H. Sočič

Effect of immobilization on the stability of Claviceps purpurea protoplasts

SummaryProtoplasts released with high efficiency from vegetative and productive hyphae ofClaviceps purpurea were immobilized in 2% Ca-alginate. The yield of active immobilized protoplasts depended upon the age of the mycelium from which protoplasts were derived and was found to be 25–43% in comparison with native hyphae. During incubation in a modified production medium immobilized protoplasts were stable for at least 10–12 days. No external growth of regenerated hyphae from spherical beads of alginate gel with entrapped protoplasts was observed for 13–15 days of the batchwise incubation.

Morphological differentiation of immobilizedClaviceps paspali mycelium during semi-continuous cultivation

SummaryThe morphological development ofClaviceps paspali immobilized in Ca-alginate gel was examined. During consecutive reincubations, the immobilized mycelia differentiated into swollen, arthrosporoid-like cells, which never appeared during fermentation of free mycelium. Such differentiation could be connected with the improved, prologed vitality and metabolic activity of the immobilized cells.

The effect of aeration and agitation on Claviceps purpurea dimorphism and alkaloid synthesis during submerged fermentation

SummaryVarying the air flow rate (vvm) in a fermentor under constant drive speed, Claviceps purpurea dimorphism as well as alkaloid biosynthesis were greatly influenced. At a high flow rate (2.5 vvm) sclerotial growth was favoured in seed and in production media, while at a low air flow rate (1.0 vvm) sphacelial growth dominated. When using high flow rates the oxygen uptake rate was small, but at low flow rates it increased markedly. In both cases the alkaloid production was lower than at the intermediate value of 1.5 vvm of air flow rate, which proved to be optimal. This could be explained by the difference in the air/water interface and two-phase oxygen uptake. At a high air/water interface direct oxygen uptake from the gaseous phase prevails, while at a low air/water interface uptake is due to the oxygen liquid-phase only. Thus for optimal fungal development and alkaloid production a compromise between uptake from the liquid and the gaseous phase has to be established by a defined ratio between aeration and agitation.

Correlation between growth and ergot alkaloid biosynthesis in Claviceps purpurea batch fermentation

SummaryFollowing the growth kinetics of a C. purpurea ergotoxine-producing strain it was observed that alkaloid synthesis and alkaloid distribution depend on fungal growth velocity during idiophase. Formation of extracellular alkaloids is favoured by higher fungal growth velocity, while intracellular alkaloids begin to accumulate at a lower rate of growth. Simple lysergic acid derivatives prevali among extracellular alkaloids, whereas ergotoxines predominate among intracellular alkaloids. By varying cultivation conditions, by feeding the culture, or by varying the inoculum size, alkaloid composition can be influenced within the limits of strain capabilities.

The effect of citric acid concentration and pH on the submerged production of lysergic acid derivatives

SummarySuccinic acid can just as well be replaced by citric acid in submerged fermentation of lysergic acid derivatives by a strain of Claviceps paspali. The highest alkaloid yields were obtained with a 1% citric acid concentration in the medium at a constant pH of 5.2. When the optimal pH was not maintained, growth was inhibited and all aspects of metabolic activity of the fungus were depressed.

Carbohydrate metabolism during submerged production of ergot alkaloids

SummaryThe mycelial sugar composition and changes in specific activities of phosphofructokinase (PFK) and glucose-6-phosphate dehydrogenase, the key enzymes of the glycolytic and pentose-phosphate pathway of glucose catabolism, were followed throughout submerged fermentation of a high-yielding Claviceps purpurea L17 strain. Experimental data indicate that the pentose-phosphate pathway in glucose breakdown prevails during the vegetative phase of fermentation, the share of the glycolytic pathway becoming more pronounced during alkaloid synthesis. Both enzymes exhibit hyperbolic saturation kinetics, which is not usual for the PFK of eukaryotes.

Regulation of ergotoxine biosynthesis in Claviceps purpurea submerged fermentation

SummaryThe effect of exogenously administered l-valine on the ratio of ergocornine/ergokryptine in submerged cultures of Claviceps purpurea was studied. The desired ratio of alkaloids (1:1) was achieved by the use of very small concentrations of l-valine when proper conditions had been established.