Screening of yeasts capable of producing cellulase-free xylanase

Xylanases have largely been obtained from filamentous fungi and bacteria; few studies have investigated the production of this enzyme by yeasts. The aim of this study was to isolate yeasts from different sources, such as vegetables, cereal grains, fruits, and agro-industrial waste and to obtain yeasts capable of producing celulase-free xylanase. Samples were enriched using yeast malt broth, and yeasts were isolated on Wallerstein nutrient agar. In all, 119 yeast strains were isolated and evaluated in terms of their ability to degrade xylan, which was found in the medium by using agar degradation halos, the basis of this polysaccharide, and Congo red dye. Selected microorganisms were grown in complex medium and the enzymatic activities of endo-xylanase, β-xylosidase, carboxymetilcellulase, and filter paper cellulose were determined over 96 h of cultivation; the pH and biomass concentration were also evaluated. The yeast strain 18Y, which was isolated from chicory and later identified as Cryptococcus laurentii, showed the highest endo-xylanase activity (2.7 U.mL-1). This strain had the ability to produce xylanase with low levels of cellulase production (both CMCase [0.11 U.mL-1] and FPase [0.10 U.mL-1]). This result gives this strain great biotechnological potential since this enzyme can be used for industrial pulp and paper bleaching.   Key words: Cryptococcus laurentii, endo-xylanase, xylan.