An Improved and Simplified Radial Gel Diffusion Assay for the Detection of Xylanase Activity

Abstract

Xylanase (E.C. 3.2.1.8) degrades β-1, 4 xylan by cleaving β-1, 4 glycosidic linkages randomly, resulting in the generation of xylose and xylo-oligosaccharides. Xylanases are produced by organisms including fungi, bacteria, yeast, marine algae, protozoans, snails, crustaceans and insects. Xylanases present considerable industrial interest for their use in paper manufacturing, improvement of animal feed digestibility, and clarification of fruit juices. In addition, this enzyme is the component of cell wall-degrading enzymes (CWDEs) during plant–pathogen interaction. Thus, considering their various applications in plant defence and also in industry, the characterization of xylanase activity becomes an important aspect. Conventionally, xylanase activity is determined by radial gel diffusion assay using Congo red staining (Emami and Hack, 2001) and by DNSA assay which is a colorimetric method for xylanase activity (McLauchlan et al., 1999; Kutasi et al., 2001). Comparatively, radial gel diffusion assay using Congo red staining is a qualitative assay whereas DNSA method is a quantitative assay. Moreover, Congo red is a chemical considered as hazardous category 1B (Carcinogenicity) and category 12 (Reproductive toxicity) by the 2012 OSHA Hazard Communication Standard (29 CFR 1910.1200). In the present study, the proposed method enables qualitative detection of xylanase activity using ethanol precipitation in the radial gel diffusion assay which is safer and simpler. The ethanol precipitation in agar plate has been adapted from the method for detecting xylanase activity in polyacrylamide gels (Royer and Nakas, 1990).