Dextran-hydrolyse durch Hefen der Gattungen Cryptococcus und Trichosporon

Abstract

One strain of each of the yeast genera Cryptococcus (Cryptococcus laurentii (Kuff.) Skinner var. laurentii) and Trichosporon cutaneum (DSM 70703) was examined respective of its ability to form extracellular dextranase on different media. Neither both of the two strains are capable of hydrolyzing starch. When using dextran 20000 or maltose as nutrients, dextranase production by both strains was high. With sucrose, only the Trichosporon strain produced dextranase in appreciable amounts. Preliminary studies with Cryptococcus grown on several other C-sources, e.g. isomaltulose and α-methylglucopyranoside, indicated that dextranase was produced in large amounts. Traces of the enzyme were produced by both strains on all C-sources offered, thus demonstrating a basal level of constitutional dextranase initiation.

Dextranase production by both strains reaches its maximum extent during the logarithmic phase, and diminishes to almost zero values when cell division ceases. With Cryptococcus a steady increase in enzyme production results when the pH is raised from 4 to 8. The optima for enzyme production are in the region of near pH 7 and pH 8 for Cryptococcus or Trichosporon, respectively.

Enzyme extracts from both strains were purified for further studies. When examining the pH-dependence of the enzyme activities, Cryptococcus dextranase showed an optimum between pH 4 and 5.5, whereas Trichosporon dextranase was most active at about pH 6.6. Varying pH-conditions and the influence on enzyme stability were tested after 4 days of incubation at 37 °C. The smallest activity losses of the Cryptococcus and Trichosporon preparations were observed in the regions of pH 5-7.5 and pH 4-6, respectively. Degradation under elevated temperatures occurred with Cryptococcus dextranase of approximately 45°C and with Trichosporon dextranase at approximately 40°C.

Time course studies of dextran degradation with the two preparations led to the conclusion that both enzymes belong to the category of endo-dextranases (α-1.6-glucan-6-glucanohydrolase).