Process optimization involving critical evaluation of oxygen transfer, oxygen uptake and nitrogen limitation for enhanced biomass and lipid production by oleaginous yeast for biofuel application
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Lipid accumulation in oleaginous yeast is generally induced by nitrogen starvation, while oxygen saturation can influence biomass growth. Systematic shake flask studies that help in identifying the right nitrogen source and relate its uptake kinetics to lipid biosynthesis under varying oxygen saturation conditions are very essential for addressing the bioprocessing-related issues, which are envisaged to occur in the fermenter scale production. In the present study, lipid bioaccumulation by P. guilliermondii at varying C:N ratios and oxygen transfer conditions (assessed in terms of kLa) was investigated in shake flasks using a pre-optimized N-source and a two-stage inoculum formulated in a hybrid medium. A maximum lipid concentration of 10.8 ± 0.5 g L−1 was obtained in shake flask study at the optimal condition with an initial C:N and kLa of 60:1 and 0.6 min−1, respectively, at a biomass specific growth rate of 0.11 h−1. Translating these optimal shake flask conditions to a 3.7 L stirred tank reactor resulted in biomass and lipid concentrations of 16.74 ± 0.8 and 8 ± 0.4 g L−1. The fatty acid methyl ester (FAME) profile of lipids obtained by gas chromatography was found to be suitable for biodiesel application. We strongly believe that the rationalistic approach-based design of experiments adopted in the study would help in achieving high cell density with improved lipid accumulation and also minimize the efforts towards process optimization during bioreactor level operations, consequently reducing the research and development-associated costs.
KeywordsBiodiesel kLa Nitrogen limitation Oleaginous yeast Oxygen saturation
Fatty acid methyl esters
Malt extract glucose yeast extract peptone
Volumetric oxygen transfer rate
JC is thankful to Ministry of New and Renewable Energy, Government of India for her fellowship and contingency grants. The authors gratefully acknowledge Department of Biotechnology, Government of India (Project Grant No. BT/PR6909/PBD/26/391/2013, 21/03/2014) for the financial support. JC is also thankful to Mr. Ravi Ranjan Kumar, Ms. Moumita Bhaumik and Mr. Lakshmi Kanta Dolai for their timely help during reactor operation.
Compliance with ethical standards
Conflict of interest
The authors have declared no conflict of interest.
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