Abstract

Agro-byproducts can be utilized as effective and low-cost nutrient sources for microbial fermentation to produce a variety of usable products. In this study, wheat bran powder (WBP) was found to be the most effective carbon source for xylanase production by Streptomyces thermocarboxydus TKU045. The optimal media for xylanase production was 2% (w/v) WBP, 1.50% (w/v) KNO3, 0.05% (w/v) MgSO4, and 0.10% (w/v) K2HPO4, and the optimal culture conditions were 50 mL (in a 250 mL-volume Erlenmeyer flask), initial pH 9.0, 37 °C, 125 rpm, and 48 h. Accordingly, the highest xylanase activity was 6.393 ± 0.130 U/mL, 6.9-fold higher than that from un-optimized conditions. S. thermocarboxydus TKU045 secreted at least four xylanases with the molecular weights of >180, 36, 29, and 27 kDa when cultured on the WBP-containing medium. The enzyme cocktail produced by S. thermocarboxydus TKU045 was optimally active over a broad range of temperature and pH (40–70 °C and pH 5–8, respectively) and could hydrolyze birchwood xylan to produce xylobiose as the major product. The obtained xylose oligosaccharide (XOS) were investigated for 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and the growth effect of lactic acid bacteria. Finally, the solid waste from the WBP fermentation using S. thermocarboxydus TKU045 revealed the high adsorption of Congo red, Red 7, and Methyl blue. Thus, S. thermocarboxydus TKU045 could be a potential strain to utilize wheat bran to produce xylanases for XOS preparation and dye adsorbent.

Highlights

  • Hemicellulose, cellulose, and lignin are the three major types of polymers that compose the plant cell-wall [1,2]

  • Wheat bran powder (WBP), an inexpensive agro-byproduct was utilized as the sole carbon source to produce xylanases by S. thermocarboxydus TKU045

  • Various carbon sources were investigated for the preparation of an optimum culture medium for the production of xylanase by S. thermocarboxydus TKU045

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Summary

Introduction

Hemicellulose, cellulose, and lignin are the three major types of polymers that compose the plant cell-wall [1,2]. Vast applications of xylanase have been extensively explored based on its ability in xylan degradation, for example, biofuels production [6,7,8], pulp and paper bleaching [9,10,11], bioactive compounds [12,13,14], animal feed [15,16], and baking [17,18,19]. Some of the agro-byproducts that could give a high-efficiency in xylanase production via microbial fermentation include wheat bran, rice bran, rice straw, sugarcane bagasse, sawdust, and wheat husk [39,49] This leads to the idea of using agrobyproducts as economically effective nutritional supplements for the synthesis of xylanase by Streptomyces strains. Wheat bran powder (WBP), an inexpensive agro-byproduct was utilized as the sole carbon source to produce xylanases by S. thermocarboxydus TKU045 This strain produced at least four xylanases on medium which contains wheat bran.

Materials
Xylanase Assay
Agro-Byproducts as the Sole Carbon Source for Xylanase Production
Effects of Nitrogen Sources on Xylanase Production
Effects of Culture Conditions on Xylanase Production
Effects of Temperature and pH
Xylan Hydrolysis
2.11. Growth Effect Assay
2.12. Dye Adsorption Assay
Agro-Byproducts as the Sole Carbon Source for the Xylanase Production
Effects
Effects of Culture
Molecular Weight Determination of the Xylanases
Biochemical Characterization of Crude Enzyme Cocktail
Utilization of Solid Waste from the WBP Fermentation as a Dye Adsorbent
Conclusions

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