Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, IL 61810, USA.
Appl Environ Microbiol. 2010 Mar;76(5):1524-32. doi: 10.1128/AEM.01970-09. Epub 2009 Dec 18.
Bacteria such as Escherichia coli will often consume one sugar at a time when fed multiple sugars, in a process known as carbon catabolite repression. The classic example involves glucose and lactose, where E. coli will first consume glucose, and only when it has consumed all of the glucose will it begin to consume lactose. In addition to that of lactose, glucose also represses the consumption of many other sugars, including arabinose and xylose. In this work, we characterized a second hierarchy in E. coli, that between arabinose and xylose. We show that, when grown in a mixture of the two pentoses, E. coli will consume arabinose before it consumes xylose. Consistent with a mechanism involving catabolite repression, the expression of the xylose metabolic genes is repressed in the presence of arabinose. We found that this repression is AraC dependent and involves a mechanism where arabinose-bound AraC binds to the xylose promoters and represses gene expression. Collectively, these results demonstrate that sugar utilization in E. coli involves multiple layers of regulation, where cells will consume first glucose, then arabinose, and finally xylose. These results may be pertinent in the metabolic engineering of E. coli strains capable of producing chemical and biofuels from mixtures of hexose and pentose sugars derived from plant biomass.
当同时提供多种糖时，细菌（如大肠杆菌）通常会一次消耗一种糖，这个过程被称为碳分解代谢物阻遏。经典的例子涉及葡萄糖和乳糖，大肠杆菌首先会消耗葡萄糖，只有当它消耗完所有的葡萄糖后，才会开始消耗乳糖。除了乳糖之外，葡萄糖还会抑制其他许多糖的消耗，包括阿拉伯糖和木糖。在这项工作中，我们描述了大肠杆菌中的第二个层次，即阿拉伯糖和木糖之间的层次。我们表明，当在两种戊糖的混合物中生长时，大肠杆菌会先消耗阿拉伯糖，然后再消耗木糖。与涉及分解代谢物阻遏的机制一致，在阿拉伯糖存在的情况下，木糖代谢基因的表达受到抑制。我们发现这种抑制是依赖于 AraC 的，并且涉及一种机制，其中阿拉伯糖结合的 AraC 结合到木糖启动子上并抑制基因表达。总的来说，这些结果表明，大肠杆菌中的糖利用涉及多个层次的调节，细胞首先消耗葡萄糖，然后是阿拉伯糖，最后是木糖。这些结果在代谢工程中可能是相关的，代谢工程旨在利用源自植物生物质的己糖和戊糖混合物来生产化学品和生物燃料。
