title: Alkaliphilic endoxylanase from lignocellulolytic microbial consortium metagenome for biobleaching of eucalyptus pulp.
abstract: Enzymatic pre-bleaching by modification of pulp fibers with xylanases is an attractive approach to reduce the consumption of toxic bleaching chemicals in the paper industry. In this study, an alkaliphilic endoxylanase gene was isolated from metagenomic DNA of a structurally stable thermophilic lignocellulose-degrading microbial consortium using amplification with conserved glycosyl hydrolase family 10 primers and subsequent genome walking. The full-length xylanase showed 78% sequence identity to an endo-beta-1,4-xylanase of Clostridium phytofermentans and was expressed in a mature form with an N-terminal His6 tag fusion in Escherichia coli. The recombinant xylanase Xyn3F was thermotolerant and alkaliphilic, working optimally at 65-70 degrees C with an optimal pH at 9- 10 and retaining >80% activity at pH 9, 60 degrees C for 1 h. Xyn3F showed a Vmax of 2,327 IU/mg and Km of 3.5 mg/ml on birchwood xylan. Pre-bleaching of industrial eucalyptus pulp with no prior pH adjustment (pH 9) using Xyn3F at 50 IU/g dried pulp led to 4.5-5.1% increase in final pulp brightness and 90.4-102.4% increase in whiteness after a single-step hypochlorite bleaching over the untreated pulp, which allowed at least 20% decrease in hypochlorite consumption to achieve the same final bleaching indices. The alkaliphilic xylanase is promising for application in an environmentally friendly bleaching step of kraft and soda pulps with no requirement for pH adjustment, leading to improved economic feasibility of the process.
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Nakornpathom, Thailand.
authors.forename: Chawannapak
authors.initials: C
authors.lastname: Weerachavangkul
authors.forename: Thanaporn
authors.initials: T
authors.lastname: Laothanachareon
authors.forename: Katewadee
authors.initials: K
authors.lastname: Boonyapakron
authors.forename: Sarunyou
authors.initials: S
authors.lastname: Wongwilaiwalin
authors.forename: Thidarat
authors.initials: T
authors.lastname: Nimchua
authors.forename: Lily
authors.initials: L
authors.lastname: Eurwilaichitr
authors.forename: Kusol
authors.initials: K
authors.lastname: Pootanakit
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Igarashi
authors.forename: Verawat
authors.initials: V
authors.lastname: Champreda
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D057886:Bleaching Agents / Q000737:chemistry / Q000378:metabolism*; D003001:Cloning, Molecular; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005052:Eucalyptus; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008031:Lignin / Q000378:metabolism*; D054892:Metagenome; D059013:Microbial Consortia; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D057886:Bleaching Agents; D011994:Recombinant Proteins; C036909:lignocellulose; D008031:Lignin; D043364:Endo-1,4-beta Xylanases