Application of In-House Xylanases as an Addition to a Commercial Cellulase Cocktail for the Sustainable Saccharification of Pretreated Blue Agave Bagasse Used for Bioethanol Production

Abstract

The study involves the use of commercial cellulase Cellic CTec2 in combination with two in-house xylanases, PxXyn10A (XynA), a recombinant purified enzyme from Paenibacillus xylanivorans A59, and a xylanase enzymatic extract from native Moesziomyces aphidis PYCC 5535T (MaPYCC 5535T), for the enzymatic hydrolysis of pretreated blue agave bagasse (BAB) at the high solids load of 20% (w/v). Three different combinations of cellulase and xylanases were evaluated. When Cellic® CTec2 was used at a dosage of 10 FPU/g oven-dried solids (ODS) supplemented with XynA or MaPYCC 5535T at an endo-xylanase dosage of 100 U/g ODS, increases in the xylose yield of 30% and 33%, respectively, were obtained. When applying in-house xylanases alone (at an endo-xylanase dosage of 100 U/g ODS), xylan in BAB was selectively hydrolyzed into xylose with 5% yield with MaPYCC 5535T, while no xylose was detected with XynA. Interestingly, a synergic effect of Cellic® CTec 2 with both xylanases was observed when using a low dosage of 1 FPU/g ODS (allowing for some liquefaction of the reaction mixture), promoting xylose and glucose release by either xylanase. A higher concentration of monomeric sugars was obtained with 10 FPU/g ODS of Cellic® Ctec 2 supplemented with 100 U/g ODS of MaPYCC 5535T, followed by XynA. The improvement in saccharification through the synergistic combination of in-house xylanases and commercial cellulases allows for the obtention of sugar-rich hydrolysates, which enhances the technical sustainability of the process. Hydrolysates were then fermented using recombinant Cellux 4TM yeast to yield 45 g/L ethanol, representing an increase of about 30% with respect to the control obtained with only the commercial cellulase cocktail. The surface modification of agave biomass with the different combinations of enzymes was evidenced by scanning electron microscopy (SEM).