Study On The Biosynthesis Of S-Adenosylmethionine By Saccharomyces Cerevisiae

S-adenosylmethionine (S-adenosyl-L-methionine, also known as SAM, SAMe orAdoMet) is an important intermediate in all living organisms and exhibits pivotal roles invarious biological reactions, which has been estimated that only ATP participates in morereactions than SAM. In addition to serving as a major biological methyl donor, SAM is alsoa precursor to produce aliphatid polyamine, or glutathione (GSH) via trans-sulfuration. Ithas been successfully used in human therapy for liver disorders, depression, osteoarthritis,fibromyalgia and Alzheimer’s diseases etc. SAM production by yeast fermentation, whichcompared with by chemical coupling or by enzymatic synthesize, is efficient and practicalapproach through the extraction of yeast cells cultured in media supplemented withL-methionine (L-Met). Construction of recombinant yeast on an industrialized scale canmake great sense through new strategy of metabolic engineering.Saccharomyces cerevisiae is common in eukaryotes, now, which is certified as safemicroorganisms by U.S. Food and Drug Safety Administration. Research shows that theaccumulation of SAM in Saccharomyces cerevisiae is greater than the others and primarilyfocused on strain screening, optimization of fermentation conditions. But, which has notbeen possible to achieve SAM of industrial production in the country.In order to improve the S-adenosylmethionine（SAM）yields, the fermentation processof SAM biosynthesis by Saccharomyces cerevisiae CGMCC2842was optimized. Primarily,the growth curve of Saccharomyces cerevisiae CGMCC2842was detected; then, effects ofadded different concentration of cysteine as0、2、4、6、8mmol/L at20h, added2mmol/Lcysteine at different times as0、12、16、20、24h and different carbon sources of glucose、maltose、sucrose and molasses on biomass concentration and production of SAM after36hfermentation in250mL flasks, then chose the best fermentation conditions in10L stirred.The results indicated, in250mL flasks, added2mmol/L cysteine at16h and used molassesas carbon source, the SAM productions were obviously higher than others. In10L stirred,used glucose as carbon source without cysteine addition, the dry cell weight (DCW)reached maximum of15.4g/L at20h, the SAM accumulation reached maximum of3.48g/L at24h; then, also used glucose as carbon source but added cysteine as2mmol/L at16h, the DCW nearly reached15.4g/L and the maximum concentration of SAM reached to4.11g/L in36h fermentation.; used molasses as carbon source and added cysteine as2mmol/L at16h, the maximum DCW decreased to14.2g/L at26h，but the maximum concentration of SAM increased to4.90g/L at28h; Accordingly, used molasses as carbonsource and added molasses when the concentration of reducing sugar was below5g/Lwhich was equivalent to reducing sugar feeding as0.8g/L/h in fed-batch, after16h thenadded2mmol/L cysteine, the maximum DCW reached15.50g/L at26h and theconcentration of SAM improve to5.02g/L at34h in36h Fermentation. After optimizationof Fermentation process, concentration of SAM in fermented liquid increased by43.8%than used glucose as carbon source without addition of cysteine.