Isolation and cultivation of freshwater diatom Nitzschia palea HY1 for increasing biomass and fucoxanthin production

Diatoms, a type of microalgae distributed worldwide, have been identified as potential sources of biomass, lipids, and high-value compounds. While marine diatoms have been extensively studied, the potential of freshwater diatoms still needs to be explored. In this study, a novel strain of freshwater diatom was isolated from the Jungnangcheon stream located in Seoul, Republic of Korea (37°33'08.0" N, 127°02'40.0" E). This newly isolated strain was classified through phylogenetic analysis, and its morphology was investigated using light and electron microscopy; it was named Nitzschia palea HY1. N. palea HY1 grown in freshwater media (FDM) produced higher biomass (0.68 g L^-1) and fucoxanthin production (9.19 mg L^-1) than in conventional diatom media. Furthermore, increasing the bicarbonate concentration from 2 to 10 mM enhanced the maximum biomass and fucoxanthin production in FDM by 2.7 fold and 1.5 fold, respectively. Remarkably, the introduction of aeration to the modified FDM (MFDM) led to a substantial increase in the maximum biomass and fucoxanthin production of N. palea HY1, exhibiting 3.8-fold and 4.1-fold enhancement, respectively, compared to FDM alone. These findings suggest that optimizing the cultivation of N. palea HY1 using MFDM could provide an alternative to marine sources for fucoxanthin production.