| Abstract: | A number of tryptophan plus tyrosine double auxotrophic mutants isolated by the NTG treatment of a glutamate producing strain of Arthrobacter globiformis were found to excrete phenylalanine in a mineral salt medium. By controlling the pH of the medium to near neutrality, the active growth period could be extended up to 72 h and more phenylalanine was accumulated compared to the unregulated culture where the growth period took up to 48 h. Under optimum culture conditions, the best double auxotroph (TT-39) produced 3 g phenylalanine/l. Further improvement of phenylalanine production has been achieved by the step-by-step isolation of a mutant resistant to the phenylalanine analogues p-fluorophenylalanine (PFP) and β-2-thienylalanine (TA) from the TT-39 strain. Under optimum culture conditions, the best double auxotrophic analogue resistant mutant TT-39 PTr-21 yielded 8.7 g/l phenylalanine. |
