Isolation, identification and screening of potential cellulase-free xylanase producing fungi
In order to isolate cellulase-free xylanase-producing fungi, screening and isolation of fungi was done using decaying wood, agricultural wastes and other lignocellulosic wastes as microbial source. Thirty (30) fungal species were selected for further analysis based upon clearing zones formation on xylan enriched agar plates. Submerged fermentation was done with 30 fungal isolates to identify strain that could produce highest amount of cellulase-free xylanase at a pH of 5.5 and at 28 ± 2°C temperature. Under screening conditions, 90% of the strains produced xylanase (6.6 to 495 U/ml) and negligible amount of cellulase ( 0.6 U/ml) with growth. Growth was determined in terms of mycelial dry weight which ranged between 0.6 to 2.34 mg/ml. The amount of soluble protein was also determined which ranged between 102 to 300 g/ml. The pH change after incubation was in between 5.0 to 8.0. Strain specific variability in xylanase production was confirmed in Aspergillus sp. and Penicillium sp. In addition, this study shows here that Rhizopus sp. can also produce xylanase under given conditions.
Key words: Cellulase-free xylanase, xylan, xylanase, submerged fermentation, malt extract agar.