Abstract
Single cell oils (SCOs) accumulated by oleaginous yeasts have emerged as potential alternative feedstocks for biodiesel production. As lipid accumulation is species and substrate specific, selection of an appropriate strain is critical. Five strains of Y. lipolytica, a known model oleaginous yeast, were investigated to explore their potential for biodiesel production when grown on glucose and inexpensive wastes. All the strains were found to accumulate > 20% (w/w) of their dry cell mass as lipids with neutral lipid as the major fraction when grown on glucose and on wastes such as waste cooking oil (WCO), waste motor oil (WMO). However, amongst them, Y. lipolytica NCIM 3589, a tropical marine yeast, exhibited a maximal lipid/biomass coefficient, YL/X on 30 g L-1 glucose (0.29 g g-1) and on 100 g L-1 WCO (0.43 g g-1) with a high content of saturated and monounsaturated fatty acids similar to conventional vegetable oils used for biodiesel production. The experimentally determined and predicted biodiesel properties of strain 3589 when grown on glucose and WCO, such as density (0.81 and 1.04 g cm-3), viscosity (4.44 and 3.6 mm2 s-1), SN (190.81 and 256), IV (65.7 and 37.8) and CN (56.6 and 50.8) are reported for the first time for Y. lipolytica and correlate well with specified standards. Thus, the SCO of oleaginous tropical marine yeast Y. lipolytica NCIM 3589 could be used as a potential feedstock for biodiesel production.
Highlights
The widespread use of fossil fuels such as petroleum, coal and natural gas, due to the high energy demand in today’s industrial world has led to problems of resource scarcity and environmental pollution
Growth and Single Cell Oils (SCOs) yields of Y. lipolytica strains on glucose Lipid accumulation in oleaginous yeasts occurs as lipid bodies (LBs) when a nutrient in the medium e.g., nitrogen or phosphorous is limiting and carbon is in excess
Determination of lipid accumulation by Nile red staining In the present study, all five strains of Y. lipolytica when grown in 30 g L -1 glucose revealed a variable number of LBs which could be visualized by light microscopy of formaldehyde fixed cells or by fluorescence microscopy of cells stained with Nile red (Figure 1 insets)
Summary
The widespread use of fossil fuels such as petroleum, coal and natural gas, due to the high energy demand in today’s industrial world has led to problems of resource scarcity and environmental pollution. Lipid content and fatty acid composition of SCOs varies in response to environmental factors such as type of carbon source, pH, temperature and is species and strainspecific (Subramaniam et al 2010; Venkata Subhash and Venkata Mohan 2011). This is evident from the studies on the psychrophilic oleaginous yeast Rhodotorula glacialis wherein both glucose concentration and temperature influenced the composition and degree of unsaturation of fatty acids (Amaretti et al 2010). Careful selection of the oleaginous strains of the microbial species and characterization of lipid composition need to be performed to ascertain their suitability for biodiesel production
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