Paenibacillus sp. Strain JDR-2 and XynA 1 : a Novel System for Methylglucuronoxylan Utilization

Abstract

Environmental and economic factors predicate the need for efficient processing of renewable sources of fuels and chemicals. To fulfill this need, microbial biocatalysts must be developed to efficiently process the hemicellulose fraction of lignocellulosic biomass for fermentation of pentoses. The predominance of methylglucuronoxylan (MeGAX _n ), a β-1,4 xylan in which 10% to 20% of the xylose residues are substituted with α-1,2-4- O -methylglucuronate residues, in hemicellulose fractions of hardwood and crop residues has made this a target for processing and fermentation. A Paenibacillus sp. (strain JDR-2) has been isolated and characterized for its ability to efficiently utilize MeGAX _n . A modular xylanase (XynA ₁ ) of glycosyl hydrolase family 10 (GH 10) was identified through DNA sequence analysis that consists of a triplicate family 22 carbohydrate binding module followed by a GH 10 catalytic domain followed by a single family 9 carbohydrate binding module and concluding with C-terminal triplicate surface layer homology (SLH) domains. Immunodetection of the catalytic domain of XynA ₁ (XynA ₁ CD) indicates that the enzyme is associated with the cell wall fraction, supporting an anchoring role for the SLH modules. With MeGAX _n as substrate, XynA ₁ CD generated xylobiose and aldotetrauronate (MeGAX ₃ ) as predominant products. The inability to detect depolymerization products in medium during exponential growth of Paenibacillus sp. strain JDR-2 on MeGAX _n , as well as decreased growth rate and yield with XynA ₁ CD-generated xylooligosaccharides and aldouronates as substrates, indicates that XynA ₁ catalyzes a depolymerization process coupled to product assimilation. This depolymerization/assimilation system may be utilized for development of biocatalysts to efficiently convert MeGAX _n to alternative fuels and biobased products.