Lipidome in-depth characterization highlights the nutritional value and species-specific idiosyncrasies of different Ulva species

The genus Ulva comprises a large number of species widespread in the world, several of which are of commercial value, mainly for their nutritional benefits. However, identifying Ulva species is notoriously difficult, which largely explains why very few studies have attempted to characterize physiological and nutritional differences within the genus. If environmental modulation of seaweed lipid biomass composition for a number of species is well-documented, much less is known about genetic-driven differences in lipid profiles within a species or a genus. In this study, we analyzed the lipid profile of strains belonging to three species of foliose Ulva grown in the same conditions. Fatty acid profiling revealed the presence of 25 different fatty acids, palmitic acid being the most abundant fatty acid (FA) present in all species (35.1–41.2%). Important differences between the three species studied (U. australis, U. lacinulata and U. rigida) were observed. U. lacinulata had a higher content of saturated FA and a lower content of n-3 FA, suggesting that U. australis and U. rigida have a higher nutritional value. In contrast, Ulva lacinulata exhibited the lowest n-6/n-3 ratio, an increasingly important nutritional parameter, at the expense of decreased contents in both n-6 and n-3 FAs. A comprehensive analysis of the polar lipidome showed differences in the composition of complex lipids. Major differences were found within the class of sulfolipids, which are specific to chloroplast membranes, and have been proposed as bioactive lipids. Ulva rigida contained high relative amounts of SQDG(32:2) and SQDG(36:5), although a low content of SQMG (16:0), which are sulfolipid species that have been described as having biological activity. Therefore, detailed lipid profiling highlighted inter-specific differences, contributing to a better understanding of the physiology of the species studied, while also highlighting their potential as sources of molecular lipid species with bioactivity and nutritional benefits.