Lee Brady D, Apel William A, Sheridan Peter P, DeVeaux Linda C
1Biological Systems Department, Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 USA.
2Department of Biological Sciences, Idaho State University, Campus Box 8007, Pocatello, ID 83209 USA.
Biotechnol Biofuels. 2018 Apr 16;11:110. doi: 10.1186/s13068-018-1110-3. eCollection 2018.
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.
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.
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.
细菌对小麦阿拉伯木聚糖（WAX）多糖中碳的代谢需要多种对糖与其他分子之间不同键具有活性的糖苷水解酶。嗜酸热栖放线菌是一种革兰氏阳性嗜热嗜酸菌，能够在多种单糖、双糖、寡糖和多糖上生长。在嗜酸热栖放线菌模式菌株ATCC27009/DSM 446基因组中已注释了19种推测的糖苷水解酶。进行实验以了解单糖对在多糖WAX上生长期间基因表达的影响。
在嗜酸热栖放线菌菌株ATCC27009利用WAX生长时，使用高密度寡核苷酸微阵列进行了分子分析。当以阿拉伯木聚糖糖类为代价指数生长的培养物受到葡萄糖或木糖挑战时，大多数糖苷水解酶被下调。有趣的是，向培养物中添加木糖时的调节比添加葡萄糖时更强烈，这表明与许多革兰氏阳性细菌所表现出的经典碳分解代谢物阻遏明显不同。对受调节的糖苷水解酶的计算机分析以及微阵列分析结果，得出了嗜酸热栖放线菌代谢阿拉伯木聚糖的潜在机制。该菌株表达的糖苷水解酶可能具有广泛的底物特异性，初始水解由细胞外木聚糖酶催化，而后续步骤可能在生长中的细胞内进行。
糖苷水解酶在很大程度上似乎在嗜酸热栖放线菌整个基因组中呈簇状分布。在这些簇内位点发现的并非所有糖苷水解酶基因在实验期间都受到调节，这表明在嗜酸热栖放线菌中发现并在WAX代谢过程中使用的19种糖苷水解酶基因中有一个特定子集。虽然糖苷水解酶的具体功能未作为所讨论研究的一部分进行测试，但在嗜酸热栖放线菌模式菌株中发现的许多糖苷水解酶似乎具有比其所属糖苷水解酶家族所代表的更广泛的底物范围。
