Optimization of biomass and dihydroorotase (DHOase) production by Saccharomyces cerevisiae MNJ3 (pMNJ1)

Growth conditions which maintains DHOase overproduction by Saccharomyces cerevisiae MNJ3 (pMNJ1) and allow sufficient biomass production to ensure DHoase's purification were investigated. We used as basal medium the Yeast Carbon Base (YCB; Difco), especially designed for studies of nitrogen metabolism in yeasts. Thus the effects of an additional carbon source (glucose or citric acid) and the influence of the nitrogen source (asparagine or ammonium sulphate) as well as that of pH on growth of this strain were studied by supplementing the Yeast Carbon Base medium (Difco) with the above components. Cells were collected and DHOase activity was determined. This study showed that the best conditions for biomass production required supplementation of YCB with asparagines 5 g/l, glucose 20 g/l at pH 5.5 (M12 medium). In this medium DHOase activity decrease with time; thus in terms of DHOase yield, the best time for havesting cells is reached after 30 to 38 h of growth.