Caulobacter crescentus β-Xylosidase II Is Highly Tolerant to Inhibitors Present in Fermentative Processes Involving Lignocellulosic Biomass

More stable enzymes with improved properties are in constant demand for various biotechnological processes. In this work, it was found that the activity of recombinant purified β-xylosidase II (CcXynB2) from the bacterium Caulobacter crescentus is increased 62% by 5 mM KCl, likely due to the presence of K+ ions. CcXynB2 activity was measured in the presence of various compounds that have been described as inhibitors of lignocellulosic biomass hydrolysis and fermentation. CcXynB2 was found to be 61% more tolerant than 200 mM ethanol over a 48-h incubation at 37 °C. The specific activity of CcXynB2 was determined in the presence of phenol, hydroxymethylfurfural, ferulic, acetic, and coumaric acids; arabinose, glucose, xylose, and pectin. After 48 h, CcXynB2 activity in the presence of these compounds was found to be equal to 100% or higher than CcXynB2 activity in the absence of these compounds. When inhibitors were used in combination, CcXynB2 retained 67% of its initial activity over 48 h at 37 °C. Enzymatic hydrolysis of hemicellulose from corncobs was performed with CcXynB2 alone or with CcXynB2 in conjunction with recombinant xylanase and β-glucosidase-β-xylosidase-α-arabinosidase from C. crescentus producing reducing sugars. The immobilized CcXynB2 was more active than the soluble enzyme at both temperatures tested, 37 and 50 °C. In addition, immobilized CcXynB2 retained most of the enzyme activity incubated at 50 °C than at 37 °C, maintaining more than 70% of its initial activity after 1 h of incubation. In general, the CCXynB2 has potential to be applied in a bioprocess since it showed robust resistance in presence of many chemical compounds that may be generated during fermentation steps and physicochemical pre-treatment of biomass if considering a simultaneous saccharification fermentation process in a biorefinery.