Enhanced lipid accumulation in Metschnikowia pulcherrima using volatile fatty acids under non-sterile repeated batch cultivation

Abstract Metschnikowia pulcherrima, a non-traditional oleaginous yeast, was investigated using 0.5–20 g/L of acetic, propionic, butyric and valeric acid (four model products of anaerobic acidification) respectively as carbon sources to accumulate microbial lipids so as to produce biodiesel. The results showed that acetic acid was the most efficient carbon source for improving cell growth, lipid content and biodiesel quality. After 8 cycles non-sterile batch cultivation, M. pulcherrima still dominated in bioreactor. Controlling C/P ratio, K+ and Na+ concentrations, and initial pH could effectively enhance the lipid content to 25.79 ± 0.51%. Under nitrogen starvation, M. pulcherrima performed higher cellular activity and lipid productivity than that of phosphorous limitation. The biomass yield was about twice and the lipid content was 3% higher. Besides, different from the lipid improvement strategy of traditional oleaginous yeast, acetate from ethanol served as the precursor of M. pulcherrima cytoplasmic acetyl-CoA instead of citric acid, and pentose phosphate pathway (PPP) was the main donor of reducing equivalent NADPH by transcriptomics sequencing analysis. These results demonstrate M. pulcherrima is a promising species for large-scale production of biofuel from organic wastes due to the low operating and maintenance costs of non-sterile cultivation, which is beneficial for reducing environmental pollution and energy shortages.