GIULIETTI Ana Maria
Stability of Escherichia coli strain harboring recombinant plasmis for L-threonine production
NUDEL, CB; PUEYO, MG; JUDEWICZ, N; GIULIETTI, A.M.
Antonie van Leeuwenhoek
Año: 1989 p. 273 - 273
Escherichia coli recombinant strain bearing the thr operon had been previously selected for threonine production and classified according to antibiotic resistente properties. Further analysis of those trains permitted the isolation and restriction mapping of two different plasmid of 13 Kb and 18,6 Kb. The smaller one which expressed the tetracycline resistence gave better results on threonine accumulation but it was rather unstable when grown without antibiotic pressure. Therefore other hosts were transformed with those plasmids to improve stability. A threonine-auxotrophic strain was a better host for plasmid maintenance and expression of thr operon. Host influence in plasmid-mediated threonine production was studied in terms of specific yields (the ratios of threonine accumulated to biomass values) and of plasmid maintenance. (percent of Apr Tcr clones after cultivation in non selective media). We also determined that semi synthetic media of defined composition were better thann rich media for threonine expression due to feed back control exerted by undesired catabolites accumulated in complex media