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Xu L, Dong Z, Chiniquy D, Pierroz G, Deng S, Gao C, Diamond S, Simmons T, Wipf HML, Caddell D, Varoquaux N, Madera MA, Hutmacher R, Deutschbauer A, Dahlberg JA, Guerinot ML, Purdom E, Banfield JF, Taylor JW, Lemaux PG, Coleman-Derr D. Genome-resolved metagenomics reveals role of iron metabolism in drought-induced rhizosphere microbiome dynamics. Nat Commun 2021; 12:3209. [PMID: 34050180 PMCID: PMC8163885 DOI: 10.1038/s41467-021-23553-7] [Citation(s) in RCA: 56] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 04/27/2021] [Indexed: 02/04/2023] Open
Abstract
Recent studies have demonstrated that drought leads to dramatic, highly conserved shifts in the root microbiome. At present, the molecular mechanisms underlying these responses remain largely uncharacterized. Here we employ genome-resolved metagenomics and comparative genomics to demonstrate that carbohydrate and secondary metabolite transport functionalities are overrepresented within drought-enriched taxa. These data also reveal that bacterial iron transport and metabolism functionality is highly correlated with drought enrichment. Using time-series root RNA-Seq data, we demonstrate that iron homeostasis within the root is impacted by drought stress, and that loss of a plant phytosiderophore iron transporter impacts microbial community composition, leading to significant increases in the drought-enriched lineage, Actinobacteria. Finally, we show that exogenous application of iron disrupts the drought-induced enrichment of Actinobacteria, as well as their improvement in host phenotype during drought stress. Collectively, our findings implicate iron metabolism in the root microbiome's response to drought and may inform efforts to improve plant drought tolerance to increase food security.
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Affiliation(s)
- Ling Xu
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA ,grid.22935.3f0000 0004 0530 8290State Key Laboratory of Plant Physiology and Biochemistry, Department of Microbiology and Immunology, College of Biological Sciences, China Agricultural University, Beijing, China
| | - Zhaobin Dong
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Dawn Chiniquy
- grid.184769.50000 0001 2231 4551Department of Energy, Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA USA
| | - Grady Pierroz
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Siwen Deng
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Cheng Gao
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Spencer Diamond
- grid.47840.3f0000 0001 2181 7878Department of Earth and Planetary Science, University of California, Berkeley, CA USA
| | - Tuesday Simmons
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Heidi M.-L. Wipf
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Daniel Caddell
- grid.507310.0Plant Gene Expression Center, USDA-ARS, Albany, CA USA
| | - Nelle Varoquaux
- grid.463716.10000 0004 4687 1979CNRS, University Grenoble Alpes, TIMC-IMAG, Grenoble, France
| | - Mary A. Madera
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Robert Hutmacher
- grid.27860.3b0000 0004 1936 9684Westside Research & Extension Center, UC Department of Plant Sciences, University of California, Davis, CA USA
| | - Adam Deutschbauer
- grid.184769.50000 0001 2231 4551Department of Energy, Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA USA
| | | | - Mary Lou Guerinot
- grid.254880.30000 0001 2179 2404Department of Biological Scienes, Dartmouth College, Hanover, NH USA
| | - Elizabeth Purdom
- grid.47840.3f0000 0001 2181 7878Department of Statistics, University of California, Berkeley, CA USA
| | - Jillian F. Banfield
- grid.47840.3f0000 0001 2181 7878Department of Earth and Planetary Science, University of California, Berkeley, CA USA
| | - John W. Taylor
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Peggy G. Lemaux
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA
| | - Devin Coleman-Derr
- grid.47840.3f0000 0001 2181 7878Department of Plant and Microbial Biology, University of California, Berkeley, CA USA ,grid.507310.0Plant Gene Expression Center, USDA-ARS, Albany, CA USA
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Metabolic Interactions between Brachypodium and Pseudomonas fluorescens under Controlled Iron-Limited Conditions. mSystems 2021; 6:6/1/e00580-20. [PMID: 33402348 PMCID: PMC7786132 DOI: 10.1128/msystems.00580-20] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Rhizosphere bacteria influence the growth of their host plant by consuming and producing metabolites, nutrients, and antibiotic compounds within the root system that affect plant metabolism. Under Fe-limited growth conditions, different plant and microbial species have distinct Fe acquisition strategies, often involving the secretion of strong Fe-binding chelators that scavenge Fe and facilitate uptake. Iron (Fe) availability has well-known effects on plant and microbial metabolism, but its effects on interspecies interactions are poorly understood. The purpose of this study was to investigate metabolite exchange between the grass Brachypodium distachyon strain Bd21 and the soil bacterium Pseudomonas fluorescens SBW25::gfp/lux (SBW25) during Fe limitation under axenic conditions. We compared the transcriptional profiles and root exudate metabolites of B. distachyon plants grown semihydroponically with and without SBW25 inoculation and Fe amendment. Liquid chromatography-mass spectrometry analysis of the hydroponic solution revealed an increase in the abundance of the phytosiderophores mugineic acid and deoxymugineic acid under Fe-limited conditions compared to Fe-replete conditions, indicating greater secretion by roots presumably to facilitate Fe uptake. In SBW25-inoculated roots, expression of genes encoding phytosiderophore biosynthesis and uptake proteins increased compared to that in sterile roots, but external phytosiderophore abundances decreased. P. fluorescens siderophores were not detected in treatments without Fe. Rather, expression of SBW25 genes encoding a porin, a transporter, and a monooxygenase was significantly upregulated in response to Fe deprivation. Collectively, these results suggest that SBW25 consumed root-exuded phytosiderophores in response to Fe deficiency, and we propose target genes that may be involved. SBW25 also altered the expression of root genes encoding defense-related enzymes and regulators, including thionin and cyanogenic glycoside production, chitinase, and peroxidase activity, and transcription factors. Our findings provide insights into the molecular bases for the stress response and metabolite exchange of interacting plants and bacteria under Fe-deficient conditions. IMPORTANCE Rhizosphere bacteria influence the growth of their host plant by consuming and producing metabolites, nutrients, and antibiotic compounds within the root system that affect plant metabolism. Under Fe-limited growth conditions, different plant and microbial species have distinct Fe acquisition strategies, often involving the secretion of strong Fe-binding chelators that scavenge Fe and facilitate uptake. Here, we studied interactions between P. fluorescens SBW25, a plant-colonizing bacterium that produces siderophores with antifungal properties, and B. distachyon, a genetic model for cereal grain and biofuel grasses. Under controlled growth conditions, bacterial siderophore production was inhibited in the root system of Fe-deficient plants, bacterial inoculation altered transcription of genes involved in defense and stress response in the roots of B. distachyon, and SBW25 degraded phytosiderophores secreted by the host plant. These findings provide mechanistic insight into interactions that may play a role in rhizosphere dynamics and plant health in soils with low Fe solubility.
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Sinegani AAS, Tahmasbian I, Sinegani MS. Chelating Agents and Heavy Metal Phytoextraction. SOIL BIOLOGY 2015. [DOI: 10.1007/978-3-319-14526-6_20] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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López-Berges MS, Turrà D, Capilla J, Schafferer L, Matthijs S, Jöchl C, Cornelis P, Guarro J, Haas H, Di Pietro A. Iron competition in fungus-plant interactions: the battle takes place in the rhizosphere. PLANT SIGNALING & BEHAVIOR 2013; 8:e23012. [PMID: 23299422 PMCID: PMC3656999 DOI: 10.4161/psb.23012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 11/27/2012] [Accepted: 11/27/2012] [Indexed: 05/19/2023]
Abstract
Soilborne fungal pathogens are highly persistent and provoke important crop losses. During saprophytic and infectious stages in the soil, these organisms face situations of nutrient limitation and lack of essential elements, such as iron. We investigated the role of the bZIP transcription factor HapX as a central regulator of iron homeostasis and virulence in the vascular wilt fungus Fusarium oxysporum. This root-infecting plant pathogen attacks more than hundred different crops and is an emerging human opportunistic invader. Although iron uptake remains unaffected in a strain lacking HapX, de-repression of genes implicated in iron-consuming processes such as respiration, amino acid metabolism, TCA cycle and heme biosynthesis lead to severely impaired growth under iron-limiting conditions. HapX is required for full virulence of F. oxysporum in tomato plants and essential for infection in immunodepressed mice. Virulence attenuation of the ΔhapX strain on tomato plants is more pronounced by co-inoculation of roots with the biocontrol strain Pseudomonas putida KT2440, but not with a mutant deficient in siderophores production. These results demonstrate that HapX is required for iron competition of F. oxysporum in the tomato rhizosphere and establish a conserved role for HapX-mediated iron homeostasis in fungal infection of plants and mammals.
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Affiliation(s)
- Manuel S. López-Berges
- Departamento de Genética; Universidad de Córdoba; Córdoba, Spain
- Campus de Excelencia Internacional Agroalimentario (ceiA3); Córdoba, Spain
| | - David Turrà
- Departamento de Genética; Universidad de Córdoba; Córdoba, Spain
- Campus de Excelencia Internacional Agroalimentario (ceiA3); Córdoba, Spain
| | - Javier Capilla
- Unitat de Microbiologia; Facultat de Medicina i Ciències de la Salut; Institut d’Investigació Sanitària Pere Virgili; Universitat Rovira i Virgili; Reus, Spain
| | - Lukas Schafferer
- Division of Molecular Biology/Biocenter; Innsbruck Medical University; Innsbruck, Austria
| | - Sandra Matthijs
- Institut de Recherches Microbiologiques Jean-Marie Wiame; Brussels, Belgium
| | - Christoph Jöchl
- Division of Molecular Biology/Biocenter; Innsbruck Medical University; Innsbruck, Austria
| | - Pierre Cornelis
- Department of Bioengineering Sciences; Research Group Microbiology and Flanders Institute for Biotechnology; Department of Structural Biology; Vrije Universiteit Brussel; Brussels, Belgium
| | - Josep Guarro
- Unitat de Microbiologia; Facultat de Medicina i Ciències de la Salut; Institut d’Investigació Sanitària Pere Virgili; Universitat Rovira i Virgili; Reus, Spain
| | - Hubertus Haas
- Division of Molecular Biology/Biocenter; Innsbruck Medical University; Innsbruck, Austria
| | - Antonio Di Pietro
- Departamento de Genética; Universidad de Córdoba; Córdoba, Spain
- Unitat de Microbiologia; Facultat de Medicina i Ciències de la Salut; Institut d’Investigació Sanitària Pere Virgili; Universitat Rovira i Virgili; Reus, Spain
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López-Berges MS, Capilla J, Turrà D, Schafferer L, Matthijs S, Jöchl C, Cornelis P, Guarro J, Haas H, Di Pietro A. HapX-mediated iron homeostasis is essential for rhizosphere competence and virulence of the soilborne pathogen Fusarium oxysporum. THE PLANT CELL 2012; 24:3805-22. [PMID: 22968717 PMCID: PMC3480304 DOI: 10.1105/tpc.112.098624] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Soilborne fungal pathogens cause devastating yield losses and are highly persistent and difficult to control. During the infection process, these organisms must cope with limited availability of iron. Here we show that the bZIP protein HapX functions as a key regulator of iron homeostasis and virulence in the vascular wilt fungus Fusarium oxysporum. Deletion of hapX does not affect iron uptake but causes derepression of genes involved in iron-consuming pathways, leading to impaired growth under iron-depleted conditions. F. oxysporum strains lacking HapX are reduced in their capacity to invade and kill tomato (Solanum lycopersicum) plants and immunodepressed mice. The virulence defect of ΔhapX on tomato plants is exacerbated by coinoculation of roots with a biocontrol strain of Pseudomonas putida, but not with a siderophore-deficient mutant, indicating that HapX contributes to iron competition of F. oxysporum in the tomato rhizosphere. These results establish a conserved role for HapX-mediated iron homeostasis in fungal infection of plants and mammals.
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Affiliation(s)
- Manuel S. López-Berges
- Departamento de Genética, Universidad de Córdoba, 14071 Córdoba, Spain
- Campus de Excelencia Internacional Agroalimentario ceiA3, 14071 Córdoba, Spain
| | - Javier Capilla
- Unitat de Microbiologia, Facultat de Medicina i Ciències de la Salut, Institut d'Investigació Sanitària Pere Virgili, Universitat Rovira i Virgili, 43201 Reus, Spain
| | - David Turrà
- Departamento de Genética, Universidad de Córdoba, 14071 Córdoba, Spain
- Campus de Excelencia Internacional Agroalimentario ceiA3, 14071 Córdoba, Spain
| | - Lukas Schafferer
- Division of Molecular Biology/Biocenter, Innsbruck Medical University, 6020 Innsbruck, Austria
| | - Sandra Matthijs
- Institut de Recherches Microbiologiques Jean-Marie Wiame, 1070 Brussels, Belgium
| | - Christoph Jöchl
- Division of Molecular Biology/Biocenter, Innsbruck Medical University, 6020 Innsbruck, Austria
| | - Pierre Cornelis
- Department of Bioengineering Sciences, Research Group Microbiology, and Flanders Institute for Biotechnology, Department of Structural Biology, Vrije Universiteit Brussel, 1050 Brussels, Belgium
| | - Josep Guarro
- Unitat de Microbiologia, Facultat de Medicina i Ciències de la Salut, Institut d'Investigació Sanitària Pere Virgili, Universitat Rovira i Virgili, 43201 Reus, Spain
| | - Hubertus Haas
- Division of Molecular Biology/Biocenter, Innsbruck Medical University, 6020 Innsbruck, Austria
| | - Antonio Di Pietro
- Departamento de Genética, Universidad de Córdoba, 14071 Córdoba, Spain
- Campus de Excelencia Internacional Agroalimentario ceiA3, 14071 Córdoba, Spain
- Address correspondence to
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Lemanceau P, Robin A, Mazurier S, Vansuyt G. Implication of Pyoverdines in the Interactions of Fluorescent Pseudomonads with Soil Microflora and Plant in the Rhizosphere. SOIL BIOLOGY 2007. [DOI: 10.1007/978-3-540-71160-5_8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Brandl MT. Fitness of human enteric pathogens on plants and implications for food safety. ANNUAL REVIEW OF PHYTOPATHOLOGY 2006; 44:367-92. [PMID: 16704355 DOI: 10.1146/annurev.phyto.44.070505.143359] [Citation(s) in RCA: 342] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The continuous rise in the number of outbreaks of foodborne illness linked to fresh fruit and vegetables challenges the notion that enteric pathogens are defined mostly by their ability to colonize the intestinal habitat. This review describes the epidemiology of produce-associated outbreaks of foodborne disease and presents recently acquired knowledge about the behavior of enteric pathogens on plants, with an emphasis on Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes. The growth and survival of enteric pathogens on plants are discussed in the light of knowledge and concepts in plant microbial ecology, including epiphytic fitness, the physicochemical nature of plant surfaces, biofilm formation, and microbe-microbe and plant-microbe interactions. Information regarding the various stresses that affect the survival of enteric pathogens and the molecular events that underlie their interactions in the plant environment provides a good foundation for assessing their role in the infectious dose of the pathogens when contaminated fresh produce is the vehicle of illness.
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Affiliation(s)
- Maria T Brandl
- Produce Safety and Microbiology Research Unit, Agricultural Research Services, U.S. Department of Agriculture, Albany, California 94710, USA.
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Loper JE, Henkels MD. Utilization of heterologous siderophores enhances levels of iron available to Pseudomonas putida in the rhizosphere. Appl Environ Microbiol 1999; 65:5357-63. [PMID: 10583989 PMCID: PMC91729 DOI: 10.1128/aem.65.12.5357-5363.1999] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas spp. have the capacity to utilize siderophores produced by diverse species of bacteria and fungi, and the present study was initiated to determine if siderophores produced by rhizosphere microorganisms enhance the levels of iron available to a strain of Pseudomonas putida in this natural habitat. We used a previously described transcriptional fusion (pvd-inaZ) between an iron-regulated promoter (pvd) and the ice nucleation reporter gene (inaZ) to detect alterations in iron availability to P. putida. Ice nucleation activity (INA) expressed from the pvd-inaZ fusion by P. putida N1R or N1R Pvd(-), a derivative deficient in the production of a pyoverdine siderophore, was inversely related to the concentration of ferric citrate in a culture medium. In culture, INA expressed by N1R Pvd(-) (pvd-inaZ) was reduced in the presence of the ferric complex of pseudobactin-358, a pyoverdine siderophore produced by P. putida WCS358 that can be utilized as a source of iron by N1R Pvd(-). In the rhizosphere of cucumbers grown in sterilized soil, N1R Pvd(-) (pvd-inaZ) expressed INA, indicating that iron availability was sufficiently low in that habitat to allow transcription of the iron-regulated pvd promoter. Coinoculation with WCS358 or N1R significantly decreased INA expressed by N1R Pvd(-) (pvd-inaZ) in the rhizosphere, whereas coinoculation with a pyoverdine-deficient mutant of WCS358 did not reduce INA expressed by N1R Pvd(-) (pvd-inaZ). These results indicate that iron availability to N1R Pvd(-) (pvd-inaZ) in the rhizosphere was enhanced by the presence of another strain of P. putida that produces a pyoverdine that N1R Pvd(-) (pvd-inaZ) was able to utilize as a source of iron. In culture, strain N1R Pvd(-) also utilized ferric complexes of the siderophores enterobactin and aerobactin as sources of iron. In the rhizosphere of cucumbers grown in sterilized soil, INA expressed by N1R Pvd(-) (pvd-inaZ) was reduced in the presence of strains of Enterobacter cloacae that produced enterobactin, aerobactin, or both siderophores, but INA expressed by N1R Pvd(-) (pvd-inaZ) was not altered in the presence of a mutant of E. cloacae deficient in both enterobactin and aerobactin production. Therefore, the iron status of P. putida was altered by siderophores produced by an unrelated bacterium coinhabiting the rhizosphere. Finally, we demonstrated that INA expressed by N1R containing pvd-inaZ in the rhizosphere differed between plants grown in sterilized versus nonsterilized field soil. The results of this study demonstrate that (i) P. putida expresses genes for pyoverdine production and uptake in the rhizosphere, but the level of gene expression is influenced by other bacteria that coexist with P. putida in this habitat, and (ii) diverse groups of microorganisms can alter the availability of chemical resources in microbial habitats on root surfaces.
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Affiliation(s)
- J E Loper
- Agricultural Research Service, U.S. Department of Agriculture, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97330, USA.
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Fan TW, Lane AN, Pedler J, Crowley D, Higashi RM. Comprehensive analysis of organic ligands in whole root exudates using nuclear magnetic resonance and gas chromatography-mass spectrometry. Anal Biochem 1997; 251:57-68. [PMID: 9300083 DOI: 10.1006/abio.1997.2235] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Root exudates in the rhizosphere are vital to the normal life cycle of plants. A key factor is phytometallophores, which function in the nutritional acquisition of iron and zinc and are likely to be important in the uptake of pollutant metals by plants. Unraveling the biochemistry of these compounds is tedious using traditional analyses, which also fall short in providing the overall chemical composition or in detecting unknown or unexpected organic ligands in the exudates. Here, we demonstrate a comprehensive analysis of the exudate composition directly by 1H and 13C multidimensional NMR and silylation GC-MS. The advantages are (a) minimal sample preparation, with no loss of unknown compounds, and reduced net analysis time; (b) structure-based analysis for universal detection and identification; and (c) simultaneous analysis of a large number of constituents in a complex mixture. Using barley root exudates, a large number of common organic and amino acids were identified. Three derivatives of mugineic acid phytosiderophores were also determined, the major one being 3-epihydroxymugineic acid, for which complete 1H and 13C NMR assignments were obtained. Quantification of all major components using these methods revealed a sevenfold increase in total exudation under moderate iron deficiency, with 3-epihydroxymugineic acid comprising approximately 22% of the exudate mixture. As iron deficiency increased, total quantities of exudate per gram of root remained unchanged, but the relative quantity of carbon allocated to phytosiderophore increased to approximately 50% of the total exudate in response to severe iron deficiency.
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Affiliation(s)
- T W Fan
- Department of Land, Air, and Water Resources, University of California, Davis 95616, USA
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Marschner P, Crowley DE. Iron Stress and Pyoverdin Production by a Fluorescent Pseudomonad in the Rhizosphere of White Lupine (Lupinus albus L.) and Barley (Hordeum vulgare L.). Appl Environ Microbiol 1997; 63:277-81. [PMID: 16535491 PMCID: PMC1389105 DOI: 10.1128/aem.63.1.277-281.1997] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Induction of high-affinity iron transport during root colonization by Pseudomonas fluorescens Pf-5 (pvd-inaZ) was examined in lupine and barley growing in microcosms. P. fluorescens Pf-5 (pvd-inaZ) contains a plasmid carrying pvd-inaZ; thus, in this strain, ice nucleation activity is regulated by pyoverdin production. Lupine or barley plants were grown for 18 or 8 days, respectively, in soil amended with 2% calcium carbonate and inoculated with P. fluorescens Pf-5 (pvd-inaZ) at a density of 4 x 10(sup8) CFU g (dry weight) of soil(sup-1). A filter paper blotting technique was used to sample cells from the rhizosphere in different root zones, and then the cells were resuspended for enumeration and measurement of ice nucleation activity. The population density of P. fluorescens Pf-5 (pvd-inaZ) in the rhizosphere decreased by one order of magnitude in both lupine and barley over time. The ice nucleation activity ranged from -3.4 to -3.0 log ice nuclei CFU(sup-1) for lupine and -3.0 to -2.8 log ice nuclei CFU(sup-1) for barley, was similar in all root zones, and did not change over time. An in vitro experiment was conducted to determine the relationship between ice nucleation activity and pyoverdin production in P. fluorescens Pf-5 (pvd-inaZ). An ice nucleation activity of approximately -3.0 log ice nuclei CFU(sup-1) was measured in the in vitro experiment at 25 to 50 (mu)M FeCl(inf3). By using the regression between ice nucleation activity and pyoverdin production determined in vitro and assuming a P. fluorescens Pf-5 (pvd-inaZ) population density of 10(sup8) CFU g of root(sup-1), the maximum possible pyoverdin accumulation by P. fluorescens Pf-5 (pvd-inaZ) in the rhizosphere was estimated to be 0.5 and 0.8 nmol g of root(sup-1) for lupine and barley, respectively. The low ice nucleation activity measured in the rhizosphere suggests that nutritional competition for iron in the rhizosphere may not be a major factor influencing root colonization by P. fluorescens Pf-5 (pvd-inaZ).
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Loper JE, Henkels MD. Availability of iron to Pseudomonas fluorescens in rhizosphere and bulk soil evaluated with an ice nucleation reporter gene. Appl Environ Microbiol 1997; 63:99-105. [PMID: 8979343 PMCID: PMC168306 DOI: 10.1128/aem.63.1.99-105.1997] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The biological availability of iron in the rhizosphere was assessed by evaluating ice nucleation activity (INA) expressed in situ by Pseudomonas fluorescens Pf-5 containing a transcriptional fusion (pvd-inaZ) of an iron-regulated promoter to an ice nucleation reporter gene (inaZ). Pf-5 containing pvd-inaZ expresses INA that is inversely related to the iron availability of a growth medium (J. E. Loper and S. E. Lindow, Appl. Environ. Microbiol. 60:1934-1941, 1994). INA expressed by rhizosphere populations of Pf-5 containing pvd-inaZ was at a maximum within 12 to 24 h following inoculation of the bacterium onto bean roots and typically decreased gradually during the following 4 days. Iron availability in the soil, which was altered by the addition of chelators, influenced INA expressed by rhizosphere populations of Pf-5 containing pvd-inaZ. In soil adjusted to a pH of 7.0 or 8.0 by adding Ca(OH)2, rhizosphere populations of Pf-5 containing pvd-inaZ expressed greater INA, indicating lower iron availability, than they did in the nonamended soil at a pH of 5.4. Similarly, rhizosphere populations of Pf-5 containing pvd-inaZ expressed less INA in an agricultural soil of pH 5.4 than in other agricultural soils ranging in pH from 6.4 to 7.7. These results conform to the predictions of chemical models stating that pH is a major factor influencing iron availability in soil solutions. The results of this study indicate that P. fluorescens Pf-5 encountered an iron-limited environment immediately after it was inoculated onto bean roots planted in agricultural field soils. One to two days after the bacterium was inoculated onto root surfaces, however, iron became more available to rhizosphere populations of Pf-5. We speculate that iron acquisition systems of plants and other rhizosphere organisms may provide available sources of iron to established rhizosphere populations of P. fluorescens.
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Affiliation(s)
- J E Loper
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture, Corvallis, Oregon 97330, USA.
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Caris C, Baret P, Beguin C, Serratrice G, Pierre JL, Laulhère JP. Metabolization of iron by plant cells using O-Trensox, a high-affinity abiotic iron-chelating agent. Biochem J 1995; 312 ( Pt 3):879-85. [PMID: 8554534 PMCID: PMC1136196 DOI: 10.1042/bj3120879] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A synthetic siderophore, O-Trensox (L), has been designed and synthesized to improve iron nutrition of plants. The affinity for iron of this ligand [pFe(III) = 29.5 and pFe(II) = 17.9] is very high compared with EDTA. In spite of its high and specific affinity for iron, O-Trensox was found to be able to prevent, and to reverse, iron chlorosis in several plant species grown in axenic conditions. It also allows the iron nutrition and growth of Acer pseudoplatanus L. cell suspensions. The rate of iron metabolization was monitored by 59Fe radioiron. Ferritins, the iron storage proteins, are shown to be the first iron-labelled proteins during iron metabolization and to be able to further dispatch the metal. Using Fe(III)-Trensox, the rate of iron incorporation into ferritin was found to be higher than when using Fe-EDTA, but slower than with Fe-citrate, the natural iron carrier in xylem. During a plant cell culture, the extracellular concentrations of iron complex and free ligand were measured; changes in their relative amounts showed that the iron complex is dissociated extracellularly and that only iron is internalized. This suggests a high affinity for iron of a putative carrier on the plasmalemma. In contrast with Fe-citrate and Fe-EDTA complexes, Fe(III)-Trensox is not photoreducible. Its ability to induce radical damage as a Fenton reagent was tested using supercoiled DNA as target molecule. Unlike Fe-citrate and Fe-EDTA, Fe(II)-Trensox and Fe(III)-Trensox were proven to be harmless even during ascorbate-driven reduction, while Fe-EDTA and Fe-citrate generate heavy damage to DNA.
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Affiliation(s)
- C Caris
- Laboratoire d'Etudes Dynamiques et Structurales de la Sélectivité, Université J. Fourier, URA CNRS 0332, Grenoble, France
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