L-Lysine Production Using Lignocellulose Feedstock Through Dry Milling Biorefinery Processing

L-lysine is the second-ranking amino acid after glutamate in terms of annual production and belongs to one of the leading fermentation products.Commercial L-lysine is produced by microbial fermentation using starch-based feedstocks,including corn,wheat and cassava.The cheaper lignocellulose feedstock can be used as alternative feedstock for L-lysine production to reduce feedstock cost,which is beneficial for L-lysine market expansion and chemical applications.In this thesis,Corynebacterium glutamicum SIIM B253 with strong tolerance for lignocellulose derived inhibitors was employed to produce L-lysine using corn stover after it is dry acid pretreated,biodetoxified,and enzymatically hydrolyzed into glucose.L-lysine fermentation was preliminarily conducted using corn stover hydrolysate by C.glutamicum SIIM B253 and only 7.3 g/L L-lysine with the yield of 0.13 g L-lysine/g glucose was obtained.In order to improve L-lysine fermentation performance,various nutrients required and fermentation conditions affecting L-lysine production were carefully examined and a maximum L-lysine titer of 14.7 g/L with the yield of 0.29 g L-lysine/g glucose was produced.Then,fermentable sugar in corn stover hydrolysate was increased for L-lysine production by increasing the solid loading of corn stover during enzymatic hydrolysis.L-lysine of 28.4 g/L was accumulated with 0.5 g/L of L-threonine and 0.15 g/L of L-methionine addition.Simultaneous saccharification and L-lysine fermentation(SSF)was tried for L-lysine production using corn stover.Due to the pH and temperature difference between the optimum fermentation(pH 7.0,30?)and the cellulose hydrolysis(pH 4.8,50?),a L-lysine titer of 28.8 g/L obtained was close to that of separate enzymatic hydrolysis and fermentation(SHF)with low cellulase activity and glucose from enzymatic hydrolysis during fermentation process(pH 7.0,30?).Therefore,no solid/liquid separation and continuous hydrolysis fermentation that pH and temperature of corn stover slurry were adjusted to optimal fermentation conditions(pH 7.0,30?)without solid/liquid separation after that most cellulose converted into glucose in enzymatic hydrolysis at optimal conditions(pH 4.8,50?)was tried.A L-lysine of 33.8 g/L with yield of 0.24 g L-lysine/g cellulose and productivity of 0.28 g/L/h obtained using corn stover at 30%(w/w)solid loading was higher than that of SHF.This study optimized fermentation process to increase L-lysine fermentation performance using corn stover and showed the great potential and imformation of lignocellulose feedstock for future L-lysine production.