초록
<P>Xylans are the predominant polysaccharides in hemicelluloses and an important potential source of biofuels and chemicals. The ability of <I>Bacillus subtilis</I> subsp. <I>subtilis</I> strain 168 to utilize xylans has been ascribed to secreted glycoside hydrolase family 11 (GH11) and GH30 endoxylanases, encoded by the <I>xynA</I> and <I>xynC</I> genes, respectively. Both of these enzymes have been defined with respect to structure and function. In this study, the effects of deletion of the <I>xynA</I> and <I>xynC</I> genes, individually and in combination, were evaluated for xylan utilization and formation of acidic xylooligosaccharides. Parent strain 168 depolymerizes methylglucuronoxylans (MeGX<SUB><I>n</I></SUB>), releasing the xylobiose and xylotriose utilized for growth and accumulating the aldouronate methylglucuronoxylotriose (MeGX<SUB>3</SUB>) with some methylglucuronoxylotetraose (MeGX<SUB>4</SUB>). The combined GH11 and GH30 activities process the products generated by their respective actions on MeGX<SUB><I>n</I></SUB> to release a maximal amount of neutral xylooligosaccharides for assimilation and growth, at the same time forming MeGX<SUB>3</SUB> in which the internal xylose is substituted with methylglucuronate (MeG). Deletion of <I>xynA</I> results in the accumulation of β-1,4-xylooligosaccharides with degrees of polymerization ranging from 4 to 18 and an average degree of substitution of 1 in 7.2, each with a single MeG linked α-1,2 to the xylose penultimate to the xylose at the reducing terminus. Deletion of the <I>xynC</I> gene results in the accumulation of aldouronates comprised of 4 or more xylose residues in which the MeG may be linked α-1,2 to the xylose penultimate to the nonreducing xylose. These <I>B. subtilis</I> lines may be used for the production of acidic xylooligosaccharides with applications in human and veterinary medicine.</P>