High-density cultivation of sporeformers

Abstract

Sporeformers are sources of a large number of industrially important biological products including enzymes, antibiotics, and bioinsecticides. Cultivation of these microorganisms to high cell densities offers potential for enhancing the rates of formation as well as the concentration of the desired products in the fermentation broths in bioreactors. With this objective, investigations have been carried out involving fed-batch cultivation of Bacillus thuringiensis, which is known to produce an insecticidal crystal protein during sporulation. With appropriate management of aeration and nutrient supply, it was possible to grow the cells to > 50 g DW/l density. Nevertheless, the achievement of high cell density did not enhance the formation of crystal protein in the same proportion as the cell concentration. Further examination of this system suggested a complex interplay of energetic requirements for protein turnover during sporulation. Energy reserve material, poly-beta-hydroxybutyric acid, appeared to be linked to formation of spores and crystal protein during the sporulation phase.