Electrostimulation of cellulase fermentation by pulsatile electromagnetically induced currents

Abstract

Electrostimulation has been an established method in medicine for many years. However, the application of electrostimulation to fermentation processes in biotechnology is a recent development. Although there are many publications 111 and patents in this field, only a few applications on the industrial scale have been reported. Electrostimulation in biology has been reviewed by Berg [1,21. Examples of electrostimulation in biotechnology are the increase in CO, formation at Succharomyces cerevisiae [31 and the influence of pulsatile electromagnetically induced currents (PEMIC) on the production of the antibiotic Nourseothricin from Streptomyces noursei [4]. One reason why electrostimulation is seldom applied in fermentation processes may be the complicated mechanisms and the unknown limiting step on the molecular level of most microbial fermentation processes, particularly in the case of syntheses of extracellular products. We are interested in the production of fungal cellulase which is a very complex system. The limiting step in the formation and secretion of the cellulase enzyme complex is governed by different biochemical and genetic control mechanisms, mainly the induction of enzyme formation and carbon catabolite repression. Carbon catabolite repression suppresses cellulase formation even if the concentration of easily utilizable sugars in the fermentation medium is very low, e.g. less than 20 mg 1-r of glucose. The mechanism of these regulatory processes on the molecular level is not yet completely understood. Many fungal mutant strains with improved cellulase formation have altered regulation of cellulase formation [5,6]. By using mutants with “switched off’ carbon catabolite repression it is possible to enhance cellulase formation significantly if the induction is optimal. We have previously developed such a Tricho-