DISPERSION-INDUCED BEHAVIOR IN SUBCRITICAL OPERATION OF A RECOMBINANTFED-BATCH FERMENTATION WITH RUN-AWAY PLASMIDS

Fermentations with recombinant bacteria containing run-away plasmids a re typically operated alternately above and below a critical temperatu re. To minimize the risks of run away reactions, it is preferable to k eep the high temperature periods as short as possible. In this study t he possibility of sustained low temperature (sub-critical) operation i n a suitably non-homogeneous broth is analyzed. Fluid dispersion is us ed as a measure of non-homogeneity. The fed-batch production of beta-g alactosidase by Escherichia coli containing the plasmid pOU140 and ope rated below 37 degrees C is analysed as a model system. To characteriz e non-homogeneity, an earlier model visualizing the broth as a set of two reactors with internal recycle has been modified for fed-batch fer mentation. Three dilution rates, two internal and one external, quanti fy fluid dispersion. While plasmid replication and fermentation become quenched in sub-critical operation in a well-mixed reactor, with fini te dispersion there may be an increase in the concentration of plasmid -containing cells and the recombinant protein. The concentration profi les many also have one or more peaks in the time domain. Thus, sustain ed fermentation with run-away plasmids appears feasible in a bioreacto r with controlled non-homogeneity.