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. 2018 Oct 19;8:15509. doi: 10.1038/s41598-018-33647-w

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© The Author(s) 2018

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Suggested model for the regulation of extracellular ADPG uptake and utilization in E. coli in the mammalian intestine. According to this model, NupC and NupG, as well as the integrity of the outer membrane (OM), act as major determinants of the process. Under conditions of glucose (primary carbon source) limitation, augmented cAMP levels and concomitant activation of CRP will enhance the expression of nupC and nupG, thus favoring the scavenging of extracellular ADPG. These conditions will also enhance the expression of pathways involved in the catabolism of mono- and disaccharides derived from the degradation of complex polysaccharides by the intestine microbiota. It is conceivable that the OM of E. coli will be periodically damaged by bile acids and other membrane-damaging substances and conditions occurring in the intestine, allowing passive diffusion of ADPG molecules into the periplasm and access to the inner membrane NupC and NupG transporters. In the cytoplasm, the scavenged ADPG is employed to produce glycogen and ADP by GlgA, the former used as a carbon and energy storage compound for survival and colonization^2,29 and the latter to fuel purine nucleotides metabolism (this work).