Screening of bacterial extracellular xylanase producers with potential for cellulose pulp biobleaching

Isabela Da Silva Vasconcelos Rodrigues,Roberta Pereira Miranda Fernandes,Rafael Salomão Da Silva,Silvio Santana Dolabella,Marcelo Ferreira Fernandes,Carolina Goes Silva E Silva

doi:10.4025/actascibiolsci.v41i1.42101

Isabela Da Silva Vasconcelos Rodrigues, Roberta Pereira Miranda Fernandes + Show 4 more

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https://doi.org/10.4025/actascibiolsci.v41i1.42101

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Abstract

In this study, two hundred fifty-seven bacterial isolates from a suppressive soil library were screened to study their secretion of alkali-thermostable xylanases for potential use in cellulose pulp biobleaching. Xylanase activity was evaluated in solid and liquid media using xylan as the carbon source. Isolates were initially evaluated for the degradation of xylan in solid media by the congo red test. Selected strains were evaluated in liquid media for enzymatic activity and determination of total protein concentration using a crude protein extract (CPE). An isolate identified as Bacillus species TC-DT13 produced the highest amount of xylanase (1808 U mL-1). The isolate was active and stable at 70°C and pH 9.0, conditions which are necessary for the paper industry. This isolate can grow and produce xylanase in medium containing wheat fiber as a substrate. The CPE of this isolate was used in preliminary testing on cellulose pulp bleaching; enzyme treatment of the pulp resulted in a 5% increase of whiteness.

Highlights

Cellulose and hemicellulose are carbohydrate polymers and serve as the two major components of lignocellulosic biomass, which is generated through photosynthesis
Two hundred fifty-seven soil bacterial isolates belonging to the collection of the Soil Microbiology Laboratory (Embrapa Tabuleiros Costeiros) were reactivated in yeast mannitol (YMA) media consisting of K2HPO4 0.2 g L-1, MgS04 0.2 g L-1, mannitol 10.0 g L-1, and yeast extract 0.3 g L-1 NaCl 0.05 g L-1 and incubated at 32°C at 150 RPM until reaching an optical density (OD) of 0.5
During screening we identified a very promising strain TC-DT13, which had the highest level of xylanase production approximately 1800 U mL-1

Summary

Introduction

Cellulose and hemicellulose are carbohydrate polymers and serve as the two major components of lignocellulosic biomass, which is generated through photosynthesis. Cellulose and hemicellulose are located in the cell walls of plants and interlaced through covalent bonds with a non-carbohydrate polymer named lignin (Pérez, Muñoz-Dourado, Rubia, & Martínez, 2002). Xylan is the largest component of hemicellulose and is the second most abundant polysaccharide in the cell walls of terrestrial plants (Thomas, Joseph, Arumugam, & Pandey, 2013a). The endo-β-1,4-D-xylanase (EC 3.2.1.8) and β-xylosidase (EC 3.2.1.37) are the major enzymes responsible for the hydrolysis of xylan (Juturu & Wu, 2012). A variety of microorganisms including bacteria, fungi, yeasts and actinomycetes can produce xylandegrading enzymes. While fungi generally produce a large amount of xylanase, these enzymes produced by bacteria are more stable. Soil bacterial isolates have been investigated due to their potential for xylanase production (Whang et al, 2010)

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