Developing a soluble inducer for robust production of cellulases by Trichoderma reesei through submerged fermentation

Abstract

Cellulases hydrolyze the cellulose component of lignocellulosic biomass to release sugars as a feedstock for microbial fermentation for producing bio-based products. Cellulases are predominately produced by Trichoderma reesei through submerged fermentation under induction and aerobic conditions, where consumption of the inducer accounts for the major portion of the overall cost of the process. In this work, we developed an acid-catalyzed process for producing a mixture of sugars (ACSM) from glucose through a transglycosylation reaction as an inducer for cellulases production by T. reesei RUT-C30. Component analysis indicated that the ACSM contained unconverted glucose and oligosaccharides, with the degree of polymerization ranging from 2 to 7, in which β-disaccharides, including sophorose, cellobiose and gentiobiose, were recognized as effective inducers for cellulases production. When the ACSM was supplemented as an inducer, the transcription of genes encoding glycoside hydrolases was up-regulated, and cellulases production was increased by 62.1% in comparison to that induced by lactose, while it was on a par with the process induced by microcrystalline cellulose. Moreover, when fed-batch fermentation was employed, the cellulases activity reached 19.2 U per mL. Economic analysis conducted using Aspen Plus suggested that the preparation cost of the ACSM was 52.4% of that associated with lactose and 41.4% of that associated with microcrystalline cellulose, highlighting the economic competitiveness of the ACSM as an inducer for cellulases production. Furthermore, solid-acid catalysis was developed to produce the ACSM more efficiently, which not only made the process environmentally friendly through acid regeneration but also cellulases production was enhanced by 27.0% in comparison to the production with sulfuric acid. The reported progress is significant for producing cellulases at low cost to support the biorefining of lignocellulosic biomass for sustainable socioeconomic development.