Chlorophyta microalgae as dietary protein supplement: a comparative analysis of productivity related to photosynthesis

Microalgae are studied as innovative sources of a wide range of highly valuable products, including proteins for the food/feed sectors. However, protein content varies depending on algal species, culture conditions and harvesting period. The Phylum Chlorophyta includes most of the described species of green algae. Due to their remarkable peculiarities, four Chlorophyta species belonging to two distinct classes were selected for the research: Chlorella vulgaris and Chlorella protothecoides as Trebouxiophyceae, and Neochloris oleoabundans and Scenedesmus acutus as Chlorophyceae. The algae were studied to obtain comparative results about their growth performance, and total protein content and profile under the same culture conditions. Since photosynthetic process directly influences biomass production, photosynthetic pigment, PSII maximum quantum yield and thylakoid protein content and profile were analysed. SDS-PAGE and 2D BN/SDS-PAGE were performed to expand information on the organization and assembly of the resolved thylakoid complexes of samples. Despite the algal species showed similar growth rates and photosynthetic efficiency, S. acutus showed the highest capability to accumulate proteins and photosynthetic pigments. Regarding the thylakoid protein profile, the two Trebouxiophyceae showed very similar pattern, whereas different amounts of LHCII occurred within the two Chlorophyceae. Finally, the separation of thylakoid protein complexes in 2D BN/SDS-PAGE revealed a more complex pattern in S. acutus as compared to the other species. Overall, it is suggested that a higher stability of the photosynthetic membranes can result in higher biomass and protein production. Altogether, results have highlighted the metabolic uniqueness of each strain, resulting in a non-obvious comparison with the other species