Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The effect of the concentration of nitrogen, temperature, pH and their possible synergistic effect on the production of lipids by Rhodosporidium toruloides ATCC 10788 were studied. In particular, the effect of these variables on the change in composition of the oil during fermentation was investigated.;Eight initial concentrations of nitrogen as NH{dollar}\sbsp{lcub}4{rcub}{lcub}+{rcub}{dollar} (from 10{dollar}\sp{lcub}-4{rcub}{dollar}M to 10{dollar}\sp{lcub}-2{rcub}{dollar}M) were supplied to 1 g/l of lean cells (fat content {dollar}\sim{dollar}7%) in shake flasks at 30{dollar}\sp\circ{dollar}C. The rates of lipid production, shortly after nitrogen-depletion, were found to increase from a constant value of 0.040 g/ for (N) = 10{dollar}\sp{lcub}-4{rcub}{dollar} to 2 {dollar}\times{dollar} 10{dollar}\sp{lcub}-3{rcub}{dollar}M to a value of 0.0854 g/ at (N) = 10{dollar}\sp{lcub}-2{rcub}{dollar}M, although no upper limit was determined. However, the specific rates of lipid production (per lipid-free cellular material) were found to be statistically equivalent.;Temperature and pH were investigated simultaneously using a factorial design approach in large fermenters. In a batch mode, three temperatures (25, 30 and 35{dollar}\sp\circ{dollar}C) were each studied at three levels of pH (4.5, 6 and 7.5) for a given nitrogen-limited medium composition at 300 rpm, 0.6 vvm (volume of air/volume of solution/minute); the dissolved oxygen (D.O.) was monitored by not controlled. From the temporal profile of growth and of lipid composition and production, the following results were found. The maximum Double Bond Index (DBI) of the intracellular oil was found to be constant at 1.34 for all values of pH and temperature. Similarly the minimum degree of unsaturation {dollar}(\Delta{dollar}U) appeared to be unaffected by pH or temperature {dollar}(\Delta{dollar}U = 1.90) except for 35{dollar}\sp\circ{dollar}C and pH 7.5 where {dollar}{lcub}\Delta{rcub}{dollar}U fell to 1.32. The specific growth rates of the cells as well as the specific production rates of the lipids showed no systematic variation with temperature and pH. The lipid content increased from a value of 25% at 25{dollar}\sp\circ{dollar}C and pH 4.5 to 40% at 35{dollar}\sp\circ{dollar}C and pH 6 or 7.5; however the factorial design statistical method failed to develop a model that could predict the trend. Finally the productivities of both DBI and polyunsaturated C 18 fatty acids showed no trend with changes in temperature or pH.



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