Metabolic Mechanism Of Glycerol Production By Candida Glycerinogenes

Glycerol is an important material for the light and chemical industries that display a wide range of industrial applications. It is often used in the fields of cosmetic, toothpaste, tobacco, essence, printing and dyeing, textile, paint, pulp and paper, synthetic resin, leather, pharmaceutical, food and defense industries, more than 1,700 varieties of products. In recent years, glycerol production by osmophilic yeasts has received significant attention. Especially, Candida glycerinogenes, a wild-type osmotolerant yeast that our laboratory possessed the independent intellectual property, is used industrially in China for the glycerol production because of its high glycerol concentration, yield and recovery yield. However, up to now, we know a little about its genetic background and havn't deeply studied the relationship between the glycerol synthetic pathway and various metabolic pathways from the cellular overall level. Most of the information is from the studyof other yeasts, mainly Saccharomyces cerevisiae.The objective of this study was to investigate the metabolic mechnism of glycerol production by C. glycerinogenes according to microbial metabolism and its manipulative theoretics. It is beneficial to explore the inherent relationship between glycerol synthetic pathway and central metabolic pathways, including EMP pathway, HMP pathway and TCA cycle, and further to explain the real cause of its high glycerol yield. Moreover, it is also important for the metabolic engineering of glycerol and its downstream products (such as 1,3-propanediol) biosynthesis.The main contents of this dissertation follow:1. Using chemically defined medium as the control, mechanism of corn steep liquor (CSL) in complex medium during the glycerol production by C. glycerinogenes was studied. It was found that the change of cell growth, glycerol formation and glucose consumption depended mainly on the content of CSL. The impact of CSL was so prominent that even minor variation of it's quality or quantity of CSL caused much difference of experimental results. The content of phosphorus in CSL could regulate the distribution of carbon metabolic flux between EMP pathway and HMP pathway. With the increase in CSL concentration, superfluous phosphorus could restrain HMP pathway and activate EMP pathway, then result in the increase of biomass concentration. Nitrogen in CSL could play a cooperative role in the regulative function of phosphorus. However, it was not a suitable nitrogen source for C. glycerinogenes. Trace elements in CSL could markedly improve the glucose consumption rate, accelerate the cell growth and enhance the glycerol yield.2. The glucose consumption in glycerol production, cell growth, basic metabolism maintenance and by-products formation during different fermentation phases was also analyzed...