PURPOSE: To obtain L-threonine industrially, efficiently and inexpensively by cultivating a bacterium belonging to the genus Escherichia coli having deficient or reduced acetic acid biosynthesis activity and capable of producing L-threonine in a medium.
CONSTITUTION: Escherichia coli H-4258 strain is varied with N-methyl N'-nitro- N-nitrosoguanidine to give strain Escherichia coli H-7596 strain (A) having deficient or reduced acetic acid synthesis activity. Then the strain A is inoculated into a medium containing a carbon source such as glucose, a nitrogen source such as meat essence and an inorganic substance such as NaCl, aerobically cultured at 20-40°C at pH 5-9 for 2-7 days by submerged aerated culture to give a culture mixture (B). Then a cell and precipitate are removed from the component B and the resulting substance is purified by ion exchange treatment, salting-out, etc., to produce L-threonine.
TAKANO JUNICHI
KURATO YOSHIYUKI
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