Koirala Santosh, Wang Xiaoyi, Rao Christopher V
Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
J Bacteriol. 2015 Nov 2;198(3):386-93. doi: 10.1128/JB.00709-15. Print 2016 Feb 1.
Glucose is known to inhibit the transport and metabolism of many sugars in Escherichia coli. This mechanism leads to its preferential consumption. Far less is known about the preferential utilization of nonglucose sugars in E. coli. Two exceptions are l-arabinose and d-xylose. Previous studies have shown that l-arabinose inhibits d-xylose metabolism in Escherichia coli. This repression results from l-arabinose-bound AraC binding to the promoter of the d-xylose metabolic genes and inhibiting their expression. This mechanism, however, has not been explored in single cells. Both the l-arabinose and d-xylose utilization systems are known to exhibit a bimodal induction response to their cognate sugar, where mixed populations of cells either expressing the metabolic genes or not are observed at intermediate sugar concentrations. This suggests that l-arabinose can only inhibit d-xylose metabolism in l-arabinose-induced cells. To understand how cross talk between these systems affects their response, we investigated E. coli during growth on mixtures of l-arabinose and d-xylose at single-cell resolution. Our results showed that mixed, multimodal populations of l-arabinose- and d-xylose-induced cells occurred at intermediate sugar concentrations. We also found that d-xylose inhibited the expression of the l-arabinose metabolic genes and that this repression was due to XylR. These results demonstrate that a strict hierarchy does not exist between l-arabinose and d-xylose as previously thought. The results may also aid in the design of E. coli strains capable of simultaneous sugar consumption.
Glucose, d-xylose, and l-arabinose are the most abundant sugars in plant biomass. Developing efficient fermentation processes that convert these sugars into chemicals and fuels will require strains capable of coutilizing these sugars. Glucose has long been known to repress the expression of the l-arabinose and d-xylose metabolic genes in Escherichia coli. Recent studies found that l-arabinose also represses the expression of the d-xylose metabolic genes. In the present study, we found that d-xylose also represses the expression of the l-arabinose metabolic genes, leading to mixed populations of cells capable of utilizing l-arabinose and d-xylose. These results further our understanding of mixed-sugar utilization and may aid in strain design.
已知葡萄糖会抑制大肠杆菌中多种糖类的转运和代谢。这种机制导致其被优先消耗。关于大肠杆菌中非葡萄糖糖类的优先利用情况，人们了解得要少得多。两个例外是L-阿拉伯糖和D-木糖。先前的研究表明，L-阿拉伯糖会抑制大肠杆菌中D-木糖的代谢。这种抑制作用源于与L-阿拉伯糖结合的AraC与D-木糖代谢基因的启动子结合并抑制其表达。然而，这种机制尚未在单细胞水平上进行探究。已知L-阿拉伯糖和D-木糖利用系统对其同源糖类均表现出双峰诱导反应，即在中等糖浓度下会观察到细胞群体中既有表达代谢基因的，也有不表达的。这表明L-阿拉伯糖只能抑制L-阿拉伯糖诱导的细胞中D-木糖的代谢。为了了解这些系统之间的相互作用如何影响它们的反应，我们以单细胞分辨率研究了在L-阿拉伯糖和D-木糖混合物上生长的大肠杆菌。我们的结果表明，在中等糖浓度下出现了L-阿拉伯糖和D-木糖诱导细胞的混合多峰群体。我们还发现D-木糖会抑制L-阿拉伯糖代谢基因的表达，且这种抑制作用是由XylR引起的。这些结果表明，L-阿拉伯糖和D-木糖之间并不像之前认为的那样存在严格的等级关系。这些结果也可能有助于设计能够同时消耗糖类的大肠杆菌菌株。
葡萄糖、D-木糖和L-阿拉伯糖是植物生物质中最丰富的糖类。开发将这些糖类转化为化学品和燃料的高效发酵工艺将需要能够同时利用这些糖类的菌株。长期以来已知葡萄糖会抑制大肠杆菌中L-阿拉伯糖和D-木糖代谢基因的表达。最近的研究发现L-阿拉伯糖也会抑制D-木糖代谢基因的表达。在本研究中，我们发现D-木糖也会抑制L-阿拉伯糖代谢基因的表达，从而导致能够利用L-阿拉伯糖和D-木糖的细胞混合群体出现。这些结果加深了我们对混合糖利用的理解，并可能有助于菌株设计。
