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Jusufovic N, Krusenstjerna AC, Savage CR, Saylor TC, Brissette CA, Zückert WR, Schlax PJ, Motaleb MA, Stevenson B. Borrelia burgdorferi PlzA is a cyclic-di-GMP dependent DNA and RNA binding protein. Mol Microbiol 2024; 121:1039-1062. [PMID: 38527857 DOI: 10.1111/mmi.15254] [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: 09/04/2023] [Revised: 03/05/2024] [Accepted: 03/13/2024] [Indexed: 03/27/2024]
Abstract
The PilZ domain-containing protein, PlzA, is the only known cyclic di-GMP binding protein encoded by all Lyme disease spirochetes. PlzA has been implicated in the regulation of many borrelial processes, but the effector mechanism of PlzA was not previously known. Here, we report that PlzA can bind DNA and RNA and that nucleic acid binding requires c-di-GMP, with the affinity of PlzA for nucleic acids increasing as concentrations of c-di-GMP were increased. A mutant PlzA that is incapable of binding c-di-GMP did not bind to any tested nucleic acids. We also determined that PlzA interacts predominantly with the major groove of DNA and that sequence length and G-C content play a role in DNA binding affinity. PlzA is a dual-domain protein with a PilZ-like N-terminal domain linked to a canonical C-terminal PilZ domain. Dissection of the domains demonstrated that the separated N-terminal domain bound nucleic acids independently of c-di-GMP. The C-terminal domain, which includes the c-di-GMP binding motifs, did not bind nucleic acids under any tested conditions. Our data are supported by computational docking, which predicts that c-di-GMP binding at the C-terminal domain stabilizes the overall protein structure and facilitates PlzA-DNA interactions via residues in the N-terminal domain. Based on our data, we propose that levels of c-di-GMP during the various stages of the enzootic life cycle direct PlzA binding to regulatory targets.
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Affiliation(s)
- Nerina Jusufovic
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, USA
| | - Andrew C Krusenstjerna
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, USA
| | - Christina R Savage
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, USA
| | - Timothy C Saylor
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, USA
| | - Catherine A Brissette
- Department of Biomedical Sciences, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, North Dakota, USA
| | - Wolfram R Zückert
- Department of Microbiology, Molecular Genetics and Immunology, University of Kansas School of Medicine, Kansas City, Kansas, USA
| | - Paula J Schlax
- Department of Chemistry and Biochemistry, Bates College, Lewiston, Maine, USA
| | - Md A Motaleb
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, North Carolina, USA
| | - Brian Stevenson
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, USA
- Department of Entomology, University of Kentucky, Lexington, Kentucky, USA
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2
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Jusufovic N, Krusenstjerna AC, Savage CR, Saylor TC, Brissette CA, Zückert WR, Schlax PJ, Motaleb MA, Stevenson B. Borrelia burgdorferi PlzA is a cyclic-di-GMP dependent DNA and RNA binding protein. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.01.30.526351. [PMID: 36778503 PMCID: PMC9915621 DOI: 10.1101/2023.01.30.526351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The PilZ domain-containing protein, PlzA, is the only known cyclic di-GMP binding protein encoded by all Lyme disease spirochetes. PlzA has been implicated in the regulation of many borrelial processes, but the effector mechanism of PlzA was not previously known. Here we report that PlzA can bind DNA and RNA and that nucleic acid binding requires c-di-GMP, with the affinity of PlzA for nucleic acids increasing as concentrations of c-di-GMP were increased. A mutant PlzA that is incapable of binding c-di-GMP did not bind to any tested nucleic acids. We also determined that PlzA interacts predominantly with the major groove of DNA and that sequence length plays a role in DNA binding affinity. PlzA is a dual-domain protein with a PilZ-like N-terminal domain linked to a canonical C-terminal PilZ domain. Dissection of the domains demonstrated that the separated N-terminal domain bound nucleic acids independently of c-di-GMP. The C-terminal domain, which includes the c-di-GMP binding motifs, did not bind nucleic acids under any tested conditions. Our data are supported by computational docking, which predicts that c-di-GMP binding at the C-terminal domain stabilizes the overall protein structure and facilitates PlzA-DNA interactions via residues in the N-terminal domain. Based on our data, we propose that levels of c-di-GMP during the various stages of the enzootic life cycle direct PlzA binding to regulatory targets.
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Affiliation(s)
- Nerina Jusufovic
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, 40526-0001, USA
| | - Andrew C. Krusenstjerna
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, 40526-0001, USA
| | - Christina R. Savage
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, 40526-0001, USA
| | - Timothy C. Saylor
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, 40526-0001, USA
| | - Catherine A. Brissette
- Department of Biomedical Sciences, University of North Dakota, School of Medicine and Health Sciences, Grand Forks, ND 58203-9061, USA
| | - Wolfram R. Zückert
- Department of Microbiology, Molecular Genetics and Immunology, University of Kansas School of Medicine, Kansas City, KS 66160, USA
| | - Paula J. Schlax
- Department of Chemistry and Biochemistry, Bates College, Lewiston, ME, 04240-6030, USA
| | - Md A. Motaleb
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC 27834-435, USA
| | - Brian Stevenson
- Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, University of Kentucky, Lexington, Kentucky, 40526-0001, USA
- Department of Entomology, University of Kentucky, Lexington, Kentucky, 40526-0001, USA
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3
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Condinho M, Carvalho B, Cruz A, Pinto SN, Arraiano CM, Pobre V. The role of RNA regulators, quorum sensing and c-di-GMP in bacterial biofilm formation. FEBS Open Bio 2023; 13:975-991. [PMID: 35234364 PMCID: PMC10240345 DOI: 10.1002/2211-5463.13389] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 02/15/2022] [Accepted: 02/28/2022] [Indexed: 11/10/2022] Open
Abstract
Biofilms provide an ecological advantage against many environmental stressors, such as pH and temperature, making it the most common life-cycle stage for many bacteria. These protective characteristics make eradication of bacterial biofilms challenging. This is especially true in the health sector where biofilm formation on hospital or patient equipment, such as respirators, or catheters, can quickly become a source of anti-microbial resistant strains. Biofilms are complex structures encased in a self-produced polymeric matrix containing numerous components such as polysaccharides, proteins, signalling molecules, extracellular DNA and extracellular RNA. Biofilm formation is tightly controlled by several regulators, including quorum sensing (QS), cyclic diguanylate (c-di-GMP) and small non-coding RNAs (sRNAs). These three regulators in particular are fundamental in all stages of biofilm formation; in addition, their pathways overlap, and the significance of their role is strain-dependent. Currently, ribonucleases are also of interest for their potential role as biofilm regulators, and their relationships with QS, c-di-GMP and sRNAs have been investigated. This review article will focus on these four biofilm regulators (ribonucleases, QS, c-di-GMP and sRNAs) and the relationships between them.
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Affiliation(s)
- Manuel Condinho
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaOeirasPortugal
| | - Beatriz Carvalho
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaOeirasPortugal
| | - Adriana Cruz
- iBB‐Institute for Bioengineering and Biosciences (IBB)Instituto Superior TécnicoLisboaPortugal
- i4HB‐Institute for Health and BioeconomyInstituto Superior TécnicoLisboaPortugal
| | - Sandra N. Pinto
- iBB‐Institute for Bioengineering and Biosciences (IBB)Instituto Superior TécnicoLisboaPortugal
- i4HB‐Institute for Health and BioeconomyInstituto Superior TécnicoLisboaPortugal
| | - Cecília M. Arraiano
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaOeirasPortugal
| | - Vânia Pobre
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaOeirasPortugal
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4
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Singh S, Wilksch JJ, Dunstan RA, Mularski A, Wang N, Hocking D, Jebeli L, Cao H, Clements A, Jenney AWJ, Lithgow T, Strugnell RA. LPS O Antigen Plays a Key Role in Klebsiella pneumoniae Capsule Retention. Microbiol Spectr 2022; 10:e0151721. [PMID: 35913154 PMCID: PMC9431683 DOI: 10.1128/spectrum.01517-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 06/14/2022] [Indexed: 11/24/2022] Open
Abstract
Despite the importance of encapsulation in bacterial pathogenesis, the biochemical mechanisms and forces that underpin retention of capsule by encapsulated bacteria are poorly understood. In Gram-negative bacteria, there may be interactions between lipopolysaccharide (LPS) core and capsule polymers, between capsule polymers with retained acyl carriers and the outer membrane, and in some bacteria, between the capsule polymers and Wzi, an outer membrane protein lectin. Our transposon studies in Klebsiella pneumoniae B5055 identified additional genes that, when insertionally inactivated, resulted in reduced encapsulation. Inactivation of the gene waaL, which encodes the ligase responsible for attaching the repeated O antigen of LPS to the LPS core, resulted in a significant reduction in capsule retention, measured by atomic force microscopy. This reduction in encapsulation was associated with increased sensitivity to human serum and decreased virulence in a murine model of respiratory infection and, paradoxically, with increased biofilm formation. The capsule in the WaaL mutant was physically smaller than that of the Wzi mutant of K. pneumoniae B5055. These results suggest that interactions between surface carbohydrate polymers may enhance encapsulation, a key phenotype in bacterial virulence, and provide another target for the development of antimicrobials that may avoid resistance issues associated with growth inhibition. IMPORTANCE Bacterial capsules, typically comprised of complex sugars, enable pathogens to avoid key host responses to infection, including phagocytosis. These capsules are synthesized within the bacteria, exported through the outer envelope, and then secured to the external surface of the organism by a force or forces that are incompletely described. This study shows that in the important hospital pathogen Klebsiella pneumoniae, the polysaccharide capsule is retained by interactions with other surface sugars, especially the repeated sugar molecule of the LPS molecule in Gram-negative bacteria known as "O antigen." This O antigen is joined to the LPS molecule by ligation, and loss of the enzyme responsible for ligation, a protein called WaaL, results in reduced encapsulation. Since capsules are essential to the virulence of many pathogens, WaaL might provide a target for new antimicrobial development, critical to the control of pathogens like K. pneumoniae that have become highly drug resistant.
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Affiliation(s)
- Shweta Singh
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Jonathan J. Wilksch
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia
| | - Rhys A. Dunstan
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia
| | - Anna Mularski
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Nancy Wang
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Dianna Hocking
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Leila Jebeli
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Hanwei Cao
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Abigail Clements
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Adam W. J. Jenney
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Trevor Lithgow
- Infection and Immunity Program, Biomedicine Discovery Institute and Department of Microbiology, Monash University, Clayton, Victoria, Australia
| | - Richard A. Strugnell
- Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
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5
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Fontaine BM, Duggal Y, Weinert EE. Exploring the Links between Nucleotide Signaling and Quorum Sensing Pathways in Regulating Bacterial Virulence. ACS Infect Dis 2018; 4:1645-1655. [PMID: 30381948 DOI: 10.1021/acsinfecdis.8b00255] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The survival of all organisms depends on implementation of appropriate phenotypic responses upon perception of relevant environmental stimuli. Sensory inputs are propagated via interconnected biochemical and/or electrical cascades mediated by diverse signaling molecules, including gases, metal cations, lipids, peptides, and nucleotides. These networks often comprise second messenger signaling systems in which a ligand (the primary messenger) binds to an extracellular receptor, thereby altering the intracellular concentration of a second messenger molecule which ultimately modulates gene expression through interaction with various effectors. The identification of intersections of these signaling pathways, such as nucleotide second messengers and quorum sensing, provides new insights into the mechanisms by which bacteria use multiple inputs to regulate cellular metabolism and phenotypes. Further investigations of the overlap between bacterial signaling pathways may yield new targets and methods to control bacterial behavior, such as biofilm formation and virulence.
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Affiliation(s)
- Benjamin M. Fontaine
- Department of Chemistry, Emory University, 1515 Dickey Drive NE, Atlanta, Georgia 30322, United States
| | - Yashasvika Duggal
- Department of Chemistry, Emory University, 1515 Dickey Drive NE, Atlanta, Georgia 30322, United States
| | - Emily E. Weinert
- Department of Chemistry, Emory University, 1515 Dickey Drive NE, Atlanta, Georgia 30322, United States
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6
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Lin TH, Chen Y, Kuo JT, Lai YC, Wu CC, Huang CF, Lin CT. Phosphorylated OmpR Is Required for Type 3 Fimbriae Expression in Klebsiella pneumoniae Under Hypertonic Conditions. Front Microbiol 2018; 9:2405. [PMID: 30369914 PMCID: PMC6194325 DOI: 10.3389/fmicb.2018.02405] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 09/20/2018] [Indexed: 11/28/2022] Open
Abstract
OmpR/EnvZ is a two-component system that senses osmotic signals and controls downstream gene expression in many species of Enterobacteriaceae. However, the role of OmpR/EnvZ in Klebsiella pneumoniae remains unknown. In this study, we found that production of MrkA, the major subunit of type 3 fimbriae, was decreased under hypertonic conditions. A deletion mutant of ompR and a site-directed mutant with a single amino acid substitution of aspartate 55 to alanine (D55A), which mimics the unphosphorylated form of OmpR, markedly reduced MrkA production under hypertonic conditions. These results indicate that K. pneumoniae type 3 fimbriae expression is activated by the phosphorylated form of OmpR (OmpR∼P). Although no typical OmpR∼P binding site was found in the PmrkA sequence, mrkA mRNA levels and PmrkA activity were decreased in the ΔompR and ompRD55A strains compared with the wild type (WT) strain, indicating that OmpR∼P mediates type 3 fimbriae expression at the transcriptional level. Previous reports have demonstrated that a cyclic-di-GMP (c-di-GMP) related gene cluster, mrkHIJ, regulates the expression of type 3 fimbriae. We found that both the ompR and ompRD55A mutants exhibited decreased mrkHIJ mRNA levels, intracellular c-di-GMP concentration, and bacterial biofilm amount, but increased total intracellular phosphodiesterase activity in response to hypertonic conditions. These results indicate that OmpR∼P regulates type 3 fimbriae expression to influence K. pneumoniae biofilm formation via MrkHIJ and modulation of intracellular c-di-GMP levels. Taken together, we herein provide evidence that OmpR∼P acts as a critical factor in the regulation of the c-di-GMP signaling pathway, type 3 fimbriae expression, and biofilm amount in K. pneumoniae in response to osmotic stresses.
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Affiliation(s)
- Tien-Huang Lin
- Department of Urology, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan.,School of Post-Baccalaureate Chinese Medicine, Tzu Chi University, Hualian, Taiwan
| | - Yeh Chen
- Department of Biotechnology, Hungkuang University, Taichung, Taiwan
| | - Jong-Tar Kuo
- Department of Biological Science and Technology, China University of Science and Technology, Taipei, Taiwan
| | - Yi-Chyi Lai
- Department of Microbiology and Immunology, Chung-Shan Medical University, Taichung, Taiwan
| | - Chien-Chen Wu
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan
| | - Chun-Fa Huang
- School of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Ching-Ting Lin
- School of Chinese Medicine, China Medical University, Taichung, Taiwan
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7
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Selection and validation of reference genes for gene expression studies in Klebsiella pneumoniae using Reverse Transcription Quantitative real-time PCR. Sci Rep 2018; 8:9001. [PMID: 29899556 PMCID: PMC5998039 DOI: 10.1038/s41598-018-27420-2] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/23/2018] [Indexed: 12/27/2022] Open
Abstract
For reliable results, Reverse Transcription Quantitative real-time Polymerase Chain Reaction (RT-qPCR) analyses depend on stably expressed reference genes for data normalization purposes. Klebsiella pneumoniae is an opportunistic Gram-negative bacterium that has become a serious threat worldwide. Unfortunately, there is no consensus for an ideal reference gene for RT-qPCR data normalization on K. pneumoniae. In this study, the expression profile of eleven candidate reference genes was assessed in K. pneumoniae cells submitted to various experimental conditions, and the expression stability of these candidate genes was evaluated using statistical algorithms BestKeeper, NormFinder, geNorm, Delta CT and RefFinder. The statistical analyses ranked recA, rho, proC and rpoD as the most suitable reference genes for accurate RT-qPCR data normalization in K. pneumoniae. The reliability of the proposed reference genes was validated by normalizing the relative expression of iron-regulated genes in K. pneumoniae cells submitted to iron-replete and iron-limited conditions. This work emphasizes that the stable expression of any potential reference candidate gene must be validated in each physiological condition or experimental treatment under study.
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8
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High Levels of Cyclic Di-GMP in Klebsiella pneumoniae Attenuate Virulence in the Lung. Infect Immun 2018; 86:IAI.00647-17. [PMID: 29158434 DOI: 10.1128/iai.00647-17] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Accepted: 11/15/2017] [Indexed: 01/22/2023] Open
Abstract
The bacterial second messenger bis-(3'-5')-cyclic dimeric GMP (c-di-GMP) has been shown to influence the expression of virulence factors in certain pathogenic bacteria, but little is known about its activity in the increasingly antibiotic-resistant pathogen Klebsiella pneumoniae Here, the expression in K. pneumoniae of a heterologous diguanylate cyclase increased the bacterial c-di-GMP concentration and attenuated pathogenesis in murine pneumonia. This attenuation remained evident in mice lacking the c-di-GMP sensor STING, indicating that the high c-di-GMP concentration exerted its influence not on host responses but on bacterial physiology. While serum resistance and capsule expression were unaffected by the increased c-di-GMP concentration, both type 3 and type 1 pili were strongly upregulated. Importantly, attenuation of K. pneumoniae virulence by high c-di-GMP levels was abrogated when type 1 pilus expression was silenced. We conclude that increased type 1 piliation may hamper K. pneumoniae virulence in the respiratory tract and that c-di-GMP signaling represents a potential therapeutic target for antibiotic-resistant K. pneumoniae in this niche.
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9
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Wang F, He Q, Su K, Gao F, Huang Y, Lin Z, Zhu D, Gu L. The PilZ domain of MrkH represents a novel DNA binding motif. Protein Cell 2018; 7:766-772. [PMID: 27650952 PMCID: PMC5055493 DOI: 10.1007/s13238-016-0317-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Affiliation(s)
- Feng Wang
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China
| | - Qing He
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China
| | - Kaixuan Su
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China
| | - Fei Gao
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China
| | - Yan Huang
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China
| | - Zong Lin
- Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, 314006, China
| | - Deyu Zhu
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China.
| | - Lichuan Gu
- State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, China.
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10
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Hall CL, Lee VT. Cyclic-di-GMP regulation of virulence in bacterial pathogens. WILEY INTERDISCIPLINARY REVIEWS. RNA 2018; 9:10.1002/wrna.1454. [PMID: 28990312 PMCID: PMC5739959 DOI: 10.1002/wrna.1454] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 08/29/2017] [Accepted: 09/01/2017] [Indexed: 12/16/2022]
Abstract
Signaling pathways allow bacteria to adapt to changing environments. For pathogenic bacteria, signaling pathways allow for timely expression of virulence factors and the repression of antivirulence factors within the mammalian host. As the bacteria exit the mammalian host, signaling pathways enable the expression of factors promoting survival in the environment and/or nonmammalian hosts. One such signaling pathway uses the dinucleotide cyclic-di-GMP (c-di-GMP), and many bacterial genomes encode numerous proteins that are responsible for synthesizing and degrading c-di-GMP. Once made, c-di-GMP binds to individual protein and RNA receptors to allosterically alter the macromolecule function to drive phenotypic changes. Each bacterial genome encodes unique sets of genes for c-di-GMP signaling and virulence factors so the regulation by c-di-GMP is organism specific. Recent works have pointed to evidence that c-di-GMP regulates virulence in different bacterial pathogens of mammalian hosts. In this review, we discuss the criteria for determining the contribution of signaling nucleotides to pathogenesis using a well-characterized signaling nucleotide, cyclic AMP (cAMP), in Pseudomonas aeruginosa. Using these criteria, we review the roles of c-di-GMP in mediating virulence and highlight common themes that exist among eight diverse pathogens that cause different diseases through different routes of infection and transmission. WIREs RNA 2018, 9:e1454. doi: 10.1002/wrna.1454 This article is categorized under: RNA in Disease and Development > RNA in Disease.
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Affiliation(s)
- Cherisse L Hall
- Department of Cell Biology and Molecular Genetics, University of Maryland at College Park, College Park, MD, USA
| | - Vincent T Lee
- Department of Cell Biology and Molecular Genetics, University of Maryland at College Park, College Park, MD, USA
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11
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Lin TH, Tseng CY, Lai YC, Wu CC, Huang CF, Lin CT. IscR Regulation of Type 3 Fimbriae Expression in Klebsiella pneumoniae CG43. Front Microbiol 2017; 8:1984. [PMID: 29085346 PMCID: PMC5650617 DOI: 10.3389/fmicb.2017.01984] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Accepted: 09/26/2017] [Indexed: 01/25/2023] Open
Abstract
In Klebsiella pneumoniae, we have previously shown that IscR, an Fe–S cluster-containing transcriptional factor, plays a dual role in controlling capsular polysaccharide biosynthesis and iron-acquisition systems by switching between its holo and apo forms. In this study, the effect of IscR on type 3 fimbriae expression and biofilm formation was investigated. We found that production of the major subunit of type 3 fimbriae, MrkA, was increased in the ΔiscR and iscR3CA strains, a strain expressing a mutant IscR that mimics apo-IscR, at both the translational and transcriptional levels. Based on the fact that type 3 fimbriae expression is the major factor affecting biofilm formation, increased biofilm formation was also found in ΔiscR or iscR3CA, suggesting that holo-IscR represses biofilm formation. However, the repression of type 3 fimbriae expression by IscR is indirect. To further understand the regulatory mechanism of IscR, the effect of IscR on the expression of mrkHIJ, which encodes cyclic di-GMP (c-di-GMP)-related regulatory proteins that control type 3 fimbriae expression, was studied. We found that holo-IscR could directly repress mrkHI transcription, indicating that MrkHI is required for IscR regulation of type 3 fimbriae expression. Finally, deletion of iscR attenuated K. pneumoniae virulence in a peritonitis model of mouse infection, while the absence of the [2Fe–2S] cluster of IscR had no effect on K. pneumoniae virulence during infection. Taken together, our results demonstrate the underlying mechanism of the [2Fe–2S] cluster of IscR in controlling type 3 fimbriae expression and its effect on K. pneumoniae pathogenesis.
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Affiliation(s)
- Tien-Huang Lin
- Division of Urology, Taichung Tzu Chi General Hospital, The Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan.,School of Post-Baccalaureate Chinese Medicine, Tzu Chi University, Hualien, Taiwan
| | - Cheng-Yin Tseng
- Graduate Institute of Chinese Medicine, China Medical University, Taichung, Taiwan.,Section of Infectious Disease, Hsinchu Mackay Memorial Hospital, Hsinchu, Taiwan
| | - Yi-Chyi Lai
- Department of Microbiology and Immunology, Chung-Shan Medical University, Taichung, Taiwan
| | - Chien-Chen Wu
- School of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Chun-Fa Huang
- Graduate Institute of Chinese Medicine, China Medical University, Taichung, Taiwan.,School of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Ching-Ting Lin
- Graduate Institute of Chinese Medicine, China Medical University, Taichung, Taiwan.,School of Chinese Medicine, China Medical University, Taichung, Taiwan
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12
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Additional regulatory activities of MrkH for the transcriptional expression of the Klebsiella pneumoniae mrk genes: Antagonist of H-NS and repressor. PLoS One 2017; 12:e0173285. [PMID: 28278272 PMCID: PMC5344390 DOI: 10.1371/journal.pone.0173285] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 02/07/2017] [Indexed: 11/19/2022] Open
Abstract
Klebsiella pneumoniae is a common opportunistic pathogen causing nosocomial infections. One of the main virulence determinants of K. pneumoniae is the type 3 pilus (T3P). T3P helps the bacterial interaction to both abiotic and biotic surfaces and it is crucial for the biofilm formation. T3P is genetically organized in three transcriptional units: the mrkABCDF polycistronic operon, the mrkHI bicistronic operon and the mrkJ gene. MrkH is a regulatory protein encoded in the mrkHI operon, which positively regulates the mrkA pilin gene and its own expression. In contrast, the H-NS nucleoid protein represses the transcriptional expression of T3P. Here we reported that MrkH and H-NS positively and negatively regulate mrkJ expression, respectively, by binding to the promoter of mrkJ. MrkH protein recognized a sequence located at position -63.5 relative to the transcriptional start site of mrkJ gene. Interestingly, our results show that, in addition to its known function as classic transcriptional activator, MrkH also positively controls the expression of mrk genes by acting as an anti-repressor of H-NS; moreover, our results support the notion that high levels of MrkH repress T3P expression. Our data provide new insights about the complex regulatory role of the MrkH protein on the transcriptional control of T3P in K. pneumoniae.
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Lin CT, Lin TH, Wu CC, Wan L, Huang CF, Peng HL. CRP-Cyclic AMP Regulates the Expression of Type 3 Fimbriae via Cyclic di-GMP in Klebsiella pneumoniae. PLoS One 2016; 11:e0162884. [PMID: 27631471 PMCID: PMC5025149 DOI: 10.1371/journal.pone.0162884] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 08/30/2016] [Indexed: 12/18/2022] Open
Abstract
Klebsiella pneumoniae is the predominant pathogen isolated from liver abscesses of diabetic patients in Asian countries. However, the effects of elevated blood glucose levels on the virulence of this pathogen remain largely unknown. Type 3 fimbriae, encoded by the mrkABCDF genes, are important virulence factors in K. pneumoniae pathogenesis. In this study, the effects of exogenous glucose and the intracellular cyclic AMP (cAMP) signaling pathway on type 3 fimbriae expression regulation were investigated. The production of MrkA, the major subunit of type 3 fimbriae, was increased in glucose-rich medium, whereas cAMP supplementation reversed the effect. MrkA production was markedly increased by cyaA or crp deletion, but slightly decreased by cpdA deletion. In addition, the mRNA levels of mrkABCDF genes and the activity of PmrkA were increased in Δcrp strain, as well as the mRNA levels of mrkHIJ genes that encode cyclic di-GMP (c-di-GMP)-related regulatory proteins that influence type 3 fimbriae expression. Moreover, the activities of PmrkHI and PmrkJ were decreased in ΔlacZΔcrp strain. These results indicate that CRP-cAMP down-regulates mrkABCDF and mrkHIJ at the transcriptional level. Further deletion of mrkH or mrkI in Δcrp strain diminished the production of MrkA, indicating that MrkH and MrkI are required for the CRP regulation of type 3 fimbriae expression. Furthermore, the high activity of PmrkHI in the ΔlacZΔcrp strain was diminished in ΔlacZΔcrpΔmrkHI, but increased in the ΔlacZΔcrpΔmrkJ strain. Deletion of crp increased the intracellular c-di-GMP concentration and reduced the phosphodiesterase activity. Moreover, we found that the mRNA levels of multiple genes related to c-di-GMP metabolism were altered in Δcrp strain. These indicate that CRP regulates type 3 fimbriae expression indirectly via the c-di-GMP signaling pathway. In conclusion, we found evidence of a coordinated regulation of type 3 fimbriae expression by the CRP-cAMP and c-di-GMP signaling pathways in K. pneumoniae.
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Affiliation(s)
- Ching-Ting Lin
- School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China
- * E-mail: (CTL); (HLP)
| | - Tien-Huang Lin
- Division of Urology, Taichung Tzu Chi Hospital, The Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, Republic of China
- Tzu Chi University School of Post-Baccalaureate Chinese Medicine, Hualien, Taiwan, Republic of China
| | - Chien-Chen Wu
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
| | - Lei Wan
- School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China
| | - Chun-Fa Huang
- School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China
| | - Hwei-Ling Peng
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
- * E-mail: (CTL); (HLP)
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Madsen JS, Riber L, Kot W, Basfeld A, Burmølle M, Hansen LH, Sørensen SJ. Type 3 Fimbriae Encoded on Plasmids Are Expressed from a Unique Promoter without Affecting Host Motility, Facilitating an Exceptional Phenotype That Enhances Conjugal Plasmid Transfer. PLoS One 2016; 11:e0162390. [PMID: 27627107 PMCID: PMC5023117 DOI: 10.1371/journal.pone.0162390] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Accepted: 08/22/2016] [Indexed: 11/19/2022] Open
Abstract
Horizontal gene transfer (HGT), the transmission of genetic material to a recipient that is not the progeny of the donor, is fundamental in bacterial evolution. HGT is often mediated by mobile genetic elements such as conjugative plasmids, which may be in conflict with the chromosomal elements of the genome because they are independent replicons that may petition their own evolutionary strategy. Here we study differences between type 3 fimbriae encoded on wild type plasmids and in chromosomes. Using known and newly characterized plasmids we show that the expression of type 3 fimbriae encoded on plasmids is systematically different, as MrkH, a c-di-GMP dependent transcriptional activator is not needed for strong expression of the fimbriae. MrkH is required for expression of type 3 fimbriae of the Klebsiella pneumoniae chromosome, wherefrom the fimbriae operon (mrkABCDF) of plasmids is believed to have originated. We find that mrkABCDFs of plasmids are highly expressed via a unique promoter that differs from the original Klebsiella promoter resulting in fundamental behavioral consequences. Plasmid associated mrkABCDFs did not influence the swimming behavior of the host, that hereby acquired an exceptional phenotype being able to both actively swim (planktonic behavior) and express biofilm associated fimbriae (sessile behavior). We show that this exceptional phenotype enhances the conjugal transfer of the plasmid.
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Affiliation(s)
| | - Leise Riber
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Witold Kot
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
- Department of Environmental Sciences, Aarhus University, Aarhus, Denmark
| | - Alrun Basfeld
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
- Max Planck Research Group Chromosome Organization and Dynamics, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Mette Burmølle
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Lars Hestbjerg Hansen
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
- Department of Environmental Sciences, Aarhus University, Aarhus, Denmark
- * E-mail:
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15
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Structures of the activator of K. pneumonia biofilm formation, MrkH, indicates PilZ domains involved in c-di-GMP and DNA binding. Proc Natl Acad Sci U S A 2016; 113:10067-72. [PMID: 27551088 DOI: 10.1073/pnas.1607503113] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The pathogenesis of Klebsiella pneumonia is linked to the bacteria's ability to form biofilms. Mannose-resistant Klebsiella-like (Mrk) hemagglutinins are critical for K pneumonia biofilm development, and the expression of the genes encoding these proteins is activated by a 3',5'-cyclic diguanylic acid (c-di-GMP)-regulated transcription factor, MrkH. To gain insight into MrkH function, we performed structural and biochemical analyses. Data revealed MrkH to be a monomer with a two-domain architecture consisting of a PilZ C-domain connected to an N domain that unexpectedly also harbors a PilZ-like fold. Comparison of apo- and c-di-GMP-bound MrkH structures reveals a large 138° interdomain rotation that is induced by binding an intercalated c-di-GMP dimer. c-di-GMP interacts with PilZ C-domain motifs 1 and 2 (RxxxR and D/NxSxxG) and a newly described c-di-GMP-binding motif in the MrkH N domain. Strikingly, these c-di-GMP-binding motifs also stabilize an open state conformation in apo MrkH via contacts from the PilZ motif 1 to residues in the C-domain motif 2 and the c-di-GMP-binding N-domain motif. Use of the same regions in apo structure stabilization and c-di-GMP interaction allows distinction between the states. Indeed, domain reorientation by c-di-GMP complexation with MrkH, which leads to a highly compacted structure, suggests a mechanism by which the protein is activated to bind DNA. To our knowledge, MrkH represents the first instance of specific DNA binding mediated by PilZ domains. The MrkH structures also pave the way for the rational design of inhibitors that target K pneumonia biofilm formation.
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16
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Jones CJ, Utada A, Davis KR, Thongsomboon W, Zamorano Sanchez D, Banakar V, Cegelski L, Wong GCL, Yildiz FH. C-di-GMP Regulates Motile to Sessile Transition by Modulating MshA Pili Biogenesis and Near-Surface Motility Behavior in Vibrio cholerae. PLoS Pathog 2015; 11:e1005068. [PMID: 26505896 PMCID: PMC4624765 DOI: 10.1371/journal.ppat.1005068] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 07/06/2015] [Indexed: 01/11/2023] Open
Abstract
In many bacteria, including Vibrio cholerae, cyclic dimeric guanosine monophosphate (c-di-GMP) controls the motile to biofilm life style switch. Yet, little is known about how this occurs. In this study, we report that changes in c-di-GMP concentration impact the biosynthesis of the MshA pili, resulting in altered motility and biofilm phenotypes in V. cholerae. Previously, we reported that cdgJ encodes a c-di-GMP phosphodiesterase and a ΔcdgJ mutant has reduced motility and enhanced biofilm formation. Here we show that loss of the genes required for the mannose-sensitive hemagglutinin (MshA) pilus biogenesis restores motility in the ΔcdgJ mutant. Mutations of the predicted ATPase proteins mshE or pilT, responsible for polymerizing and depolymerizing MshA pili, impair near surface motility behavior and initial surface attachment dynamics. A ΔcdgJ mutant has enhanced surface attachment, while the ΔcdgJmshA mutant phenocopies the high motility and low attachment phenotypes observed in a ΔmshA strain. Elevated concentrations of c-di-GMP enhance surface MshA pilus production. MshE, but not PilT binds c-di-GMP directly, establishing a mechanism for c-di-GMP signaling input in MshA pilus production. Collectively, our results suggest that the dynamic nature of the MshA pilus established by the assembly and disassembly of pilin subunits is essential for transition from the motile to sessile lifestyle and that c-di-GMP affects MshA pilus assembly and function through direct interactions with the MshE ATPase.
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Affiliation(s)
- Christopher J. Jones
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, California, United States of America
| | - Andrew Utada
- Department of Bioengineering, Department of Chemistry and Biochemistry, California Nano Systems Institute, University of California, Los Angeles, Los Angeles, California, United States of America
| | - Kimberly R. Davis
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, California, United States of America
| | - Wiriya Thongsomboon
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - David Zamorano Sanchez
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, California, United States of America
| | - Vinita Banakar
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, California, United States of America
| | - Lynette Cegelski
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Gerard C. L. Wong
- Department of Bioengineering, Department of Chemistry and Biochemistry, California Nano Systems Institute, University of California, Los Angeles, Los Angeles, California, United States of America
| | - Fitnat H. Yildiz
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, California, United States of America
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Mularski A, Wilksch JJ, Wang H, Hossain MA, Wade JD, Separovic F, Strugnell RA, Gee ML. Atomic Force Microscopy Reveals the Mechanobiology of Lytic Peptide Action on Bacteria. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6164-71. [PMID: 25978768 DOI: 10.1021/acs.langmuir.5b01011] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Increasing rates of antimicrobial-resistant medically important bacteria require the development of new, effective therapeutics, of which antimicrobial peptides (AMPs) are among the promising candidates. Many AMPs are membrane-active, but their mode of action in killing bacteria or in inhibiting their growth remains elusive. This study used atomic force microscopy (AFM) to probe the mechanobiology of a model AMP (a derivative of melittin) on living Klebsiella pneumoniae bacterial cells. We performed in situ biophysical measurements to understand how the melittin peptide modulates various biophysical behaviors of individual bacteria, including the turgor pressure, cell wall elasticity, and bacterial capsule thickness and organization. Exposure of K. pneumoniae to the peptide had a significant effect on the turgor pressure and Young's modulus of the cell wall. The turgor pressure increased upon peptide addition followed by a later decrease, suggesting that cell lysis occurred and pressure was lost through destruction of the cell envelope. The Young's modulus also increased, indicating that interaction with the peptide increased the rigidity of the cell wall. The bacterial capsule did not prevent cell lysis by the peptide, and surprisingly, the capsule appeared unaffected by exposure to the peptide, as capsule thickness and inferred organization were within the control limits, determined by mechanical measurements. These data show that AFM measurements may provide valuable insights into the physical events that precede bacterial lysis by AMPs.
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Affiliation(s)
- Anna Mularski
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - Jonathan J Wilksch
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - Huabin Wang
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - Mohammed Akhter Hossain
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - John D Wade
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - Frances Separovic
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - Richard A Strugnell
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
| | - Michelle L Gee
- †School of Chemistry, ‡Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, and §Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC 3010, Australia
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18
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Positive autoregulation of mrkHI by the cyclic di-GMP-dependent MrkH protein in the biofilm regulatory circuit of Klebsiella pneumoniae. J Bacteriol 2015; 197:1659-67. [PMID: 25733612 DOI: 10.1128/jb.02615-14] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2015] [Accepted: 02/22/2015] [Indexed: 01/07/2023] Open
Abstract
UNLABELLED Klebsiella pneumoniae is an important cause of nosocomial infections, primarily through the formation of surface-associated biofilms to promote microbial colonization on host tissues. Expression of type 3 fimbriae by K. pneumoniae facilitates surface adherence, a process strongly activated by the cyclic di-GMP (c-di-GMP)-dependent transcriptional activator MrkH. In this study, we demonstrated the critical importance of MrkH in facilitating K. pneumoniae attachment on a variety of medically relevant materials and demonstrated the mechanism by which bacteria activate expression of type 3 fimbriae to colonize these materials. Sequence analysis revealed a putative MrkH recognition DNA sequence ("MrkH box"; TATCAA) located in the regulatory region of the mrkHI operon. Mutational analysis, electrophoretic mobility shift assay, and quantitative PCR experiments demonstrated that MrkH binds to the cognate DNA sequence to autoregulate mrkHI expression in a c-di-GMP-dependent manner. A half-turn deletion, but not a full-turn deletion, between the MrkH box and the -35 promoter element rendered MrkH ineffective in activating mrkHI expression, implying that a direct interaction between MrkH and RNA polymerase exists. In vivo analyses showed that residues L260, R265, N268, C269, E273, and I275 in the C-terminal domain of the RNA polymerase α subunit are involved in the positive control of mrkHI expression by MrkH and revealed the regions of MrkH required for DNA binding and transcriptional activation. Taken together, the data suggest a model whereby c-di-GMP-dependent MrkH recruits RNA polymerase to the mrkHI promoter to autoactivate mrkH expression. Increased MrkH production subsequently drives mrkABCDF expression when activated by c-di-GMP, leading to biosynthesis of type 3 fimbriae and biofilm formation. IMPORTANCE Bacterial biofilms can cause persistent infections that are refractory to antimicrobial treatments. This study investigated how a commonly encountered hospital-acquired pathogen, Klebsiella pneumoniae, controls the expression of MrkH, the principal regulator of type 3 fimbriae and biofilm formation. We discovered a regulatory circuit whereby MrkH acts as a c-di-GMP-dependent transcriptional activator of both the gene cluster of type 3 fimbriae and the mrkHI operon. In this positive-feedback loop, whereby MrkH activates its own production, K. pneumoniae has evolved a mechanism to ensure rapid MrkH production, expression of type 3 fimbriae, and subsequent biofilm formation under favorable conditions. Deciphering the molecular mechanisms of biofilm formation by bacterial pathogens is important for the development of innovative treatment strategies for biofilm infections.
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