strains can be inoculated into a culture containing 20 ml of m9 salts about 4 mg ml glucose 1 u03bcg ml thiamine and a determinate amount of succinate the strain is incubated at about 37 u00b0 c and growth ensues after a period of time that depends on the initial level of succinate in the medium growth stops addition of more succinate at this point restores growth thereby identifying insufficient tac intermediates as the cause ofgrowth limitation in this kind of experiment the ppc cells exhibitbehavior that is entirely different from the ppc ymc9 parent strains the latter will not cease growth due to succinate depletion from the medium so long as glucose is supplied and growth continues until other factors exert control cultures of kb285 pkb702 or ymc9 pkb702 are grown on the medium described in table 1 below with between 0 3 and 1 0 mg ml succinate during growthand at the end of growth phenylalanine production is monitored both during growth and significantly after succinate limitation of the ppc culture the productivity of phenylalanine is significantly enhanced in the ppc strain as compared to the ppc strain in an alternative method growth is enabled by the inclusion of acetate in the growth medium and the absence from that medium of glucose or other carbohydrates specifically one of the ppc strains is cultivated on a carbohydrate free medium if carbohydrates are present initially they will be metabolized to inhibiting compounds which will stop growth eventually the carbohydrates and glycolytic intermediates may be depletedby various metabolic pathways and growth can begin once desired cell massis achieved a carbohydrate is added to inhibit continued cell growth by inhibiting the glyoxalate shunt thus depriving.