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Biomass value upgrade of a stress-resistant, lipid-rich marine microalga Tetraselmis sp. CTP4

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Improved production of lutein and β-carotene by thermal and light intensity upshifts in the marine microalga Tetraselmis sp. CTP4
Publication . Schüler, Lisa Maylin; Santos, Tamara; Pereira, Hugo; Duarte, Paulo; Katkam, Dr. Gangadhar N.; Florindo, Claudia; Schulze, Peter S.C.; Barreira, Luísa; Varela, João
The industrial microalga Tetraselmis sp. CTP4 is a promising candidate for aquaculture feed, novel food, cosmeceutical and nutraceutical due to its balanced biochemical profile. To further upgrade its biomass value, carotenogenesis was investigated by testing four environmental factors, namely temperature, light intensity, salinity and nutrient availability over different growth stages. The most important factor for carotenoid induction in this species is a sufficient supply of nitrates leading to an exponential growth of the cells. Furthermore, high temperatures of over 30 degrees C compared to lower temperatures (10 and 20 degrees C) induced the accumulation of carotenoids in this species. Remarkably, the two different branches of carotenoid synthesis were regulated depending on different light intensities. Contents of beta-carotene were 3-fold higher under low light intensities (33 mu mol m(-2) s(-1)) while lutein contents increased 1.5-fold under higher light intensities (170 and 280 mu mol m(-2) s(-1)). Nevertheless, highest contents of carotenoids (8.48 +/- 0.47 mg g(-1) DW) were found upon a thermal upshift from 20 degrees C to 35 degrees C after only two days at a light intensity of 170 mu mol m(-2) s(-1). Under these conditions, high contents of both lutein and beta-carotene were reached accounting for 3.17 +/- 0.18 and 3.21 +/- 0.18 mg g(-1) DW, respectively. This study indicates that Tetraselmis sp. CTP4 could be a sustainable source of lutein and beta-carotene at locations where a robust, euryhaline, thermotolerant microalgal strain is required.
Improvement of microalgal biomass using physiological and genetic approaches
Publication . Schüler, Lisa Maylin; Varela, J.; Corre, Erwan; Barreira, Luísa
Microalgae are sustainable biological feedstocks of proteins, carbohydrates, and lipids rich in high-valuable carotenoids and n-3 fatty acids. To facilitate the application of microalgal biomass to food, feed and pharmaceutical markets, microalgal compounds extraction and production needs to be improved. In this thesis, carotenoid extraction was optimised using the euryhaline microalga Tetraselmis striata CTP4, which is known for its mechanical resistant cell covering. Glass bead-assisted disruption using wet biomass and acetone led to the best carotenoid recovery from this species. The same disruption method was afterwards successfully applied to the freshwater species Chlorella vulgaris. Thereafter, the carotenoid and EPA production of the obligate photoautotroph species T. striata was optimised by physiological and genetic approaches. The highest carotenoid content of 8.48 mg g-1 DW was achieved upon a thermal upshift from 20 to 35 °C under high light for only two days. The carotenoid profile contained high amounts of violaxanthin, lutein and β-carotene. However, upon random mutagenesis two norflurazon-resistant T. striata strains were isolated, displaying carotenoid contents of up to 10.2 mg g-1 DW. Comparative gene expression analysis of these mutants and the wildtype (CTP4) revealed the upregulation of several carotenogenesisrelated transcripts in the novel strains. Interestingly, these mutants displayed also fatty acid profiles enriched in EPA. A similar genetic approach applied to C. vulgaris under heterotrophic growth resulted into chlorophyll-deficient mutants with high protein contents of up to 48.7% of DW. Additionally, the norflurazon-resistant strain of C. vulgaris showed a deficiency in carotenoid accumulation. Overall, this study revealed that T. striata is a promising candidate for carotenoids and EPA production. Moreover, the mutants of C. vulgaris broaden the potential of algal biomass for based food products. Furthermore, the study of randomly mutagenized strains provided further insights into the regulation of metabolic pathways, being a powerful tool for strain improvement.
Dunaliella viridis TAV01: A halotolerant, Protein-Rich Microalga from the Algarve Coast
Publication . Bombo, Gabriel; Cristofoli, N. L.; Santos, Tamara; Schüler, Lisa M.; Maia, Inês Beatriz; Pereira, Hugo; Barreira, Luísa; Varela, João
Tolerance to harsh environmental conditions, high growth rates and an amino acid profile adequate for human consumption are beneficial features observed in Dunaliella viridis TAV01, a novel strain isolated from a salt pond in the Algarve, Portugal. TAV01 was identified down to the species level by maximum likelihood and Bayesian phylogenetic analyses of the ribosomal internal transcribed spacers one and two regions (ITS1 and ITS-2) and was supported by ITS2 secondary structure analysis. The biochemical profile revealed high protein (35.7 g 100 g−1 DW; 65% higher than the minimum recommended by the World Health Organization) and lipid contents (21.3 g 100 g−1 DW), a relatively higher proportion of the polyunsaturated fatty acids (PUFAs), α-linolenic (26.3% of total fatty acids (TFA)) and linoleic acids (22.8% of TFA), compared to those of other Dunaliella strains, and a balanced essential amino acids profile containing significant levels of leucine, phenylalanine, valine, and threonine. The major carotenoid was lutein, making up over 85% of total carotenoids. The presence of high-quality natural products in D. viridis TAV01 offers the possibility of using this new strain as a valuable biological resource for novel feed or food products as ingredients or supplements.

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Funding agency

Fundação para a Ciência e a Tecnologia

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Funding Award Number

SFRH/BD/115325/2016

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