Characterization of salt-tolerant mutant for enhancement of L-threonine production in Escherichia coli

Escherichia coli strain HS3, metabolically engineered to have Met(-), AHV(r ), Ile(L) and AEC(r) characteristics, produced 58.0 g/l of L-threonine, but it was neither salt-tolerant nor osmotolerant; and the growth and threonin e production of the strain were severely inhibited both by the addition of NaCl with a concentration higher than 2% and by the presence of glucose wit h a concentration higher than 10%. Therefore, salt-tolerant mutants were is olated. The salt-tolerant mutants, HS454 and HS528 which were derived from strain HS3, were both tolerant to salt (2%) and hyperproductive. The growth and L-threonine production by the mutant strain HS454 were almost unaffect ed by a glucose concentration lower than 10%, but gradually reduced with in creasing glucose concentration, up to 15%. However, the mutant strain HS528 showed slightly enhanced growth and L-threonine production with increasing glucose concentration, up to 10-12.5%. Strains HS454 and HS528 produced 69 .8 g/l and 74.0 g/l of L-threonine, respectively in a 5-1 jar fermenter.