Production of algal biomass production and high-value compounds mediated by the interaction of microalgal Oocystis sp. KNUA044 and bacterium Sphingomonas KNU100

There is growing interest in the production of microalgae-based high-value by-products as an emerging green biotechnology. However, a cultivation platform for Oocystis sp. has yet to be established. To overcome this limitation, we examined the effect of bacterial culture additions on the growth and production of valuable compounds the Oocystis sp. KNUA044 microalgal strain isolated from a locally adapted region in Korea. This microalgal strain grew only in the presence of a clear supernatant of Sphingomonas sp. KNU100 culture solution and generated 28.57 mg/L/d of biomass productivity. Protein content (43.9 wt%) was approximately two-fold higher than carbohydrate content (29.4 wt%) and lipid content (13.9 wt%). Among monosaccharides, the microalgal strain produced fucose (33 µg/mg and 0.94 mg/L/d), which has not been reported to date. Fatty acid profiling showed high accumulation of polyunsaturated fatty acids (PUFAs; over 60%) compared to saturated (29.4%) and monounsaturated fatty acids (9.9%) under the same culture conditions. Of these PUFAs, the algal strain produced the highest concentration of linolenic acid (C18:3 ω3; 40.2%) in the omega-3 family and generated eicosapentaenoic acid (C20:5 ω3; 6.0%), better known as EPA. Based on these results, we suggest that the application of a Sphingomonas sp. KNU100 strain-dependent culture for cultivation of Oocystis sp. KNUA044 is a promising future bioprocess for increasing algal biomass and high-value bioactive by-products, including fucose and PUFAs such as linolenic acid and EPA.