Production of acidic xylooligosaccharides from methylglucuronoarabinoxylans by Bacillus subtilis strain MR44

BACKGROUND: Bacillus subtilis 168 secretes endoxylanases Xyn11A and Xyn30C and arabinofuranohydrolase Axh43 that process xylans in hemicellulose fractions. Engineered strain MR44 with a deletion in the xynA gene encoding Xyn11A, converts hardwood methylglucuronoxylans (MeGXₙ) of dicots to defined acidic xylooligosaccharides (U‐XOS) with a single methylglucuronate linked to xylooligosaccharides with an average ratio of one methylglucuronate to 6–7 xyloses as value‐added products. The MR44 strain also secretes Axh43 that catalyses release of arabinose from methylglucuronoarabinoxylans (MeGAXₙ) of monocots. RESULTS: MR44 strain efficiently processes sorghum MeGAXₙ with 493 mg g⁻¹ yields of purified U‐XOS. ¹H‐NMR analysis of U‐XOS purified by anion exchange chromatography structurally defined the U‐XOS with an average degree of polymerization of xylose units (DP) of 11–12 and a single 4‐O‐methyl‐glucuronic acid α‐1,2‐linked on average to one of 11–12 xylose residues each penultimate to the reducing terminal xylose. CONCLUSION: This study demonstrates the ability of Bacillus subtilis strains to process MeGAXₙ for production of U‐XOS from monocots, including energy crops and agricultural residues. The U‐XOS with an average DP of 11–12 from sweet sorghum MeGAXₙ compared with 6–7 from sweetgum MeGXₙ extends their applications as biologicals and for production of pentosan polysulfates with applications in human and veterinary medicine. © 2015 Society of Chemical Industry