Study On Lipid Production From Lignocellulosic-derived Sugars And Acetic Acid By Trichosporon Cutaneum

Lignocellulosic biomass is the most abundant biomass resource on earth and it can be served as a potential raw material for microbial lipid production.However,using lignocellulosic hydrolysate to culture oleaginous microorganisms suffers from various prominent problems,including high pretreatment cost,difficulty in complete utilization all the sugars in the hydrolysates,and acetic acid toxicity.In this thesis,microbial lipid production from lignocellulosic-derived carbon sources were investigated,and the results were obtained as follows:It was found that a variety of lignocellulosic-derived carbon sources including glucose,xylose,arabinose,galactose,mannose,cellulobiose and acetic acid could serve as building blocks for lipid production by T.cutaneum GIM 2.67,indicating a good complete sugar utilization potential.There was no glucose repression when glucose was co-fermentated with other carbon sources.All the sugars were totally consumed by T.cutaneum.All sugars were completely consumed with an overall consumption rates of 13.8-14.3 g/L/d,when the simulated corn stover hydrolysate and enzymatic hydrolysates of alkaline methanol pretreated corn stover were used to culture T.cutaneum.Lipid content and yield were up to 47.2-54.9% and 14.5-19.6 g/g,respectively.The lipid synthesized by the strain were mainly composed of palmitic acid,stearic acid,oleic acid,and linoleic acid,indicating the suitability for biodiesel industry.T.cutaneum was observed to be robust at high concentration of acetic acid under neutral pH and conventional fermentation conditions.Cell mass,lipid content,and lipid yield were 8.9 g/L,4.4 g/L,and 0.1 g/g,respectively,on 50 g/L acetic acid under the optimal conditions.It was worth mentioning that these data were increased by 16.9%,18.2% and 7.2%,respectively,when 50 g/L of volatile fatty acids(VFAs,the mass concentration of acetic acid,propionic acid,butyric acid,ratio of 6: 3: 1)blend were used as carbon sources.Meanwhile,the yeast accumulated two odd-chain fatty acids including 6.1% of C17: 0 and 2.5% of C17: 1.Corn stover was pretreated with a mild and programmable deep eutectic solvent(DES),volatile fatty acid-choline chloride at atmospheric pressure and posttreated with calcium hydroxide.The concentrations of glucose and xylose were 31.1 g/L and 8.9 g/L,respectively,after 72 h of enzymatic hydrolysis with a solid-liquid ratio of 8%(w/v).Cell mass and lipid titre were 15.6 g/L and 5.6 g/L,respectively,when T.cutaneum was cultured with the enzymatic hydrolysates of the regenerated corn stover.The pretreated liquor contained a certain amounts of sugars and acetic acid.Cell mass and lipid titre increased by 42.3% and 33.9%,respectively,when the pretreatment liquor was added twice to the medium during a fed-batch culture.This study lays a foundation for the preparation of microbial lipid from complete conversion of lignocellulosicderived sugars by T.cutaneum,and proposes a co-utilization strategy of lignocellulosic sugars and acetic acid based on VFAs mediated pretreatment,which provides a new idea for lowering the cost of lignocelluloses-into-lipid routes.