Effects of co-culturing Schizochytrium sp. and Escherichia coli cells on biomass and Docosahexaenoic acid (DHA) production

Abstract

Heterotrophic marine microalga Schizochytrium sp. is one of the most studied microorganisms for docosahexaenoic acid (DHA) production. Severeal strategies were reported to enhance DHA production, including co-culturing algal cells with different microorganisms. In this study, Schizochytrium sp. and Escherichia coli were co-cultured to examine the effect of bacterial cells on the algal growth and DHA production. The cells were incubated for 168 h and recovered to analyze biomass production, lipid content and DHA yield in the mixed culture medium. Cultivation of algal and bacterial species together decreased the biomass production (g/L), total lipid concentration (ml/L), DHA yield (g/L) and DHA percentage in lipid content about 4.1, 1.7, 3.8 and 2.2 folds, respectively, compared to algal monoculture. The only increasing amount was obtained with DHA yield per biomass (mg/gCDW) which was about 1.1 fold higher in the mixed culture. The results showed that presence of Escherichia coli cells in the medium affected the growth of Schizochytrium sp. cells and DHA production negatively. It was estimated that the interaction between algal and bacterial cells were competition instead of mutualistic interaction in which bacterial cells outcompeted the algal cells and limited the cell density increase of algal cells in the mixed culture.