Process Integration To Facilitate Microbial Lipid Production From Cheap Raw Materials By L.starkeyi

Microbial lipids,especially those produced by oleaginous yeasts,whose fatty acid compositional profiles are similar to animal and vegetable oils,are emerging feedstocks in the fields of biodiesel,food additives,oleochemicals,etc.Microbial lipid can be produced by oleaginous species using a variety of low-cost substrates such as agricultural waste,crude glycerol,and industrial wastewater and residues.However,the current microbial lipid production technology suffers from various issues such as high raw material cost,low lipid yield and complicated processes,which greatly prohibit the commercial success.In this thesis,processes integration was applied to simplify the process flow of lipid production,reduce enzyme cost and promote lipid accumulation,as Lipomyces Starkeyi AS 2.1560 has great potential to metabolize a variety of complex and cheap raw materials.The results were as follows:(1)Firstly,the genome of L.starkeyi AS 2.1560 was sequenced and assembled,and a 21.4 Mb genomic sketch was obtained with a GC content of 46.87% based on a three-generation sequencing technology.Through gene prediction,homology search and manual curation,7378 protein coding genes were then annotated.A genome annotation database was obtained accordingly.The genes related to hydrolysis,transportation,and metabolism were analyzed and discussed according to bioinformatics analysis.Finally,the lipid production potential of L.starkeyi on a variety of cheap and complex raw materials was predicted.(2)The consolidated bioprocessing(CBP)of cassava starch for microbial lipid production by L.starkeyi was investigated,as the oleaginous yeast contained 18 amylase genes.When 100 g/L of starch was used as sole carbon source by L.starkeyi,lipid titer reached 18.3 g/L at 144 h.The amylase was secreted to the extracellular space and the amylase activity was up to 3.65 U/mL.(3)Simultaneous saccharification and lipid fermentation(SSLF)on cellulose by L.starkeyi without supplementing ?-glucosidase was studied,as the oleaginous yeast contained 13 cellulase genes.It was found that cellulose was effectively degraded and converted into lipid,and there was no cellobiose accumulation during the fermentation process,which avoided the glucose effect.The cellulose conversion,lipid titer and lipid yield were 92.4%,9.1 g/L and 0.197 g/g,respectively,when the culture was terminated at 144 h.In contrast,the cellulose conversion,lipid titer and lipid yield were merely89.6%,7.7 g/L and 0.172 g/g,respectively,when large amount of ?-glucosidase existed in the cellulase blend during the SSLF.The glucosidase produced by the yeast was mainly distributed in the cytoplasm,and the glycosidase activity was as high as 475.8U/L.In addition,the introduction of a pre-hydrolysis step before SSLF significantly increased the initial sugar concentration and reduced the fermentation time.