Study On The Lipid Production By Oleaginous Yeast Rhodotorula Glutinis From Lignocellulosic Hydrolysate

At present, there are increasing studies focused on the biomass energy of noval, renewable, sustainable, and economical. Lignocellulosic materials are aboundant, extensive, low-cost and renewable in the world, and its hydrolysate contains rich fermentable sugars such as hexose and pentose, so it is meaningful to have a study on the lipid production by oleaginous yeast Rhodotorula glutinis (R. glutinis) from lignocellulosic hydrolysate.In this work, I first studied the basic growth characteristics of R. glutinis especially on the utilization of hexose and pentose of different percentage. Results showed that, R. glutinis always first used glucose completely before xylose and then arabinose. And glucose (hexose) inhibited the utilization of xylose and arabinose (pentose), and such inhibition is positive correlated to its concentration.Then I utilized the lignocellulosic hydrolysate to culture R. glutinis. Results showed that it is feasiable to utilize lignocellulosic hydrolysate to culture R. glutinis, but the inhibitors also affected the growth of yeasts. Additional nutrient elements should be added to ensure the normal growth of yeasts. There was no big difference about the grain size for the pre-treatment of cellulosic metarials, but particle diameter of< 1mm was more favorable than diameter of>1mm for the enzymolysis.Further study showed that, both acetate acid and furfural, two of the most common inhibitory compounds in lignocellulosic hydrolysate, had inhibitory effects on R.glutinis, heavier to glucose utilization but also with better growth and lipid accumulation of yeasts, than xylose. In the concentrations of 0-1.5 g/L of furfural, the inhibition degree of furfural was positive correlated to the concentration of furfural without significant differences, and showed extension of the lag phase, shortage of log phase, decrease of biomass and lipid production and carotenoids accumulation, as well as the utilization of sugars. More C18 fatty acids or unsaturated C18 fatty acids were generated in the presence of furfural.In the last part of this work, I focused on the study of furfural inhibition mechanism from both fermentation level and metabolism level. Results showed that, the inhibitory effects of furfural on the growth and lipid production of oleaginous yeast R.glutinis were mainly attributed to more toxic compounds generated, including furfuryl alcohol and furoic acid, the relative toxicity among the three compounds was:furoic acid>> furfuryl alcohol> furfural. It was recoverable for the inhibitory effects of furfural on the sugar utilization for growth, but it was might more complex for the lipid and carotenoids production, which might involved with the conversions of furfural. Both the reduction and oxidation power among the conversion of these three inhibitors came from the yeasts. From the metabolism aspect, the metabolism of R. glutinis was heavily inhibited in the lag phase, and recovered to a normal or slightly higher level in the log phase, but nearly no any metabolite were detected in the stationary phase, which indicated that the yeasts gradually became feeable and died in the stationary phase.