Enhanced lipid productivity of Monoraphidium strains in co-cultures and their potential for biodiesel production

The primary aim of this research was to establish a co-culture system involving two closely related microalgal species, Monoraphidium sp. HDMA-20 and Monoraphidium sp. HDMA-11, with the aim of enhancing overall lipid productivity. The strains were cultivated in TAP medium with different inoculum ratios of HDMA-20/HDMA-11 at 1:1, 3:1, and 1:3. Compared to the monoculture control, the co-cultures exhibited improved biomass accumulation, increased lipid productivity, a notable shift in the C18:2 content, and a decrease in the production of extracellular polymeric substances (EPS). The co-culture with an inoculum ratio of HDMA-20/HDMA-11 at 1:1 achieved the highest biomass yield of 831 mg/L. The lipid productivity in the co-cultures ranged from 15.37 to 15.62 mg/L d-1, representing a 27.9 % to 29.9 % increase compared to monoculture of HDMA-20 and a 44.2 % to 46.5 % increase compared to monoculture of HDMA-11. These results highlight the significance of exploring potential synergistic effects between closely related species. The fatty acid profiles revealed that, except for the co-culture with an inoculation ratio of HDMA-20/HDMA-11 at 3:1, the lipids derived from other ratios largely conformed to the criteria established by American Society for Testing and Materials (ASTM D6751) and EN 14214. The observation strongly indicated that the co-culture system possesses significant potential to be further developed as a promising approach for biodiesel production.