The cyanobacterial genus Arthrospira Stizenberger ex Gomont 1892 includes some of the most commercially significant microalgae, commonly known under the taxonomically incorrect brand name ‘Spirulina’. However, the infrageneric classification of the genus is still undefined. Herein, the classification of two Arthrospira strains (Nigrita M1 and Nigrita C1) from a commercial culture installation was studied and a polyphasic meta-analysis approach to a representative number (> 30) of strains was applied, in an attempt to determine the taxonomic relationships among the existing Arthrospira strains. The combined analysis of molecular (16S rRNA, 16S-23S rRNA ITS and cpcBA-IGS sequences) and phenotypic (13 morphological and morphometric characters) data of the studied Arthrospira strains divided them into three clusters/taxa. The main two taxa, namely Taxon I and Taxon II, include planktonic representatives, with irregular and regular helical structure of the filament, respectively. In contrast, Taxon III comprises the benthic representatives of the genus. Arthrospira strains Nigrita M1 and Nigrita C1 fall into Taxon I and II, respectively. The combined phenotypic and phylogenetic analysis suggests classification of Arthrospira strains into three taxa as subspecies of a single species within the genus Arthrospira.

Chlorella sorokiniana is a well-studied microalga with significant nutritional potential due to its health-promoting nutrients. C. sorokiniana is rich in proteins (~50%), lipids (~14%), vitamins, and other bioactive compounds, making it an attractive ingredient for the food industry. Other properties of C. sorokiniana, such as its foaming properties, have not been extensively investigated. The present work examines the foaming properties of C. sorokiniana biomass and of its fractions, namely the foaming properties of the whole-cell biomass, the disrupted-cell biomass, the water-soluble protein-rich extract, and the disrupted-cell biomass residue after oil extraction. The water/air interfacial tension, zeta potential, foaming capacity, foam stability, and foam morphology of C. sorokiniana biomass and its fractions were determined. Furthermore, the effect of the pH on the foaming properties of the water-soluble protein-rich extract was also investigated. The results show that the examined fractions decrease the water-air interfacial tension and form foams. The type of biomass fraction affects strongly the foam characteristics and foam stability. Furthermore, the stability and characteristics of the foam are significantly affected by pH. Overall, the water-soluble protein-rich extract at pH 7 presented the best foam stability, as the foam remained stable for more than 24 h and had a narrow bubble size distribution. The obtained results suggest that fractionated microalgae biomass could be used as an effective foaming agent in different commercial applications.

The green microalga Monoraphidium sp. has potential for biodiesel production since it grows fast and can accumulate high levels of lipids. However, there is a lack of information on the potential use in human nutrition. In this work Monoraphidium sp. was characterized in terms of macronutrients with a special focus on the fatty acid profile of the lipid fraction and on the amino acid profile of the proteins. Furthermore, aiming at nutrient valorization, various methods for lipid extraction that could be used in the production of high quality and safe foods were investigated. To this end, the focus was on cell disruption methods in order to optimize oil recovery. The Monoraphidium sp. biomass had a high protein concentration (44.5 %) and a relatively low lipid concentration (12.5 %) but was rich in ω-3 fatty acids demonstrating its high nutritive value. Regarding cell disruption, ultrasonication and high-speed homogenization were insufficient to disrupt cells under the conditions examined. On the other hand, the effectiveness of the ball milling was regulated via processing time and water-to-biomass ratio and complete cell disruption could be achieved by this method. For lipid extraction, solvent extraction using a mixture of food-grade hexane and ethanol resulted in an oil recovery of 70.4 %, whereas using ethanol alone as an environmentally friendly solvent resulted in an oil recovery equal to 54 %. Supercritical CO₂ extraction resulted in a lower oil recovery (25 %), whereas ethanol addition, as a cosolvent to CO₂, significantly increased the oil recovery (60 %).

The genus Dunaliella belongs to the division Chlorophyta and is known for its ability to survive in highly saline environments. Dunaliella is an important source of carotenoids, especially beta-carotene and has a wide range of applications. In this study, we aimed to isolate and identify Dunaliella strains from active and abandoned saltworks in Greece. Four seasonal samplings were carried out in seven active saltworks and two samplings were performed in an abandoned saltwork throughout the year 2020. Strains were characterized based on their morphological and phylogenetic traits, whilst their beta-carotene potential were evaluated. Fifteen (15) Dunaliella strains were isolated and classified into nine species based on morphological and morphometrical features. The isolated strains were assigned to different species such as D. parva, D. granulata, D. minuta, D. terricola, D. asymmetrica, D. bioculata, D. viridis, D. minutissima, and D. polymorpha. The results of the phylogenetic analysis indicate the formation of distinct clades among different Dunaliella species and suggest that morphological and morphometrical features may not always align with the phylogenetic position of species in the Dunaliella clade. Strains were found to produce a low amount of beta-carotene under default laboratory conditions. This study comprises the first phylogenetic inference of several Dunaliella species and highlights a gap on molecular data for Dunaliella spp. We provide valuable information on the diversity of Dunaliella strains in the saltworks of Greece, which can be used for further research and biotechnological applications.

Microalgae are a promising alternative source of PUFAs, with Chlorella being one of the few microalgae widely available in the nutraceuticals market authorized for human consumption. This study explores the fatty acid (FA) profiles of nine C. sorokiniana biomass feedstocks produced under different combinations of light intensity and nitrogen and inorganic carbon loadings, derived via a Taguchi L9 (3³⁻¹) orthogonal array design. Additionally, the nutritional and medical value of Chlorella lipids using several nutritional indices is assessed. PUFAs were maximized under low light intensity and high nitrogen loading; however, these conditions favored the overaccumulation of omega-6 FAs. For omega-3 FA maximization, high light intensity must be applied, suggesting that high illumination induces the desaturation of linoleic acid to alpha-linolenic acid (ALA) in C. sorokiniana cells. Additionally, nitrogen-depleted conditions significantly downgraded its quality due to the overaccumulation of saturated FAs. Despite lacking EPA and DHA, C. sorokiniana lipids are an excellent source of ALA, surpassing concentrations met in plant-based oils. Thus, Chlorella lipids can be included in humans’ diet, satisfying daily ALA requirements; however, accurately labeling the FA profile of Chlorella products, prior to any nutritional claims, is indispensable, considering the sizeable variations in their profile under the impact of cultivation conditions.