Influence of Microalgal Cell Division Tendency on OD to DCW Conversion Factor and Chlorophyll Contents

As the importance of achieving a carbon-neutral society grow, research on the production of microalgal bioproducts have gained significant attention. Among the production processes, cultivation has emerged as a critical step as it determines overall productivity and feasibility. However, changes in cell properties during cultivation pose challenges, and there is currently no direct method to simultaneously assess cell growth, cellular division properties and cell enlargement. In this study, two green algae (<i>Chlorella</i> sp. ABC001 and <i>Chlorella</i> sp. HS2) were cultivated under photo and mixotrophic conditions to evaluate their growth, cell size profile, and changes in optical density. The mixotrophic condition resulted in 2.1 and 1.6-fold higher biomass yields than the photoautotrophic condition for ABC001 and HS2, respectively at day 4. Over the 4-day cultivation, cell sizes ranged from 2.51 to 5.57 μm for ABC001 and from 2.56 to 4.41 μm for HS2. By analyzing changes in the conversion factor between dry cell weight (DCW) and optical density (OD), it was observed that variations in the slope correlated with changes in cell size. Additionally, chlorophyll content fluctuated during cultivation, reaching maximum levels (14.34 and 16.58 μg/mg biomass, respectively) under phototrophic condition on day 2. This study highlights the relationship between cell division tendencies, DCW, cell size, and OD, demonstrating their critical role in determining cellular component content. For future optimization of algal product production processes, further research on these cellular differentiation mechanisms will be essential.