Co-fermentation Of Glucose-xylose By Trichosporon Dermatis For Lipids Production

As alternative to animal and vegetable oils,lipids from microbes are considered to be a promising feedstock for biodiesel production.However,the high nutrients cost and low pro-duction yield always limit the development of microbial lipids.Compared with conventional starch,carbon sources from lignocellulosic hydrolysate hold great potential to improve the economics of microbial lipids production.However,fermentation inhibitors and mixed sugars in hydrolysate tend to affect the cell growth and final product accumulation.With an oleagi-nous yeast Trichosporon dermatis ZZ-46 stored in the lab,this thesis focused on mutating the strain,co-fermenting the glucose/xylose and bioprocessing the lignocellulosic hydrolysate into microbial lipids,detailed as follows:We firstly evaluated the production ability of the wild-type strain ZZ-46 consuming a mixed sugars(glucose and xylose)as carbon source.It was shown that the ratio of the con-sumption rate of mixed sugars was close to that of sugar concentrations,indicating that the strain was capable of using both glucose and xylose simultaneously.In addition,the growth rate of the strain was coupled with lipids accumulation.The highest cell biomass(20.12 g·L^-1),oil production(8.59 g·L^-1)and oil content(42.67%)was observed after 7 d of fermentation with a 2:1 mass ratio of mixed sugars(glucose:xylose).To obtain a high-yield lipids strain that was able to use both glucose and xylose,a dual mutagenesis consisting of atmospheric and room temperature plasma(ARTP)and diethyl sulfate(DES)was next performed on the strain ZZ-46,followed by high-throughput screen-ing using cerulenin and triphenyltetrazolium chloride combined with Nile Red fluorescent staining.A high-yield mutant L7 was finally obtained.The mutant produced 13%of the cell biomass,33%of the lipids production and 18%of the lipids content higher than those of the wild type.Additionally,the fatty acids composition of these lipids was extremely similar to vegetable oil.The media and cultivation condition of the mutant was then optimized.With several sin-gle-factor and orthogonal experiments,the media was optimized as below:53.33 g·L^-1of glucose,26.67 g·L^-1 of xylose,1.71 g·L^-1 of soybean peptone,1 g·L^-1 of Mg Cl₂·6H₂O and0.05 g·L^-1 of Na₂SO₄;the culture condition was optimized as follows:40 m L/250 m L of liq-uid volume,the initial p H 6,22 ^oC of the culture temperature,and 10%(v/v)of the inocula-tion volume.Under above optimized conditions,the cell biomass,lipids production and lipids content of the mutant L7 attained of 27.25 g·L^-1,14.74 g·L^-1 and 54.10%,respectively.Finally,the shake-flask fermentation on alkali-catalyzed atmospheric glycerol organosolv pretreated lignocellulsoic hydrolysate(AGOPLH)for microbial lipids production was carried out.Results showed that the sugarcane bagasse hydrolysate was directly used as carbon source for lipids fermentation.The highest biomass(34.89 g·L^-1),lipids production(20.21g·L^-1)and lipids content(57.92%)were achieved after 9 d of fermentation by feeding 15 g·L^-1of glucose/xylose mixed sugar at the 2nd day and 3rd day.When the fed-batch fermentation was further scaled up in a 5-L bioreactor,the strain L7 presented a prominent production,high up to 51.50 g·L^-1 of biomass,31.33 g·L^-1 of lipids production and 60.83%of lipids content after 8 d.This study has demonstrated that the oleaginous yeast strain L7 featured on co-fermentation of glucose/xylose for high lipids production.The AGOPLH was applicable directly as carbon source for microbial lipids fermentation.This thesis can shed light on on the production of microbial lipids by fermentation of lignocellulosic sugar hydrolysate.