Metabolic potential of Bacillus subtilis 168 for the direct conversion of xylans to fermentation products

Abstract

Methylglucuronoxylans (MeGXn) and methylglucuronoarabinoxylans (MeGAXn) respectively comprise most of the hemicellulose fractions in dicots and monocots and, next to cellulose, are the major resources for the production of fuels and chemicals from lignocellulosics. With either MeGXn or MeGAXn as a substrate, Bacillus subtilis 168 accumulates acidic methylglucuronoxylotriose as a limit product following the uptake and metabolism of neutral xylooligosaccharides. Secreted GH11 endoxylanase (Xyn11A), GH30 endoxylanase (Xyn30C), and GH43 arabinoxylan arabinofuranohydrolase (Axh43) respectively encoded by the xynA, xynC, and xynD genes collectively contribute to the depolymerization of MeGAXn. Studies here demonstrate the complementary roles of these enzymes in the digestion of MeGAXn. Coordinate expression of the xynD and xynC genes defines an operon accounting for the Axh43-catalyzed release of arabinose followed by Xyn30C and Xyn11A-catalyzed depolymerization of MeGAXn. Both sources generate acetate and lactate as the principal fermentation products, with yields of 26 % acetate and 32 % lactate from MeGXn compared to 22 % acetate and 21 % lactate from MeGAXn. These studies of the GH43/GH30/GH11 system in B. subtilis 168 provide a basis for the further development of B. subtilis and related species as biocatalysts for direct conversion of hemicellulose derived from energy crops as well as agricultural and forest residues to chemical feedstocks.

Novel Trifunctional Xylanolytic Enzyme Axy43A from Paenibacillus curdlanolyticus Strain B-6 Exhibiting Endo-Xylanase, β- d -Xylosidase, and Arabinoxylan Arabinofuranohydrolase Activities

“…Endo-xylanases hydrolyze the backbone of xylan to produce xylooligosaccharides (XOSs) in an endo-acting manner; however, their activities are frequently hampered by the arabinose substitutions (4). ␣-L-Arabinofuranosidases (AFs) include various types of enzymes that release arabinose from arabinose-containing substrates, e.g., p-nitrophenyl-␣-L-arabinofuranoside (pNPAf), arabinoxylo-oligosaccharides (AXOSs), arabinoxylans, linear and branched arabinans, and arabinogalactans (1,5), while arabinoxylan arabinofuranohydrolases (AXHs) are atypical AFs that prefer to release arabinose from the nonreducing terminal xylose of arabinoxylans (6) and AXOSs (7), including pNPAf (7). Based on the mode of action, AXHs are categorized into two groups.…”

Optimization of alkaline extraction of hemicellulose from sweet sorghum bagasse and its direct application for the production of acidic xylooligosaccharides by Bacillus subtilis strain MR44

“…There was no significant signal at 5.22 to 5.24 ppm indicating the absence of free arabinose in both spectra. Arabinofuranosyl substitutions could have been removed by Axh43 from the xylan backbone and assimilated to support cell growth [ 26 ].…”

Biomass to fuels and chemicals: A review of enabling processes and technologies

“…77 Bacillus subtilis has been investigated for directly processing the hemicellulose fraction for production of valuable products, including LA. 78 Researchers have reported LA production from corn stover hydrolysate using a thermophilic strain of Bacillus coagulans, resulting in an L-lactic acid titre of 92 g L −1 with a yield of 0.91 g g −1 . 79 Bacillus coagulans MA-13 has been reported as a potential thermophilic and cellulolytic strain for the production of lactic acid from lignocellulosic hydrolysate.…”