Screening of Lignocellulolytic Enzyme Activities in Fungal Species and Sequential Solid-State and Submerged Cultivation for the Production of Enzyme Cocktails.

Nenad Marđetko,Mario Novak,Roland Ludwig,Božidar Šantek,Mladen Pavlečić,Blanka Didak Ljubas,Marina Grubišić,Vlatka Petravić Tominac,Antonija Trontel

doi:10.3390/polym13213736

Abstract

Various fungal species can degrade lignocellulolytic materials with their enzyme cocktails composed of cellulolytic and lignolytic enzymes. In this work, seven fungal species (Mucor indicus DSM 2185, Paecilomyces variotii CBS 372.70, Myceliophthora thermophila CBS 663.74, Thielavia terrestris CBS 456.75, Botryosphaeria dothidea JCM 2738, Fusarium oxysporum f.sp. langenariae JCM 9293, and Fusarium verticillioides JCM 23107) and four nutrient media were used in the screening for effective lignocellulose degrading enzymes. From the seven tested fungi, F. oxysporum and F. verticilliodes, along with nutrient medium 4, were selected as the best medium and producers of lignocellulolytic enzymes based on the determined xylanase (>4 U mg−1) and glucanase activity (≈2 U mg−1). Nutrient medium 4 supplemented with pretreated corn cobs was used in the production of lignocellulolytic enzymes by sequential solid-state and submerged cultivation of F. oxysporum, F. verticilliodes, and a mixed culture of both strains. F. oxysporum showed 6 times higher exoglucanase activity (3.33 U mg−1) after 5 days of cultivation in comparison with F. verticillioides (0.55 U mg−1). F. oxysporum also showed 2 times more endoglucanase activity (0.33 U mg−1). The mixed culture cultivation showed similar endo- and exoglucanase activities compared to F. oxysporum (0.35 U mg−1; 7.84 U mg−1). Maximum xylanase activity was achieved after 7 days of cultivation of F. verticilliodes (≈16 U mg−1), while F. oxysporum showed maximum activity after 9 days that was around 2 times lower compared to that of F. verticilliodes. The mixed culture achieved maximum xylanase activity after only 4 days, but the specific activity was similar to activities observed for F. oxysporum. It can be concluded that both fungal strains can be used as producers of enzyme cocktails for the degradation of lignocellulose containing raw materials, and that corn cobs can be used as an inducer for enzyme production.

Highlights

IntroductionGlobalization and rapid advances in technological development have positive effects on society (exchange of information, capital and labour mobility, open markets), but can have a negative impact on the environment and climate; there is a necessity for the constant optimization and improvement of the biotechnological production of new materials, biochemicals, and biofuels
Globalization and rapid advances in technological development have positive effects on society, but can have a negative impact on the environment and climate; there is a necessity for the constant optimization and improvement of the biotechnological production of new materials, biochemicals, and biofuels
The conversion of cellulose and hemicellulose to simple fermentable sugars is caused by the synergistic actions of various enzymes that belong to a complex system of cellulase and hemicellulase enzymes

Summary

Introduction

Globalization and rapid advances in technological development have positive effects on society (exchange of information, capital and labour mobility, open markets), but can have a negative impact on the environment and climate; there is a necessity for the constant optimization and improvement of the biotechnological production of new materials, biochemicals, and biofuels. The usage of residual lignocellulosic biomass as a feedstock for biofuels production, in the long term, can be an economically and environmentally viable solution if the cost-effective conversion of lignocellulosic biomass to fermentable sugars is achieved using the synergistic action of multiple enzymes [2]. The main sources of fermentable sugars in lignocellulosic biomass are cellulose and hemicellulose, which are very resistant to microbial degradation because of their complex and compact structures [3,4] with few access sites available for enzyme binding. Thermo-chemical pretreatment breaks the rigid structure of lignocellulose by disrupting the lignin coating and enables subsequent enzymatic processing of polysaccharides [5,6]. They are various flavin-containing oxidases that are H2O2-dependent, and which can be located either intra- or extracellularly [3,8]

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