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Suppressors of dGTP Starvation in Escherichia coli. J Bacteriol 2017; 199:JB.00142-17. [PMID: 28373271 DOI: 10.1128/jb.00142-17] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 03/23/2017] [Indexed: 11/20/2022] Open
Abstract
dGTP starvation, a newly discovered phenomenon in which Escherichia coli cells are starved specifically for the DNA precursor dGTP, leads to impaired growth and, ultimately, cell death. Phenomenologically, it represents an example of nutritionally induced unbalanced growth: cell mass amplifies normally as dictated by the nutritional status of the medium, but DNA content growth is specifically impaired. The other known example of such a condition, thymineless death (TLD), involves starvation for the DNA precursor dTTP, which has been found to have important chemotherapeutic applications. Experimentally, dGTP starvation is induced by depriving an E. coligpt optA1 strain of its required purine source, hypoxanthine. In our studies of this phenomenon, we noted the emergence of a relatively high frequency of suppressor mutants that proved resistant to the treatment. To study such suppressors, we used next-generation sequencing on a collection of independently obtained mutants. A significant fraction was found to carry a defect in the PurR transcriptional repressor, controlling de novo purine biosynthesis, or in its downstream purEK operon. Thus, upregulation of de novo purine biosynthesis appears to be a major mode of overcoming the lethal effects of dGTP starvation. In addition, another large fraction of the suppressors contained a large tandem duplication of a 250- to 300-kb genomic region that included the purEK operon as well as the acrAB-encoded multidrug efflux system. Thus, the suppressive effects of the duplications could potentially involve beneficial effects of a number of genes/operons within the amplified regions.IMPORTANCE Concentrations of the four precursors for DNA synthesis (2'-deoxynucleoside-5'-triphosphates [dNTPs]) are critical for both the speed of DNA replication and its accuracy. Previously, we investigated consequences of dGTP starvation, where the DNA precursor dGTP was specifically reduced to a low level. Under this condition, E. coli cells continued cell growth but eventually developed a DNA replication defect, leading to cell death due to formation of unresolvable DNA structures. Nevertheless, dGTP-starved cultures eventually resumed growth due to the appearance of resistant mutants. Here, we used whole-genome DNA sequencing to identify the responsible suppressor mutations. We show that the majority of suppressors can circumvent death by upregulating purine de novo biosynthesis, leading to restoration of dGTP to acceptable levels.
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Oancea I, Movva R, Das I, Aguirre de Cárcer D, Schreiber V, Yang Y, Purdon A, Harrington B, Proctor M, Wang R, Sheng Y, Lobb M, Lourie R, Ó Cuív P, Duley JA, Begun J, Florin THJ. Colonic microbiota can promote rapid local improvement of murine colitis by thioguanine independently of T lymphocytes and host metabolism. Gut 2017; 66:59-69. [PMID: 27411368 PMCID: PMC5256391 DOI: 10.1136/gutjnl-2015-310874] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Revised: 06/13/2016] [Accepted: 06/15/2016] [Indexed: 01/19/2023]
Abstract
OBJECTIVE Mercaptopurine (MP) and pro-drug azathioprine are 'first-line' oral therapies for maintaining remission in IBD. It is believed that their pharmacodynamic action is due to a slow cumulative decrease in activated lymphocytes homing to inflamed gut. We examined the role of host metabolism, lymphocytes and microbiome for the amelioration of colitis by the related thioguanine (TG). DESIGN C57Bl/6 mice with or without specific genes altered to elucidate mechanisms responsible for TG's actions were treated daily with oral or intrarectal TG, MP or water. Disease activity was scored daily. At sacrifice, colonic histology, cytokine message, caecal luminal and mucosal microbiomes were analysed. RESULTS Oral and intrarectal TG but not MP rapidly ameliorated spontaneous chronic colitis in Winnie mice (point mutation in Muc2 secretory mucin). TG ameliorated dextran sodium sulfate-induced chronic colitis in wild-type (WT) mice and in mice lacking T and B lymphocytes. Remarkably, colitis improved without immunosuppressive effects in the absence of host hypoxanthine (guanine) phosphoribosyltransferase (Hprt)-mediated conversion of TG to active drug, the thioguanine nucleotides (TGN). Colonic bacteria converted TG and less so MP to TGN, consistent with intestinal bacterial conversion of TG to so reduce inflammation in the mice lacking host Hprt. TG rapidly induced autophagic flux in epithelial, macrophage and WT but not Hprt-/- fibroblast cell lines and augmented epithelial intracellular bacterial killing. CONCLUSIONS Treatment by TG is not necessarily dependent on the adaptive immune system. TG is a more efficacious treatment than MP in Winnie spontaneous colitis. Rapid local bacterial conversion of TG correlated with decreased intestinal inflammation and immune activation.
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Affiliation(s)
- I Oancea
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - R Movva
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia,School of Pharmacy, Griffith University, Brisbane, Queensland, Australia
| | - I Das
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia
| | - D Aguirre de Cárcer
- Division of Livestock Industries, CSIRO Preventative Health National Research Flagship, Brisbane, Queensland, Australia
| | - V Schreiber
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - Y Yang
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,School of Pharmacy, University of Queensland, Brisbane, Queensland, Australia
| | - A Purdon
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - B Harrington
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - M Proctor
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - R Wang
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - Y Sheng
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - M Lobb
- Inflammatory Diseases Biology & Therapeutics Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia
| | - R Lourie
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia
| | - P Ó Cuív
- Translational Research Institute, Woolloongabba, Queensland, Australia,Diamantina Institute-University of Queensland, Brisbane, Queensland, Australia
| | - J A Duley
- Division of Livestock Industries, CSIRO Preventative Health National Research Flagship, Brisbane, Queensland, Australia,Inflammatory Diseases Biology & Therapeutics Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia
| | - J Begun
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia,School of Medicine-University of Queensland, St Lucia, Queensland, Australia
| | - T H J Florin
- Immunity Infection and Inflammation Program, Mater Research Institute-University of Queensland, Brisbane, Queensland, Australia,Translational Research Institute, Woolloongabba, Queensland, Australia,School of Medicine-University of Queensland, St Lucia, Queensland, Australia
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