The role of temperature, pH and nutrition in process development of the unique oleaginous yeast Metschnikowia pulcherrima

BACKGROUND: Lipids produced from oleaginous yeasts are a promising alternative to terrestrial oils. Despite promising cellular yields of lipid however, an industrial process remains elusive. One key processing bottleneck is the need to provide nutrient-rich conditions for cellular growth and then extended nutrient-depleted conditions for lipid accumulation. Surprisingly, investigations detailing process development, particularly with a focus on kinetics, are rare in this field.

RESULTS: In this investigation we report on the unique oleaginous yeast Metschnikowia pulcherrima, where lipid accumulation ≥ 29.8% (w/w) was achieved without apparent nutrient limitation. The process was developed in stirred tank reactors through determining the influence of temperature, pH and nutrition on lipid production. A temperature of up to 25 °C and initial pH 5 could be applied to enhance initial reaction kinetics. Through the increased supply of yeast extract of up to 5% (w/w) of glucose, a maximum lipid production rate of 0.60 g L⁻¹ h⁻¹ (4 h-average), productivity of 0.29 g L⁻¹ h⁻¹, and yield of 0.17 g g⁻¹ glucose were achieved – the highest yet recorded with this yeast. Suitable to combat the excessive secretion of polyols of up to 0.11 g g⁻¹ glucose was an excess nutrient supply as well as a low cultivation temperature of 15 °C and moderate pH 5.
CONCLUSIONS: This study demonstrates that the lack of a starvation stage, coupled with effective process development is required for oleaginous yeasts to achieve the yields and productivities required for commercial lipid production.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 665992