Enzymatic potential of endophytic fungi: xylanase production by Colletotrichum boninense from sugarcane biomass.

Abstract

Endophytic fungi constitute a major part of the still unexplored fungal diversity and have gained interest as new biological sources of natural active compounds, including enzymes. Endophytic fungi were isolated from soybean leaves and initially screened on agar plates for the production of CMCase (carboxymethylcellulase), xylanase, amylase and protease. The highest Enzymatic Indexes (IE) were verified for xylanase (2.14 and 1.31) with the fungi M6-A6P5F2 and M12-A5P3F1.2 and CMCase (1.92 and 1.62) with the fungi M13-A9P2F1 and M12-A5P3F1.2, respectively. The production of xylanase and CMCase by the selected fungi was evaluated in submerged cultivation using beechwood xylan and carboxymethylcellulose (CMC), as well as sugarcane straw and bagasse in different ratios as carbon sources. Both types of lignocellulosic biomass proved to be good inducers of enzymatic activity. The best xylanase producer among the isolates was identified as Colletotrichum boninense. With this fungus, the highest xylanase activity was obtained with a sugarcane straw-bagasse mixture in a 50:50 ratio (383.63 U mL-1), a result superior to that obtained with the use of beechwood xylan (296.65 U mL-1). Regardingthe kinetic behavior of the crude xylanase, there was found optimal pH of 5.0 and optimal temperatures of 50°C and 60°C. At 40°C and 50°C, xylanase retained 87% and 76% of its initial catalytic activity, respectively. These results bring new perspectives on bioprospecting endophytic fungi for the production of enzymes, mainly xylanase, as well as the exploitation of agro-industrial by-products, such as sugarcane straw and bagasse.