EFFECT OF NITROGEN-SOURCES ON THE LEVELS OF ALDOSE REDUCTASE AND XYLITOL DEHYDROGENASE-ACTIVITIES IN THE XYLOSE-FERMENTING YEAST CANDIDA-TENUIS

The effects of different medium components on growth of the D-xylose-f ermenting yeast Candida tenuis CBS 4435 as well as on formation of ald ose reductase (ALR, xylose reductase) and xylitol dehydrogenase (XDH) were investigated. By using the Plackett-Burman statistical screening method, important effects for the two N sources yeast extract and NH4N O3 were found, while a change in the concentration of the other medium components (D-xylose, peptone from casein, a vitamin solution, a trac e element solution, KH2PO4) neither significantly affected growth nor enzyme synthesis in C. tenuis. The importance of these two N sources w as confirmed by subsequent shaken flask experiments planned according to a full factorial design and by bioreactor cultivations. Yeast extra ct was identified as important for growth as well as for the formation of ALR and XDH. Ammonium (NH4Cl) was also shown to have a stimulatory effect on the levels of these two enzymes formed in C. tenuis, wherea s it reduced growth when present in the medium in a concentration of 1 00 mM.