Presentation Information
[2BRBP-08]Process-Driven Acetate-Based Lipid Production by the
Oleaginous Yeast Lipomyces starkeyi
○Chiaki OGINO OGINO1, Prihardi Kahar1, Akihiro Ishioka1, Yutaro Mori1 (1. Kobe University (Japan))
Keywords:
Lipomyces starkeyi,oleaginous yeast,single-cell oi
[Purpose] The purpose of this study was to evaluate acetate-based lipid production using the oleaginous yeast Lipomyces starkeyi, with a particular focus on understanding the role of culture pH as a key physiological and process constraint. Although acetate is a promising non-food carbon source for sustainable lipid production, its utilization is often limited by pH instability during cultivation. This study aimed to clarify how acetate concentration and pH dynamics affect acetate assimilation, biomass formation, and lipid production, and to develop an effective pH control strategy for scalable fermentation processes.
[Method] In flask experiments, L. starkeyi was cultured with varying initial acetate concentrations (0–200 mM) to evaluate acetate utilization, biomass (DCW), lipid production, and pH changes over time. In fed-batch cultivation, two different pH control strategies were compared: (1) hydrochloric acid (HCl)-based pH control and (2) acetic acid-based pH control. Acetate feeding was regulated using a DO-stat strategy in the HCl condition, while acetic acid addition maintained both pH and substrate supply.
[Results] Flask experiments showed that acetate utilization was significantly affected by both acetate concentration and cultivation time. Moderate acetate levels (60–100 mM) enabled efficient consumption and balanced growth, whereas high concentrations (200 mM) led to incomplete utilization and strong alkalization (pH up to 9), indicating pH as a major limiting factor. Biomass increased with acetate concentration, but lipid content (12–15%) and fatty acid composition remained unchanged, indicating that lipid production was primarily biomass-driven. In fed-batch cultivation, clear differences were observed between pH control strategies. Under HCl control, acetate levels fluctuated, biomass remained relatively low (~8–9 g/L), and lipid production reached only ~3–4 g/L. In contrast, acetic acid-based pH control stabilized acetate availability, significantly enhanced biomass (~22 g/L), and increased lipid production up to ~13.7 g/L with lipid content exceeding 60% .
[Consideration] The results demonstrate that culture pH is not merely an operational parameter but a central determinant of acetate metabolism. Alkalization during acetate uptake reduces the availability of undissociated acetic acid, limiting transport and metabolic activity. This leads to incomplete substrate utilization despite sufficient carbon supply. Acetic acid-based pH control offers dual functionality: stabilizing pH and simultaneously supplying assimilable carbon. This creates a favorable metabolic environment by maintaining acetate transport equilibrium and intracellular homeostasis. The findings also indicate that process-level constraints (pH, substrate availability) dominate over intrinsic metabolic limitations in determining lipid productivity.
[Conclusion] Culture pH is a critical factor governing acetate utilization and lipid production in L. starkeyi. High acetate concentrations induce alkalization, which limits substrate uptake and process efficiency. Acetic acid-based pH control effectively overcomes this limitation by stabilizing pH and enhancing acetate availability, resulting in significantly improved biomass and lipid production.
[Method] In flask experiments, L. starkeyi was cultured with varying initial acetate concentrations (0–200 mM) to evaluate acetate utilization, biomass (DCW), lipid production, and pH changes over time. In fed-batch cultivation, two different pH control strategies were compared: (1) hydrochloric acid (HCl)-based pH control and (2) acetic acid-based pH control. Acetate feeding was regulated using a DO-stat strategy in the HCl condition, while acetic acid addition maintained both pH and substrate supply.
[Results] Flask experiments showed that acetate utilization was significantly affected by both acetate concentration and cultivation time. Moderate acetate levels (60–100 mM) enabled efficient consumption and balanced growth, whereas high concentrations (200 mM) led to incomplete utilization and strong alkalization (pH up to 9), indicating pH as a major limiting factor. Biomass increased with acetate concentration, but lipid content (12–15%) and fatty acid composition remained unchanged, indicating that lipid production was primarily biomass-driven. In fed-batch cultivation, clear differences were observed between pH control strategies. Under HCl control, acetate levels fluctuated, biomass remained relatively low (~8–9 g/L), and lipid production reached only ~3–4 g/L. In contrast, acetic acid-based pH control stabilized acetate availability, significantly enhanced biomass (~22 g/L), and increased lipid production up to ~13.7 g/L with lipid content exceeding 60% .
[Consideration] The results demonstrate that culture pH is not merely an operational parameter but a central determinant of acetate metabolism. Alkalization during acetate uptake reduces the availability of undissociated acetic acid, limiting transport and metabolic activity. This leads to incomplete substrate utilization despite sufficient carbon supply. Acetic acid-based pH control offers dual functionality: stabilizing pH and simultaneously supplying assimilable carbon. This creates a favorable metabolic environment by maintaining acetate transport equilibrium and intracellular homeostasis. The findings also indicate that process-level constraints (pH, substrate availability) dominate over intrinsic metabolic limitations in determining lipid productivity.
[Conclusion] Culture pH is a critical factor governing acetate utilization and lipid production in L. starkeyi. High acetate concentrations induce alkalization, which limits substrate uptake and process efficiency. Acetic acid-based pH control effectively overcomes this limitation by stabilizing pH and enhancing acetate availability, resulting in significantly improved biomass and lipid production.
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