bioreactor studies of heterologous protein production by ...

selective medium because an essential amino acid that was excreted into the medium by
the plasmid-bearing cells could support the growth of piasmid-fke œlls @iboasio and
Sardonini, 1986; Sardonini and Dibiasio, 1987). Kleinman et ai. (1 986) also reported that
the selective medium only reduced the htibility but couid not remove it completely. In
the present case. leucine could be synthçsized by pllasnid-positive cells and secreted into
the medium. The srnaII amount of amino acid is probably enough to keep a certain portion
of plasmid-free ceb viable in the bioreactor.
Corn parison of the speciflc enzyme ac tivity between selective and nonselective
media is shown in Figure 4.27. As expected, higher specifïc enzyme activity and higher
stabitity of glucoamyk production were observed in the selective medium. But higher
celi mas and enzyme concentration were obtained in the nonselective medium (Figure
4.28). Therefore, the selective medium is not an economical medium especially if the
higher cost of this medium is considend