High-level production of xylose from agricultural wastes using GH11 endo-xylanase and GH43 ß-xylosidase from Bacillus sp.

As a promising feedstock, alkali-extracted xylan from lignocellulosic biomass is desired for producing xylose, which can be used for renewable biofuels production. In this study, an efficient pathway has been established for low-cost and high-yield production of xylose by hydrolysis of alkali-extracted xylan from agricultural wastes using an endo-1,4-xylanase (XYLA) from Bacillus safensis TCCC 111022 and a ß-xylosidase (XYLO) from B. pumilus TCCC 11573. The optimum activities of recombinant XYLA (rXYLA) and XYLO (rXYLO) were 60 â„ƒ and pH 8.0, and 30 â„ƒ and pH 7.0, respectively. They were stable over a broad pH range (pH 6.0-11.0 and 7.0-10.0). rXYLO showed a relatively high xylose tolerance up to 100 mM. Furthermore, the yield of xylose from wheat straw, rice straw, corn stover, corncob and sugarcane bagasse by rXYLA and rXYLO was 63.77%, 71.76%, 68.55%, 53.81%, and 58.58%, respectively. This study demonstrated a strategy to produce xylose from agricultural wastes by integrating alkali-extracted xylan and enzymatic hydrolysis.

Insights into the mechanism for the high-alkaline activity of a novel GH43 ß-xylosidase from Bacillus clausii with a promising application to produce xylose.

Nowadays, alkali-tolerant ß-xylosidases and their molecular mechanism of pH adaptability have been poorly studied. Here, a novel GH43 ß-xylosidase (XYLO) was isolated from Bacillus clausii TCCC 11004, and the recombinant ß-xylosidase (rXYLO) was most active at pH 8.0 and stable in a broad pH range (7.0-11.0), exhibiting superior alkali tolerance. Molecular dynamics simulation indicated that XYLO showed a notable overall structural stability and an enlargement of substrate binding pocket under alkaline condition, resulting in the formation of a new hydrogen bond between substrate and Arg286 of XYLO, and the tight binding played a key role in improving the XYLO activity with the increasing pH. Moreover, rXYLO with an endo-xylanase resulted in high xylose yields by hydrolyzing alkali-extracted xylan from agricultural wastes. This work would provide an alkali-tolerant ß-xylosidase, enhance the understanding for the relationship of structure and activity adapted to the high-alkaline environment, and promote its application in xylose production.

Biochemical and Structural Properties of a High-Temperature-Active Laccase from Bacillus pumilus and Its Application in the Decolorization of Food Dyes.

A novel laccase gene isolated from Bacillus pumilus TCCC 11568 was expressed, and the recombinant laccase (rLAC) displayed maximal activity at 80 °C and at pH 6.0 against ABTS. rLAC maintained its structural integrity at a high temperature (355 K) compared to its tertiary structure at a low temperature (325 K), except for some minor adjustments of certain loops. However, those adjustments were presumed to be responsible for the formation of a more open access aisle that facilitated the binding of ABTS in the active site, resulting in a shorter distance between the catalytic residue and the elevated binding energy. Additionally, rLAC showed good thermostability (≤70 °C) and pH stability over a wide range (3.0-10.0), and displayed high efficiency in decolorizing azo dyes that are applicable to the food industry. This work will improve our knowledge on the relationship of structure-function for thermophilic laccase, and provide a candidate for dye effluent treatment in the food industry.