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Walker RM, Sanabria VC, Youk H. Microbial life in slow and stopped lanes. Trends Microbiol 2024; 32:650-662. [PMID: 38123400 PMCID: PMC11187706 DOI: 10.1016/j.tim.2023.11.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 11/27/2023] [Accepted: 11/28/2023] [Indexed: 12/23/2023]
Abstract
Microbes in nature often lack nutrients and face extreme or widely fluctuating temperatures, unlike microbes in growth-optimized settings in laboratories that much of the literature examines. Slowed or suspended lives are the norm for microbes. Studying them is important for understanding the consequences of climate change and for addressing fundamental questions about life: are there limits to how slowly a cell's life can progress, and how long cells can remain viable without self-replicating? Recent studies began addressing these questions with single-cell-level measurements and mathematical models. Emerging principles that govern slowed or suspended lives of cells - including lives of dormant spores and microbes at extreme temperatures - are re-defining discrete cellular states as continuums and revealing intracellular dynamics at new timescales. Nearly inactive, lifeless-appearing microbes are transforming our understanding of life.
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Affiliation(s)
- Rachel M Walker
- Department of Systems Biology, University of Massachusetts Chan Medical School, Worcester, MA, USA
| | - Valeria C Sanabria
- Department of Systems Biology, University of Massachusetts Chan Medical School, Worcester, MA, USA
| | - Hyun Youk
- Department of Systems Biology, University of Massachusetts Chan Medical School, Worcester, MA, USA.
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2
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Chan C, Groisman EA. Chaperone Hsp70 helps Salmonella survive infection-relevant stress by reducing protein synthesis. PLoS Biol 2024; 22:e3002560. [PMID: 38574172 PMCID: PMC10994381 DOI: 10.1371/journal.pbio.3002560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2023] [Accepted: 02/23/2024] [Indexed: 04/06/2024] Open
Abstract
In all domains of life, Hsp70 chaperones preserve protein homeostasis by promoting protein folding and degradation and preventing protein aggregation. We now report that the Hsp70 from the bacterial pathogen Salmonella enterica serovar Typhimurium-termed DnaK-independently reduces protein synthesis in vitro and in S. Typhimurium facing cytoplasmic Mg2+ starvation, a condition encountered during infection. This reduction reflects a 3-fold increase in ribosome association with DnaK and a 30-fold decrease in ribosome association with trigger factor, the chaperone normally associated with translating ribosomes. Surprisingly, this reduction does not involve J-domain cochaperones, unlike previously known functions of DnaK. Removing the 74 C-terminal amino acids of the 638-residue long DnaK impeded DnaK association with ribosomes and reduction of protein synthesis, rendering S. Typhimurium defective in protein homeostasis during cytoplasmic Mg2+ starvation. DnaK-dependent reduction in protein synthesis is critical for survival against Mg2+ starvation because inhibiting protein synthesis in a dnaK-independent manner overcame the 10,000-fold loss in viability resulting from DnaK truncation. Our results indicate that DnaK protects bacteria from infection-relevant stresses by coordinating protein synthesis with protein folding capacity.
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Affiliation(s)
- Carissa Chan
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, United States of America
| | - Eduardo A. Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, United States of America
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3
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Brugger C, Srirangam S, Deaconescu AM. IraM remodels the RssB segmented helical linker to stabilize σ s against degradation by ClpXP. J Biol Chem 2024; 300:105568. [PMID: 38103640 PMCID: PMC10844676 DOI: 10.1016/j.jbc.2023.105568] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 11/20/2023] [Accepted: 12/08/2023] [Indexed: 12/19/2023] Open
Abstract
Upon Mg2+ starvation, a condition often associated with virulence, enterobacteria inhibit the ClpXP-dependent proteolysis of the master transcriptional regulator, σs, via IraM, a poorly understood antiadaptor that prevents RssB-dependent loading of σs onto ClpXP. This inhibition results in σs accumulation and expression of stress resistance genes. Here, we report on the structural analysis of RssB bound to IraM, which reveals that IraM induces two folding transitions within RssB, amplified via a segmented helical linker. These conformational changes result in an open, yet inhibited RssB structure in which IraM associates with both the C-terminal and N-terminal domains of RssB and prevents binding of σs to the 4-5-5 face of the N-terminal receiver domain. This work highlights the remarkable structural plasticity of RssB and reveals how a stress-specific RssB antagonist modulates a core stress response pathway that could be leveraged to control biofilm formation, virulence, and the development of antibiotic resistance.
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Affiliation(s)
- Christiane Brugger
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island, USA
| | - Srinivas Srirangam
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island, USA
| | - Alexandra M Deaconescu
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island, USA.
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4
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Groisman EA, Choi J. Advancing evolution: Bacteria break down gene silencer to express horizontally acquired genes. Bioessays 2023; 45:e2300062. [PMID: 37533411 PMCID: PMC10530229 DOI: 10.1002/bies.202300062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2023] [Revised: 07/25/2023] [Accepted: 07/28/2023] [Indexed: 08/04/2023]
Abstract
Horizontal gene transfer advances bacterial evolution. To benefit from horizontally acquired genes, enteric bacteria must overcome silencing caused when the widespread heat-stable nucleoid structuring (H-NS) protein binds to AT-rich horizontally acquired genes. This ability had previously been ascribed to both anti-silencing proteins outcompeting H-NS for binding to AT-rich DNA and RNA polymerase initiating transcription from alternative promoters. However, we now know that pathogenic Salmonella enterica serovar Typhimurium and commensal Escherichia coli break down H-NS when this silencer is not bound to DNA. Curiously, both species use the same protease - Lon - to destroy H-NS in distinct environments. Anti-silencing proteins promote the expression of horizontally acquired genes without binding to them by displacing H-NS from AT-rich DNA, thus leaving H-NS susceptible to proteolysis and decreasing H-NS amounts overall. Conserved amino acid sequences in the Lon protease and H-NS cleavage site suggest that diverse bacteria degrade H-NS to exploit horizontally acquired genes.
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Affiliation(s)
- Eduardo A. Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
- Yale Microbial Sciences Institute, P.O. Box 27389, West Haven, CT, 06516, USA
| | - Jeongjoon Choi
- Department of Genetics, Yale School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
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5
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Pokorzynski ND, Groisman EA. How Bacterial Pathogens Coordinate Appetite with Virulence. Microbiol Mol Biol Rev 2023; 87:e0019822. [PMID: 37358444 PMCID: PMC10521370 DOI: 10.1128/mmbr.00198-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023] Open
Abstract
Cells adjust growth and metabolism to nutrient availability. Having access to a variety of carbon sources during infection of their animal hosts, facultative intracellular pathogens must efficiently prioritize carbon utilization. Here, we discuss how carbon source controls bacterial virulence, with an emphasis on Salmonella enterica serovar Typhimurium, which causes gastroenteritis in immunocompetent humans and a typhoid-like disease in mice, and propose that virulence factors can regulate carbon source prioritization by modifying cellular physiology. On the one hand, bacterial regulators of carbon metabolism control virulence programs, indicating that pathogenic traits appear in response to carbon source availability. On the other hand, signals controlling virulence regulators may impact carbon source utilization, suggesting that stimuli that bacterial pathogens experience within the host can directly impinge on carbon source prioritization. In addition, pathogen-triggered intestinal inflammation can disrupt the gut microbiota and thus the availability of carbon sources. By coordinating virulence factors with carbon utilization determinants, pathogens adopt metabolic pathways that may not be the most energy efficient because such pathways promote resistance to antimicrobial agents and also because host-imposed deprivation of specific nutrients may hinder the operation of certain pathways. We propose that metabolic prioritization by bacteria underlies the pathogenic outcome of an infection.
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Affiliation(s)
- Nick D. Pokorzynski
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, USA
| | - Eduardo A. Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, USA
- Yale Microbial Sciences Institute, West Haven, Connecticut, USA
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6
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Bekale LA, Sharma D, Bacacao B, Chen J, Santa Maria PL. Eradication of Bacterial Persister Cells By Leveraging Their Low Metabolic Activity Using Adenosine Triphosphate Coated Gold Nanoclusters. NANO TODAY 2023; 51:101895. [PMID: 37575958 PMCID: PMC10421611 DOI: 10.1016/j.nantod.2023.101895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Bacteria first develop tolerance after antibiotic exposure; later genetic resistance emerges through the population of tolerant bacteria. Bacterial persister cells are the multidrug-tolerant subpopulation within an isogenic bacteria culture that maintains genetic susceptibility to antibiotics. Because of this link between antibiotic tolerance and resistance and the rise of antibiotic resistance, there is a pressing need to develop treatments to eradicate persister cells. Current anti persister cell strategies are based on the paradigm of "awakening" them from their low metabolic state before attempting eradication with traditional antibiotics. Herein, we demonstrate that the low metabolic activity of persister cells can be exploited for eradication over their metabolically active counterparts. We engineered gold nanoclusters coated with adenosine triphosphate (AuNC@ATP) as a benchmark nanocluster that kills persister cells over exponential growth bacterial cells and prove the feasibility of this new concept. Finally, using AuNC@ATP as a new research tool, we demonstrated that it is possible to prevent the emergence of antibiotic-resistant superbugs with an anti-persister compound. Eradicating persister cells with AuNC@ATP in an isogenic culture of bacteria stops the emergence of superbug bacteria mediated by the sub-lethal dose of conventional antibiotics. Our findings lay the groundwork for developing novel nano-antibiotics targeting persister cells, which promise to prevent the emergence of superbugs and prolong the lifespan of currently available antibiotics.
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Affiliation(s)
- Laurent A. Bekale
- Department of Otolaryngology, Head and Neck Surgery, Stanford University, 801 Welch Road Stanford, CA 94305-5739, USA
| | - Devesh Sharma
- Department of Otolaryngology, Head and Neck Surgery, Stanford University, 801 Welch Road Stanford, CA 94305-5739, USA
| | - Brian Bacacao
- Department of Otolaryngology, Head and Neck Surgery, Stanford University, 801 Welch Road Stanford, CA 94305-5739, USA
| | - Jing Chen
- Department of Otolaryngology, Head and Neck Surgery, Stanford University, 801 Welch Road Stanford, CA 94305-5739, USA
| | - Peter L. Santa Maria
- Department of Otolaryngology, Head and Neck Surgery, Stanford University, 801 Welch Road Stanford, CA 94305-5739, USA
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Yee JX, Kim J, Yeom J. Membrane Proteins as a Regulator for Antibiotic Persistence in Gram-Negative Bacteria. J Microbiol 2023; 61:331-341. [PMID: 36800168 DOI: 10.1007/s12275-023-00024-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Revised: 01/26/2023] [Accepted: 01/27/2023] [Indexed: 02/18/2023]
Abstract
Antibiotic treatment failure threatens our ability to control bacterial infections that can cause chronic diseases. Persister bacteria are a subpopulation of physiological variants that becomes highly tolerant to antibiotics. Membrane proteins play crucial roles in all living organisms to regulate cellular physiology. Although a diverse membrane component involved in persistence can result in antibiotic treatment failure, the regulations of antibiotic persistence by membrane proteins has not been fully understood. In this review, we summarize the recent advances in our understanding with regards to membrane proteins in Gram-negative bacteria as a regulator for antibiotic persistence, highlighting various physiological mechanisms in bacteria.
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Affiliation(s)
- Jia Xin Yee
- Programme in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore, 169857, Singapore
| | - Juhyun Kim
- School of Life Science, BK21 FOUR KNU Creative BioResearch Group, Kyungpook National University, Daegu, 41566, Republic of Korea.
| | - Jinki Yeom
- Programme in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore, 169857, Singapore. .,Department of Microbiology and Immunology, College of Medicine, Seoul National University, Seoul, 03080, Republic of Korea. .,Department of Biomedical Sciences, College of Medicine, Seoul National University, Seoul, 03080, Republic of Korea. .,Cancer Research Institute, Seoul National University, Seoul, 03080, Republic of Korea.
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8
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Tan YS, Zhang RK, Liu ZH, Li BZ, Yuan YJ. Microbial Adaptation to Enhance Stress Tolerance. Front Microbiol 2022; 13:888746. [PMID: 35572687 PMCID: PMC9093737 DOI: 10.3389/fmicb.2022.888746] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Accepted: 03/18/2022] [Indexed: 01/28/2023] Open
Abstract
Microbial cell factories have been widely used in the production of various chemicals. Although synthetic biology is useful in improving the cell factories, adaptation is still widely applied to enhance its complex properties. Adaptation is an important strategy for enhancing stress tolerance in microbial cell factories. Adaptation involves gradual modifications of microorganisms in a stressful environment to enhance their tolerance. During adaptation, microorganisms use different mechanisms to enhance non-preferred substrate utilization and stress tolerance, thereby improving their ability to adapt for growth and survival. In this paper, the progress on the effects of adaptation on microbial substrate utilization capacity and environmental stress tolerance are reviewed, and the mechanisms involved in enhancing microbial adaptive capacity are discussed.
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Affiliation(s)
- Yong-Shui Tan
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Synthetic Biology Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin, China
| | - Ren-Kuan Zhang
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Synthetic Biology Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin, China
| | - Zhi-Hua Liu
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Synthetic Biology Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin, China
| | - Bing-Zhi Li
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Synthetic Biology Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin, China
| | - Ying-Jin Yuan
- Frontiers Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.,Synthetic Biology Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin, China
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9
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Song S, Kim JS, Yamasaki R, Oh S, Benedik MJ, Wood TK. Escherichia coli cryptic prophages sense nutrients to influence persister cell resuscitation. Environ Microbiol 2021; 23:7245-7254. [PMID: 34668292 DOI: 10.1111/1462-2920.15816] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Accepted: 10/07/2021] [Indexed: 11/28/2022]
Abstract
Cryptic prophages are not genomic junk but instead enable cells to combat myriad stresses as an active stress response. How these phage fossils affect persister cell resuscitation has, however, not been explored. Persister cells form as a result of stresses such as starvation, antibiotics and oxidative conditions, and resuscitation of these persister cells likely causes recurring infections such as those associated with tuberculosis, cystic fibrosis and Lyme disease. Deletion of each of the nine Escherichia coli cryptic prophages has no effect on persister cell formation. Strikingly, elimination of each cryptic prophage results in an increase in persister cell resuscitation with a dramatic increase in resuscitation upon deleting all nine prophages. This increased resuscitation includes eliminating the need for a carbon source and is due to activation of the phosphate import system resulting from inactivating the transcriptional regulator AlpA of the CP4-57 cryptic prophage. Deletion of alpA increases persister resuscitation, and AlpA represses phosphate regulator PhoR. Both phosphate regulators PhoP and PhoB stimulate resuscitation. This suggests a novel cellular stress mechanism controlled by cryptic prophages: regulation of phosphate uptake which controls the exit of the cell from dormancy and prevents premature resuscitation in the absence of nutrients.
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Affiliation(s)
- Sooyeon Song
- Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania, 16802-4400, USA.,Department of Animal Science, Jeonbuk National University, 587 Baekje-Daero, Deokjin-Gu, Jeonju-Si, Jeollabuk-Do, 54896, South Korea.,Department of Agricultural Convergence Technology, Jeonbuk National University, 587 Baekje-Daero, Deokjin-Gu, Jeonju-Si, Jeollabuk-Do, 54896, South Korea
| | - Jun-Seob Kim
- Department of Nano-Bioengineering, Incheon National University, 119 Academy-ro, Incheon, 22012, South Korea
| | - Ryota Yamasaki
- Department of Health Promotion, Kyushu Dental University, Kitakyushu, Fukuoka, 803-8580, Japan
| | - Sejong Oh
- Division of Animal Science, Chonnam National University, 77 Yongbong-Ro, Buk-Gu, Gwangju, 61186, South Korea
| | - Michael J Benedik
- Department of Biology, Texas A&M University, College Station, TX, 77843, USA
| | - Thomas K Wood
- Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania, 16802-4400, USA
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Abstract
Mg2+ is the most abundant divalent cation in living cells. It is essential for charge neutralization, macromolecule stabilization, and the assembly and activity of ribosomes and as a cofactor for enzymatic reactions. When experiencing low cytoplasmic Mg2+, bacteria adopt two main strategies: They increase the abundance and activity of Mg2+ importers and decrease the abundance of Mg2+-chelating ATP and rRNA. These changes reduce regulated proteolysis by ATP-dependent proteases and protein synthesis in a systemic fashion. In many bacterial species, the transcriptional regulator PhoP controls expression of proteins mediating these changes. The 5' leader region of some mRNAs responds to low cytoplasmic Mg2+ or to disruptions in translation of open reading frames in the leader regions by furthering expression of the associated coding regions, which specify proteins mediating survival when the cytoplasmic Mg2+ concentration is low. Microbial species often utilize similar adaptation strategies to cope with low cytoplasmic Mg2+ despite relying on different genes to do so.
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Affiliation(s)
- Eduardo A Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut 06536, USA; .,Yale Microbial Sciences Institute, West Haven, Connecticut 06516, USA
| | - Carissa Chan
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut 06536, USA;
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Groisman EA, Duprey A, Choi J. How the PhoP/PhoQ System Controls Virulence and Mg 2+ Homeostasis: Lessons in Signal Transduction, Pathogenesis, Physiology, and Evolution. Microbiol Mol Biol Rev 2021; 85:e0017620. [PMID: 34191587 PMCID: PMC8483708 DOI: 10.1128/mmbr.00176-20] [Citation(s) in RCA: 63] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The PhoP/PhoQ two-component system governs virulence, Mg2+ homeostasis, and resistance to a variety of antimicrobial agents, including acidic pH and cationic antimicrobial peptides, in several Gram-negative bacterial species. Best understood in Salmonella enterica serovar Typhimurium, the PhoP/PhoQ system consists o-regulated gene products alter PhoP-P amounts, even under constant inducing conditions. PhoP-P controls the abundance of hundreds of proteins both directly, by having transcriptional effects on the corresponding genes, and indirectly, by modifying the abundance, activity, or stability of other transcription factors, regulatory RNAs, protease regulators, and metabolites. The investigation of PhoP/PhoQ has uncovered novel forms of signal transduction and the physiological consequences of regulon evolution.
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Affiliation(s)
- Eduardo A. Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, USA
- Yale Microbial Sciences Institute, West Haven, Connecticut, USA
| | - Alexandre Duprey
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, USA
| | - Jeongjoon Choi
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, USA
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12
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Low Cytoplasmic Magnesium Increases the Specificity of the Lon and ClpAP Proteases. J Bacteriol 2021; 203:e0014321. [PMID: 33941609 DOI: 10.1128/jb.00143-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Proteolysis is a fundamental property of all living cells. In the bacterium Salmonella enterica serovar Typhimurium, the HspQ protein controls the specificities of the Lon and ClpAP proteases. Upon acetylation, HspQ stops being a Lon substrate and no longer enhances proteolysis of the Lon substrate Hha. The accumulated HspQ protein binds to the protease adaptor ClpS, hindering proteolysis of ClpS-dependent substrates of ClpAP, such as Oat, a promoter of antibiotic persistence. HspQ is acetylated by the protein acetyltransferase Pat from acetyl coenzyme A (acetyl-CoA) bound to the acetyl-CoA binding protein Qad. We now report that low cytoplasmic Mg2+ promotes qad expression, which protects substrates of Lon and ClpSAP by increasing HspQ amounts. The qad promoter is activated by PhoP, a regulatory protein highly activated in low cytoplasmic Mg2+ that also represses clpS transcription. Both the qad gene and PhoP repression of the clpS promoter are necessary for antibiotic persistence. PhoP also promotes qad transcription in Escherichia coli, which shares a similar PhoP box in the qad promoter region with S. Typhimurium, Salmonella bongori, and Enterobacter cloacae. Our findings identify cytoplasmic Mg2+ and the PhoP protein as critical regulators of protease specificity in multiple enteric bacteria. IMPORTANCE The bacterium Salmonella enterica serovar Typhimurium narrows down the spectrum of substrates degraded by the proteases Lon and ClpAP in response to low cytoplasmic Mg2+, a condition that decreases protein synthesis. This control is exerted by PhoP, a transcriptional regulator activated in low cytoplasmic Mg2+ that governs proteostasis and is conserved in enteric bacteria. The uncovered mechanism enables bacteria to control the abundance of preexisting proteins.
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