Glycoside hydrolase gene transcription by during growth on wheat arabinoxylan and monosaccharides: a proposed xylan hydrolysis mechanism.

Background: Metabolism of carbon bound in wheat arabinoxylan (WAX) polysaccharides by bacteria requires a number of glycoside hydrolases active toward different bonds between sugars and other molecules. is a Gram-positive thermoacidophilic bacterium capable of growth on a variety of mono-, di-, oligo-, and polysaccharides. Nineteen proposed glycoside hydrolases have been annotated in the Type Strain ATCC27009/DSM 446 genome. Experiments were performed to understand the effect of monosaccharides on gene expression during growth on the polysaccharide, WAX.

Results: Molecular analysis using high-density oligonucleotide microarrays was performed on strain ATCC27009 when growing on WAX. When a culture growing exponentially at the expense of arabinoxylan saccharides was challenged with glucose or xylose, most glycoside hydrolases were downregulated. Interestingly, regulation was more intense when xylose was added to the culture than when glucose was added, showing a clear departure from classical carbon catabolite repression demonstrated by many Gram-positive bacteria. In silico analyses of the regulated glycoside hydrolases, along with the results from the microarray analyses, yielded a potential mechanism for arabinoxylan metabolism by . Glycoside hydrolases expressed by this strain may have broad substrate specificity, and initial hydrolysis is catalyzed by an extracellular xylanase, while subsequent steps are likely performed inside the growing cell.

Conclusions: Glycoside hydrolases, for the most part, appear to be found in clusters, throughout the genome. Not all of the glycoside hydrolase genes found at loci within these clusters were regulated during the experiment, indicating that a specific subset of the 19 glycoside hydrolase genes found in were used during metabolism of WAX. While specific functions of the glycoside hydrolases were not tested as part of the research discussed, many of the glycoside hydrolases found in the Type Strain appear to have a broader substrate range than that represented by the glycoside hydrolase family in which the enzymes were categorized.