Comprehensive utilization of the filamentous oleaginous microalga Tribonema utriculosum for the production of lipids and chrysolaminarin in a biorefinery concept

Abstract

Previous studies have focused on the accumulation of lipid and palmitoleic acid in Tribonema spp., while chrysolaminarin produced by these filamentous oleaginous microalgae has rarely been reported. In this study, the effects of different initial nitrogen concentrations on the growth, lipid and chrysolaminarin accumulation of T. utriculosum were investigated, and the extraction route of lipid was also optimized, accompanied by the isolation and characterization of chrysolaminarin. The results showed that the highest biomass concentration (6.21 ± 0.17 g/L) of T. utriculosum was obtained at 3 mM of initial nitrogen concentration with the lowest level of chrysolaminarin (10.74 ± 0.42% of dry weight (DW)), while higher initial nitrogen concentrations were more conducive to lipid and chrysolaminarin accumulation, especially for 18 mM, leading to the highest lipid content (43.80 ± 0.57% of DW). To minimize the biorefinery process cost, an optimized route for lipid extraction was suggested to simultaneously achieve the goal of disintegration of algal structure and extraction of intracellular polysaccharides by dilute acid pretreatment, which improved lipid extraction efficiency from 38.70% to 87.09%. Most importantly, a homogeneous chrysolaminarin was successfully isolated from T. utriculosum and characterized with an average molecular weight of 5.99 kDa. It was found to mainly comprise glucose (60.13%) and was linked by the β-D-(1 → 3) (main chain) and β-D-(1 → 6) (branch chain) glycosidic bonds. This study is the first report on the isolation and characterization of chrysolaminarin from microalgae Tribonema, and provides new insights into fully utilizing T. utriculosum biomass for broadening the potential applications of microalgae-based products.