Afroz Taliman, Biliouris Konstantinos, Kaznessis Yiannis, Beisel Chase L
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA.
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.
Mol Microbiol. 2014 Sep;93(6):1093-1103. doi: 10.1111/mmi.12695. Epub 2014 Jul 16.
Inducible utilization pathways reflect widespread microbial strategies to uptake and consume sugars from the environment. Despite their broad importance and extensive characterization, little is known how these pathways naturally respond to their inducing sugar in individual cells. Here, we performed single-cell analyses to probe the behaviour of representative pathways in the model bacterium Escherichia coli. We observed diverse single-cell behaviours, including uniform responses (d-lactose, d-galactose, N-acetylglucosamine, N-acetylneuraminic acid), 'all-or-none' responses (d-xylose, l-rhamnose) and complex combinations thereof (l-arabinose, d-gluconate). Mathematical modelling and probing of genetically modified pathways revealed that the simple framework underlying these pathways - inducible transport and inducible catabolism - could give rise to most of these behaviours. Sugar catabolism was also an important feature, as disruption of catabolism eliminated tunable induction as well as enhanced memory of previous conditions. For instance, disruption of catabolism in pathways that respond to endogenously synthesized sugars led to full pathway induction even in the absence of exogenous sugar. Our findings demonstrate the remarkable flexibility of this simple biological framework, with direct implications for environmental adaptation and the engineering of synthetic utilization pathways as titratable expression systems and for metabolic engineering.
可诱导利用途径反映了微生物从环境中摄取和消耗糖类的广泛策略。尽管它们具有广泛的重要性并得到了广泛的表征，但对于这些途径在单个细胞中如何自然响应其诱导糖类却知之甚少。在这里，我们进行了单细胞分析，以探究模式细菌大肠杆菌中代表性途径的行为。我们观察到了多种单细胞行为，包括一致反应（d-乳糖、d-半乳糖、N-乙酰葡糖胺、N-乙酰神经氨酸）、“全或无”反应（d-木糖、l-鼠李糖）及其复杂组合（l-阿拉伯糖、d-葡糖酸盐）。对基因改造途径的数学建模和探究表明，这些途径背后的简单框架——可诱导转运和可诱导分解代谢——可以产生大多数这些行为。糖类分解代谢也是一个重要特征，因为分解代谢的破坏消除了可调节的诱导以及对先前条件的增强记忆。例如，对响应内源性合成糖类的途径中分解代谢的破坏导致即使在没有外源糖类的情况下也会出现全途径诱导。我们的研究结果证明了这个简单生物框架的显著灵活性，这对环境适应以及作为可滴定表达系统的合成利用途径工程和代谢工程具有直接影响。
