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Williams JT, Baker JJ, Zheng H, Dechow SJ, Fallon J, Murto M, Albrecht VJ, Gilliland HN, Olive AJ, Abramovitch RB. A genetic selection for Mycobacterium smegmatis mutants tolerant to killing by sodium citrate defines a combined role for cation homeostasis and osmotic stress in cell death. mSphere 2023; 8:e0035823. [PMID: 37681985 PMCID: PMC10597346 DOI: 10.1128/msphere.00358-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 07/23/2023] [Indexed: 09/09/2023] Open
Abstract
Mycobacteria can colonize environments where the availability of metal ions is limited. Biological or inorganic chelators play an important role in limiting metal availability, and we developed a model to examine Mycobacterium smegmatis survival in the presence of the chelator sodium citrate. We observed that instead of restricting M. smegmatis growth, concentrated sodium citrate killed M. smegmatis. RNAseq analysis during sodium citrate treatment revealed transcriptional signatures of metal starvation and hyperosmotic stress. Notably, metal starvation and hyperosmotic stress, individually, do not kill M. smegmatis under these conditions. A forward genetic transposon selection was conducted to examine why sodium citrate was lethal, and several sodium-citrate-tolerant mutants were isolated. Based on the identity of three tolerant mutants, mgtE, treZ, and fadD6, we propose a dual stress model of killing by sodium citrate, where sodium citrate chelate metals from the cell envelope and then osmotic stress in combination with a weakened cell envelope causes cell lysis. This sodium citrate tolerance screen identified mutants in several other genes with no known function, with most conserved in the pathogen M. tuberculosis. Therefore, this model will serve as a basis to define their functions, potentially in maintaining cell wall integrity, cation homeostasis, or osmotolerance. IMPORTANCE Bacteria require mechanisms to adapt to environments with differing metal availability. When Mycobacterium smegmatis is treated with high concentrations of the metal chelator sodium citrate, the bacteria are killed. To define the mechanisms underlying killing by sodium citrate, we conducted a genetic selection and observed tolerance to killing in mutants of the mgtE magnesium transporter. Further characterization studies support a model where killing by sodium citrate is driven by a weakened cell wall and osmotic stress, that in combination cause cell lysis.
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Affiliation(s)
- John T. Williams
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Jacob J. Baker
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Huiqing Zheng
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Shelby J. Dechow
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Jared Fallon
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Megan Murto
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Veronica J. Albrecht
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Haleigh N. Gilliland
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Andrew J. Olive
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
| | - Robert B. Abramovitch
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA
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Dechow SJ, Coulson GB, Wilson MW, Larsen SD, Abramovitch RB. AC2P20 selectively kills Mycobacterium tuberculosis at acidic pH by depleting free thiols. RSC Adv 2021; 11:20089-20100. [PMID: 34168865 PMCID: PMC8176622 DOI: 10.1039/d1ra03181c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Mycobacterium tuberculosis (Mtb) senses and adapts to host immune cues as part of its pathogenesis. One environmental cue sensed by Mtb is the acidic pH of its host niche in the macrophage phagosome. Disrupting the ability of Mtb to sense and adapt to acidic pH has the potential to reduce survival of Mtb in macrophages. Previously, a high throughput screen of a ∼220 000 compound small molecule library was conducted to discover chemical probes that inhibit Mtb growth at acidic pH. The screen discovered chemical probes that kill Mtb at pH 5.7 but are inactive at pH 7.0. In this study, AC2P20 was prioritized for continued study to test the hypothesis that it was targeting Mtb pathways associated with pH-driven adaptation. RNAseq transcriptional profiling studies showed AC2P20 modulates expression of genes associated with redox homeostasis. Gene enrichment analysis revealed that the AC2P20 transcriptional profile had significant overlap with a previously characterized pH-selective inhibitor, AC2P36. Like AC2P36, we show that AC2P20 kills Mtb by selectively depleting free thiols at acidic pH. Mass spectrometry studies show the formation of a disulfide bond between AC2P20 and reduced glutathione, supporting a mechanism where AC2P20 is able to deplete intracellular thiols and dysregulate redox homeostasis. The observation of two independent molecules targeting free thiols to kill Mtb at acidic pH further supports that Mtb has restricted redox homeostasis and sensitivity to thiol-oxidative stress at acidic pH.
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Affiliation(s)
- Shelby J Dechow
- Department of Microbiology and Molecular Genetics, Michigan State University East Lansing MI 48824 USA +1 517 353-8957 +1 517 884-5416
| | - Garry B Coulson
- Department of Microbiology and Molecular Genetics, Michigan State University East Lansing MI 48824 USA +1 517 353-8957 +1 517 884-5416
| | - Michael W Wilson
- Vahlteich Medicinal Chemistry Core, College of Pharmacy, University of Michigan Ann Arbor MI 48109 USA
| | - Scott D Larsen
- Vahlteich Medicinal Chemistry Core, College of Pharmacy, University of Michigan Ann Arbor MI 48109 USA
| | - Robert B Abramovitch
- Department of Microbiology and Molecular Genetics, Michigan State University East Lansing MI 48824 USA +1 517 353-8957 +1 517 884-5416
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Baker JJ, Dechow SJ, Abramovitch RB. Acid Fasting: Modulation of Mycobacterium tuberculosis Metabolism at Acidic pH. Trends Microbiol 2019; 27:942-953. [PMID: 31324436 DOI: 10.1016/j.tim.2019.06.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 05/29/2019] [Accepted: 06/14/2019] [Indexed: 01/22/2023]
Abstract
Mycobacterium tuberculosis (Mtb) senses and adapts to acidic host environments during the course of pathogenesis. Mutants defective in acidic pH-dependent adaptations are often attenuated during macrophage or animal infections, supporting that these pathways are essential for pathogenesis and represent important new targets for drug discovery. This review examines a confluence of findings supporting that Mtb has restricted metabolism at acidic pH that results in the slowing of bacterial growth and changes in redox homeostasis. It is proposed that induction of the PhoPR regulon and anaplerotic metabolism, in concert with the restricted use of specific carbon sources, functions to counter reductive stress associated with acidic pH.
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Affiliation(s)
- Jacob J Baker
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
| | - Shelby J Dechow
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
| | - Robert B Abramovitch
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA.
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