Preparation of l-threonine
L-Threonine is prepared by cultivating Escherichia coli A.T.C.C. 13070 or 13071 under submerged aerobic conditions at temperatures between 20 and 40 DEG C. and at a pH of between 6 and 8 in an aqueous nutrient medium comprising sorbitol or mannitol, sources of nitrogen, magnesium, potassium and trace metals together with from 100 to 140 mg. of diaminopimelic acid per litre of nutrient medium when E. coli A.T.C.C. 13071 is used, or with from 100 to 250 m. of diaminopimelic acid and up to 100 mg. of L-methionine per litre of nutrient medium when E. coli A.T.C.C. 13070 is used. Yields are improved by the addition of Llycine, sucrose, cornsteep liquor and/or crude beet molasses to the nutrient medium. The product is purified by ion exchange techniques, small amounts of glycine, serine and glutamic acid being separated as by-products. Specification 610,527 is referred to.