Method for producing nucleotide by fermentation

Abstract

Nucleoside 5′-phosphate ester is produced by culturing a bacterium belonging to the genus Escherichia having an ability to produce nucleoside 5′-phosphate ester, in which ushA gene and aphA gene do not function normally, in a medium to produce and accumulate nucleoside 5′-phosphate ester in the medium, and collecting the nucleoside 5′-phosphate ester from the medium.

What is claimed is:  
     
         1 . A method for producing nucleoside 5′-phosphate ester, comprising the steps of culturing a bacterium belonging to the genus Escherichia having an ability to produce nucleoside 5′-phosphate ester, in which ushA gene and aphA gene do not function normally, in a medium to produce and accumulate nucleoside 5′-phosphate ester in the medium, and collecting the nucleoside 5′-phosphate ester from the medium.  
     
     
         2 . The method for producing nucleoside 5′-phosphate ester according to  claim 1 , wherein mutations are introduced into the ushA gene and the aphA gene or these genes are disrupted so that they do not function normally.  
     
     
         3 . The method for producing nucleoside 5′-phosphate ester according to  claim 1  or  2 , wherein the nucleoside 5′-phosphate ester is selected from the group consisting of 5′-inosinic acid or 5′-guanylic acid.  
     
     
         4 . A bacterium belonging to the genus Escherichia having an ability to produce nucleoside 5′-phosphate ester, in which ushA gene and aphA gene are disrupted.  
     
     
         5 . The bacterium belonging to the genus Escherichia according to  claim 4 , wherein the nucleoside 5′-phosphate ester is selected from the group consisting of 5′-inosinic acid or 5′-guanylic acid.  
     
     
         6 . A method for searching for a 5′-nucleotidase gene affecting accumulation of nucleoside 5′-phosphate ester, comprising the steps of: 
 culturing a parent strain of microorganism and a derivative strain thereof in which a known 5′-nucleotidase is deleted in a minimal medium containing a first nucleoside 5′-phosphate ester as a sole carbon source and a minimal medium containing a second nucleoside 5′-phosphate ester as a sole carbon source to examine expression profiles of genes in the parent strain and the derivative strain,  
 calculating a product of a ratio of expression amounts of each gene in the parent strain and the derivative strain when they are cultured in the medium containing the first nucleoside 5′-phosphate ester as a carbon source and a ratio of expression amounts of each gene in the parent strain and the derivative strain when they are cultured in the medium containing the second nucleoside 5′-phosphate ester as a carbon source,  
 and selecting one or more genes showing a larger value of the product.  
 
     
     
         7 . The method for searching for a 5′-nucleotidase gene according to  claim 6 , wherein the first and second nucleoside 5′-phosphate esters are 5′-inosinic acid and 5′-guanylic acid.  
     
     
         8 . The method for searching for a 5′-nucleotidase gene according to  claim 6  or  7 , further comprising the step of selecting a gene that can code for a signal sequence required for transition of a protein into periplasm from the selected genes.