Strategies towards reduction of cellulases consumption: the emergent concept of consolidated bioprocessing (CBP)

Abstract

Lignocellulosic waste is a promising source of polysaccharides that can be converted into a variety of compounds, ranging from biofuels to bioplastics. Most of these residues can replace products originating from petroleum, representing an important environmental advantage. Lignocellulosic materials are theoretically unlimited, cheaper and do not compete with food crops. However, the main limitation of its use is the conversion of these materials into simple sugars, usually requires cellulolytic enzymes, which are still associated with a high production cost, being considered one of the main obstacles in the economic valorization of this process. Consolidated Bioprocessing (CBP) is a promising approach for the economical conversion of plant biomass into fuels and chemicals, and it has been described as a potential strategy toward reduction of cellulases consumption. This concept is based on the use of microorganisms that can hydrolyze the cellulosic and hemicellulose fractions of the pretreated biomass and, simultaneously, convert the monomeric sugars released into useful products. Yeasts are the microorganisms of choice in CBP, because they can produce high levels of biofuels or molecular precursors. However, the yeasts are not capable of producing enzymes that degrade efficiently biomass, and in this sense, yeast engineering, together with synthetic biology, stand out for the expression of cellulolytic and hemicellulolytic enzymes in fermentative yeasts. Results of ongoing and recent research at our FFCLRP Protein Biotechnology Laboratory (FAPESP: Processes 2014/10466-0, 2016/19095-0 and 2018/10296-8) point to the feasibility of using new enzymes identified by our group, in the hydrolysis of biomass. Thus, our proposal is the expression of cellulolytic enzymes in S. cerevisiae strains of industrial interest, which can be used in Consolidated Bioprocessing. Genomic editing will be performed by the CRISPR-Cas chimeric enzymatic system, a powerful tool that revolutionized the genetic engineering approaches and expanding the repertoire of genetically modified organisms (GMOs), and therefore arouses interest not only in basic research, but also from the biotechnology industry. The constructed strains will be applied in Consolidated Bioprocessing, using different biomasses. This stage of the project will be carried out in cooperation with Dr. Lucília Domingues from the "B. Factory group- Molecular Biotechnology, Bioreactors, Biofuels and Food research group" at the University of Minho (Braga, Portugal). The results are expected to enable the implementation of second-generation technologies for the sustainable production of bioethanol and chemical derivatives from biomass at a much lower cost than current technology. (AU)