Isolation and screening of xylanase-producing microorganisms.

Abstract

Xylanases are enzymes that break down the complex polysaccharide xylan, the major component of hemicellulose. Xylanase hydrolyzes xylan by breaking the β-1,4- glycoside linkage to produce xylose and other degradation compounds. Many degradative microorganisms such as fungi, bacteria and yeast have been found to produce xylanases. In this study, xylanase-producing microorganisms were isolated from different environmental samples - paddy field rhizosphere, earthen pond sludge, decayed wood, cow dung, and sediments from Tagwai Dam, Minna, Nigeria. The samples were serially diluted and plated on a selective agar medium, which contains xylan (1.5 g), peptone (5 g), yeast extract (3 g), sodium chloride (5 g), and agar (15 g) per 1 L of distilled water using spread plate method and incubated at 37 °C for 48 hours and 25 °C for 5 days for bacteria and fungi respectively. The plate screening method was used to screen the microbial isolates for xylanase activity. Colonies with zones of inhibition indicated xylanase activity. Positive isolates were further subcultured to obtain pure isolates and were kept in slant bottles and stored at 4°C for further analysis. The pure isolates were cultured in nutrient broth for bacteria and Sabouraud dextrose broth for fungi and from the broth, into selective broth which was used to determine xylanase activity using DNS (dinitrosalicylic acid) method. The bacterial isolates were identified based on their cultural, morphological and biochemical characteristics while the fungal isolates were stained with lactophenol cotton blue. Ten (10) bacteria were isolated from the samples, of which four (Clostridium sp., Escherichia coli, Salmonella sp., and Staphylococcus sp) were xylanase producers and four (4) xylanase-producing fungi (Aspergillus niger, A. fumigatus, A. flavus, and A. sydowii were identified for fungi) were isolated. Escherichia coli gave the highest activity for the bacteria (0.8260) while Aspergillus flavus gave the highest xylanase activity for fungi (2.1118). Aspergillus flavus can therefore be recommended for large-scale production of xylanase.