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Zgadzaj R, James EK, Kelly S, Kawaharada Y, de Jonge N, Jensen DB, Madsen LH, Radutoiu S. A legume genetic framework controls infection of nodules by symbiotic and endophytic bacteria. PLoS Genet 2015; 11:e1005280. [PMID: 26042417 PMCID: PMC4456278 DOI: 10.1371/journal.pgen.1005280] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 05/14/2015] [Indexed: 11/18/2022] Open
Abstract
Legumes have an intrinsic capacity to accommodate both symbiotic and endophytic bacteria within root nodules. For the symbionts, a complex genetic mechanism that allows mutual recognition and plant infection has emerged from genetic studies under axenic conditions. In contrast, little is known about the mechanisms controlling the endophytic infection. Here we investigate the contribution of both the host and the symbiotic microbe to endophyte infection and development of mixed colonised nodules in Lotus japonicus. We found that infection threads initiated by Mesorhizobium loti, the natural symbiont of Lotus, can selectively guide endophytic bacteria towards nodule primordia, where competent strains multiply and colonise the nodule together with the nitrogen-fixing symbiotic partner. Further co-inoculation studies with the competent coloniser, Rhizobium mesosinicum strain KAW12, show that endophytic nodule infection depends on functional and efficient M. loti-driven Nod factor signalling. KAW12 exopolysaccharide (EPS) enabled endophyte nodule infection whilst compatible M. loti EPS restricted it. Analysis of plant mutants that control different stages of the symbiotic infection showed that both symbiont and endophyte accommodation within nodules is under host genetic control. This demonstrates that when legume plants are exposed to complex communities they selectively regulate access and accommodation of bacteria occupying this specialized environmental niche, the root nodule. Plants have evolved elaborated mechanisms to monitor microbial presence and to control their infection, therefore only particular microbes, so called “endophytes,” are able to colonise the internal tissues with minimal or no host damage. The legume root nodule is a unique environmental niche induced by symbiotic bacteria, but where multiple species, symbiotic and endophytic co-exist. Genetic studies of the binary interaction legume-symbiont led to the discovery of key components evolved in the two partners allowing mutual recognition and nodule infection. In contrast, there is limited knowledge about the endophytic nodule infection, the role of the legume host, or the symbiont in the process of nodule colonisation by endophytes. Here we focus on the early stages of nodule infection in order to identify which molecular signatures and genetic components favour/allow endophyte accommodation, and multiple species co-existence inside nodules. We found that colonisation of Lotus japonicus nodules by endophytic bacteria is a selective process, that endophyte nodule occupancy is host-controlled, and that exopolysaccharides are key bacterial features for chronic infection of nodules. Our strategy based on model legume genetics and co-inoculation can thus be used for identifying mechanisms operating behind host-microbes compatibility in environments where multiple species co-exist.
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Affiliation(s)
- Rafal Zgadzaj
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Euan K. James
- Ecological Sciences, The James Hutton Institute, Invergowrie, Dundee, United Kingdom
| | - Simon Kelly
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Yasuyuki Kawaharada
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Nadieh de Jonge
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Dorthe B. Jensen
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Lene H. Madsen
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
| | - Simona Radutoiu
- Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, Aarhus, Denmark
- Carbohydrate Recognition and Signalling (CARB) Centre, Aarhus, Denmark
- * E-mail:
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PssP2 is a polysaccharide co-polymerase involved in exopolysaccharide chain-length determination in Rhizobium leguminosarum. PLoS One 2014; 9:e109106. [PMID: 25268738 PMCID: PMC4182512 DOI: 10.1371/journal.pone.0109106] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 09/02/2014] [Indexed: 12/16/2022] Open
Abstract
Production of extracellular polysaccharides is a complex process engaging proteins localized in different subcellular compartments, yet communicating with each other or even directly interacting in multicomponent complexes. Proteins involved in polymerization and transport of exopolysaccharide (EPS) in Rhizobium leguminosarum are encoded within the chromosomal Pss-I cluster. However, genes implicated in polysaccharide synthesis are common in rhizobia, with several homologues of pss genes identified in other regions of the R. leguminosarum genome. One such region is chromosomally located Pss-II encoding proteins homologous to known components of the Wzx/Wzy-dependent polysaccharide synthesis and transport systems. The pssP2 gene encodes a protein similar to polysaccharide co-polymerases involved in determination of the length of polysaccharide chains in capsule and O-antigen biosynthesis. In this work, a mutant with a disrupted pssP2 gene was constructed and its capabilities to produce EPS and enter into a symbiotic relationship with clover were studied. The pssP2 mutant, while not altered in lipopolysaccharide (LPS), displayed changes in molecular mass distribution profile of EPS. Lack of the full-length PssP2 protein resulted in a reduction of high molecular weight EPS, yet polymerized to a longer length than in the RtTA1 wild type. The mutant strain was also more efficient in symbiotic performance. The functional interrelation between PssP2 and proteins encoded within the Pss-I region was further supported by data from bacterial two-hybrid assays providing evidence for PssP2 interactions with PssT polymerase, as well as glycosyltransferase PssC. A possible role for PssP2 in a complex involved in EPS chain-length determination is discussed.
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Yuan B, Cheng A, Wang M. Polysaccharide export outer membrane proteins in Gram-negative bacteria. Future Microbiol 2013; 8:525-35. [DOI: 10.2217/fmb.13.13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Polysaccharide export outer membrane proteins of Gram-negative bacteria are involved in the export of polysaccharides across the outer membrane. The mechanisms of polysaccharide export across the outer membrane in Gram-negative bacteria are not yet completely clear. However, the mechanisms of polysaccharide assembly in Escherichia coli have been intensively investigated. Here, we mainly review the current understanding of the assembly mechanisms of group 1 capsular polysaccharide, group 2 capsular polysaccharide and lipopolysaccharide of E. coli, and the current structures and interactions of some polysaccharide export outer membrane proteins with other proteins involved in polysaccharide export in Gram-negative bacteria. In addition, LptD may be targeted by peptidomimetic antibiotics in Gram-negative bacteria. We also give insights into the directions of future research regarding the mechanisms of polysaccharide export.
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Affiliation(s)
- Biao Yuan
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China.
| | - Anchun Cheng
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China
- Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, 46 Xinkang Road, Ya’an, Sichuan 625014, China
- Key Laboratory of Animal Disease & Human Health of Sichuan Province, Sichuan Agricultural University, Wenjiang, Chengdu city, Sichuan 611130, China
| | - Mingshu Wang
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China
- Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, 46 Xinkang Road, Ya’an, Sichuan 625014, China
- Key Laboratory of Animal Disease & Human Health of Sichuan Province, Sichuan Agricultural University, Wenjiang, Chengdu city, Sichuan 611130, China
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Influence of the sigmaB stress factor and yxaB, the gene for a putative exopolysaccharide synthase under sigmaB Control, on biofilm formation. J Bacteriol 2008; 190:3546-56. [PMID: 18326573 DOI: 10.1128/jb.01665-07] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacillus subtilis forms structured communities of biofilms encased in an exopolysaccharide matrix on solid surfaces and at the air-liquid interface. It is postulated that nonoptimal growth conditions induce this multicellular behavior. We showed that under laboratory conditions a strain deleted for sigB was unable to form a floating pellicle on the surface of a liquid medium. However, overexpression of yxaB, encoding a putative exopolysaccharide synthase, from a p(Spac) promoter in a sigB-deleted strain resulted in partial recovery of the wild-type phenotype, indicating the participation of the YxaB protein in this multicellular process. We present data concerning the regulation of transcription of genes yxaB and yxaA, encoding a putative glycerate kinase. Both genes are cotranscribed as a single transcription unit from a sigma(A)-dependent promoter during vegetative growth of a liquid bacterial culture. The promoter driving transcription of the yxaAB operon is regulated by AbrB. In addition, the second gene in the operon, yxaB, possesses its own promoter, which is recognized by RNA polymerase containing the sigma(B) subunit. This transcription start site is used under general stress conditions, resulting in increased expression.
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Marczak M, Mazur A, Król JE, Gruszecki WI, Skorupska A. Lipoprotein PssN of Rhizobium leguminosarum bv. trifolii: subcellular localization and possible involvement in exopolysaccharide export. J Bacteriol 2006; 188:6943-52. [PMID: 16980497 PMCID: PMC1595502 DOI: 10.1128/jb.00651-06] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Surface expression of exopolysaccharides (EPS) in gram-negative bacteria depends on the activity of proteins found in the cytoplasmic membrane, the periplasmic space, and the outer membrane. pssTNOP genes identified in Rhizobium leguminosarum bv. trifolii strain TA1 encode proteins that might be components of the EPS polymerization and secretion system. In this study, we have characterized PssN protein. Employing pssN-phoA and pssN-lacZ gene fusions and in vivo acylation with [3H]palmitate, we demonstrated that PssN is a 43-kDa lipoprotein directed to the periplasm by an N-terminal signal sequence. Membrane detergent fractionation followed by sucrose gradient centrifugation showed that PssN is an outer membrane-associated protein. Indirect immunofluorescence with anti-PssN and fluorescein isothiocyanate-conjugated antibodies and protease digestion of spheroplasts and intact cells of TA1 provided evidence that PssN is oriented towards the periplasmic space. Chemical cross-linking of TA1 and E. coli cells overproducing PssN-His6 protein showed that PssN might exist as a homo-oligomer of at least two monomers. Investigation of the secondary structure of purified PssN-His6 protein by Fourier transform infrared spectroscopy revealed the predominant presence of beta-structure; however, alpha-helices were also detected. Influence of an increased amount of PssN protein on the TA1 phenotype was assessed and correlated with a moderate enhancement of EPS production.
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Affiliation(s)
- Małgorzata Marczak
- Department of General Microbiology, Institute of Microbiology and Biotechnology, Maria Curie-Skłodowska University, Akademicka 19, 20-033 Lublin, Poland
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Russo DM, Williams A, Edwards A, Posadas DM, Finnie C, Dankert M, Downie JA, Zorreguieta A. Proteins exported via the PrsD-PrsE type I secretion system and the acidic exopolysaccharide are involved in biofilm formation by Rhizobium leguminosarum. J Bacteriol 2006; 188:4474-86. [PMID: 16740954 PMCID: PMC1482952 DOI: 10.1128/jb.00246-06] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The type I protein secretion system of Rhizobium leguminosarum bv. viciae encoded by the prsD and prsE genes is responsible for secretion of the exopolysaccharide (EPS)-glycanases PlyA and PlyB. The formation of a ring of biofilm on the surface of the glass in shaken cultures by both the prsD and prsE secretion mutants was greatly affected. Confocal laser scanning microscopy analysis of green-fluorescent-protein-labeled bacteria showed that during growth in minimal medium, R. leguminosarum wild type developed microcolonies, which progress to a characteristic three-dimensional biofilm structure. However, the prsD and prsE secretion mutants were able to form only an immature biofilm structure. A mutant disrupted in the EPS-glycanase plyB gene showed altered timing of biofilm formation, and its structure was atypical. A mutation in an essential gene for EPS synthesis (pssA) or deletion of several other pss genes involved in EPS synthesis completely abolished the ability of R. leguminosarum to develop a biofilm. Extracellular complementation studies of mixed bacterial cultures confirmed the role of the EPS and the modulation of the biofilm structure by the PrsD-PrsE secreted proteins. Protein analysis identified several additional proteins secreted by the PrsD-PrsE secretion system, and N-terminal sequencing revealed peptides homologous to the N termini of proteins from the Rap family (Rhizobium adhering proteins), which could have roles in cellular adhesion in R. leguminosarum. We propose a model for R. leguminosarum in which synthesis of the EPS leads the formation of a biofilm and several PrsD-PrsE secreted proteins are involved in different aspects of biofilm maturation, such as modulation of the EPS length or mediating attachment between bacteria.
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Affiliation(s)
- Daniela M Russo
- Fundación Instituto Leloir, CONICET, and Inst. de Investigaciones Bioquímicas, FCEyN, University of Buenos Aires, Patricias Argentinas 435, (C1405BWE) Buenos Aires, Argentina
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Skorupska A, Janczarek M, Marczak M, Mazur A, Król J. Rhizobial exopolysaccharides: genetic control and symbiotic functions. Microb Cell Fact 2006; 5:7. [PMID: 16483356 PMCID: PMC1403797 DOI: 10.1186/1475-2859-5-7] [Citation(s) in RCA: 180] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Accepted: 02/16/2006] [Indexed: 11/10/2022] Open
Abstract
Specific complex interactions between soil bacteria belonging to Rhizobium, Sinorhizobium, Mesorhizobium, Phylorhizobium, Bradyrhizobium and Azorhizobium commonly known as rhizobia, and their host leguminous plants result in development of root nodules. Nodules are new organs that consist mainly of plant cells infected with bacteroids that provide the host plant with fixed nitrogen. Proper nodule development requires the synthesis and perception of signal molecules such as lipochitooligosaccharides, called Nod factors that are important for induction of nodule development. Bacterial surface polysaccharides are also crucial for establishment of successful symbiosis with legumes. Sugar polymers of rhizobia are composed of a number of different polysaccharides, such as lipopolysaccharides (LPS), capsular polysaccharides (CPS or K-antigens), neutral β-1, 2-glucans and acidic extracellular polysaccharides (EPS). Despite extensive research, the molecular function of the surface polysaccharides in symbiosis remains unclear. This review focuses on exopolysaccharides that are especially important for the invasion that leads to formation of indetermined (with persistent meristem) type of nodules on legumes such as clover, vetch, peas or alfalfa. The significance of EPS synthesis in symbiotic interactions of Rhizobium leguminosarum with clover is especially noticed. Accumulating data suggest that exopolysaccharides may be involved in invasion and nodule development, bacterial release from infection threads, bacteroid development, suppression of plant defense response and protection against plant antimicrobial compounds. Rhizobial exopolysaccharides are species-specific heteropolysaccharide polymers composed of common sugars that are substituted with non-carbohydrate residues. Synthesis of repeating units of exopolysaccharide, their modification, polymerization and export to the cell surface is controlled by clusters of genes, named exo/exs, exp or pss that are localized on rhizobial megaplasmids or chromosome. The function of these genes was identified by isolation and characterization of several mutants disabled in exopolysaccharide synthesis. The effect of exopolysaccharide deficiency on nodule development has been extensively studied. Production of exopolysaccharides is influenced by a complex network of environmental factors such as phosphate, nitrogen or sulphur. There is a strong suggestion that production of a variety of symbiotically active polysaccharides may allow rhizobial strains to adapt to changing environmental conditions and interact efficiently with legumes.
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Affiliation(s)
- Anna Skorupska
- Department of General Microbiology, University of M. Curie-Skłodowska, Akademicka 19 st., 20-033 Lublin, Poland
| | - Monika Janczarek
- Department of General Microbiology, University of M. Curie-Skłodowska, Akademicka 19 st., 20-033 Lublin, Poland
| | - Małgorzata Marczak
- Department of General Microbiology, University of M. Curie-Skłodowska, Akademicka 19 st., 20-033 Lublin, Poland
| | - Andrzej Mazur
- Department of General Microbiology, University of M. Curie-Skłodowska, Akademicka 19 st., 20-033 Lublin, Poland
| | - Jarosław Król
- Department of General Microbiology, University of M. Curie-Skłodowska, Akademicka 19 st., 20-033 Lublin, Poland
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Mazur A, Marczak M, Król JE, Skorupska A. Topological and transcriptional analysis of pssL gene product: a putative Wzx-like exopolysaccharide translocase in Rhizobium leguminosarum bv. trifolii TA1. Arch Microbiol 2005; 184:1-10. [PMID: 16044265 DOI: 10.1007/s00203-005-0018-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2004] [Revised: 03/29/2005] [Accepted: 04/04/2005] [Indexed: 11/30/2022]
Abstract
An identified pssL gene is yet another one, besides the pssT, pssN and pssP genes, encoding for a protein engaged in polysaccharide polymerization and export in Rhizobium leguminosarum bv. trifolii strain TA1 (RtTA1). Amino acid sequence similarity and hypothetical protein secondary structure placed the PssL protein within Wzx (RfbX) translocases with putative flippase function that belong to the polysaccharide specific transport (PST) family. The predicted secondary structure of the PssL membrane protein was examined with a series of PssL-PhoA and PssL-LacZ translational fusions. The results support the hypothesis of PssL being a member of PST protein family comprising transporters with 12 membrane spanning segments and amino and carboxyl termini located in the cytoplasm. Results of semi-quantitative RT-PCR showed that the initial abundance of mRNA encoding PssL protein was relatively lower when compared to the quantity of the previously identified PssT membrane protein. PssL might be a good candidate for Wzx-like protein that together with PssT (Wzy protein) could be responsible for Wzx/Wzy-like-dependent EPS polymerization and translocation in RtTA1.
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Affiliation(s)
- Andrzej Mazur
- Department of General Microbiology, Institute of Microbiology and Biotechnology, University of M. Curie-Skłodowska, 19 Akademicka St., 20-033, Lublin, Poland.
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Laus MC, Logman TJ, Van Brussel AAN, Carlson RW, Azadi P, Gao MY, Kijne JW. Involvement of exo5 in production of surface polysaccharides in Rhizobium leguminosarum and its role in nodulation of Vicia sativa subsp. nigra. J Bacteriol 2004; 186:6617-25. [PMID: 15375143 PMCID: PMC516619 DOI: 10.1128/jb.186.19.6617-6625.2004] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Analysis of two exopolysaccharide-deficient mutants of Rhizobium leguminosarum, RBL5808 and RBL5812, revealed independent Tn5 transposon integrations in a single gene, designated exo5. As judged from structural and functional homology, this gene encodes a UDP-glucose dehydrogenase responsible for the oxidation of UDP-glucose to UDP-glucuronic acid. A mutation in exo5 affects all glucuronic acid-containing polysaccharides and, consequently, all galacturonic acid-containing polysaccharides. Exo5-deficient rhizobia do not produce extracellular polysaccharide (EPS) or capsular polysaccharide (CPS), both of which contain glucuronic acid. Carbohydrate composition analysis and nuclear magnetic resonance studies demonstrated that EPS and CPS from the parent strain have very similar structures. Lipopolysaccharide (LPS) molecules produced by the mutant strains are deficient in galacturonic acid, which is normally present in the core and lipid A portions of the LPS. The sensitivity of exo5 mutant rhizobia to hydrophobic compounds shows the involvement of the galacturonic acid residues in the outer membrane structure. Nodulation studies with Vicia sativa subsp. nigra showed that exo5 mutant rhizobia are impaired in successful infection thread colonization. This is caused by strong agglutination of EPS-deficient bacteria in the root hair curl. Root infection could be restored by simultaneous inoculation with a Nod factor-defective strain which retained the ability to produce EPS and CPS. However, in this case colonization of the nodule tissue was impaired.
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Affiliation(s)
- Marc C Laus
- Institute of Biology Leiden, Leiden University, Leiden, The Netherlands.
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Mazur A, Król JE, Marczak M, Skorupska A. Membrane topology of PssT, the transmembrane protein component of the type I exopolysaccharide transport system in Rhizobium leguminosarum bv. trifolii strain TA1. J Bacteriol 2003; 185:2503-11. [PMID: 12670974 PMCID: PMC152602 DOI: 10.1128/jb.185.8.2503-2511.2003] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2002] [Accepted: 01/17/2003] [Indexed: 11/20/2022] Open
Abstract
The pssT gene was identified as the fourth gene located upstream of the pssNOP gene cluster possibly involved in the biosynthesis, polymerization, and transport of exopolysaccharide (EPS) in Rhizobium leguminosarum bv. trifolii strain TA1. The hydropathy profile and homology searches indicated that PssT belongs to the polysaccharide-specific transport family of proteins, a component of the type I system of the polysaccharide transport. The predicted membrane topology of the PssT protein was examined with a series of PssT-PhoA fusion proteins and a complementary set of PssT-LacZ fusions. The results generally support a predicted topological model for PssT consisting of 12 transmembrane segments, with amino and carboxyl termini located in the cytoplasm. A mutant lacking the C-terminal part of PssT produced increased amounts of total EPS with an altered distribution of high- and low-molecular-weight forms in comparison to the wild-type RtTA1 strain. The PssT mutant produced an increased number of nitrogen fixing nodules on clover.
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Affiliation(s)
- Andrzej Mazur
- Department of General Microbiology, M. Curie-Skłodowska University, 20-033 Lublin, Poland
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Mazur A, Król JE, Wielbo J, Urbanik-Sypniewska T, Skorupska A. Rhizobium leguminosarum bv. trifolii PssP protein is required for exopolysaccharide biosynthesis and polymerization. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2002; 15:388-397. [PMID: 12026178 DOI: 10.1094/mpmi.2002.15.4.388] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Rhizobium leguminosarum bv. trifolii produces an acidic exopolysaccharide (EPS) that is important for the induction of nitrogen-fixing nodules on clover. Recently, three genes, pssN, pssO, and pssP, possibly involved in EPS biosynthesis and polymerization were identified. The predicted protein product of the pssP gene shows a significant sequence similarity to other proteins belonging to the PCP2a family that are involved in the synthesis of high-molecular-weight EPS. An R. leguminosarum bv. trifolii TA1 mutant with the entire coding region of pssP deleted did not produce the EPS. A pssP mutant with the 5' end of the gene disrupted produced exclusively low-molecular-weight EPS. A mutant that synthesized a functional N-terminal periplasmic domain but lacked the C-terminal part of PssP produced significantly reduced amounts of EPS with a slightly changed low to high molecular form ratio. Mutants affected in the PssP protein carrying a stable plasmid with a constitutively expressed gusA gene induced nodules on red clover that were not fully occupied by bacteria. A mutant with the entire pssP gene deleted infected only a few plant cells in the nodule. The pssP promoter-gusA reporter fusion was active in bacteroids during nodule development.
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Affiliation(s)
- Andrzej Mazur
- Department of General Microbiology, M. Curie-Skłodowska University, Lublin, Poland
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