bag photobioreactors for 12 days (stationary phase), under continuous light intensity (150 µmol.m².s^-1, 16 h light - 8 h dark), controlled temperature (20ºC ± 2) and cultures were grown in concentrated modified Algal culture medium (MAM) under continuous mixing with filtered air. IMP3 follows the usual pattern for microalgae growth, with a lag phase, followed by an exponential growth phase, starting after the first day, reaching the stationary phase at day 7, with a starting inoculum concentration of 3.4 x 10 ⁴ ± 1.1 x 10³ cells mL^-1. The maximum concentration of  IMP 3  was  6.5 x 10 ⁵ ± 1.0 x 10⁴  cells mL^-1 (figure 1),   while its maximum specific growth rate was 0.26 d^-1, between days 1 and 7. The biomass was harvested by centrifugation (2500  g for 10 minutes) with a total yield of 28.3 g. L^-1 , and was stored at -80 ºC and freeze-dried before analyses. The biomass of Skeletonema sp., provided by Necton S.A. (Necton , Companhia Portuguesa de Culturas Marinhas , S.A., Olhão, Portugal) was produced in tubular photobioreactors using semi-continuous cultivation approach. Key bioactivities were analysed in order to assess their potential for the development of an aquaculture nutraceutical. Skeletonema had the highest total polyphenol content, reaching 300-400 mg/100 g dw . Gentisic acid was the main phenolic compound in the aqueous and ethanolic extracts of this microalga. Skeletonema also displayed the highest antioxidant activity. The Ferric Ion Reducing Antioxidant Power (FRAP) and 2,2'-azino-bis  (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) methods showed higher antioxidant power for Skeletonema sp. extracts, reaching an ABTS reduction of more than 80 %. Concerning anti-inflammatory activity, ethanolic extracts of Skeletonema sp. exhibited the highest inhibitory capacity of cyclooxygenase-2 (COX45 2) for an extract concentration of 1 mg/ml, 82 ± 2 %, which compares to 45 ± 5 % in Tetraselmis sp. IMP3. Aqueous extracts had, always, a lower anti-inflammatory capacity. We can, t herefore,  conclude that these microalgae have potential for multiple applications, ranging from bioactive feedstocks to nutraceutical and pharmaceutical uses.

T his study had the support of the project ALGARED+ (INTERREG VA (POCTEP), ID: 1398).