CULTIVATION OF IMMOBILIZED CELLS OF CLAVICEPS-PURPUREA IN BIOREACTORS

For the first time, immobilized cells of Claviceps purpurea forming al kaloids of the ergot peptide group were investigated during fermentati on in normal laboratory bioreactors and compared with suspended cells. In a fixed-bed reactor, cells of Claviceps were immobilized by adsorp tion on sintered glass. These cells were almost unproductive, exhibiti ng the unusual shape of sphacelia-like mycelium. In contrast to this, significant production of ergot peptides was observed with beads of al ginate-immobilized cells in shake culture, a bubble-column reactor, an d a stirred-tank reactor. While scale-up hardly affected growth and su gar consumption, alkaloid production was significantly reduced in all cases, demonstrating its specific sensitivity. The main disadvantages of free-cell fermentation in the bioreactors were: severe foam product ion, the tendency of cells to stick to the reactor walls, their sensit ivity to mechanical stress, and a generally high medium viscosity. In this regard, alginate beads exhibited superior rheological properties, besides their obviously easier handling. With alginate-immobilized my celia, indications were found of beneficial mechanical protection of c ells inside the polymer matrix, while the consistantly low viscosity o f the medium proved to be advantageous to the oxygen supply of immobil ized cultures. The stability of the alginate beads was found to be suf ficient under all conditions, and could be easily improved by optimizi ng the medium composition. Thus, alkaloid production in bioreactors by immobilized cells of C. purpurea was shown to be feasible not only in principle. Moreover, in addition to the unique long-term stability of immobilized C. purpurea mycelia, the advantages presented favour this method for future applications like alkaloid production in continuous culture.