A strategic approach to apply bacterial substances for increasing metabolite productions of Euglena gracilis in the bioreactor

Bacterial extracellular polymeric substances (EPS) are promising materials that have a role in enhancing growth, metabolite production, and harvesting efficiency. However, the validity of the EPS effectiveness in scale-up cultivation of microalgae is still unknown. Therefore, in order to verify whether the bacterial metabolites work in the scale-up fermentation of microalgae, we conducted a bioreactor fermentation following the addition of bacterial EPS derived from the marine bacterium, Pseudoalteromonas sp., to Euglena gracilis . Various culture strategies (i.e., batch, glucose fed-batch, and glucose and EPS fed-batch) were conducted to maximize metabolite production of E. gracilis in scale-up cultivation. Consequently, biomass and paramylon concentrations in the continuous glucose and EPS-treated culture were enhanced by 3.0-fold and 4.2-fold (36.1 ± 1.4 g L −1 and 25.6 ± 0.1 g L −1 ), respectively, compared to the non-treated control (12.0 ± 0.3 g L −1 and 6.1 ± 0.1 g L −1 ). Also, the supplementation led to the enhanced concentrations of α-tocopherols and total fatty acids by 3.7-fold and 2.8-fold, respectively. The harvesting efficiency was enhanced in EPS-supplemented cultivation due to the flocculation of E. gracilis . To the best of our knowledge, this is the first study that verifies the effect of bacterial EPS in scale-up cultivation of microalgae. Also, our results showed the highest paramylon productivity than any other previous reports . The results obtained in this study showed that the scale-up cultivation of E. gracilis using bacterial EPS has the potential to be used as a platform to guide further increases in scale and in the industrial environment. Key points Effect of EPS on Euglena gracilis fermentation was tested in bioreactor scale. EPS supplement was effective for the paramylon, α-tocopherol, and lipid production. EPS supplement induced the flocculation of E. gracilis.