The production of microbial lipids through single-cell oil (SCO) technologies has gained increasing attention as a sustainable alternative source of lipids for industrial applications. This development is driven by the limitations of plant-based oils, particularly their competition with food production and demand for arable land. Cutaneotrichosporon oleaginosus has been recognized as one of the most promising oleaginous microorganisms for efficient SCO production. To improve sustainability and economic viability, it is vital to understand the underlying metabolic mechanism of SCO production as well as needs and limitations in bioprocess engineering for the efficient utilization of carbon sources derived from diverse agricultural and industrial side streams. This review focuses on recent studies exploring the potential of SCO production through C. oleaginosus in a bioprocess context through the application of low-cost agro-industrial by-products as alternative carbon sources aiming to supply lipid raw materials for various industrial applications. C. oleaginosus can grow on different agro-industrial waste-derived substrates, including lignocellulosic biomass hydrolysates, biodiesel production process side streams, chitin-based by-products, cheese whey permeates, fungal biomass hydrolysates and algal biomass hydrolysates. These substrates contain various carbon sources, such as glucose, galactose, mannose, xylose, lactose, N-acetyl-glucosamine and glycerol, facilitating efficient SCO production. Additionally, the specific composition of SCO sourced from C. oleaginosus, including the presence of functional compounds like squalene and prevalent long-chain unsaturated fatty acids in its fatty acid profile, make it an ideal option to be used as a raw material in cosmetics, biofuel and food products. This comprehensive overview aims to shed light on the potential of C. oleaginosus in leveraging carbon source alternatives for sustainable SCO production for multifaceted, industrial applications of SCO.

There is an increasing industrial demand for sustainable resources for lipid-based biofuels and platform chemical production. A promising, CO₂-efficient resource is autotrophically cultivated microalgae, either for direct single-cell oil (SCO) production or as a biomass substrate for fermentative SCO production via organisms like yeasts. Regarding the latter, chemical biomass hydrolysis typically results in high sugar yield and high salt concentrations due to the required neutralization prior to fermentation. In contrast, enzymatic hydrolysis is often lacking in mass efficiency. In this study, the enzymatic hydrolysis of both nutrient-replete and lipid-rich autotrophic Microchloropsis salina biomass was optimized, testing different pre-treatments and enzyme activities. Hereby, the protease treatment to weaken the cell wall integrity and the dosing of the Cellic CTec3 was identified to have the highest effect on hydrolysis efficiency. Sugar yields of 63% (nutrient-replete) and almost 100% (lipid-rich) could be achieved. The process was successfully scaled-up in mini bioreactors at a 250 mL scale. The resulting hydrolysate of the lipid-rich biomass was tested as a substrate of the oleaginous yeast Cutaneotrichosporon oleaginosus in a consumption-based acetic acid fed-batch setup. It outperformed both the model substrate and the glucose control, demonstrating the high potential of the hydrolysate as feedstock for yeast oil production. The presented sequential and circular SCO-producing value chain highlights the potential for mass- and space–time-efficient biofuel production, combining the autotrophic cultivation of oleaginous algae with decoupled yeast oil fermentation for the first time.