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In the pursuit of sustainable sources for food, energy, and health products, microalgae have gained attention. In the present study, the lagoonal system of the Nestos River delta was selected as a sampling point in order to search for opportunistic and robust species. Two new strains of Tetraselmis are described with regards to their taxonomic features (as observed using light and transmission electron microscopy and molecular phylogenetics) and their biochemical properties (total lipid, total protein, and total carbohydrate content, photosynthetic pigments, and antioxidant capacity). The studied strains were identified as representatives of Tetraselmis verrucosa f. rubens. Furthermore, both strains exhibited an interesting biochemical profile coupled with high growth rates and promising antioxidant activity, without the use of enhancement and induction culture methods, warranting further investigation and showing potential for biotechnological use.

The culture growth and carotenogenic activity of two Greek Dunaliella salina strains (AthU-Al D30 and AthU-Al D31) under stress conditions are investigated herein, with emphasis on β-carotene production as well as on lutein and zeaxanthin. In particular, the strains were cultivated in “standard” conditions (60 ‰ salinity and 1.18 M of NaNO3), under salinity stress conditions (160 ‰ salinity and 1.18 M of NaNO3) and under nitrogen deprivation conditions (60 ‰ salinity and 0 M of NaNO3). In addition to the two Greek strains, the D. salina CCAP 19/18 strain, which has been extensively studied regarding carotenogenesis, is included in this study as a reference. All three strains were found to produce increased amounts of β-carotene when cultivated under nitrogen deprivation conditions, while the AthU-Al D31 strain also produced high amounts of carotenoids under salt stress. The HPLC carotenoid profiles of the strains revealed reduced production of lutein in nitrogen deprivation conditions, coupled with a high production of β-carotene. The strains exhibited various responses in terms of carotenogenic activity, indicating an intraspecific variation in the metabolic reactions related to carotenogenesis.

Cyanobacteria are a group of oxygenic photosynthetic prokaryotes found in almost all habitats on earth including those characterized as extreme environments. It has been observed that the number of studies dealing with the biodiversity of extremophilic cyanobacteria is limited while studies exploring their bioactive potential are even scarcer. The taxonomy of three Nostoc-like cyanobacterial strains isolated from a shallow lake in Brazil was studied by applying a polyphasic approach. The bioactive potential of the strains was also evaluated using antimicrobial susceptibility testing. The metabolites present in the bioactive HPLC fractions were identified by UPLC/ESI/Q-TOF. Based on our phylogenetic inferences in combination with morphological and ecological information, we describe Aliinostoc alkaliphilum sp. nov., exhibiting antibacterial and antifungal activities. The main bioactive metabolite in all three strains was nocuolin A, which represents the first report of this metabolite in Aliinostoc. Our phylogenetic studies also revealed that many bioactive metabolite-producting strains that are currently assigned to Nostoc belong to other distinct evolutionary lineages. These findings highlight the importance of polyphasic approach studies in both cyanobacterial taxonomy and natural product discovery programs.