Amino acids profile of 56 species of microalgae reveals that free amino acids allow to distinguish between phylogenetic groups

Microalgae represent a phototrophic resource with a high protein content, whose nutritional value is very high as a result of its amino acid profile. Although the total amino acid profile has been repeatedly described to change little among phylogenetic groups of microalgae, some variability has occasionally been reported. Part of this uncertainty is associated with the low phylogenetic diversity encompassed in the work to date and the high methodological variability between studies. Among these studies, very few have differentiated between total and free amino acid content for common microalgae samples. Thus, in the present work, the profile of total and free amino acids has been determined in a diverse group composed of 56 species of microalgae belonging to 7 phyla. A multivariate analysis of the total amino acid profile in the studied microalgae group revealed close amino acid patterns throughout microalgae phylogeny and agreed with results obtained from similar analysis performed with published data. Conversely, the free amino acid profile strongly differentiated between phylogenetic groups. On the one hand, species of Cyanobacteria, Plantae, Cryptophyta, and Bacillariophyta showed close free amino acid patterns, characterized by the highest abundance of free glutamic acid. Ochrophyta species were particularly rich in free proline, while the free amino acid profile of Miozoa and Haptophyta species stood out from the rest of the phylogenetic groups for their outstanding levels of the two essential amino acids phenylalanine and lysine. Haptophyta species were also characterized by their much higher free tyrosine content.