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Bruna RE, Kendra CG, Pontes MH. Phosphorus starvation response and PhoB-independent utilization of organic phosphate sources by Salmonella enterica. Microbiol Spectr 2023; 11:e0226023. [PMID: 37787565 PMCID: PMC10715179 DOI: 10.1128/spectrum.02260-23] [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: 06/02/2023] [Accepted: 08/21/2023] [Indexed: 10/04/2023] Open
Abstract
IMPORTANCE Phosphorus (P) is the fifth most abundant element in living cells. This element is acquired mainly as inorganic phosphate (Pi, PO4 3-). In enteric bacteria, P starvation activates a two-component signal transduction system which is composed of the membrane sensor protein PhoR and its cognate transcription regulator PhoB. PhoB, in turn, promotes the transcription of genes that help maintain Pi homeostasis. Here, we characterize the P starvation response of the bacterium Salmonella enterica. We determine the PhoB-dependent and independent transcriptional changes promoted by P starvation and identify proteins enabling the utilization of a range of organic substrates as sole P sources. We show that transcription and activity of a subset of these proteins are independent of PhoB and Pi availability. These results establish that Salmonella enterica can maintain Pi homeostasis and repress PhoB/PhoR activation even when cells are grown in medium lacking Pi.
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Affiliation(s)
- Roberto E. Bruna
- Department of Pathology and Laboratory Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
- The One Health Microbiome Center, Huck Institute of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Christopher G. Kendra
- Department of Pathology and Laboratory Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
- The One Health Microbiome Center, Huck Institute of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Mauricio H. Pontes
- Department of Pathology and Laboratory Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
- The One Health Microbiome Center, Huck Institute of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, USA
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2
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Gorski L, Noriega AA. Comparison of Phenotype Nutritional Profiles and Phosphate Metabolism Genes in Four Serovars of Salmonella enterica from Water Sources. Microorganisms 2023; 11:2109. [PMID: 37630669 PMCID: PMC10459026 DOI: 10.3390/microorganisms11082109] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 08/03/2023] [Accepted: 08/14/2023] [Indexed: 08/27/2023] Open
Abstract
The surveillance of foods for Salmonella is hindered by bias in common enrichment media where serovars implicated in human illness are outgrown by less virulent serovars. We examined four Salmonella serovars, two common in human illness (Enteritidis and Typhimurium) and two that often dominate enrichments (Give and Kentucky), for factors that might influence culture bias. The four serovars had similar growth kinetics in Tryptic Soy Broth and Buffered Peptone Water. Phenotype microarray analysis with 950 chemical substrates to assess nutrient utilization and stress resistance revealed phenotype differences between serovars. Strains of S. Enteritidis had better utilization of plant-derived sugars such as xylose, mannitol, rhamnose, and fructose, while S. Typhimurium strains were able to metabolize tagatose. Strains of S. Kentucky used more compounds as phosphorus sources and grew better with inorganic phosphate as the sole phosphorus source. The sequences of nine genes involved in phosphate metabolism were compared, and there were differences between serovars in the catalytic ATP-binding domain of the histidine kinase phoR. Analysis of the predicted PhoR amino acid sequences from additional Salmonella genomes indicated a conservation of sequences each within the Typhimurium, Give, and Enteritidis serovars. However, three different PhoR versions were observed in S. Kentucky.
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Affiliation(s)
- Lisa Gorski
- Produce Safety and Microbiology Research Unit, Agricultural Research Service, United States Department of Agriculture, Albany, CA 94710, USA
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3
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Park Y, Solhtalab M, Thongsomboon W, Aristilde L. Strategies of organic phosphorus recycling by soil bacteria: acquisition, metabolism, and regulation. ENVIRONMENTAL MICROBIOLOGY REPORTS 2022; 14:3-24. [PMID: 35001516 PMCID: PMC9306846 DOI: 10.1111/1758-2229.13040] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 12/07/2021] [Accepted: 12/14/2021] [Indexed: 05/12/2023]
Abstract
Critical to meeting cellular phosphorus (P) demand, soil bacteria deploy a number of strategies to overcome limitation in inorganic P (Pi ) in soils. As a significant contributor to P recycling, soil bacteria secrete extracellular enzymes to degrade organic P (Po ) in soils into the readily bioavailable Pi . In addition, several Po compounds can be transported directly via specific transporters and subsequently enter intracellular metabolic pathways. In this review, we highlight the strategies that soil bacteria employ to recycle Po from the soil environment. We discuss the diversity of extracellular phosphatases in soils, the selectivity of these enzymes towards various Po biomolecules and the influence of the soil environmental conditions on the enzyme's activities. Moreover, we outline the intracellular metabolic pathways for Po biosynthesis and transporter-assisted Po and Pi uptake at different Pi availabilities. We further highlight the regulatory mechanisms that govern the production of phosphatases, the expression of Po transporters and the key metabolic changes in P metabolism in response to environmental Pi availability. Due to the depletion of natural resources for Pi , we propose future studies needed to leverage bacteria-mediated P recycling from the large pools of Po in soils or organic wastes to benefit agricultural productivity.
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Affiliation(s)
- Yeonsoo Park
- Department of Civil and Environmental Engineering, McCormick School of Engineering and Applied ScienceNorthwestern UniversityEvanstonIL60208USA
- Department of Biological and Environmental EngineeringCornell University, Riley‐Robb HallIthacaNY14853USA
| | - Mina Solhtalab
- Department of Civil and Environmental Engineering, McCormick School of Engineering and Applied ScienceNorthwestern UniversityEvanstonIL60208USA
- Department of Biological and Environmental EngineeringCornell University, Riley‐Robb HallIthacaNY14853USA
| | - Wiriya Thongsomboon
- Department of Civil and Environmental Engineering, McCormick School of Engineering and Applied ScienceNorthwestern UniversityEvanstonIL60208USA
- Department of Chemistry, Faculty of ScienceMahasarakham UniversityMahasarakham44150Thailand
| | - Ludmilla Aristilde
- Department of Civil and Environmental Engineering, McCormick School of Engineering and Applied ScienceNorthwestern UniversityEvanstonIL60208USA
- Department of Biological and Environmental EngineeringCornell University, Riley‐Robb HallIthacaNY14853USA
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Wu Q, Liu X, Chai Z, Cheng K, Xu G, Jiang L, Liu M, Li C. Lanmodulin Remains Unfold and Fails to Interact with Lanthanide Ions in Escherichia coli Cells. Chem Commun (Camb) 2022; 58:8230-8233. [DOI: 10.1039/d2cc02038f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report the conformation of a newly discovered specific lanthanide ions (Ln3+) binding protein, Lanmodulin (LanM), and its inteaction with Ln3+ in Escherichia coli cells using In-cell NMR. We found...
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Kim IJ, Brack Y, Bayer T, Bornscheuer UT. Two novel cyanobacterial α-dioxygenases for the biosynthesis of fatty aldehydes. Appl Microbiol Biotechnol 2021; 106:197-210. [PMID: 34882252 PMCID: PMC8720084 DOI: 10.1007/s00253-021-11724-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 11/27/2021] [Accepted: 11/30/2021] [Indexed: 11/21/2022]
Abstract
α-Dioxygenases (α-DOXs) are known as plant enzymes involved in the α-oxidation of fatty acids through which fatty aldehydes, with a high commercial value as flavor and fragrance compounds, are synthesized as products. Currently, little is known about α-DOXs from non-plant organisms. The phylogenic analysis reported here identified a substantial number of α-DOX enzymes across various taxa. Here, we report the functional characterization and Escherichia coli whole-cell application of two novel α-DOXs identified from cyanobacteria: CalDOX from Calothrix parietina and LepDOX from Leptolyngbya sp. The catalytic behavior of the recombinantly expressed CalDOX and LepDOX revealed that they are heme-dependent like plant α-DOXs but exhibit activities toward medium carbon fatty acids ranging from C10 to C14 unlike plant α-DOXs. The in-depth molecular investigation of cyanobacterial α-DOXs and their application in an E. coli whole system employed in this study is useful not only for the understanding of the molecular function of α-DOXs, but also for their industrial utilization in fatty aldehyde biosynthesis. Key points • Two novel α-dioxygenases from Cyanobacteria are reported • Both enzymes prefer medium-chain fatty acids • Both enzymes are useful for fatty aldehyde biosynthesis
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Affiliation(s)
- In Jung Kim
- Department of Biotechnology and Enzyme Catalysis, Institute of Biochemistry, University of Greifswald, 17489, Greifswald, Germany
| | - Yannik Brack
- Department of Biotechnology and Enzyme Catalysis, Institute of Biochemistry, University of Greifswald, 17489, Greifswald, Germany
| | - Thomas Bayer
- Department of Biotechnology and Enzyme Catalysis, Institute of Biochemistry, University of Greifswald, 17489, Greifswald, Germany
| | - Uwe T Bornscheuer
- Department of Biotechnology and Enzyme Catalysis, Institute of Biochemistry, University of Greifswald, 17489, Greifswald, Germany.
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6
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Ortiz-Padilla M, Portillo-Calderón I, Maldonado N, Rodríguez-Martínez J, de Gregorio-Iaria B, Merino-Bohórquez V, Rodríguez-Baño J, Pascual Á, Docobo-Pérez F. Role of inorganic phosphate concentrations in in vitro activity of fosfomycin. Clin Microbiol Infect 2021; 28:302.e1-302.e4. [PMID: 34634457 DOI: 10.1016/j.cmi.2021.09.037] [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: 05/26/2021] [Revised: 09/16/2021] [Accepted: 09/28/2021] [Indexed: 11/16/2022]
Abstract
OBJECTIVES The objective of this study was to evaluate the in vitro activity of fosfomycin under different physiological concentrations of inorganic phosphate (Pi). METHODS The wild-type BW25113 strain, four isogenic mutants (ΔglpT, ΔuhpT, ΔglpT-uhpT, and ΔphoB) and six clinical isolates of Escherichia coli with different fosfomycin susceptibilities were used. EUCAST breakpoints were used. Susceptibility was evaluated by agar dilution using standard Mueller-Hinton agar (Pi concentration of 1 mM similar to human plasma concentration) and supplemented with Pi (13 and 42 mM, minimum and maximum urinary Pi concentrations) and/or glucose-6-phosphate (25 mg/L). Fosfomycin transporter promoter activity was assayed using PglpT::gfpmut2 or PuhpT::gfpmut2 promoter fusions in standard Mueller-Hinton Broth (MHB), supplemented with Pi (13 or 42 mM) ± glucose-6-phosphate. Fosfomycin activity was quantified, estimating fosfomycin EC50 under different Pi concentrations (1, 13 and 42 mM + glucose-6-phosphate) and in time-kill assays using fosfomycin concentrations of 307 (maximum plasma concentration (Cmax)), 1053 and 4415 mg/L (urine Cmax range), using MHB with 28 mM Pi (mean urine Pi concentration) + 25 mg/L glucose-6-phosphate. RESULTS All the strains showed decreased susceptibility to fosfomycin linked to increased Pi concentrations: 1-4 log2 dilution differences from 1 to 13 mM, and 1-8 log2 dilution differences at 42 mM Pi. Changes in phosphate concentration did not affect the expression of fosfomycin transporters. By increasing Pi concentrations higher fosfomycin EC50 bacterial viability was observed, except against ΔglpT-uhpT. The increase in Pi reduced the bactericidal effect of fosfomycin. DISCUSSION Pi variations in physiological fluids may reduce fosfomycin activity against E. coli. Elevated Pi concentrations in urine may explain oral fosfomycin failure in non-wild-type but fosfomycin-susceptible E. coli strains.
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Affiliation(s)
- Miriam Ortiz-Padilla
- Unidad de Gestión Clínica de Enfermedades Infecciosas y Microbiología Clínica, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain
| | - Inés Portillo-Calderón
- Unidad de Gestión Clínica de Enfermedades Infecciosas y Microbiología Clínica, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain
| | - Natalia Maldonado
- Unidad de Gestión Clínica de Enfermedades Infecciosas y Microbiología Clínica, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain
| | - José Rodríguez-Martínez
- Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain; Departamento de Microbiología, Universidad de Sevilla, Sevilla, Spain
| | - Belén de Gregorio-Iaria
- Unidad de Gestión Clínica de Enfermedades Infecciosas y Microbiología Clínica, Hospital Universitario Virgen Macarena, Seville, Spain
| | - Vicente Merino-Bohórquez
- Unidad de Gestión de Farmacia Hospitalaria, Hospital Universitario Virgen Macarena, Seville, Spain; Departamento de Farmacología, Universidad de Sevilla, Spain
| | - Jesús Rodríguez-Baño
- Unidad de Gestión Clínica de Enfermedades Infecciosas y Microbiología Clínica, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain; Departamento de Medicina, Universidad de Sevilla, Sevilla, Spain
| | - Álvaro Pascual
- Unidad de Gestión Clínica de Enfermedades Infecciosas y Microbiología Clínica, Hospital Universitario Virgen Macarena, Seville, Spain; Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain; Departamento de Microbiología, Universidad de Sevilla, Sevilla, Spain
| | - Fernando Docobo-Pérez
- Instituto de Biomedicina de Sevilla IBIS, Hospital Universitario Virgen Macarena/CSIC/Universidad de Sevilla, Seville, Spain; Departamento de Microbiología, Universidad de Sevilla, Sevilla, Spain.
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7
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Abstract
Phosphorus is required for many biological molecules and essential functions, including DNA replication, transcription of RNA, protein translation, posttranslational modifications, and numerous facets of metabolism. In order to maintain the proper level of phosphate for these processes, many bacteria adapt to changes in environmental phosphate levels. The mechanisms for sensing phosphate levels and adapting to changes have been extensively studied for multiple organisms. The phosphate response of Escherichia coli alters the expression of numerous genes, many of which are involved in the acquisition and scavenging of phosphate more efficiently. This review shares findings on the mechanisms by which E. coli cells sense and respond to changes in environmental inorganic phosphate concentrations by reviewing the genes and proteins that regulate this response. The PhoR/PhoB two-component signal transduction system is central to this process and works in association with the high-affinity phosphate transporter encoded by the pstSCAB genes and the PhoU protein. Multiple models to explain how this process is regulated are discussed.
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8
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Asplund-Samuelsson J, Janasch M, Hudson EP. Thermodynamic analysis of computed pathways integrated into the metabolic networks of E. coli and Synechocystis reveals contrasting expansion potential. Metab Eng 2017; 45:223-236. [PMID: 29278749 DOI: 10.1016/j.ymben.2017.12.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 12/04/2017] [Accepted: 12/20/2017] [Indexed: 01/09/2023]
Abstract
Introducing biosynthetic pathways into an organism is both reliant on and challenged by endogenous biochemistry. Here we compared the expansion potential of the metabolic network in the photoautotroph Synechocystis with that of the heterotroph E. coli using the novel workflow POPPY (Prospecting Optimal Pathways with PYthon). First, E. coli and Synechocystis metabolomic and fluxomic data were combined with metabolic models to identify thermodynamic constraints on metabolite concentrations (NET analysis). Then, thousands of automatically constructed pathways were placed within each network and subjected to a network-embedded variant of the max-min driving force analysis (NEM). We found that the networks had different capabilities for imparting thermodynamic driving forces toward certain compounds. Key metabolites were constrained differently in Synechocystis due to opposing flux directions in glycolysis and carbon fixation, the forked tri-carboxylic acid cycle, and photorespiration. Furthermore, the lysine biosynthesis pathway in Synechocystis was identified as thermodynamically constrained, impacting both endogenous and heterologous reactions through low 2-oxoglutarate levels. Our study also identified important yet poorly covered areas in existing metabolomics data and provides a reference for future thermodynamics-based engineering in Synechocystis and beyond. The POPPY methodology represents a step in making optimal pathway-host matches, which is likely to become important as the practical range of host organisms is diversified.
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Affiliation(s)
- Johannes Asplund-Samuelsson
- Science for Life Laboratory, School of Biotechnology, KTH Royal Institute of Technology, P-Box 1031, 171 21 Solna, Sweden.
| | - Markus Janasch
- Science for Life Laboratory, School of Biotechnology, KTH Royal Institute of Technology, P-Box 1031, 171 21 Solna, Sweden.
| | - Elton P Hudson
- Science for Life Laboratory, School of Biotechnology, KTH Royal Institute of Technology, P-Box 1031, 171 21 Solna, Sweden.
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9
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Schramke H, Laermann V, Tegetmeyer HE, Brachmann A, Jung K, Altendorf K. Revisiting regulation of potassium homeostasis in Escherichia coli: the connection to phosphate limitation. Microbiologyopen 2017; 6. [PMID: 28097817 PMCID: PMC5458449 DOI: 10.1002/mbo3.438] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 11/29/2016] [Accepted: 12/06/2016] [Indexed: 11/10/2022] Open
Abstract
Two-component signal transduction constitutes the predominant strategy used by bacteria to adapt to fluctuating environments. The KdpD/KdpE system is one of the most widespread, and is crucial for K+ homeostasis. In Escherichia coli, the histidine kinase KdpD senses K+ availability, whereas the response regulator KdpE activates synthesis of the high-affinity K+ uptake system KdpFABC. Here we show that, in the absence of KdpD, kdpFABC expression can be activated via phosphorylation of KdpE by the histidine kinase PhoR. PhoR and its cognate response regulator PhoB comprise a phosphate-responsive two-component system, which senses phosphate limitation indirectly through the phosphate transporter PstCAB and its accessory protein PhoU. In vivo two-hybrid interaction studies based on the bacterial adenylate cyclase reveal pairwise interactions between KdpD, PhoR, and PhoU. Finally, we demonstrate that cross-regulation between the kdpFABC and pstSCAB operons occurs in both directions under simultaneous K+ and phosphate limitation, both in vitro and in vivo. This study for the first time demonstrates direct coupling between intracellular K+ and phosphate homeostasis and provides a mechanism for fine-tuning of the balance between positively and negatively charged ions in the bacterial cell.
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Affiliation(s)
- Hannah Schramke
- Department of Biology I, Microbiology, Center for integrated Protein Science Munich (CiPSM), Ludwig-Maximilians-Universität München, Martinsried, Germany
| | - Vera Laermann
- Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany
| | - Halina E Tegetmeyer
- Centrum für Biotechnologie, Universität Bielefeld, Bielefeld, Germany.,Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.,Max Planck Institute for Marine Microbiology, Bremen, Germany
| | - Andreas Brachmann
- Department of Biology I, Genetics, Ludwig-Maximilians-Universität München, Martinsried, Germany
| | - Kirsten Jung
- Department of Biology I, Microbiology, Center for integrated Protein Science Munich (CiPSM), Ludwig-Maximilians-Universität München, Martinsried, Germany
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Proteomic Analyses of Intracellular Salmonella enterica Serovar Typhimurium Reveal Extensive Bacterial Adaptations to Infected Host Epithelial Cells. Infect Immun 2015; 83:2897-906. [PMID: 25939512 DOI: 10.1128/iai.02882-14] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Accepted: 04/27/2015] [Indexed: 12/22/2022] Open
Abstract
Salmonella species can gain access into nonphagocytic cells, where the bacterium proliferates in a unique membrane-bounded compartment. In order to reveal bacterial adaptations to their intracellular niche, here we conducted the first comprehensive proteomic survey of Salmonella isolated from infected epithelial cells. Among ∼ 3,300 identified bacterial proteins, we found that about 100 proteins were significantly altered at the onset of Salmonella intracellular replication. In addition to substantially increased iron-uptake capacities, bacterial high-affinity manganese and zinc transporters were also upregulated, suggesting an overall limitation of metal ions in host epithelial cells. We also found that Salmonella induced multiple phosphate utilization pathways. Furthermore, our data suggested upregulation of the two-component PhoPQ system as well as of many downstream virulence factors under its regulation. Our survey also revealed that intracellular Salmonella has increased needs for certain amino acids and biotin. In contrast, Salmonella downregulated glycerol and maltose utilization as well as chemotaxis pathways.
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11
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Kim HM, Park YH, Yoon CK, Seok YJ. Histidine phosphocarrier protein regulates pyruvate kinase A activity in response to glucose in Vibrio vulnificus. Mol Microbiol 2015; 96:293-305. [PMID: 25598011 DOI: 10.1111/mmi.12936] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/14/2015] [Indexed: 11/29/2022]
Abstract
The bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) consists of two general energy-coupling proteins [enzyme I and histidine phosphocarrier protein (HPr)] and several sugar-specific enzyme IIs. Although, in addition to the phosphorylation-coupled transport of sugars, various regulatory roles of PTS components have been identified in Escherichia coli, much less is known about the PTS in the opportunistic human pathogen Vibrio vulnificus. In this study, we have identified pyruvate kinase A (PykA) as a binding partner of HPr in V. vulnificus. The interaction between HPr and PykA was strictly dependent on the presence of inorganic phosphate, and only dephosphorylated HPr interacted with PykA. Experiments involving domain swapping between the PykAs of V. vulnificus and E. coli revealed the requirement for the C-terminal domain of V. vulnificus PykA for a specific interaction with V. vulnificus HPr. Dephosphorylated HPr decreased the Km of PykA for phosphoenolpyruvate by approximately fourfold without affecting Vmax . Taken together, these findings indicate that the V. vulnificus PTS catalyzing the first step of glycolysis stimulates the final step of glycolysis in the presence of glucose through the direct interaction of dephospho-HPr with the C-terminal domain of PykA.
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Affiliation(s)
- Hey-Min Kim
- Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul, 151-742, South Korea
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12
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Noor E, Bar-Even A, Flamholz A, Reznik E, Liebermeister W, Milo R. Pathway thermodynamics highlights kinetic obstacles in central metabolism. PLoS Comput Biol 2014; 10:e1003483. [PMID: 24586134 PMCID: PMC3930492 DOI: 10.1371/journal.pcbi.1003483] [Citation(s) in RCA: 193] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Accepted: 01/08/2014] [Indexed: 12/05/2022] Open
Abstract
In metabolism research, thermodynamics is usually used to determine the directionality of a reaction or the feasibility of a pathway. However, the relationship between thermodynamic potentials and fluxes is not limited to questions of directionality: thermodynamics also affects the kinetics of reactions through the flux-force relationship, which states that the logarithm of the ratio between the forward and reverse fluxes is directly proportional to the change in Gibbs energy due to a reaction (ΔrG′). Accordingly, if an enzyme catalyzes a reaction with a ΔrG′ of -5.7 kJ/mol then the forward flux will be roughly ten times the reverse flux. As ΔrG′ approaches equilibrium (ΔrG′ = 0 kJ/mol), exponentially more enzyme counterproductively catalyzes the reverse reaction, reducing the net rate at which the reaction proceeds. Thus, the enzyme level required to achieve a given flux increases dramatically near equilibrium. Here, we develop a framework for quantifying the degree to which pathways suffer these thermodynamic limitations on flux. For each pathway, we calculate a single thermodynamically-derived metric (the Max-min Driving Force, MDF), which enables objective ranking of pathways by the degree to which their flux is constrained by low thermodynamic driving force. Our framework accounts for the effect of pH, ionic strength and metabolite concentration ranges and allows us to quantify how alterations to the pathway structure affect the pathway's thermodynamics. Applying this methodology to pathways of central metabolism sheds light on some of their features, including metabolic bypasses (e.g., fermentation pathways bypassing substrate-level phosphorylation), substrate channeling (e.g., of oxaloacetate from malate dehydrogenase to citrate synthase), and use of alternative cofactors (e.g., quinone as an electron acceptor instead of NAD). The methods presented here place another arrow in metabolic engineers' quiver, providing a simple means of evaluating the thermodynamic and kinetic quality of different pathway chemistries that produce the same molecules. Given data about enzyme kinetics and reaction thermodynamics, traditional metabolic control analysis (MCA) can pinpoint the enzymes whose expression will have the largest effect on steady-state flux through the pathway. These analyses can aid experimentalists in tuning enzyme expression levels along a metabolic pathway. In this work, we offer a framework that is complementary to MCA. Rather than focusing on the relationship between enzyme levels and pathway flux, we examine a pathway's stoichiometry and thermodynamics and ask whether it is likely to support high flux in cellular conditions. Our framework calculates a single thermodynamically-derived metric (the MDF) for each pathway, which is convenient for selecting the promising pathways from a large collection. This approach has several advantages. First, enzyme kinetic properties are laborious to measure and differ between organisms and isozymes, but no kinetic data is required to calculate the MDF. Second, as our framework accounts for pH, ionic strength and allowed concentration ranges, it is simple to model the effect of these parameters on the MDF. Finally, as it can be difficult to control the exact expression level of enzymes within cells, the MDF helps identify alternative pathways that are less sensitive to the levels of their constituent enzymes.
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Affiliation(s)
- Elad Noor
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot, Israel
| | - Arren Bar-Even
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot, Israel
| | - Avi Flamholz
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot, Israel
- Department of Molecular and Cellular Biology, University of California, Berkely, Berkely, California, United States of America
| | - Ed Reznik
- Computational Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America
| | | | - Ron Milo
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot, Israel
- * E-mail:
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13
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From physiology to systems metabolic engineering for the production of biochemicals by lactic acid bacteria. Biotechnol Adv 2013; 31:764-88. [DOI: 10.1016/j.biotechadv.2013.03.011] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 03/28/2013] [Accepted: 03/31/2013] [Indexed: 11/21/2022]
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14
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Pereira CS, Santos AJM, Bejerano-Sagie M, Correia PB, Marques JC, Xavier KB. Phosphoenolpyruvate phosphotransferase system regulates detection and processing of the quorum sensing signal autoinducer-2. Mol Microbiol 2012; 84:93-104. [PMID: 22384939 DOI: 10.1111/j.1365-2958.2012.08010.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Autoinducer-2 (AI-2) a signal produced by a range of phylogenetically distant microorganisms, enables inter-species cell-cell communication and regulates many bacterial phenotypes. Certain bacteria can interfere with AI-2-regulated behaviours of neighbouring species by internalizing AI-2 using the Lsr transport system (encoded by the lsr operon). AI-2 imported by the Lsr is phosphorylated by the LsrK kinase and AI-2-phosphate is the inducer of the lsr operon. Here we show that in Escherichia coli the phosphoenolpyruvate phosphotransferase system (PTS) is required for Lsr activation and is essential for AI-2 internalization. Although the phosphorylation state of Enzyme I of PTS is important for this regulation, LsrK is necessary for the phosphorylation of AI-2, indicating that AI-2 is not phosphorylated by PTS. Our results suggest that AI-2 internalization is initiated by a PTS-dependent mechanism, which provides sufficient intracellular AI-2 to relieve repression of the lsr operon and, thus induce depletion of AI-2 from the extracellular environment. The fact that AI-2 internalization is not only controlled by the community-dependent accumulation of AI-2, but also depends on the phosphorylation state of PTS suggests that E. coli can integrate information on the availability of substrates with external communal information to control quorum sensing and its interference.
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Affiliation(s)
- Catarina S Pereira
- Instituto Gulbenkian de Ciência, Oeiras, Portugal. Instituto de Tecnologia Química e Biológica, Oeiras, Portugal
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15
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Interaction of fosfomycin with the Glycerol 3-phosphate Transporter of Escherichia coli. Biochim Biophys Acta Gen Subj 2011; 1810:1323-9. [DOI: 10.1016/j.bbagen.2011.07.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2011] [Revised: 07/11/2011] [Accepted: 07/12/2011] [Indexed: 11/23/2022]
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16
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Motomura K, Hirota R, Ohnaka N, Okada M, Ikeda T, Morohoshi T, Ohtake H, Kuroda A. Overproduction of YjbB reduces the level of polyphosphate in Escherichia coli : a hypothetical role of YjbB in phosphate export and polyphosphate accumulation. FEMS Microbiol Lett 2011; 320:25-32. [DOI: 10.1111/j.1574-6968.2011.02285.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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17
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Affiliation(s)
- Lynn L Silver
- LL Silver Consulting LLC, 955 S. Springfield Avenue, Unit C403, Springfield, NJ 07081, USA
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18
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Employment of a promoter-swapping technique shows that PhoU modulates the activity of the PstSCAB2 ABC transporter in Escherichia coli. Appl Environ Microbiol 2008; 75:573-82. [PMID: 19047379 DOI: 10.1128/aem.01046-08] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of the Pho regulon in Escherichia coli is induced in response to low levels of environmental phosphate (P(i)). Under these conditions, the high-affinity PstSCAB(2) protein (i.e., with two PstB proteins) is the primary P(i) transporter. Expression from the pstSCAB-phoU operon is regulated by the PhoB/PhoR two-component regulatory system. PhoU is a negative regulator of the Pho regulon; however, the mechanism by which PhoU accomplishes this is currently unknown. Genetic studies of phoU have proven to be difficult because deletion of the phoU gene leads to a severe growth defect and creates strong selection for compensatory mutations resulting in confounding data. To overcome the instability of phoU deletions, we employed a promoter-swapping technique that places expression of the phoBR two-component system under control of the P(tac) promoter and the lacO(ID) regulatory module. This technique may be generally applicable for controlling expression of other chromosomal genes in E. coli. Here we utilized P(phoB)::P(tac) and P(pstS)::P(tac) strains to characterize phenotypes resulting from various DeltaphoU mutations. Our results indicate that PhoU controls the activity of the PstSCAB(2) transporter, as well as its abundance within the cell. In addition, we used the P(phoB)::P(tac) DeltaphoU strain as a platform to begin characterizing new phoU mutations in plasmids.
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19
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Patton-Vogt J. Transport and metabolism of glycerophosphodiesters produced through phospholipid deacylation. Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1771:337-42. [PMID: 16781190 DOI: 10.1016/j.bbalip.2006.04.013] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2006] [Revised: 04/20/2006] [Accepted: 04/26/2006] [Indexed: 10/25/2022]
Abstract
Phospholipid deacylation results in the formation of glycerophosphodiesters and free fatty acids. In Saccharomyces cerevisiae, four gene products with phospholipase B (deacylating) activity have been characterized (PLB1, PLB2, PLB3, NTE1), and those activities account for most, if not all, of the glycerophosphodiester production observed to date. The glycerophosphodiesters themselves are hydrolyzed into glycerol-3-phosphate and the corresponding alcohol by glycerophosphodiester phosphodiesterases. Although only one glycerophosphodiester phosphodiesterase-encoding gene (GDE1) has been characterized in S. cerevisiae, others certainly exist. Both internal and external glycerophosphodiesters (primarily glycerophosphocholine and glycerophosphoinositol) are formed as a result of phospholipid turnover in S. cerevisiae. A permease encoded by the GIT1 gene imports extracellular glycerophosphodiesters across the plasma membrane, where their hydrolytic products can provide crucial nutrients such as inositol, choline, and phosphate to the cell. The importance of this metabolic pathway in various aspects of S. cerevisiae cell physiology is being explored.
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Affiliation(s)
- Jana Patton-Vogt
- Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA.
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20
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Lemieux MJ, Huang Y, Wang DN. Glycerol-3-phosphate transporter of Escherichia coli: structure, function and regulation. Res Microbiol 2005; 155:623-9. [PMID: 15380549 DOI: 10.1016/j.resmic.2004.05.016] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2004] [Accepted: 05/14/2004] [Indexed: 11/22/2022]
Abstract
Glycerol-3-phosphate (G3P) plays a major role in glycolysis and phospholipid biosynthesis in the cell. Escherichia coli uses a secondary membrane transporter protein, GlpT, to uptake G3P into the cytoplasm. The crystal structure of the protein was recently determined to 3.3 A resolution. The protein consists of an N- and a C-terminal domain, each formed by a compact bundle of six transmembrane alpha-helices. The substrate-translocation pore is found at the domain interface and faces the cytoplasm. At the closed end of the pore is the substrate binding site, which is formed by two arginine residues. In combination with biochemical data, the crystal structure suggests a single binding site, alternating access mechanism for substrate translocation, namely, the substrate bound at the N- and C-terminal domain interface is transported across the membrane via a rocker-switch type of movement of the domains. Furthermore, GlpT may serve as a structural and mechanistic paradigm for other secondary active membrane transporters.
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Affiliation(s)
- M Joanne Lemieux
- Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
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21
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Sharfstein ST, van Dien SJ, Keasling JD. Modulation of the phosphate-starvation response in Escherichia coli by genetic manipulation of the polyphosphate pathways. Biotechnol Bioeng 2000; 51:434-8. [DOI: 10.1002/(sici)1097-0290(19960820)51:4<434::aid-bit6>3.0.co;2-j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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22
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Boos W. Binding protein-dependent ABC transport system for glycerol 3-phosphate of Escherichia coli. Methods Enzymol 1998; 292:40-51. [PMID: 9711545 DOI: 10.1016/s0076-6879(98)92006-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- W Boos
- Faculty of Biology, University of Konstanz, Germany
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23
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Patton-Vogt JL, Henry SA. GIT1, a gene encoding a novel transporter for glycerophosphoinositol in Saccharomyces cerevisiae. Genetics 1998; 149:1707-15. [PMID: 9691030 PMCID: PMC1460278 DOI: 10.1093/genetics/149.4.1707] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Phosphatidylinositol catabolism in Saccharomyces cerevisiae cells cultured in media containing inositol results in the release of glycerophosphoinositol (GroPIns) into the medium. As the extracellular concentration of inositol decreases with growth, the released GroPIns is transported back into the cell. Exploiting the ability of the inositol auxotroph, ino1, to use exogenous GroPIns as an inositol source, we have isolated mutants (Git-) defective in the uptake and metabolism of GroPIns. One mutant was found to be affected in the gene encoding the transcription factor, SPT7. Mutants of the positive regulatory gene INO2, but not of its partner, INO4, also have the Git- phenotype. Another mutant was complemented by a single open reading frame (ORF) termed GIT1 (glycerophosphoinositol). This ORF consists of 1556 bp predicted to encode a polypeptide of 518 amino acids and 57.3 kD. The predicted Git1p has similarity to a variety of S. cerevisiae transporters, including a phosphate transporter (Pho84p), and both inositol transporters (Itr1p and Itr2p). Furthermore, Git1p contains a sugar transport motif and 12 potential membrane-spanning domains. Transport assays performed on a git1 mutant together with the above evidence indicate that the GIT1 gene encodes a permease involved in the uptake of GroPIns.
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Affiliation(s)
- J L Patton-Vogt
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
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24
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Abstract
Bacterial ATP-binding cassette (ABC) transporters and their homologues in eukaryotic cells form one of the largest superfamilies known today. They function as primary pumps that couple substrate translocation across the cytoplasmic membrane to ATP hydrolysis. Although ABC transporters have been studied for more than three decades, the structure of these multi-component systems is unknown, and the mechanism of transport is not understood. This article reviews one of the most widely studied ABC systems, the maltose transporter of Escherichia coli. A first structural model of the transport channel allows discussion of possible mechanisms of transport. In addition, recent experimental evidence suggests that regulation of gene expression and transport activity is far more complex than expected.
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Affiliation(s)
- M Ehrmann
- Fakultät für Biologie, Universität Konstanz, Germany.
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25
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Song XM, Forsgren A, Janson H. Glycerol-3-phosphate transport in Haemophilus influenzae: cloning, sequencing, and transcription analysis of the glpT gene. Gene 1998; 215:381-8. [PMID: 9714837 DOI: 10.1016/s0378-1119(98)00259-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The presence of a functional glpT gene in Haemophilus influenzae could be questioned, since there is only what appears to be a truncated glpT (HI0686, 143 nt in the 5'-end) available in the H. influenzae Rd genome database (Fleischmann et al. , 1995). For cloning of the glpT gene from H. influenzae type b strain Eagan, an isogenic glpT, rec-1 double mutant and a selective medium for detection of the glpT mutant strains were constructed. The recombinant plasmid carrying glpT was able to complement the isogenic glpT mutant to wild-type levels of G3P uptake and permitted growth on a selective medium with G3P as a major carbon source. The nucleotide sequences of the glpT gene were determined both directly from PCR products and from the cloned DNA insert of strain Eagan. An identical 1440 bp open reading frame with 480 deduced amino acids, highly homologous to other bacterial G3P permeases, was identified. A Northern blot analysis showed that the glpT genes in both Eagan and Rd strains were transcribed on a RNA of approximately 1.4 kb in size. Thus, it is likely that HI0686 sequence originates from a mutated glpT clone in Escherichia coli.
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Affiliation(s)
- X M Song
- Department of Medical Microbiology, Lund University, Malmö University Hospital, S-205 02, Malmö, Sweden
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26
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Elashvili I, Defrank JJ, Culotta VC. phnE and glpT genes enhance utilization of organophosphates in Escherichia coli K-12. Appl Environ Microbiol 1998; 64:2601-8. [PMID: 9647836 PMCID: PMC106432 DOI: 10.1128/aem.64.7.2601-2608.1998] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Wild-type Escherichia coli K-12 strain JA221 grows poorly on low concentrations (< or = 1 mM) of diisopropyl fluorophosphate and its hydrolysis product, diisopropyl phosphate (DIPP), as sole phosphorus sources. Spontaneous organophosphate utilization (OPU) mutants were isolated that efficiently utilized these alternate sources of phosphate. A genomic library was constructed from one such OPU mutant, and two genes were isolated that conferred the OPU phenotype to strain JA221 upon transformation. These genes were identified as phnE and glpT. The original OPU mutation represented phnE gene activation and corresponded to the same 8-bp unit deletion from the cryptic wild-type E. coli K-12 phnE gene that has been shown previously to result in phnE activation. In comparison, sequence analysis revealed that the observed OPU phenotype conferred by the glpT gene was not the result of a mutation. PCR clones of glpT from both the mutant and the wild type were found to confer the OPU phenotype to JA221 when they were present on the high-copy-number pUC19 plasmid but not when they were present on the low-copy-number pWSK29 plasmid. This suggests that the OPU phenotype associated with the glpT gene is the result of amplification and overproduction of the glpT gene product. Both the active phnE and multicopy glpT genes facilitated effective metabolism of low concentrations of DIPP, whereas only the active phnE gene could confer the ability to break down a chromogenic substrate, 5-bromo-4-chloro-3-indoxyl phosphate-p-toluidine (X-Pi). This result indicates that in E. coli, X-Pi is transported exclusively by the Phn system, whereas DIPP (or its metabolite) may be transported by both Phn and Glp systems.
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Affiliation(s)
- I Elashvili
- Department of Environmental Health Sciences, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.
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27
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Boos W, Shuman H. Maltose/maltodextrin system of Escherichia coli: transport, metabolism, and regulation. Microbiol Mol Biol Rev 1998; 62:204-29. [PMID: 9529892 PMCID: PMC98911 DOI: 10.1128/mmbr.62.1.204-229.1998] [Citation(s) in RCA: 465] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The maltose system of Escherichia coli offers an unusually rich set of enzymes, transporters, and regulators as objects of study. This system is responsible for the uptake and metabolism of glucose polymers (maltodextrins), which must be a preferred class of nutrients for E. coli in both mammalian hosts and in the environment. Because the metabolism of glucose polymers must be coordinated with both the anabolic and catabolic uses of glucose and glycogen, an intricate set of regulatory mechanisms controls the expression of mal genes, the activity of the maltose transporter, and the activities of the maltose/maltodextrin catabolic enzymes. The ease of isolating many of the mal gene products has contributed greatly to the understanding of the structures and functions of several classes of proteins. Not only was the outer membrane maltoporin, LamB, or the phage lambda receptor, the first virus receptor to be isolated, but also its three-dimensional structure, together with extensive knowledge of functional sites for ligand binding as well as for phage lambda binding, has led to a relatively complete description of this sugar-specific aqueous channel. The periplasmic maltose binding protein (MBP) has been studied with respect to its role in both maltose transport and maltose taxis. Again, the combination of structural and functional information has led to a significant understanding of how this soluble receptor participates in signaling the presence of sugar to the chemosensory apparatus as well as how it participates in sugar transport. The maltose transporter belongs to the ATP binding cassette family, and although its structure is not yet known at atomic resolution, there is some insight into the structures of several functional sites, including those that are involved in interactions with MBP and recognition of substrates and ATP. A particularly astonishing discovery is the direct participation of the transporter in transcriptional control of the mal regulon. The MalT protein activates transcription at all mal promoters. A subset also requires the cyclic AMP receptor protein for transcription. The MalT protein requires maltotriose and ATP as ligands for binding to a dodecanucleotide MalT box that appears in multiple copies upstream of all mal promoters. Recent data indicate that the ATP binding cassette transporter subunit MalK can directly inhibit MalT when the transporter is inactive due to the absence of substrate. Despite this wealth of knowledge, there are still basic issues that require clarification concerning the mechanism of MalT-mediated activation, repression by the transporter, biosynthesis and assembly of the outer membrane and inner membrane transporter proteins, and interrelationships between the mal enzymes and those of glucose and glycogen metabolism.
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Affiliation(s)
- W Boos
- Department of Biology, University of Konstanz, Germany.
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28
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Van Dien SJ, Keyhani S, Yang C, Keasling JD. Manipulation of independent synthesis and degradation of polyphosphate in Escherichia coli for investigation of phosphate secretion from the cell. Appl Environ Microbiol 1997; 63:1689-95. [PMID: 9143103 PMCID: PMC168463 DOI: 10.1128/aem.63.5.1689-1695.1997] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The genes involved in polyphosphate metabolism in Escherichia coli were cloned behind different inducible promoters on separate plasmids. The gene coding for polyphosphate kinase (PPK), the enzyme responsible for polyphosphate synthesis, was placed behind the Ptac promoter. Polyphosphatase, a polyphosphate depolymerase, was similarly expressed by using the arabinose-inducible PBAD promoter. The ability of cells containing these constructs to produce active enzymes only when induced was confirmed by polyphosphate extraction, enzyme assays, and RNA analysis. The inducer concentrations giving optimal expression of each enzyme were determined. Experiments were performed in which ppk was induced early in growth, overproducing PPK and allowing large amounts of polyphosphate to accumulate (80 mumol in phosphate monomer units per g of dry cell weight). The ppx gene was subsequently induced, and polyphosphate was degraded to inorganic phosphate. Approximately half of this polyphosphate was depleted in 210 min. The phosphate released from polyphosphate allowed the growth of phosphate-starved cells and was secreted into the medium, leading to a down-regulation of the phosphate-starvation response. In addition, the steady-state polyphosphate level was precisely controlled by manipulating the degree of ppx induction. The polyphosphate content varied from 98 to 12 mumol in phosphate monomer units per g of dry cell weight as the arabinose concentration was increased from 0 to 0.02% by weight.
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Affiliation(s)
- S J Van Dien
- Department of Chemical Engineering, University of California, Berkeley 94720-1462, USA
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