MODELING OF CELL-GROWTH AND PHOA-DIRECTED EXPRESSION OF CLONED GENES IN RECOMBINANT ESCHERICHIA-COLI

A mathematical model was formulated to describe growth and cloned prot ein production in the recombinant Escherichia coli cells containing ph oA-directed expression systems. Kinetic parameters for the strains wit h two fusion genes (phoA-lacZ either on the chromosome or on a multico py plasmid and phoA-amyE on a multicopy plasmid) were estimated and co mpared to analyze the effects of cloning site (chromosome and plasmid) , product type (E. coli beta-galactosidase and Bacillus subtilis alpha -amylase), and culture temperature on the cell's behavior. The presenc e of a multicopy plasmid reduced the specific growth rate and the phos phate uptake rate of the cell, both by 10%, compared with those of the chromosome-integrated strain. The overexpression of B. subtilis alpha -amylase decreased the specific growth rate and the glucose consumptio n rate more than the beta-galactosidase overproduction system. The pre sence of multiple copies of the phoA promoter on either an intact phoA gene or the fusion gene reduced both the repression and derepression efficiencies. Culture temperatures showed a significant effect on alph a-amylase production. A temperature of 30 degrees C is more desirable than 37 degrees C for alpha-amylase production in the recombinant E. c oli containing the phoA promoter.