Screening and Identification of Mannanase-Producing Fungi Isolated from Selected Agricultural Wastes

Abstract

Aim: The study evaluated potential performance of different fungal isolates from agricultural by-products for mannanase production. Study Design: The first experiment, fungal isolates were screened for mannanase production on agar medium containing Locust Bean Gum (LBG) and total fungal count was conducted. In the second experiment, the fungal isolates were further screened for mannanase production in submerged state fermentation. Place and Duration of Study: Microbiology Research Laboratory Federal University of Technology, Akure and Postgraduate Research Laboratory, Obafemi Awolowo University Ile-Ife, Nigeria between September 2011 and March 2012. Methodology: The fungal isolates associated with some agricultural wastes were isolated on LBG containing agar medium by plate assay techniques and counted by standard microbiological methods. Mannanase production was conducted in submerged state fermentation (shaken & static) into which copra meal had been supplemented as the sole carbon source and enzyme activity was determined by dinitrosalicylic acid method. Results: In this study, 11 fungal isolates showed positive results with clear zone around their cultures. Fungal isolate 5A showed the highest activity ratio of 1.8, while the least was observed in isolate 9A12 with activity ratio of 0.64. The highest fungal counts were recorded in fermented coconut with 7.4×102 sfu/g, while cocoa pod and groundnut shell had no fungal growth. In terms of percentage occurrence of fungal isolates from selected agro-wastes, it was revealed that Rhizopus japonicus had the highest occurrence of 66.67%, while the same value of 8.33% was observed for Aspergillus fumigatus, A. glaucus, R. stolonifer and Trichosporonoides oedocephalis. In fermentation broth, all the 11 isolates displayed mannanase activity ranging from 0.370 to 21.667 U/ml for static and 0.278 to 3.982 U/ml for shaken condition, with the highest mannanase activity observed with isolate 5A for both culture conditions. According to the cultural characters and microscopic morphology, the isolate 5A being the highest mannanase producer was identified as the Aspergillus fumigatus. Conclusion: In this study, fungal isolates screened and evaluated for mannanase production from agricultural by-products elaborated considerable mannanase activity and this could be exploited for prebiotic preparation.