The Effects Of Eukaryotic Quorum Sensing Molecules On Oleaginous Yeast

To handle constantly deteriorated situation of national energy supply, energy environ-ment and energy security, it is necessary to develope renewable energy which could replace the traditional fossil energy. Carbohydrates can be converted into renewable energy products and chemicals by enzymatic transformation or microbiol fermentation. This thesis focuses on the effects of quorum sensing molecules (QSMs) on lipid fermentation by oleaginous yeasts in order to improve microbiol oil productivity.The morphological switch of Rhodosporidium toruloides Y4# and Lipomyces starkeyi Y2# in the presence of QSMs (tryptophol,4-hydroxyphenthylalcohol, phenylethanol, farnesol, anethole and geraniol) revealed that QSMs imposed different regulatory effects on develop-mental transition from a unicellular yeast form to an invasive filamentous. R. toruloides Y4# was sensitive to QSMs.4-Hydroxyphenthylalcohol inhibited its developmental transition, while tryptophol, farnesol or anethole accelerated its developmental transition. Phenylethanol or geraniol exhibited mixed results depending on the time that the compounds were introduced. Little effects was found for L. starkeyi Y2# in the presence of QSMs on the plate culture. However, production of 4-hydroxyphenthylalcohol was found as a growth-phase-dependent phenomenon in liquid culture.4-Hydroxyphenthylalcohol reached to its maximal concentration when the culture entered the stationary phase. Therefore,4-hydroxyphenthyl-alcohol might be a true quorum sensing molecule of L. starkeyi Y2#.The effects of QSMs on lipid fermentation by L. starkeyi Y2# was investigated. The results showed that cell growth and lipid accumulation were significantly increased when tryptophol,4-hydroxyphenthylalcohol or phenylethanol was introduced at the exponential phase, while substantial negative effects were observed when farnesol was added. There were no discernible effects when anethole or geraniol was applied. Specifically, biomass, lipid coefficient and lipid increased by 5.4%,13.5% and 13.2% respectively, but fermentation time decreased by 17.9%, when 100μM TrpOH was introduced at 36 h after inoculation. However, little effect was found both on the fatty acid compositional profile of the microbial lipid produced in the presence of QSMs and on the organic acid analysis of medium in the presence of TrpOH. These results are valuable to develop more economical lipid fermentation technology.