A new specific endonuclease present in Xanthomonas holcicola, Xanthomonas papavericola and Brevibacterium luteum.
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Numerical analysis of 295 phenotypic features of 266 Xanthomonas strains and related strains and an improved taxonomy of the genus.
An extensive phenotypic description and an improved classification and nomenclature of the genus Xanthomonas are presented. A total of 266 strains obtained from different geographical areas, including representative strains of all species of the genus Xanthomonas and most pathovars of Xanthomonas campestris, as well as strains which might be genetically related to the genus Xanthomonas, were examined for 295 morphological, biochemical, and physiological features. Similarities among the strains were expressed numerically by using the coefficient of Sokal and Michener. Clustering was performed by using the unweighted average pair group method. The conclusions described below were reached. (i) The genus Xanthomonas comprises at least the following eight phena: X. campestris, Xanthomonas albilineans, Xanthomonas axonopodis, Xanthomonas fragariae, Xanthomonas populi, Xanthomonas maltophilia, Xanthomonas oryzae Swings et al. 1990, and X. campestris pv. graminis Egli and Schmidt 1982 [not X. campestris pv. graminis (Egli et al. 1975) ISPP List 1980]. (ii) X. populi (Ridé 1958) Ridé and Ridé 1978 is a separate species. (iii) X. maltophilia Swings et al. 1983 forms a separate species. (iv) X. campestris pv. oryzae ISPP List 1980 can no longer be regarded as pathovar of X. campestris, and its recent reclassification as a new species, X. oryzae (Swings et al., Int. J. Syst. Bacteriol. 40:309-311, 1990), is supported. (v) X. campestris pv. graminis Egli and Schmidt 1982 [not X. campestris pv. graminis (Egli et al. 1975) ISPP List 1980] seems to form a separate complex of highly related pathovars obtained from members of the Poaceae; the taxonomic implications of this are discussed. (vi) Strains of nearly all X. campestris pathovars cluster together in the X. campestris phenon. Within this species we were able to differentiate some entities on phenotypic grounds; these groups sometimes corresponded to named pathovars (e.g., X. campestris pv. manihotis, X. campestris pv. cassavae, X. campestris pv. phlei). In several other cases, pathovars were found to be heterogeneous. (vii) A number of dubious Pseudomonas species were identified as members of or as being close to Xanthomonas species. Both Pseudomonas betle and Pseudomonas hibiscicola are synonyms of X. maltophilia. We also confirmed that Pseudomonas mangiferaeindicae, Pseudomonas vitiswoodrowii, and Pseudomonas gardneri belong to X. campestris. (viii) Forty phenotypic features allow the differentiation of the eight Xanthomonas phena. (ix) A number of additional features of the genera Xanthomonas and Xylophilus are described.
Base Composition↗
Reinterpretation of the taxonomic position of Xanthomonas maltophilia and taxonomic criteria in this genus. Request for an opinion.
The inclusion of "Pseudomonas maltophilia" Hugh 1981 in the genus Xanthomonas as Xanthomonas maltophilia (Hugh 1981) Swings et al. 1983 is questioned in view of the significant differences between these two taxa. This reclassification is not acceptable if practical means of differentiation in this genus are considered. The proposed alteration of the description of the genus Xanthomonas is also questionable because of the implications for everyday phytobacteriology. In view of the natural similarities, as well as the profound differences, between X. maltophilia and the genus Xanthomonas, we propose that a new genus should be created for X. maltophilia, which could be placed together with the genus Xanthomonas in a separate natural group.
Base Composition↗
Rapid inter-strain comparison by pyrolysis mass spectrometry in nosocomial infection with Xanthomonas maltophilia.
Seventeen strains of Xanthomonas maltophilia and one strain of Pseudomonas cepacia were examined by pyrolysis mass spectrometry (PYMS). The Xanthomonas strains comprised 11 clinical and environmental isolates from a suspected outbreak of colonization and infection on a heart-lung transplant intensive care unit, two strains from patients elsewhere in the same hospital and four strains from a national reference collection. The single isolate of Pseudomonas cepacia was from a sink in the same affected intensive care unit. A series of discriminant analyses performed on the PYMS-derived data showed that, whereas six strains of Xanthomonas from the respiratory tract, blood and ventilatory equipment of one of the affected patients were indistinguishable, all the other isolates were distinct. The results of PYMS rapid inter-strain comparison were in accord with those of an epidemiological investigation which suggested that the episode was due to unauthorized reuse of disposable nebulizers and not to cross-infection between patients. Pyrolysis mass spectrometry with rapid data analysis is a potentially useful technique for the investigation of nosocomial infections due to organisms such as X. maltophilia.
Bacteriological Techniques↗
Degradation of hydrogen sulfide by Xanthomonas sp. strain DY44 isolated from peat.
Xanthomonas sp. strain DY44, capable of degrading H2S, was isolated from dimethyl disulfide-acclimated peat. This bacterium removed H2S either as a single gas or in the presence of the sulfur-containing compounds methanethiol, dimethyl sulfide, and dimethyl disulfide. The maximum specific H2S removal rate, obtained in the late stationary phase, was 3.92 mmol g of dry cells-1 h-1 (6.7 x 10(-16) mol cell-1 h-1) at pH 7 and 30 degrees C through a batch experiment in a basal mineral medium. Since Xanthomonas sp. strain DY44 exhibited no autotrophic growth with H2S, the H2S removal was judged not to be a consequence of chemolithotrophic activity. By using X-ray photoelectron spectroscopy, the metabolic product of H2S oxidation was determined to be polysulfide, which has properties very similar to those of elemental sulfur. Autoclaved cells (120 degrees C, 20 min) did not show H2S degradation, but cells killed by gamma-irradiation and cell extracts both oxidized H2S, suggesting the existence of a heat-labile intracellular enzymatic system for H2S oxidation. When Xanthomonas sp. strain DY44 was inoculated into fibrous peat, this strain degraded H2S without lag time, suggesting that it will be a good candidate for maintaining high H2S removability in the treatment of exhaust gases.
Biodegradation, Environmental↗
[Effect of cyclic nucleotides on beta-lactamase production and outer membrane proteins of clinical Xanthomonas maltophilia isolates].
Resistance of clinical Xanthomonas maltophilia isolates to beta-lactam compounds is influenced considerably by the nutrient medium employed for sensitivity testing; the organisms were much more resistant to beta-lactams when susceptibility testing was performed in Mueller-Hinton broth as compared to Isosensitest broth as the nutrient medium. Consequently, the influence of cyclic nucleotides was studied on beta-lactamase expression and outer membrane proteins in more detail. The exogenous supply of 5 mmol/l c-AMP or its lipophilic derivative c-AMP-N6,O2-dioctanoyl resulted in a marked reduction of enzyme production as compared to the control assay; 0.5 mmol/l c-AMP-S or 1 mmol/l c-GMP did not exhibit any effect. The analysis of the outer membrane proteins of Xanthomonas maltophilia revealed the single band of a 40 kdal protein which was expressed independently of the experimental conditions, thus confirming the classification of this pathogen as Xanthomonas maltophilia. The reduction of beta-lactamase expression in the presence of either c-AMP or c-AMP-N6,O2-dioctanoyl cannot be explained at present. The above findings emphasize again the problem of in-vitro susceptibility testing. To avoid false sensitive results, the use of Mueller-Hinton broth is recommended.
Bacterial Outer Membrane Proteins↗
[Evaluation of culture media for detecting the starch hydrolysis reaction in pathovars of Xanthomonas campestris].
Sixty strains of different pathovars of Xanthomonas campestris have been tested for the evaluation of various starch agars and compounds of starch degradation on six media: soluble starch, potato insoluble starch, corn insoluble starch, potato amylopectin, corn amylopectin and potato amylose. The purpose of the present investigation was the selection of the most suitable medium for the visualization of the starch hydrolysis test, presenting this reaction as a distinct character between pathovars of the Xanthomonas campestris group. From 60 strains tested, 74% gave positive reactions. Pathovars holcicola, pelargonii, pruni and vitians were negative. Regarding X. campestris pv. vesicatoria cultures, results were variable. Potato and corn insoluble starch agars were the most suitable media for the visualization of the starch hydrolysis reaction and at the same time the most appropriate for direct isolation. Differentiation at species level could be practicable, but within the Xanthomonas campestris group, variation amongst pathovars suggest the unsuitability of the test in spite of the high percentage of positive reactions.
Amylases↗
Antibiotic susceptibility profile of Xanthomonas maltophilia. In vitro activity of beta-lactam/beta-lactamase inhibitor combinations.
The susceptibility of 42 strains of Xanthomonas (Pseudomonas) maltophilia to 37 antibiotics (mainly beta-lactams, aminoglycosides, and fluorinated quinolones) was tested. Xanthomonas maltophilia was resistant to most beta-lactams, with ceftazidime, moxalactam, and ICI-194008 being the most active ones. Aminoglycosides had a very modest activity, with quinolones showing only moderate activity against this species. Trimethoprim/sufamethoxazole was effective against all strains tested. We also tested the synergy of several beta-lactam/beta-lactamase inhibitors against X. maltophilia. Only aztreonam/clavulanic acid at 3:1, 1:1 and, mainly, 2:1 combinations had synergistic activity, decreasing the rate of resistance from 92.8% for aztreonam alone to 32.4% for aztreonam-clavulanic acid at 1:1 and 0% for aztreonam-clavulanic acid at 2:1.
4-Quinolones↗
Structural investigations of the extracellular polysaccharide elaborated by S19, a Xanthomonas-type bacterium.
The extracellular, acidic heteropolysaccharide from Xanthomonas S19 consists of D-glucuronic acid, D-glucose, D-galactose, and D-mannose residues in the approximate molar ratios of 1.6:3:1:1, plus acetyl groups linked to C-2 and/or C-3 of a large proportion of the glucose residues. Methylation studies showed that the glucose is present as non-reducing end-group also as 1,2- and 1,4-linked units, the galactose residues are solely 1,3-linked, a major proportion of the mannose residues are 1,2,4-linked and the rest 1,2-linked. A high proportion of the glucuronic acid units are 1,4-linked. Periodate oxidation confirmed the presence of these linkages. The disaccharides D-Glc-(1 leads to 4)-D-Glc, D-Glc-(1 leads to 2)-D-Man, D-Glc-(1 leads to 3)-D-Gal, D-Gal(1 leads to 2)-D-Glc, D-GlcA-(1 leads to 4)-D-GlcA, and beta-D-GlcA-(1 leads to 4)-D-Man were isolated from a partial hydrolysate of the polysaccharide, and characterised. The similarities and differences between this polysaccharide and those from other Xanthomonas species are discussed.
Galactose↗
An Xanthomonas citri pathogenicity gene, pthA, pleiotropically encodes gratuitous avirulence on nonhosts.
The pathogenicity gene, pthA, of Xanthomonas citri is required to elicit symptoms of Asiatic citrus canker disease; introduction of pthA into Xanthomonas strains that are mildly pathogenic or opportunistic on citrus confers the ability to induce cankers on citrus (S. Swarup, R. De Feyter, R. H. Brlansky, and D. W. Gabriel, Phytopathology 81:802-809, 1991). The structure and the function of pthA in other xanthomonads and in X. citri were further investigated. When pthA was introduced into strains of X. phaseoli and X. campestris pv. malvacearum (neither pathogenic to citrus), the transconjugants remained nonpathogenic to citrus and elicited a hypersensitive response (HR) on their respective hosts, bean and cotton. In X. c. pv. malvacearum, pthA conferred cultivar-specific avirulence. Structurally, pthA is highly similar to avrBs3 and avrBsP from X. c. pv. vesicatoria and to avrB4, avrb6, avrb7, avrBIn, avrB101, and avrB102 from X. c. pv. malvacearum. Surprisingly, marker-exchanged pthA::Tn5-gusA mutant B21.2 of X. citri specifically lost the ability to induce the nonhost HR on bean, but retained the ability to induce the nonhost HR on cotton. The loss of the ability of B21.2 to elicit an HR on bean was restored by introduction of cloned pthA, indicating that the genetics of the nonhost HR may be the same as that found in homologous interactions involving specific avr genes. In contrast with expectations of homologous HR reactions, however, elimination of pthA function (resulting in loss of HR) did not result in water-soaking or even moderate levels of growth in planta of X. citri on bean; the nonhost HR, therefore, may not be responsible for the "resistance" of bean to X. citri and may not limit the host range of X. citri on bean. The pleiotropic avirulence function of pthA and the heterologous HR of bean to X. citri are both evidently gratuitous.
Amino Acid Sequence↗
Identification of a family of avirulence genes from Xanthomonas oryzae pv. oryzae.
Races of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight of rice, interact with cultivars of rice in a gene-for-gene specific manner. Multiple DNA fragments of various sizes from all strains of X. o. pv. oryzae hybridized with avrBs3, an avirulence gene from Xanthomonas campestris pv. vesicatoria, in Southern blots; this suggests the presence of several homologs and possibly a gene family. A genomic library of a race 2 strain of X. o. pv. oryzae, which is avirulent on rice cultivars carrying resistance genes xa-5, Xa-7, and Xa-10, was constructed. Six library clones, which hybridized to avrBs3, altered the interaction phenotype with rice cultivars carrying either xa-5, Xa-7, or Xa-10 when present in a virulent race 6 strain. Two avirulence genes, avrXa7 and avrXa10, which correspond to resistance genes Xa-7 and Xa-10, respectively, were identified and partially characterized from the hybridizing clones. On the basis of transposon insertion mutagenesis, sequence homology, restriction mapping, and the presence of a repeated sequence, both genes are homologs of avirulence genes from dicot xanthomonad pathogens. Two BamHI fragments that are homologous to avrBs3 and correspond to avrXa7 and avrXa10 contain a different number of copies of a 102-bp direct repeat. The DNA sequence of avrXa10 is nearly identical to avrBs3. We suggest that avrXa7 and avrXa10 are members of an avirulence gene family from xanthomonads that control the elicitation of resistance in mono- and dicotyledonous plants.
Amino Acid Sequence↗
Rapid generation of directed and unmarked deletions in Xanthomonas.
We have devised a rapid four-step procedure for the generation of directed and unmarked chromosomal deletions in bacteria, based on the use of a novel cloning vector containing the Bacillus subtilis sacB gene that encodes levansucrase and confers sucrose sensitivity, which can be used for counter-selection. Using this technique, we describe the construction of a 6.5 kb directed and unmarked deletion in a phytopathogenicity region of the chromosome in Xanthomonas campestris. This procedure allows rapid and easy transfer of a wide variety of mutant allelic DNA to the bacterial chromosome, and should be adaptable to various bacteria besides Xanthomonas spp.
Bacillus subtilis↗
Nature, type of linkage, and absolute configuration of (hydroxy) fatty acids in lipopolysaccharides from Xanthomonas sinensis and related strains.
The fatty acids present in lipopolysaccharides from Xanthomonas sinensis were identified as decanoic, 9-methyl-decanoic, 2-hydroxy-9-methyl-decanoic, 2-hydroxy-9-methyl-decanoic, D-3-hydroxy-decanoic, D-3-hydroxy-9-methyl-decanoic, D-3-hydroxy-dodecanoic, and D-3-hydroxy-11-methyl-dodecanoic acid. These fatty acids occur in the lipid A component where they are bound through ester and amide linkages to glucosamine residues. All types of fatty acids are ester bound; however, part of D-3-hydroxy-dodecanoic and D-3-hydroxy-11-methyl-dodecanoic acid is also involved in amide linkage. The hydroxyl groups of ester-linked 3-hydroxy fatty acids are not substituted. Similar fatty acid patterns were obtained from lipopolysaccharides of nine other Xanthomonas species.
Chemical Phenomena↗
A plant-inducible gene of Xanthomonas campestris pv. campestris encodes an exocellular component required for growth in the host and hypersensitivity on nonhosts.
Using Tn4431, a transposon that allows transcriptional fusions to a promoterless luciferase (lux) operon, we have isolated a nonpathogenic mutant of Xanthomonas campestris pv. campestris, i.e., JS111, that does not incite any of the black rot symptoms on all tested cruciferous host plants (J. J. Shaw, L. G. Settles, and C. I. Kado, Mol. Plant Microbe Interact. 1:39-45, 1988). In the study reported here, we determined that in contrast to the wild-type strain, JS111 is unable to induce a hypersensitive necrotic response on nonhost plants such as datura, tomato, and cucumber, suggesting that JS111 is a nonpathogenic, nonhypersensitive Hrp mutant. JS111 displayed culture growth rates, exopolysaccharide production, and protease, pectate lysase, cellulase, amylase, and phosphatase activities comparable to those of the wild-type strain. However, the growth of JS111 in host leaves was markedly attenuated. Coinoculation of JS111 with the wild-type strain in cauliflower or radish leaves rescued the growth deficiency of the mutant to normal levels. The locus mutated in JS111 was cloned and named hrpXc, and transcriptional and genetic complementation analyses of the hrpXc locus were conducted. The regulation of hrpXc expression was also investigated in vitro and in planta, using fusions to a lux or chloramphenicol acetyltransferase reporter gene. The hrpXc gene was found to be strongly induced in radish leaves. This is the first report and analysis of a hrp locus from a Xanthomonas species.
Chromosome Mapping↗
Susceptibility of Xanthomonas maltophilia and amikacin-resistant gram-negative bacteria to newer antimicrobials.
The susceptibility of Xanthomonas maltophilia and amikacin-resistant gram-negative bacteria to a variety of newer antimicrobials was determined. Sixty-three amikacin-resistant isolates were collected from 61 inpatients at a tertiary-care hospital between 1985 and 1988. The organisms included Xanthomonas maltophilia (24 isolates), Pseudomonas aeruginosa (16), Pseudomonas species (3), Serratia marcescens (10), Flavobacterium meningosepticum (4), Enterobacter species (3), Acinetobacter calcoaceticus var. anitratus (2), and Alcaligenes xylosoxidans (1). Amikacin resistance was initially determined by using the Kirby-Bauer disk diffusion method. The isolates were batched, and the minimum inhibitory concentrations (MICs) of 11 antimicrobials including amikacin were measured by using the standard agar dilution method. Of the 63 isolates initially found to be amikacin resistant by the disk diffusion method, 37% were found to be amikacin susceptible by MIC testing. Of 38 truly amikacin-resistant isolates, 76% were susceptible to ciprofloxacin, 63% to ofloxacin, 50% to imipenem-cilastatin, 47% to cefoperazone, 45% to ceftazidime, 13% to ceftizoxime, 11% to aztreonam, 11% to ceftriaxone, 5% to cefotetan, and 3% to amdinocillin. Ciprofloxacin and ofloxacin inhibited X. maltophilia to the greatest degree, with median MICs of 1 microgram/ml each. Fifteen amikacin-resistant Ps. aeruginosa isolates were inhibited by ciprofloxacin, imipenem, and ceftazidime, with median MICs of 0.375, 3, and 2 microgram/ml, respectively. Of the antimicrobials tested, ciprofloxacin had the greatest activity against amikacin-resistant organisms in vitro.
4-Quinolones↗
First isolation of Xanthomonas campestris from the blood of a Chinese woman.
Xanthomonas campestris isolated from the blood of a patient with a fever was first reported. Xanthomonas campestris is a bacterium that can cause black rot of some vegetables, such as rape. Chinese cabbage, etc. Human infection due to X. campestris has not been reported so far. The characteristics of this organism, including morphology, staining, physiology and biochemistry were studied. We believe that X. campestris is also one of the opportunistic pathogens, which can infect compromised host.
Cerebral Hemorrhage↗
DrdR Negatively Modulates the Expression of Flagellar Genes via Interaction With FleQ in Xanthomonas campestris.
Response regulators (RRs) of two-component signalling systems (TCSs) containing tandem receiver (REC) domains are widespread in bacteria, yet their functions and regulatory mechanisms remain poorly understood. In our previous study, DrdR, one such RR in the cruciferous black rot disease pathogen Xanthomonas campestris pv. campestris (Xcc) was demonstrated to positively regulate pilus-dependent motility and negatively regulate flagellum-dependent motility. We showed that DrdR modulates the ATPase activities of pili motor proteins PilT and PilB, thereby enhancing bacterial pilus-dependent swarming motility. However, how DrdR represses flagellar motility remained unknown. Here, we demonstrate that DrdR acts as a transcriptional repressor of flagellar gene expression. We used in vitro and in vivo approaches to identify FleQ, the master transcriptional regulator of flagellar genes, as a novel interaction partner of DrdR. Biochemical analyses revealed that DrdR binding inhibits FleQ's ATPase activity, which is essential for its transcriptional activation function. Microscale thermophoresis assays showed that DrdR reduces FleQ's DNA-binding capability to its cognate promoter. These findings collectively indicate that DrdR modulates FleQ transcriptional activity by reducing both its DNA-binding ability and ATPase activity. Our results demonstrate that DrdR serves as a specialized modulator of FleQ that acts upstream in the signalling cascade controlling the expression of flagellar genes in Xcc. This study exhibits a previously unknown mechanism whereby DrdR regulates bacterial motility. Combined with our previous finding, our data suggest that DrdR most likely acts as a conversion regulator between flagellum-dependent and pilus-dependent motility in Xcc.
Flagella↗
The rice cellulose synthase-like D4 gene (OsCSLD4) is required for resistance to Xanthomonas pv. oryzae.
Plant cell walls serve as a physical support and a barrier to pathogen invasion. Cellulose is the main component of cell walls. The cellulose synthase-like D (CSLD) subfamily genes are required for plant normal development. In rice, Oscsld4 mutant plants are dwarfed and have narrow, rolled leaves. The role of OsCSLD4 in rice immune responses is unclear. We carried out a forward genetic screen using rice mutants expressing the XA21 immune receptor to identify components required for the resistance to Xanthomonas oryzae pv. oryzae (Xoo). One mutant from the screen carries a loss-of-function mutation in OsCSLD4. OsCSLD4 is required for resistance to Xoo mediated by both the XA21 and XA26 immune receptors and also participates in the basal resistance to Xoo. Hallmarks of the XA21-mediated immune response, including induction of the defense marker gene KO5, reactive oxygen species (ROS) burst and the phosphorylation of mitogen-activated protein kinases (MAPKs), are not compromised in the Oscsld4 mutant. These findings suggest that OsCSLD4 does not function as a core signaling component of the immune receptor pathway, but rather maintains the structural integrity of the cell wall as an effective physical barrier. This structural defense is essential for the full manifestation of both innate and receptor-mediated immunity.
Oryza↗