Effects of culture modes on polyglucan accumulation and molecular weight distribution in Galdieria sulphuraria strains

BACKGROUND This study investigated the effects of different culture modes – autotrophy, mixotrophy and heterotrophy – on polyglucan accumulation and molecular weight distribution in four Galdieria sulphuraria strains. Understanding the impact of these culture modes helps optimize the production of reserve carbohydrates and modify their molecular properties for biotechnological applications. RESULTS The mixotrophic cultivation synergistically positively impacted microalgae growth, reserve polyglucan accumulation and productivity. Significant interaction effects between strain and culture mode were observed for all evaluated kinetic parameters, including biomass concentration ( P = 9.06E−09), biomass productivity ( P = 2.34E−06) and specific growth rate ( P = 6.01E–15). The strain G. sulphuraria SAG 107.79 exhibited the highest glycogen accumulation, reaching 20.1% (w/w) under mixotrophic conditions, compared to 13.6% (w/w) and 5.1% (w/w) under heterotrophic and autotrophic modes, respectively. Culture mode also significantly affected the molecular weight distribution of polyglucans. Autotrophic cultures displayed a bimodal distribution, which may indicate the coexistence of α‐ and β‐particle populations, while heterotrophic cultures showed a unimodal profile. The polydispersity index ranged from 1.65 to 9.18, indicating heterogeneity of the molecular weight of the polymer chains. Interestingly, under mixotrophic growth conditions, a high‐molecular‐weight polymer was obtained compared to the heterotrophic mode. CONCLUSION These findings emphasize the importance of the culture mode in regulating polyglucan synthesis and molecular characteristics in G. sulphuraria strains for their biotechnological use and further investigation connected with algae cultivation.