Phosphate Versus Nitrogen Limitation: A Reactor-Scale Process Comparison for Single-Cell Oil Production in Oleaginous Yeasts

Industrial production of single-cell oils (SCOs) by oleaginous yeasts relies predominantly on nitrogen limitation, which constrains process flexibility when nitrogen-rich substrates are used. Although phosphate limitation has been reported as an alternative lipid induction strategy, its process-level performance relative to nitrogen limitation remains insufficiently resolved under controlled reactor-scale conditions. In this study, phosphate-limited, nitrogen-limited and nutrient-replete cultivations of Cutaneotrichosporon oleaginosum ATCC 20509, Saitozyma podzolica DSM 27192, Scheffersomyces segobiensis DSM 27193 and Apiotrichum porosum DSM 27194 were benchmarked in 2.5 L stirred-tank reactors operated under identical media compositions and process parameters. Biomass formation, lipid titres, specific lipid production rates, biomass composition and fatty acid profiles were systematically compared. Nitrogen limitation resulted in the highest lipid titres, reaching up to 9.2 g L−1 (A. porosum), while maximum lipid titres under phosphate-limited conditions reached 5.0 g L−1 (C. oleaginosum) and nutrient-replete conditions 3.9 g L−1 (A. porosum), respectively. The highest specific lipid production rate under nitrogen limitation was 0.0028 g gCDW−1 h−1 (S. podzolica), while phosphate limitation yielded a maximum of 0.0037 g gCDW−1 h−1 (S. podzolica). These results demonstrate that phosphate limitation can decouple cellular lipid productivity from biomass formation and represents a process-relevant alternative for SCO production from nitrogen-rich feedstocks.