Characterization of mannanases from Clonostachys byssicola involved in the breakdown of lignocellulosic substrates

Abstract

Enzymatic saccharification of lignocellulosic agricultural residues, such as soybean hull, is increasingly used in Brazil to obtain fermentable sugars for use in biotechnological processes. The filamentous fungus, Clonostachys byssicola, is known to secrete an arsenal of holocellulolytic enzymes, including mannanases, which degrade the hemicellulosic components in soyabean hull. In this study, we investigated the biochemical characteristics of mannanases produced by C. byssicola. The mannanases in the concentrated crude extract (CCE) of C. byssicola showed high activity at acidic pH (5.0) and 55 °C. Furthermore, these enzymes do not depend on additional metal cofactors for their activation, although phenolic compounds inhibited the mannanase activity. Multiple forms of mannanases were identified in the CCE, which holds significance in the production of manno-oligosaccharides from different carbon sources. Scanning electron microscopy revealed structural modifications in lignocellulosic residues, including soybean hull and sugarcane bagasse, upon incubation with CCE. HPLC analysis detected mannotriose as the main oligosaccharide generated during the degradation of lignocellulosic residues. In contrast, hydrolysis of galactomannans (locust bean gum and guar gum) generated oligosaccharides of different sizes, such as mannobiose, mannotriose, mannotetraose, mannopentaose, and mannohexaose. These results highlight the potential of C. byssicola mannanases in hemicellulose degradation and production of prebiotic oligosaccharides.