IMPROVEMENT OF PLASMID STABILITY OF RECOMBINANT BACILLUS-SUBTILIS CELLS IN CONTINUOUS IMMOBILIZED CULTURES

The immobilization of recombinant Bacillus subtilis in K-carrageenan g el beads has been performed in order to study the growth conditions in side the gel beads and to improve plasmid stability. Bacterial colonie s showing high cell density were studied using scanning electron micro scopy. A series of continuous cultures of free and immobilized B. subt ilis MT119 (pHV1431, pIL252 and pIL252 Kpn) have been developed withou t selection pressure. In the free-cell systems, it was found that a lo ss of plasmid vectors occurred after a short period. In contrast, in t he immobilized cell systems, plasmid-free segregants were not detected in any of the cases during the first 80 h of the culture.