1
|
Chapartegui-González I, Stockton JL, Bowser S, Badten AJ, Torres AG. Unraveling the role of toxin-antitoxin systems in Burkholderia pseudomallei: exploring bacterial pathogenesis and interactions within the HigBA families. Microbiol Spectr 2024; 12:e0074824. [PMID: 38916327 PMCID: PMC11302019 DOI: 10.1128/spectrum.00748-24] [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: 03/21/2024] [Accepted: 05/28/2024] [Indexed: 06/26/2024] Open
Abstract
Burkholderia pseudomallei (Bpm) is a Gram-negative intracellular pathogen that causes melioidosis in humans, a neglected, underreported, and lethal disease that can reach a fatal outcome in over 50% of the cases. It can produce both acute and chronic infections, the latter being particularly challenging to eliminate because of the intracellular life cycle of the bacteria and its ability to generate a "persister" dormant state. The molecular mechanism that allows the switch between growing and persister phenotypes is not well understood but it is hypothesized to be due at least in part to the participation of toxin-antitoxin (TA) systems. We have previously studied the link between one of those systems (defined as HigBA) with specific expression patterns associated with levofloxacin antibiotic exposure. Through in silico methods, we predicted the presence of another three pairs of genes encoding for additional putative HigBA systems. Therefore, our main goal was to establish which mechanisms are conserved as well as which pathways are specific among different Bpm TA systems from the same family. We hypothesize that the high prevalence, and sometimes even redundancy of these systems in the Bpm chromosomes indicates that they can interact with each other and not function as only individual systems, as it was traditionally thought, and might be playing an undefined role in Bpm lifecycle. Here, we show that both the toxin and the antitoxin of the different systems contribute to bacterial survival and that toxins from the same family can have a cumulative effect under environmental stressful conditions. IMPORTANCE Toxin-antitoxin (TA) systems play a significant role in bacterial persistence, a phenomenon where bacterial cells enter a dormant or slow-growing state to survive adverse conditions such as nutrient deprivation, antibiotic exposure, or host immune responses. By studying TA systems in Burkholderia pseudomallei, we can gain insights into how this pathogen survives and persists in the host environment, contributing to its virulence and ability to cause melioidosis chronic infections.
Collapse
Affiliation(s)
| | - Jacob L. Stockton
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA
| | - Sarah Bowser
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA
| | - Alexander J. Badten
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA
- Institute for Translational Sciences, University of Texas Medical Branch, Galveston, Texas, USA
| | - Alfredo G. Torres
- Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA
- Department of Pathology, University of Texas Medical Branch, Galveston, Texas, USA
| |
Collapse
|
2
|
Fihn CA, Lembke HK, Gaulin J, Bouchard P, Villarreal AR, Penningroth MR, Crone KK, Vogt GA, Gilbertsen AJ, Ayotte Y, de Oliveira LC, Serrano-Wu MH, Drouin N, Hung DT, Hunter RC, Carlson EE. Evaluation of Expanded 2-Aminobenzothiazole Library for Inhibition of Pseudomonas aeruginosa Virulence Phenotypes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.05.02.539119. [PMID: 37205454 PMCID: PMC10187220 DOI: 10.1101/2023.05.02.539119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Bacterial resistance to antibiotics is a rapidly increasing threat to human health. New strategies to combat resistant organisms are desperately needed. One potential avenue is targeting two-component systems, which are the main bacterial signal transduction pathways used to regulate development, metabolism, virulence, and antibiotic resistance. These systems consist of a homodimeric membrane-bound sensor histidine kinase, and a cognate effector, the response regulator. The high sequence conservation in the catalytic and adenosine triphosphate-binding (CA) domain of histidine kinases and their essential role in bacterial signal transduction could enable broad-spectrum antibacterial activity. Through this signal transduction, histidine kinases regulate multiple virulence mechanisms including toxin production, immune evasion, and antibiotic resistance. Targeting virulence, as opposed to development of bactericidal compounds, could reduce evolutionary pressure for acquired resistance. Additionally, compounds targeting the CA domain have the potential to impair multiple two-component systems that regulate virulence in one or more pathogens. We conducted structure-activity relationship studies of 2-aminobenzothiazole-based inhibitors designed to target the CA domain of histidine kinases. We found these compounds have anti-virulence activities in Pseudomonas aeruginosa, reducing motility phenotypes and toxin production associated with the pathogenic functions of this bacterium.
Collapse
Affiliation(s)
- Conrad A. Fihn
- Department of Medicinal Chemistry, University of Minnesota, 308 Harvard Street SE, Minneapolis, Minnesota 55455, United States
| | - Hannah K. Lembke
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55454, United States
| | - Jeffrey Gaulin
- The Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, United States
| | - Patricia Bouchard
- NMX Research and Solution Inc., 500 Cartier Boulevard W., Suite 6000, Laval, Quebec, Canada, H1Y 2R1
| | - Alex R. Villarreal
- Department of Microbiology & Immunology, University of Minnesota, 689 23rd Ave Se Minneapolis, Minnesota 55455, United States
| | - Mitchell R. Penningroth
- Department of Microbiology & Immunology, University of Minnesota, 689 23rd Ave Se Minneapolis, Minnesota 55455, United States
| | - Kathryn K. Crone
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 321 Church Street SE, Minneapolis, Minnesota 55455, United States
| | - Grace A. Vogt
- Department of Microbiology & Immunology, University of Minnesota, 689 23rd Ave Se Minneapolis, Minnesota 55455, United States
| | - Adam J. Gilbertsen
- Department of Microbiology & Immunology, University of Minnesota, 689 23rd Ave Se Minneapolis, Minnesota 55455, United States
| | - Yann Ayotte
- NMX Research and Solution Inc., 500 Cartier Boulevard W., Suite 6000, Laval, Quebec, Canada, H1Y 2R1
| | | | | | - Nathalie Drouin
- NMX Research and Solution Inc., 500 Cartier Boulevard W., Suite 6000, Laval, Quebec, Canada, H1Y 2R1
| | - Deborah T. Hung
- The Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, United States
| | - Ryan C. Hunter
- Department of Microbiology & Immunology, University of Minnesota, 689 23rd Ave Se Minneapolis, Minnesota 55455, United States
| | - Erin E. Carlson
- Department of Medicinal Chemistry, University of Minnesota, 308 Harvard Street SE, Minneapolis, Minnesota 55455, United States
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55454, United States
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 321 Church Street SE, Minneapolis, Minnesota 55455, United States
| |
Collapse
|
3
|
Zemke AC, D'Amico EJ, Torres AM, Carreno-Florez GP, Keeley P, DuPont M, Kasturiarachi N, Bomberger JM. Bacterial respiratory inhibition triggers dispersal of Pseudomonas aeruginosa biofilms. Appl Environ Microbiol 2023; 89:e0110123. [PMID: 37728340 PMCID: PMC10617509 DOI: 10.1128/aem.01101-23] [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: 07/02/2023] [Accepted: 07/14/2023] [Indexed: 09/21/2023] Open
Abstract
Pseudomonas aeruginosa grows as a biofilm under many environmental conditions, and the bacterium can disperse from biofilms via highly regulated, dynamic processes. However, physiologic triggers of biofilm dispersal remain poorly understood. Based on prior literature describing dispersal triggered by forms of starvation, we tested bacterial respiratory inhibitors for biofilm dispersal in two models resembling chronic airway infections. Our underlying hypothesis was that respiratory inhibitors could serve as a model for the downstream effects of starvation. We used two experimental conditions. In the first condition, biofilms were grown and dispersed from the surface of airway epithelial cells, and the second condition was a model where biofilms were grown on glass in cell culture media supplemented with host-relevant iron sources. In both biofilm models, the respiratory inhibitors potassium cyanide and sodium azide each triggered biofilm dispersal. We hypothesized that cyanide-induced dispersal was due to respiratory inhibition rather than signaling via an alternative mechanism, and, indeed, if respiration was supported by overexpression of cyanide-insensitive oxidase, dispersal was prevented. Dispersal required the activity of the cyclic-di-GMP regulated protease LapG, reinforcing the role of matrix degradation in dispersal. Finally, we examined the roles of individual phosphodiesterases, previously implicated in dispersal to specific triggers, and found signaling to be highly redundant. Combined deletion of the phosphodiesterases dipA, bifA, and rbdA was required to attenuate the dispersal phenotype. In summary, this work adds insight into the physiology of biofilm dispersal under environmental conditions in which bacterial respiration is abruptly limited. IMPORTANCE The bacterium Pseudomonas aeruginosa grows in biofilm communities that are very difficult to treat in human infections. Growing as a biofilm can protect bacteria from antibiotics and the immune system. Bacteria can leave a biofilm through a process called "dispersal." Dispersed bacteria seed new growth areas and are more susceptible to killing by antibiotics. The triggers for biofilm dispersal are not well understood, and if we understood dispersal better it might lead to the development of new treatments for infection. In this paper, we find that inhibiting P. aeurginosa's ability to respire (generate energy) can trigger dispersal from a biofilm grown in association with human respiratory epithelial cells in culture. The dispersal process requires a protease which is previously known to degrade the biofilm matrix. These findings give us a better understanding of how the biofilm dispersal process works so that future research can discover better ways of clearing bacteria growing in biofilms.
Collapse
Affiliation(s)
- Anna C. Zemke
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Emily J. D'Amico
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Angela M. Torres
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Grace P. Carreno-Florez
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Patrick Keeley
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Matt DuPont
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Naomi Kasturiarachi
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Jennifer M. Bomberger
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| |
Collapse
|
4
|
Salvà-Serra F, Pérez-Pantoja D, Donoso RA, Jaén-Luchoro D, Fernández-Juárez V, Engström-Jakobsson H, Moore ERB, Lalucat J, Bennasar-Figueras A. Comparative genomics of Stutzerimonas balearica ( Pseudomonas balearica): diversity, habitats, and biodegradation of aromatic compounds. Front Microbiol 2023; 14:1159176. [PMID: 37275147 PMCID: PMC10234333 DOI: 10.3389/fmicb.2023.1159176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2023] [Accepted: 04/13/2023] [Indexed: 06/07/2023] Open
Abstract
Stutzerimonas balearica (Pseudomonas balearica) has been found principally in oil-polluted environments. The capability of S. balearica to thrive from the degradation of pollutant compounds makes it a species of interest for potential bioremediation applications. However, little has been reported about the diversity of S. balearica. In this study, genome sequences of S. balearica strains from different origins were analyzed, revealing that it is a diverse species with an open pan-genome that will continue revealing new genes and functionalities as the genomes of more strains are sequenced. The nucleotide signatures and intra- and inter-species variation of the 16S rRNA genes of S. balearica were reevaluated. A strategy of screening 16S rRNA gene sequences in public databases enabled the detection of 158 additional strains, of which only 23% were described as S. balearica. The species was detected from a wide range of environments, although mostly from aquatic and polluted environments, predominantly related to petroleum oil. Genomic and phenotypic analyses confirmed that S. balearica possesses varied inherent capabilities for aromatic compounds degradation. This study increases the knowledge of the biology and diversity of S. balearica and will serve as a basis for future work with the species.
Collapse
Affiliation(s)
- Francisco Salvà-Serra
- Microbiology, Department of Biology, University of the Balearic Islands, Palma de Mallorca, Spain
- Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
- Culture Collection University of Gothenburg (CCUG), Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Danilo Pérez-Pantoja
- Programa Institucional de Fomento a la Investigación, Desarrollo e Innovación, Universidad Tecnológica Metropolitana, Santiago, Chile
| | - Raúl A. Donoso
- Programa Institucional de Fomento a la Investigación, Desarrollo e Innovación, Universidad Tecnológica Metropolitana, Santiago, Chile
- Center of Applied Ecology and Sustainability (CAPES), Santiago, Chile
| | - Daniel Jaén-Luchoro
- Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
- Culture Collection University of Gothenburg (CCUG), Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Víctor Fernández-Juárez
- Marine Biological Section, Department of Biology, University of Copenhagen, Helsingør, Denmark
| | - Hedvig Engström-Jakobsson
- Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Edward R. B. Moore
- Department of Infectious Diseases, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
- Culture Collection University of Gothenburg (CCUG), Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Jorge Lalucat
- Microbiology, Department of Biology, University of the Balearic Islands, Palma de Mallorca, Spain
| | - Antoni Bennasar-Figueras
- Microbiology, Department of Biology, University of the Balearic Islands, Palma de Mallorca, Spain
| |
Collapse
|
5
|
Ciemniecki JA, Newman DK. NADH dehydrogenases are the predominant phenazine reductases in the electron transport chain of Pseudomonas aeruginosa. Mol Microbiol 2023; 119:560-573. [PMID: 36840394 PMCID: PMC11129870 DOI: 10.1111/mmi.15049] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 02/15/2023] [Accepted: 02/21/2023] [Indexed: 02/26/2023]
Abstract
Phenazines are redox-active secondary metabolites produced by diverse bacteria including the opportunistic pathogen Pseudomonas aeruginosa. Extracellular electron transfer via phenazines enhances anaerobic survival by serving as an electron sink for glucose catabolism. However, the specific phenazine reductase(s) used to support this catabolism are unknown. Because electron transport chain components have been previously implicated in phenazine reduction, we sought to determine which of them possess phenazine reductase activity. We show that phenazine-1-carboxamide (PCN) and pyocyanin (PYO) are reduced at the highest rate by cells and are localized to the cell envelope while reduced. Using a coupled genetic and biochemical approach, we show that phenazine reductase activity in membrane fractions is attributable to the three NADH dehydrogenases present in P. aeruginosa and that their order of phenazine reductase activity is Nqr > Nuo > Ndh. In mutants possessing only one functional NADH dehydrogenase, whole cell reduction rates of PCN, but not PYO, recapitulate the pattern of biochemical results, implying that PYO reduction is predominantly occurring in the cytosol. Lastly, we show that ubiquinone rapidly and non-enzymatically oxidizes reduced phenazines, demonstrating that phenazines have the capability to serve in a redox loop between the NADH and ubiquinone pools, a finding that carries bioenergetic implications.
Collapse
Affiliation(s)
- John A Ciemniecki
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA
| | - Dianne K Newman
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
| |
Collapse
|
6
|
Tveit AT, Söllinger A, Rainer EM, Didriksen A, Hestnes AG, Motleleng L, Hellinger HJ, Rattei T, Svenning MM. Thermal acclimation of methanotrophs from the genus Methylobacter. THE ISME JOURNAL 2023; 17:502-513. [PMID: 36650275 PMCID: PMC10030640 DOI: 10.1038/s41396-023-01363-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 12/30/2022] [Accepted: 01/10/2023] [Indexed: 01/19/2023]
Abstract
Methanotrophs oxidize most of the methane (CH4) produced in natural and anthropogenic ecosystems. Often living close to soil surfaces, these microorganisms must frequently adjust to temperature change. While many environmental studies have addressed temperature effects on CH4 oxidation and methanotrophic communities, there is little knowledge about the physiological adjustments that underlie these effects. We have studied thermal acclimation in Methylobacter, a widespread, abundant, and environmentally important methanotrophic genus. Comparisons of growth and CH4 oxidation kinetics at different temperatures in three members of the genus demonstrate that temperature has a strong influence on how much CH4 is consumed to support growth at different CH4 concentrations. However, the temperature effect varies considerably between species, suggesting that how a methanotrophic community is composed influences the temperature effect on CH4 uptake. To understand thermal acclimation mechanisms widely we carried out a transcriptomics experiment with Methylobacter tundripaludum SV96T. We observed, at different temperatures, how varying abundances of transcripts for glycogen and protein biosynthesis relate to cellular glycogen and ribosome concentrations. Our data also demonstrated transcriptional adjustment of CH4 oxidation, oxidative phosphorylation, membrane fatty acid saturation, cell wall composition, and exopolysaccharides between temperatures. In addition, we observed differences in M. tundripaludum SV96T cell sizes at different temperatures. We conclude that thermal acclimation in Methylobacter results from transcriptional adjustment of central metabolism, protein biosynthesis, cell walls and storage. Acclimation leads to large shifts in CH4 consumption and growth efficiency, but with major differences between species. Thus, our study demonstrates that physiological adjustments to temperature change can substantially influence environmental CH4 uptake rates and that consideration of methanotroph physiology might be vital for accurate predictions of warming effects on CH4 emissions.
Collapse
Affiliation(s)
- Alexander T Tveit
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway.
| | - Andrea Söllinger
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| | - Edda Marie Rainer
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| | - Alena Didriksen
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| | - Anne Grethe Hestnes
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| | - Liabo Motleleng
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| | - Hans-Jörg Hellinger
- University of Vienna, Centre for Microbiology and Environmental Systems Science, Vienna, Austria
- University of Vienna, Doctoral School in Microbiology and Environmental Science, Vienna, Austria
| | - Thomas Rattei
- University of Vienna, Centre for Microbiology and Environmental Systems Science, Vienna, Austria
| | - Mette M Svenning
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| |
Collapse
|
7
|
Curcumin-ZnO nanocomposite mediated inhibition of Pseudomonas aeruginosa biofilm and its mechanism of action. J Drug Deliv Sci Technol 2023. [DOI: 10.1016/j.jddst.2023.104301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
|
8
|
Bioenergetics and Reactive Nitrogen Species in Bacteria. Int J Mol Sci 2022; 23:ijms23137321. [PMID: 35806323 PMCID: PMC9266656 DOI: 10.3390/ijms23137321] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 06/27/2022] [Accepted: 06/28/2022] [Indexed: 11/24/2022] Open
Abstract
The production of reactive nitrogen species (RNS) by the innate immune system is part of the host’s defense against invading pathogenic bacteria. In this review, we summarize recent studies on the molecular basis of the effects of nitric oxide and peroxynitrite on microbial respiration and energy conservation. We discuss possible molecular mechanisms underlying RNS resistance in bacteria mediated by unique respiratory oxygen reductases, the mycobacterial bcc-aa3 supercomplex, and bd-type cytochromes. A complete picture of the impact of RNS on microbial bioenergetics is not yet available. However, this research area is developing very rapidly, and the knowledge gained should help us develop new methods of treating infectious diseases.
Collapse
|
9
|
Genetic and Biochemical Characterization of the Na +/H + Antiporters of Pseudomonas aeruginosa. J Bacteriol 2021; 203:e0028421. [PMID: 34280000 DOI: 10.1128/jb.00284-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas aeruginosa has four Na+/H+ antiporters that interconvert and balance Na+ and H+ gradients across the membrane. These gradients are important for bioenergetics and ionic homeostasis. To understand these transporters, we constructed four strains, each of which has only one antiporter, i.e., NhaB, NhaP, NhaP2, and Mrp. We also constructed a quadruple deletion mutant that has no Na+/H+ antiporters. Although the antiporters of P. aeruginosa have been studied previously, the strains constructed here present the opportunity to characterize their kinetic properties in their native membranes and their roles in the physiology of P. aeruginosa. The strains expressing only NhaB or Mrp, the two electrogenic antiporters, were able to grow essentially like the wild-type strain across a range of Na+ concentrations and pH values. Strains with only NhaP or NhaP2, which are electroneutral, grew more poorly at increasing Na+ concentrations, especially at high pH values, with the strain expressing NhaP being more sensitive. The strain with no Na+/H+ antiporters was extremely sensitive to the Na+ concentration and showed essentially no Na+(Li+)/H+ antiporter activity, but it retained most K+/H+ antiporter activity of the wild-type strain at pH 7.5 and approximately one-half at pH 8.5. We also used the four strains that each express one of the four antiporters to characterize the kinetic properties of each transporter. Transcriptome sequencing analysis of the quadruple deletion strain showed widespread changes, including changes in pyocyanin synthesis, biofilm formation, and nitrate and glycerol metabolism. Thus, the strains constructed for this study will open a new door to understanding the physiological roles of these proteins and their activities in P. aeruginosa. IMPORTANCE Pseudomonas aeruginosa has four Na+/H+ antiporters that connect and interconvert its Na+ and H+ gradients. We have constructed four deletion mutants, each of which has only one of the four Na+/H+ antiporters. These strains made it possible to study the properties and physiological roles of each antiporter independently in its native membrane. Mrp and NhaB are each able to sustain growth over a wide range of pH values and Na+ concentrations, whereas the two electroneutral antiporters, NhaP and NhaP2, are most effective at low pH values. We also constructed a quadruple mutant lacking all four antiporters, in which the H+ and Na+ gradients are disconnected. This will make it possible to study the role of the two gradients independently.
Collapse
|