Achieving a high-density oleaginous yeast culture: Comparison of four processing strategies using Metschnikowia...

Microbial lipids have the potential to displace terrestrial oils for fuel, value chemical, and food production, curbing the growth in tropical oil plantations and helping to reduce deforestation. However, commercialization remains elusive partly due to the lack of suitably robust organisms and their low lipid productivity. Extremely high cell densities in oleaginous cultures are needed to increase reaction rates, reduce reactor volume, and facilitate downstream processing. In this investigation, the oleaginous yeast Metschnikowia pulcherrima, a known antimicrobial producer, was cultured using four different processing strategies to achieve high cell densities and gain suitable lipid productivity. In batch mode, the yeast demonstrated lipid contents more than 40% (w/w) under high osmotic pressure. In fed-batch mode, however, high-lipid titers were prevented through inhibition above 70.0 g L^-1 yeast biomass. Highly promising were a semi-continuous and continuous mode with cell recycle where cell densities of up to 122.6 g L^-1 and maximum lipid production rates of 0.37 g L^-1  h^-1 (daily average), a nearly two-fold increase from the batch, were achieved. The findings demonstrate the importance of considering multiple fermentation modes to achieve high-density oleaginous yeast cultures generally and indicate the limitations of processing these organisms under the extreme conditions necessary for economic lipid production.