Hydrolytic potential of Trichoderma sp. strains evaluated by microplate-based screening followed by switchgrass saccharification

• Published in: Enzyme and microbial technology 2012-05, Vol.50 (6-7), p.304-310
• Main Authors: Cianchetta, Stefano, Galletti, Stefania, Burzi, Pier Luigi, Cerato, Claudio
• Format: Article
• Language: English
• Subjects: bioconversion; Biofuel; Biofuels; Biomass; biotransformation; Cellulase; Cellulases - metabolism; Cellulose; Endo-1,4-beta Xylanases - metabolism; endo-1,4-beta-glucanase; Enzymes; feedstocks; Fuels; fungi; Glucose; High-Throughput Screening Assays - methods; Hydrolysis; Lignin - metabolism; lignocellulose; Lignocellulosic biomass; Limiting factors; Panicum - metabolism; Panicum virgatum; saccharification; screening; Sugar; Switchgrass; Trichoderma; Trichoderma - classification; Trichoderma - growth & development; Trichoderma - metabolism; Xylan endo-1,3- beta -xylosidase; Xylanase; xylanases
• ISSN: 0141-0229; 1879-0909
• DOI: 10.1016/j.enzmictec.2012.02.005

► Hydrolytic potential of wild-type Trichoderma isolates was evaluated on switchgrass in miniaturised systems. ► Saccharification was performed in 96 well-plates at the same cellulase load showing relevant differences among isolates. ► One xylanolytic isolate outperformed a 5-fold load commercial enzyme on untreated switchgrass. ► Screenings for improved strains should involve evaluation of both xylanases and cellulases. Bioconversion of lignocellulosic biomass to fuel requires a hydrolysis step to obtain fermentable sugars, generally accomplished by fungal enzymes. Large-scale screening of different microbial strains would provide optimal enzyme cocktails for any target feedstock. The aim of this study was to screen a large collection of Trichoderma sp. strains for the hydrolytic potential towards switchgrass (Panicum virgatum L.). Strains were cultivated in a small-scale system and assayed in micro-plates for xylanase and cellulase activities. The population distributions of these traits are reported after growth on switchgrass in comparison with cellulose. The distribution profiles suggest that the growth on switchgrass strongly promotes xylanase production. The IK4 strain displayed the highest xylanase activity after growth on switchgrass (133U/mL). Enzymes (10FPU/g substrate) from IK4 were compared with those from 2 cellulolytic Trichoderma strains and a commercial enzyme in saccharification time-course experiments on untreated and pretreated switchgrass and on an artificial substrate. Samples were analysed by DNS assay and by an oxygraphic method for sugar equivalent or glucose concentration. On the untreated substrate, IK4 enzymes even outperformed a 5-fold load of commercial enzyme, suggesting that xylanase or accessory enzymes are a limiting factor on this type of recalcitrant substrate. On the other substrates, IK4 preparations showed intermediate behaviour if compared with the commercial enzyme at 10FPU/g substrate and at 5-fold load. IK4 also nearly halved the time to release 50% of the hydrolysable sugar equivalents (T50%), with respect to the other preparations at the same enzymatic load. DNS assay and oxygraphic method gave highly correlated results for the 3 saccharified substrates. The study suggests that accessory enzymes like xylanase play a key role in improving the performance of cellulase preparations on herbaceous lignocellulosic feedstocks like switchgrass.