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At least 685 records · Page 38Linked to original sources
PubMed1990

Inhibition by Agrobacterium tumefaciens and Pseudomonas savastanoi of development of the hypersensitive response elicited by Pseudomonas syringae pv. phaseolicola.

Injection into tobacco leaves of biotype 1 Agrobacterium tumefaciens or of Pseudomonas savastanoi inhibited the development of a visible hypersensitive response to the subsequent injection at the same site of Pseudomonas syringae pv. phaseolicola. This interference with the hypersensitive response was not seen with injection of bacterial growth medium or Escherichia coli cells. Live A. tumefaciens cells were required for the inhibitory effect. Various mutants and strains of A. tumefaciens were examined to determine the genes involved. Known chromosomal mutations generally had no effect on the ability of A. tumefaciens to inhibit the hypersensitive response, except for chvB mutants which showed a reduced (but still significant) inhibition of the hypersensitive response. Ti plasmid genes appeared to be required for the inhibition of the hypersensitive response. The bacteria did not need to be virulent in order to inhibit the hypersensitive response. Deletion of the vir region from pTi had no effect on the inhibition. However, the T region of the Ti plasmid was required for inhibition. Studies of transposon mutants suggested that the tms but not tmr or ocs genes were required. These genes were not acting after transfer to plant cells since they were effective in strains lacking vir genes and thus unable to transfer DNA to plant cells. The results suggest that the expression of the tms genes in the bacteria may inhibit the development of the hypersensitive response by the plant. An examination of the genes required in P. savastanoi for the inhibition of the hypersensitive response suggested that bacterial production of auxin was also required for the inhibition of the hypersensitive response by these bacteria.

Escherichia coli↗
PubMed1991

Sequence domains required for the activity of avirulence genes avrB and avrC from Pseudomonas syringae pv. glycinea.

avrB and avrC from Pseudomonas syringae pv. glycinea share significant amino acid homology but interact with different soybean resistance genes to elicit the hypersensitive defense reaction. Recombinant genes constructed between avrB and avrC revealed that the central regions were required for avirulence gene activity but the 5' and 3' termini were interchangeable. Recombinants involving the central regions did not yield any detectable avirulence gene activity, and no new avirulence phenotypes were observed from any of the chimeric genes. These results suggest that the protein products of avrB and avrC possess catalytic properties that are required for the avirulence phenotypes.

Amino Acid Sequence↗
PubMed1991

RNA polymerases from Pseudomonas aeruginosa and Pseudomonas syringae respond to Escherichia coli activator proteins.

The activities of RNA polymerases (RNAPs) from Pseudomonas aeruginosa and Pseudomonas syringae were compared with that of Escherichia coli RNAP. All three enzymes are able to initiate transcription at the trpBA promoter of P. aeruginosa and at the coliphage lambda promoters, pRM and pRE, in response to heterospecific activators (TrpI protein, repressor, and cII protein, respectively). However, both Pseudomonas polymerases have less stringent requirements for promoter recognition in the absence of activators than does E. coli RNAP.

Bacterial Proteins↗
PubMed1991

Molecular characterization and expression analysis of the anthranilate synthase gene of Pseudomonas syringae subsp. savastanoi.

The trpE gene, which encodes the large component of the enzyme anthranilate synthase, was isolated from a Pseudomonas syringae subsp. savastanoi (P. savastanoi) cosmid library. Cosmids that complemented an Escherichia coli trpE mutation contained a gene whose product is 86% homologous at the deduced amino acid level to TrpE of Pseudomonas aeruginosa and Pseudomonas putida. Amino acid sequence comparison with other TrpE sequences revealed the existence of conserved regions between the procaryotic and eucaryotic polypeptide sequences analyzed, regions that might be of functional importance. We also report on studies on the expression pattern of this gene. We analyzed the promoter activity of a trpE::lacZ transcriptional fusion, the relative amount of trpE steady-state mRNA, and the activity of anthranilate synthase from cells grown in minimal medium with or without exogenously added tryptophan and in complete medium. We concluded that under the conditions tested, expression of the trpE gene of P. savastanoi is independent of the concentration of tryptophan in the culture medium. Implications of such an expression pattern on the virulence of this bacterium are discussed.

Amino Acid Sequence↗
PubMed1991

Genetic and transcriptional organization of the hrp cluster of Pseudomonas syringae pv. phaseolicola.

The hrp cluster of Pseudomonas syringae pv. phaseolicola encodes functions that are essential for pathogenicity on bean plants and for the elicitation of the hypersensitive response on resistant plants. The cluster was saturated with insertions of transposon Tn3-spice that served both as a mutagen and as a sensitive reporter of the expression of the target regions. The mutations covered a 17.5-kb segment in strain NPS3121, in which seven hrp::Tn5 insertions had been previously mapped, and regions outside this segment. The cluster is organized into seven distinct complementation groups (hrpL, hrpAB, hrpC, hrpD, hrpE, hrpF, and hrpSR) on the basis of the analysis of over 100 Tn3-spice insertions in plasmids and 43 similar insertions in the chromosome; it spans nearly 22 kb and is chromosomally located. The transcriptional orientation of all genes in the cluster was established by measuring the level of ice nucleation activity of complemented merodiploids carrying chromosomal hrp::inaZ fusions after inoculation in Red Kidney bean leaves. Although all seven loci were actively expressed in Red Kidney bean leaves, none of them was substantially expressed when the bacteria were grown in King B broth medium. Mutations in all loci, except those in hrpC, greatly reduced the ability of the bacteria to multiply in bean leaves. Mutations in the hrpC locus, although preventing the bacteria from eliciting a hypersensitive reaction on tobacco, allowed the bacteria to produce delayed and attenuated symptoms in Red Kidney bean leaves and to multiply to a level 10(2)- to 10(3)-fold lower than that of the wild-type strain. This is the first comprehensive report of the genetic and transcriptional organization of the hrp gene cluster in a phytopathogenic bacterium.

Chromosome Mapping↗
PubMed1992

Plant and environmental sensory signals control the expression of hrp genes in Pseudomonas syringae pv. phaseolicola.

The hrp genes of Pseudomonas syringae pv. phaseolicola control the development of primary disease symptoms in bean plants and the elicitation of the hypersensitive response in resistant plants. We examined the expression of the seven operons located in the 22-kb hrp cluster (L. G. Rahme, M. N. Mindrinos, and N. J. Panopoulos, J. Bacteriol. 173:575-586, 1991) in planta and in vitro under different physiological and nutritional conditions by using chromosomally located hrp::inaZ reporter fusions. We show that (i) a plant signal(s) is specifically required for the induction of the seven hrp operons, during both compatible and incompatible interactions; (ii) hrpL and hrpRS are regulated by different mechanisms in planta and in vitro; and (iii) expression of individual hrp loci is differentially affected by pH, osmotic strength, and type of carbon source: hrpAB, hrpC, and hrpD were downregulated similarly by osmolarity, pH, and certain carbon sources; hrpE expression was affected strongly by pH and carbon substrate and slightly by osmolarity; and hrpF was not substantially affected by any of these factors. These findings suggest complex signaling mechanisms taking place during plant-pathogen interactions.

Amino Acids↗
PubMed1992

Physical and functional characterization of the gene cluster encoding the polyketide phytotoxin coronatine in Pseudomonas syringae pv. glycinea.

Pseudomonas syringae pv. glycinea PG4180 produces the polyketide phytotoxin coronatine. The coronatine synthesis genes in PG4180 were previously shown to reside on a 90-kb plasmid designated p4180A. In the present study, clones containing a 34-kb region of p4180A were saturated with Tn5, and 71 unique mutations were recombined into p4180A by marker exchange. The effect of each mutation on coronatine synthesis was determined by analyzing the organic acids produced by the mutants by reverse-phase high-performance liquid chromatography. The organic acids of selected mutants were derivatized to their methyl esters and analyzed by gas chromatography and gas chromatography-mass spectrometry. Mutations in a 20.5-kb region of p4180A completely blocked the synthesis of coronafacic acid and coronatine. Mutations within a 4.4-kb region of p4180A prevented the formation of coronatine but allowed for production of coronafacic acid, coronafacoylvaline, coronafacoylisoleucine, and coronafacoylalloisoleucine. The phenotypes of selected mutants were further confirmed in feeding experiments in which coronafacic acid or coronamic acid was added to the culture media. The results of this study allow us to speculate on the likely sequence of steps in the later stages of coronatine biosynthesis.

Amino Acids↗
PubMed1994

Phosphorylation of lipopolysaccharides in the Antarctic psychrotroph Pseudomonas syringae: a possible role in temperature adaptation.

Phosphorylation of lipopolysaccharide (LPS) from a psychrotrophic bacterium, Pseudomonas syringae, from Antarctica was studied by using sucrose gradient-separated membrane fractions. The bacterium was found to possess an LPS kinase which could phosphorylate more LPS postsynthetically at higher temperatures. The phosphorylation was low at a lower temperature and was also found to occur in vivo. After phosphorylation of LPS in vitro, it was found that the major part of the radioactivity (> 85%) was associated with the core oligosaccharide region of the LPS. The phosphate groups of this region are probably involved in the binding of metal ions, which could be removed by EDTA. The cells grown at the lower temperature probably contained fewer divalent cations because of the smaller amount of phosphate and thereby were more sensitive to EDTA. The cells were also more sensitive to cationic antibiotics at the lower temperature. A possible role of this differential phosphorylation of LPS in modulating the function of the outer membrane as a permeability barrier in the psychrotroph is discussed.

Adaptation, Physiological↗
PubMed1994

Structural studies of the side chain of outer membrane lipopolysaccharide from Pseudomonas syringae pv. coriandricola W-43.

The lipopolysaccharide (LPS) was isolated from Pseudomonas syringae pv. coriandricola W-43 by hot phenol-water extraction. Rhamnose and 3-N-acetyl-3-deoxyfucose were found to be the major sugar constituents of the LPS together with N-acetylglucosamine, N-acetylgalactosamine, heptose, and 3-deoxy-D-manno-octulosonic acid (Kdo). The main fatty acids of lipid A of the LPS were 3-OH-C:10, C12:0, 2-OH-C12:0, and 3-OH-C12:0. The O-specific polysaccharide liberated from the LPS by mild-acid hydrolysis was purified by gel permeation chromatography. The compositional analysis of the O-specific polysaccharide revealed the presence of L-rhamnose and 3-N-acetyl-3-deoxy-D-fucose in a molar ratio of 4:1. The primary structure of the O-specific polysaccharide was established by methylation analysis together with 1H and 13C nuclear magnetic resonance spectroscopy, including two-dimensional shift-correlated and one-dimensional nuclear Overhauser effect spectroscopy. The polysaccharide moiety was found to consist of a tetrasaccharide rhamnan backbone, and 3-N-acetyl-3-deoxy-D-fucose constitutes the side chain of the branched pentasaccharide repeating unit of the polysaccharide.

Carbohydrate Sequence↗
PubMed1995

Purification and characterization of an extracellular levansucrase from Pseudomonas syringae pv. phaseolicola.

Levansucrase (EC 2.4.1.10), an exoenzyme of Pseudomonas syringae pv. phaseolicola, was purified to homogeneity from the cell supernatant by chromatography on TMAE-Fraktogel and butyl-Fraktogel. The enzyme has molecular masses of 45 kDa under denaturing conditions and 68 kDa during gel filtration of the native form. In isoelectric focusing, active bands appeared at pH 3.55 and 3.6. Maximum sucrose cleaving activities were measured at pH 5.8 to 6.6 and 60 degrees C. The enzyme was highly tolerant to denaturing agents, proteases, and repeated freezing and thawing. The molecular weight of the produced levan depended on temperature, salinity, and sucrose concentration. The enzyme had levan-degrading activity and did not accept raffinose as a substrate. Comparison of the N-terminal amino acid sequence with the predicted amino acid sequence of levansucrases from Erwinia amylovora and Zymomonas mobilis showed 88 and 69% similarity, respectively, in amino acids 5 to 20. No similarity could be detected to levansucrases of gram-positive bacteria in the first 20 amino acids. By comparison of all levansucrases which have been sequenced to date, the enzyme seems to be conserved in the gram-negative bacteria. The rheological behavior of the product levan prompted a new assessment of the enzyme's role in pathogenesis. Depending on formation conditions, levan solutions exclude other polymer solutions. This behavior supports the presumption that the levansucrase is important in the early phase of infection by creating a separating layer between bacteria and plant cell wall to prevent the pathogen from recognition.

Amino Acid Sequence↗
PubMed1996

The Pseudomonas syringae Hrp regulation and secretion system controls the production and secretion of multiple extracellular proteins.

Pseudomonas syringae pv. tomato DC3000 produces seven to eight major extracellular proteins (EXPs) in a minimal medium inducing hrp genes. Using a polyclonal antibody against DC3000 EXPs, we have determined that the production and secretion of five EXPs (EXP-60, EXP-45, EXP-43, EXP-22, and EXP-10) are under the control of the Hrp regulation and secretion system.

Amino Acid Sequence↗
PubMed1997

A possible role for acetylated intermediates in diaminopimelate and tabtoxinine-beta-lactam biosynthesis in Pseudomonas syringae pv. tabaci BR2.024.

The deduced product of an open reading frame (ORF3) located in the tabtoxinine-beta-lactam (T beta L) biosynthetic region of Pseudomonas syringae pv. tabaci BR2.024 (BR2.024) has significant sequence homology to the dapD products of other bacteria. dapD encodes L-2,3,4,5-tetrahydrodipicolinate succinyl coenzyme A succinyltransferase (THDPA-ST), an enzyme in the diaminopimelate (DAP) and lysine biosynthetic pathway. Complementation studies, in vitro transcription-translation experiments, and enzymatic assays indicated that ORF3 encodes a product with THDPA-ST activity in Escherichia coli dapD mutant beta 274. However, a BR2.024 mutant with an insert in ORF3 was prototrophic, and only basal THDPA-ST activity was detected in extracts of both parent and mutant. This finding suggested that ORF3 was not required for DAP biosynthesis and that it did not encode a product with THDPA-ST activity. The results of enzymatic studies, indicating that BR2.024 uses acetylated intermediates for DAP biosynthesis, are consistent with the hypothesis that BR2.024 does not need THDPA-ST for DAP biosynthesis. The ORF3 mutant produced reduced levels of tabtoxin, indicating that ORF3 may have a role in T beta L biosynthesis. We have named the gene tabB and have proposed a possible function for the gene product.

Acetylation↗
PubMed1997

Characterization of dapB, a gene required by Pseudomonas syringae pv. tabaci BR2.024 for lysine and tabtoxinine-beta-lactam biosynthesis.

The dapB gene, which encodes L-2,3-dihydrodipicolinate reductase, the second enzyme of the lysine branch of the aspartic amino acid family, was cloned and sequenced from a tabtoxin-producing bacterium, Pseudomonas syringae pv. tabaci BR2.024. The deduced amino acid sequence shared 60 to 90% identity to known dapB gene products from gram-negative bacteria and 19 to 21% identity to the dapB products from gram-positive bacteria. The consensus sequence for the NAD(P)H binding site [(V/I)(A/G)(V/I)XGXXGXXG)] and the proposed substrate binding site (HHRHK) were conserved in the polypeptide. A BR2.024 dapB mutant is a diaminopimelate auxotroph and tabtoxin negative. The addition of a mixture of L-,L-, D,D-, and meso-diaminopimelate to defined media restored growth but not tabtoxin production. Cloned DNA fragments containing the parental dapB gene restored the ability to grow in defined media and tabtoxin production to the dapB mutant. These results indicate that the dapB gene is required for both lysine and tabtoxin biosynthesis, thus providing the first genetic evidence that the biosynthesis of tabtoxin proceeds in part along the lysine biosynthetic pathway. These data also suggest that L-2,3,4,5-tetrahydrodipicolinate is a common intermediate for both lysine and tabtoxin biosynthesis.

Amino Acid Sequence↗
PubMed2002

Low-temperature-induced changes in composition and fluidity of lipopolysaccharides in the antarctic psychrotrophic bacterium Pseudomonas syringae.

The Antarctic psychrotrophic bacterium Pseudomonas syringae was more sensitive to polymyxin B at a lower (4 degrees C) temperature of growth than at a higher (22 degrees C) temperature. The amount of hydroxy fatty acids in the lipopolysaccharides (LPS) also increased at the lower temperature. These changes correlated with the increase in fluidity of the hydrophobic phase of lipopolysaccharide aggregates in vitro.

Antarctic Regions↗
PubMed2002

Global regulation by gidA in Pseudomonas syringae.

Analysis of two virulence mutants of Pseudomonas syringae B728a revealed that the Tn 5 sites of insertion were within the gidA open reading frame (ORF). These mutations were pleiotropic, affecting diverse phenotypic traits, such as lipodepsipeptide (syringomycin and syringopeptin) antibiotic production, swarming, presence of fluorescent pigment, and virulence. Site-specific recombination of a disrupted gidA gene into the chromosome resulted in the same phenotypic pattern as transposon insertion. Mutant phenotypes were restored by the gidA ORF on a plasmid. The salA gene, a copy number suppressor of the syringomycin-deficient phenotype in gacS and gacA mutants, was also found to suppress the antibiotic-negative phenotypes of gidA mutants, suggesting that gidA might play some role in salA regulation. Reporter studies with chromosomal salA-lacZ translational fusions confirmed that salA reporter expression decreased approximately fivefold in a gidA mutant background, with a concurrent decrease in the expression of the syringomycin biosynthetic reporter fusion syrB-lacZ. Wild-type levels of reporter expression were restored by supplying an intact gidA gene on a plasmid. Often described as being involved in cell division, more recent evidence suggests a role for gidA in moderating translational fidelity, suggesting a mechanism by which global regulation might occur. The gidA gene is essentially universal in the domains Bacteria and Eucarya but has no counterparts in Archaea, probably reflecting specific differences in the translational machinery between the former and latter domains.

Bacterial Proteins↗
PubMed1999

Pseudomonas syringae phytotoxins: mode of action, regulation, and biosynthesis by peptide and polyketide synthetases.

Coronatine, syringomycin, syringopeptin, tabtoxin, and phaseolotoxin are the most intensively studied phytotoxins of Pseudomonas syringae, and each contributes significantly to bacterial virulence in plants. Coronatine functions partly as a mimic of methyl jasmonate, a hormone synthesized by plants undergoing biological stress. Syringomycin and syringopeptin form pores in plasma membranes, a process that leads to electrolyte leakage. Tabtoxin and phaseolotoxin are strongly antimicrobial and function by inhibiting glutamine synthetase and ornithine carbamoyltransferase, respectively. Genetic analysis has revealed the mechanisms responsible for toxin biosynthesis. Coronatine biosynthesis requires the cooperation of polyketide and peptide synthetases for the assembly of the coronafacic and coronamic acid moieties, respectively. Tabtoxin is derived from the lysine biosynthetic pathway, whereas syringomycin, syringopeptin, and phaseolotoxin biosynthesis requires peptide synthetases. Activation of phytotoxin synthesis is controlled by diverse environmental factors including plant signal molecules and temperature. Genes involved in the regulation of phytotoxin synthesis have been located within the coronatine and syringomycin gene clusters; however, additional regulatory genes are required for the synthesis of these and other phytotoxins. Global regulatory genes such as gacS modulate phytotoxin production in certain pathovars, indicating the complexity of the regulatory circuits controlling phytotoxin synthesis. The coronatine and syringomycin gene clusters have been intensively characterized and show potential for constructing modified polyketides and peptides. Genetic reprogramming of peptide and polyketide synthetases has been successful, and portions of the coronatine and syringomycin gene clusters could be valuable resources in developing new antimicrobial agents.

Amino Acids↗
PubMed1982

Bacteriocin production by Pseudomonas syringae PsW-1 in plant tissue.

The production and activity of syringacin W-1, a particulate bacteriocin made by Pseudomonas syringae PsW-1, was studied in plant tissue. The bacteriocin is rod shaped, approximately 20 nm wide and 75 nm long, and composed of an outer sheath and inner core. Both the producing strain, PsW-1, and a sensitive strain, 16, grew within red kidney bean stems. Strains PsW-1 and 16, or mutants derived from them, were injected into bean stems singly or in mixtures. All singly inoculated strains grew well. However, when the bacteriocin-producing strain was co-inoculated with the sensitive strain, the latter grew poorly, if at all. This was not due to competition for available nutrients, since the sensitive strain grew as well in the presence of a bacteriocin-nonproducing mutant as it did alone. Also, a bacteriocin-resistant mutant grew as well in the presence of a bacteriocin-nonproducing mutant as it did alone. Also, a bacteriocin-resistant mutant grew as well in the presence of the producing strain as it did alone. Bacteriocin activity and particles were recovered from infected plant tissue.

Bacteriocins↗
PubMed1992

Epiphytic populations of Pseudomonas syringae on barley.

The epiphytic populations of Pseudomonas syringae were monitored on 23 barley entries planted in the field in four replications during the summer of 1986, and on six selected entries during the summer of 1987, from the second-leaf stage until senescence. Populations were initially low (0-3 log colony-forming units (cfu) per leaf) in all but one entry; they generally increased throughout the season, and at the end they reached 3-7 log cfu/leaf. Significant differences among the average epiphytic populations were found in the 1986 trial; only one entry, however, had a significantly different average population in the 1987 trial. The slopes of population increase were also compared: significant differences were observed in 1986 but not in 1987. In addition to epiphytic population counts, the percentage of ice nucleation active bacteria was determined in the population isolated from each leaf sample, and averaged throughout the season for each entry. Significant differences were observed in 1986 and in 1987. When the entries were ranked according to their average epiphytic population and compared between the two experiments, they were found to be very similar. The same was not true for the other parameters studied in the experiment.

Freezing↗