Method for Producing L-Amino Acids Using Bacteriua of the Enterobacteriaceae Family

Abstract

There is disclosed a method for producing L-amino acid, for example L-threonine, L-lysine, L-histidine, L-phenylalanine, L-arginine or L-glutamic acid, using a bacterium of the Enterobacteriaceae family, wherein the bacterium has been modified to enhance an activity of D-xylose permease.

We claim: 
     
         1 . A method for producing an L-amino acid comprising:
 cultivating an L-amino acid-producing bacterium of the Enterobacteriaceae family in a culture medium to cause accumulation of the L-amino acid in the culture medium, and   isolating the L-amino acid from the culture medium,   wherein said bacterium has been modified to enhance an activity of D-xylose permease.   
     
     
         2 . The method according to  claim 1 , wherein said activity of D-xylose permease is enhanced by increasing the expression of a gene which encodes D-xylose permease. 
     
     
         3 . The method according to  claim 1 , wherein said activity of D-xylose permease is enhanced by modifying an expression control sequence of the gene encoding D-xylose permease or by increasing the copy number of the gene encoding D-xylose permease. 
     
     
         4 . The method according to  claim 1 , wherein said bacterium has been additionally modified to enhance an activity of glucokinase. 
     
     
         5 . The method according to  claim 1 , wherein said bacterium has been additionally modified to enhance an activity of xylose isomerase. 
     
     
         6 . The method according to  claim 1 , wherein said bacterium has been additionally modified to increase the expression of the xylABFGHR locus. 
     
     
         7 . The method according to  claim 1 , wherein said bacterium is selected from the group consisting of the genera  Escherichia, Enterobacter, Erwinia, Klebsiella, Pantoea, Providencia, Salmonella, Serratia, Shigella , and  Morganella.    
     
     
         8 . The method according to  claim 2 , wherein said gene encodes a D-xylose permease selected from the group consisting of:
 (A) a protein which comprises the amino acid sequence of SEQ ID NO: 2; and   (B) a variant protein of the amino acid sequence shown in SEQ ID NO: 2 which has an activity of D-xylose permease.   
     
     
         9 . The method according to  claim 2 , wherein said gene encoding D-xylose permease comprises a DNA selected from the group consisting of:
 (a) a DNA which comprises a nucleotide sequence of nucleotides 1 to 1476 in SEQ ID NO: 1; and   (b) a DNA which is hybridizable with a nucleotide sequence of nucleotides 1-1476 in SEQ ID NO: 1 under stringent conditions, and encodes a protein having an activity of D-xylose permease, wherein said stringent conditions comprise those in which washing is performed at 60° C. at a salt concentration of 1×SSC and 0.1% SDS for 15 minutes.   
     
     
         10 . The method according to  claim 1 , wherein said L-amino acid is L-threonine. 
     
     
         11 . The method according to  claim 10 , wherein said bacterium has been additionally modified to enhance expression of a gene selected from the group consisting of
 the mutant thrA gene which codes for aspartokinase homoserine dehydrogenase I and is resistant to feedback inhibition by threonine,   the thrB gene which codes for homoserine kinase,   the thrC gene which codes for threonine synthase,   the rhtA gene which codes for a putative transmembrane protein, and   any combination thereof.   
     
     
         12 . The method according to  claim 11 , wherein said bacterium has been modified to increase expression of said mutant thrA gene, said thrB gene, said thrC gene, and said rhtA gene. 
     
     
         13 . The method according to  claim 1 , wherein the culture medium contains xylose. 
     
     
         14 . The method according to  claim 1 , wherein said L-amino acid is L-lysine. 
     
     
         15 . The method according to  claim 1 , wherein said L-amino acid is L-histidine. 
     
     
         16 . The method according to  claim 1 , wherein said L-amino acid is L-phenylalanine. 
     
     
         17 . The method according to  claim 1 , wherein said L-amino acid is L-arginine. 
     
     
         18 . The method according to  claim 1 , wherein said L-amino acid is L-glutamic acid.