Abstract
The xylanolytic and amylolytic yeasts were qualitatively determined by Cong red xylan agar and soluble starch agar plates, respectively. The most xylanase and alpha-amylase inducible strain (AUN-02) was selected and identified using PCR amplification of 26S rRNA gene and sequence analysis. The comparison of the alignment results and phylogenetic analysis of the sequences of the isolated yeast to published rRNA gene sequences in GenBank, confirmed the identification of the isolate as Pichia membranifaciens. Xylanase and alpha-amylase production by isolated P. membranifaciens were investigated at different pH values (4-8), temperature degrees (20-45 degrees C), incubation time (1-7 days) and various substrates.A higher production of xylanase (38.8 U/mL) and alpha-amylase (28.7 U/mL) was obtained after 4 days of fermentation of P. membranifaciens. Higher activity of xylanase (36.83 U/mL) and alpha-amylase (27.7 U/ mL) was obtained in the fermentation of P. membranifaciens in a culture medium adjusted to pH 7.0. The optimum temperature showed maximum xylanase and alpha-amylase activity (42.6 and 32.5 units/m L, respectively) was estimated at 35 degrees C. The xylanase and a-amylase activities of P. membranifaciens were estimated and compared for the different substrates tested. The strain revealed 100% relative activity of xylanase and alpha-amylase on beechwood and potato starch, respectively. The affinity of enzymes towards substrate was estimated using Km values. The Km values of xylanase and alpha-amylase increased in the order of pH's 7.0, 6.0 and 4.5 (0.85, 1.6 and 3.4 mg xylan/mL and 0.22, 0.43 and 2.8 mg starch/ mL, respectively). the yeast P. membranifaciensis is suitable for produce neutral xylanase and alpha-amylase enzymes. So, it could be used as a promising strain for production of these enzymes in industrial field.