Guochang Zhang, Swalm School of Chemical Engineering, Mississippi State University, P.O.Box 9595, Mississippi State University, MS 39762, Dr. William T. French, Chemical Engineering, Mississippi State University, Starkville, MS 39759, Rafael Hernandez, Dave C. Swalm School of Chemical Engineering, Mississippi State University, 330 Swalm President's Circle Dr., Mississippi State, MS 39762, Earl G. Alley, Mississippi State Chemical Laboratory, Mississippi State University, Mississippi State, MS 39759, and Maria C. Paraschivescu, Department of Chemical Engineering, Mississippi State University, P.O.Box 9595, Mississippi State University, MS 39762.
Microbial conversion of lignocellulosic sugars to triacylglycerols, which could be further transesterified to make biodiesel, was investigated using the oleaginous yeast Rhodotorula glutinis (ATCC 15125). In the experiments, the yeast was continuously grown in a nitrogen-rich medium utilizing an artificial acid hydrolysate of lignocellulosic biomass switchgrass as the sole carbon and energy source. Once the culture had reached the stationary phase, the cells were harvested and transferred to a fresh nitrogen-free media containing artificial acid hydrolysate for lipid accumulation. The yeast grew very well in artificial acid hydrolysate mediums. Also in this study, R. glutinis was found to metabolize glucose first followed by xylose after the glucose was exhausted. The lipid accumulated in the yeast, determined by gravimetrical method, increased to 33.96% of dry cell mass while growing on 45 g/l of pure glucose, and 44.02% for using 45 g/l of pure xylose as sole carbon and energy source. When growing on artificial acid hydrolysate medium with a total sugar of 45 g/l in the second lipid accumulation phase, the lipid content of cell biomass was determined to be up to 29.76%. The majority contents of triglycerides were characterized by high temperature gas chromatography to be of C16~C20. This study demonstrated that it is feasible for oleaginous yeasts to convert lignocellulosic sugars to triglycerides: a renewable diesel feedstock.