bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic variation in eastern North American and putatively introduced populations of Ceratocystis fimbriata f. platani
Authors: ENGELBRECHT C. J. B. , HARRINGTON T. C. , STEIMEL J. , CAPRETTI P. 
Published: October 2004

AbstractThe plant pathogenic fungus Ceratocystis fimbriata f. platani attacks Platanus species (London plane, oriental plane and American sycamore) and has killed tens of thousands of plantation trees and street trees in the eastern United States, southern Europe and Modesto, California. Nuclear and mitochondrial DNA fingerprints and alleles of eight polymorphic microsatellite markers of isolates of C. fimbriata from these regions delineated major differences in gene diversities. The 33 isolates from the eastern United States had a moderate degree of gene diversity, and unique genotypes were found at each of seven collection sites. Fingerprints of 27 isolates from 21 collection sites in southern Europe were identical with each other; microsatellite markers were monomorphic within the European population, except that three isolates differed at one locus each, due perhaps to recent mutations. The genetic variability of C. fimbriata f. platani in the eastern United States suggests that the fungus is indigenous to this region. The genetic homogeneity of the fungus in Europe suggests that this population has gone through a recent genetic bottleneck, perhaps from the introduction of a single genotype. This supports the hypothesis that the pathogen was introduced to Europe through Naples, Italy during World War II on infected crating material from the eastern United States. The Californian population may also have resulted from introduction of one or a few related genotypes because it, too, had a single nuclear and mitochondrial genotype and limited variation in microsatellite alleles.
Metabolic differentiation in actively swarming Salmonella
Authors: Kim Wook , Surette Michael G. 
Published: October 2004

SummaryMost current paradigms of microbial metabolism have been derived from studying cells grown under a variety of nutrient compositions in aqueous environments. With recent advances in genomics and experimental techniques, alternative forms of bacterial growth are increasingly being explored. When propagated on nutrient‐rich semi‐solid media, several species of bacteria undergo a morphological differentiation into swarmers that are capable of migrating on surfaces. Recent studies indicate that swarmer differentiation represents much more than a motility phenotype, as several clinically important attributes are also co‐regulated. We demonstrate that migrating swarmer cells of Salmonella are metabolically differentiated compared to the vegetative swimmer cells grown in the same nutrient environment. Furthermore, once the cells have differentiated, the swarmers remain in this physiological state under conditions that do not promote the initial differentiation. The bacterium's capacity to override some of the classic paradigms of metabolic regulation established in aqueous environments represents a unique physiological response by the pathogen that may be advantageous in polymicrobial environments such as the host.
Genetic evidence for functional interactions between TolC and AcrA proteins of a major antibiotic efflux pump of Escherichia coli
Authors: Gerken Henri , Misra Rajeev 
Published: October 2004

SummaryGenetic data have suggested that TolC, AcrA and AcrB constitute a major antibiotic efflux system in Escherichia coli. Through reversion analysis of an unstable and antibiotic‐sensitive TolC mutant (TolCP246R,S350C), we isolated extragenic suppressors that mapped within the acrRAB loci. DNA sequence analysis revealed that 18 isolates contained 10 different missense mutations within the acrA gene, whereas a single isolate had a missense mutation within the acrR gene, which codes for the acrAB repressor. Besides reversing the hypersensitivity phenotype of TolCP246R,S350C, AcrA and AcrR alterations elevated the mutant TolC protein level, thus indicating that the mechanism of suppression involves the stabilization of an unstable mutant TolC protein. Eight of the 10 AcrA alterations were clustered in the 202–265 region of the mature protein, whereas the other two suppressors affected residues 30 and 146. Based on the recently solved crystal structure of MexA, an AcrA counterpart from Pseudomonas aeruginosa, the regions encompassing residues 30 and 202–265 constitute the α+β‐domain of AcrA (MexA), whereas that of 146 form the α‐domain. The data suggest that residues of these two AcrA domains either directly or indirectly influence interactions with TolC. Curiously, the stability of three mutant AcrA proteins, bearing an L222Q, L222R or P265R substitution, became dependent on the presence of either wild‐type or mutant TolC. This dependence of the mutant AcrA proteins on TolC further supported the notion of a direct physical interaction between these two proteins. Because a mutation in acrR or acrAB expression from a multicopy plasmid also suppressed the TolCP246R,S350C defects, it indicated that wild‐type AcrA when produced in high levels presumably establishes similar interactions with the mutant TolC protein as do the suppressor forms of AcrA produced from the chromosomal copy. The AcrA‐mediated suppression of mutant TolC phenotypes and the stabilization of mutant TolC protein were dependent on AcrB, reflecting the existence of a functional complex between TolC and AcrAB in vivo.
HpaB from Xanthomonas campestris pv. vesicatoria acts as an exit control protein in type III‐dependent protein secretion
Authors: Büttner Daniela , Gürlebeck Doreen , Noël Laurent D. , Bonas Ulla 
Published: October 2004

SummaryThe hrp (hypersensitive response and pathogenicity) gene cluster of the plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria encodes a type III secretion (TTS) system, which injects bacterial effector proteins into the plant cell. Here, we characterized hpaB (hpa, hrp‐associated), which encodes a pathogenicity factor with typical features of a TTS chaperone. We show that HpaB is important for the efficient secretion of at least five effector proteins but is dispensable for the secretion of non‐effectors such as XopA and the TTS translocon protein HrpF. GST pull‐down assays revealed that HpaB interacts with two unrelated effector proteins, AvrBs1 and AvrBs3, but not with XopA. The HpaB‐binding site is located within the first 50 amino acids of AvrBs3. This region also contains the targeting signal for HpaB‐dependent secretion, which is missing in HrpF and XopA. Intriguingly, the N‐termini of HrpF and XopA target the AvrBs3Δ2 reporter for translocation in a ΔhpaB mutant but not in the wild‐type strain. This indicates that HpaB plays an essential role in the exit control of the TTS system. Our data suggest that HpaB promotes the secretion of a large set of effector proteins and prevents the delivery of non‐effectors into the plant cell.
Release of DNA into the medium by competent Streptococcus pneumoniae: kinetics, mechanism and stability of the liberated DNA
Authors: Moscoso Miriam , Claverys Jean‐Pierre 
Published: October 2004

SummaryThe release of chromosomal DNA into culture media has been reported for several naturally transformable bacterial species, but a direct link between competence development and the liberation of DNA is generally lacking. Based on the analysis of strains with mutations in competence‐regulatory genes and the use of conditions favouring or preventing competence, we provide evidence that DNA release is triggered by the induction of competence in Streptococcus pneumoniae. Kinetic analyses revealed that whereas competence was maximal 20 min after addition of competence‐stimulating peptide, and then decreased, the amount of liberated DNA continued to increase and reached a maximum in stationary phase, when cells are no longer competent for DNA uptake. These data are not consistent with the proposal that release of DNA by a fraction of the population is coordinated with uptake by the remainder. Moreover, we observed that an unidentified DNase was specifically induced or released in competent cultures, and that together with the major pneumococcal endonuclease, EndA, it could degrade released DNA. Nearby complete abolition of release in a mutant lacking both the major autolysin, LytA, and the autolytic lysozyme, LytC, indicated that DNA liberation occurs by LytA‐LytC‐dependent cell lysis. These observations suggest that competence‐dependent DNA release is one facet of a more general phenomenon of sensitization to autolysis that reaches its maximum in stationary phase.
The ColR–ColS two‐component signal transduction system is involved in regulation of Tn4652 transposition in Pseudomonas putida under starvation conditions
Authors: Hõrak Rita , Ilves Heili , Pruunsild Priit , Kuljus Martin , Kivisaar Maia 
Published: October 2004

SummaryBacteria use two‐component signal transduction pathways to sense both extracellular and intracellular environment and to coordinate cellular events according to changing conditions. Adaptation can be either physiological or genetical. Here, we present evidence that a genome reorganization process such as transposition can be controlled by certain environmental cues  sensed  by  a  two‐component  signal  transduction system. We demonstrate that transposition‐dependent accumulation of phenol‐utilizing mutants is severely decreased in Pseudomonas putida defective in a two‐component system colRS. Translocation of Tn4652 is decreased both in colR‐ and colS‐defective strains, indicating that signal transduction from a histidine kinase ColS to a response regulator ColR is necessary for the activation of Tn4652 in bacteria starving on phenol. However, overexpression of ColR in a colS‐defective strain restores Tn4652 transposition, suggesting that absence of the signal from ColS can be compensated by an elevated amount of ColR. In vitro analysis of purified ColR and ColS proteins evidenced that they constitute a functional phosphorelay. Site‐directed mutagenesis revealed that a conserved H221 can be the phosphoryl‐accepting residue in ColS and that aspartate residues D8 and D51 of ColR are necessary for the phosphotransfer from ColS to ColR. To our knowledge, Tn4652 is the first bacterial transposon regulated by a two‐component system. This finding indicates that transpositional activity can respond to signals sensed and processed by the host.
Export of Plasmodium falciparum calcium‐dependent protein kinase 1 to the parasitophorous vacuole is dependent on three N‐terminal membrane anchor motifs
Authors: Möskes Christian , Burghaus Petra A. , Wernli Barbara , Sauder Ursula , Dürrenberger Markus , Kappes Barbara 
Published: October 2004

SummaryCalcium‐dependent protein kinases play a pivotal role in calcium signalling in plants and some protozoa, including the malaria parasites. They are found in various subcellular locations, suggesting an involvement in multiple signal transduction pathways. Recently, Plasmodium falciparum calcium‐dependent protein kinase 1 (PfCDPK1) has been found in the membrane and organelle fraction of the parasite. The kinase contains three motifs for membrane binding at its N‐terminus, a consensus sequence for myristoylation, a putative palmitoylation site and a basic motif. Endogenous PfCDPK1 and the in vitro translated kinase were both shown to be myristoylated. The supposed membrane attachment function of the basic cluster was experimentally verified and shown to participate together with N‐myristoylation in membrane anchoring of the kinase. Using immunogold electron microscopy, the protein was detected in the parasitophorous vacuole and the tubovesicular system of the parasite. Mutagenesis of the predicted acylated residues and the basic motif confirmed that dual acylation and the basic cluster are required for correct targeting of Aequorea victoria green fluorescent protein to the parasitophorous vacuole, suggesting that PfCDPK1 as the leishmanial hydrophilic acylated surface protein B is a representative of a novel class of proteins whose export is dependent on a ‘non‐classical’ pathway involving N‐myristoylation/palmitoylation.
The response regulator SsrB activates transcription and binds to a region overlapping OmpR binding sites at Salmonella pathogenicity island 2
Authors: Feng Xiuhong , Walthers Don , Oropeza Ricardo , Kenney Linda J. 
Published: October 2004

SummaryOmpR activates expression of the two‐component regulatory system located on Salmonella pathogenicity island 2 (SPI‐2) that controls the expression of a type III secretion system, as well as many other genes required for systemic infection in mice. Measurements of SsrA and SsrB protein levels under different growth conditions indicate that expression of these two components is uncoupled, i.e. SsrB is produced in the absence of ssrA and vice versa. This result was suggested from our previous studies, in which two promoters at ssrA/B were identified. The isolated C‐terminus of SsrB binds to DNA and protects regions upstream of ssrA, ssrB and srfH from DNase I digestion. Furthermore, the C‐terminus of SsrB alone is capable of activating transcription in the absence of the N‐terminus. Results from β‐galactosidase assays indicate that the N‐terminal phosphorylation domain inhibits the C‐terminal effector domain. A previous study from our laboratory reported that ssrA–lacZ and ssrB–lacZ transcriptional fusions were substantially reduced in an ssrB null strain. Results from DNase I protection assays provide direct evidence that SsrB binds at ssrA and ssrB, although the binding sites lie within the transcribed regions. Additional regulators clearly affect gene expression at this important locus, and here we provide evidence that SlyA, a transcription factor that contributes to Salmonella virulence, also affects ssrA/B gene expression.
Axiom of determining transcription start points by RNA polymerase in Escherichia coli
Authors: Lewis Dale E. A. , Adhya Sankar 
Published: October 2004

SummaryTo investigate the determining factors in the selection of the transcription start points (tsp) by RNA polymerase of Escherichia coli, we systematically deleted or substituted single base pairs (bps) at 25 putative critical positions in the two extended −10 promoters, P1 and P2, of the gal operon. These changes extend downstream from −24 to +1 of the P1 promoter. In vitro transcription assays using supercoiled DNA templates revealed a preference for a purine in the non‐template strand for tsp in both promoters. The optimal tsp is the 11th bp counting downstream from the −10 position. A single bp deletion anywhere from −10 to +1 switched the tsp to the next available purine 2–3 bp downstream on the non‐template strand whereas deleting a single bp at position from −24 to −11 did not affect the tsp. The nature of the 10 bp sequence of the −10 to −1 region, while affecting promoter strength, did not influence tsp. The cAMP–CRP complex, which stimulates P1 and represses P2, did not affect the tsp selection process. The rules of tsp selection by RNA polymerase containing σ70 in gal and pyr promoters discussed here may be applicable to others.
Resistance to human β‐defensins is common among oral treponemes
Authors: Brissette C. A. , Simonson L. G. , Lukehart S. A. 
Published: October 2004

Background/aims:  Oral treponemes are implicated in the pathogenesis of periodontal disease. We have previously shown that Treponema denticola ATCC type strains and strain GM‐1 are resistant to killing by human β‐defensins (hβD)‐1 and ‐2. We hypothesize that resistance to β‐defensins is a common feature of oral treponemes, which allows colonization and persistence in the oral cavity. In this study, we tested additional isolates of T. denticola, as well as six other species of treponemes, for resistance to hβD‐1, ‐2 and ‐3. We also examined the four ATCC strains of T. denticola and strain GM‐1 for resistance to hβD‐3.Methods:  Resistance was determined by motility and Alamar Blue assays for metabolic activity.Results:  All T. denticola strains tested were resistant to hβD‐1, ‐2 and ‐3, with the exception of strain Ambigua, which was sensitive to hβD‐2 and ‐3. All other treponemes except Treponema vincentii were resistant to hβD‐1. Treponema pectinovorum was sensitive to hβD‐2, while T. vincentii, T. pectinovorum and Treponema maltophilum were sensitive to hβD‐3. Escherichia coli was used as a control organism and was killed by all three defensins.Conclusion:  Resistance to the constitutively expressed hβD‐1 may assist treponemes in initial colonization of epithelial surfaces, while resistance to the inducible hβD‐2 and ‐3 would allow some treponemes to survive in active periodontal lesions.
Differential Implication of Glutathione, Glutathione‐Metabolizing Enzymes and Ascorbate in Tomato Resistance toPseudomonas syringae
Authors: Kuźniak E. , SkŁodowska M. 
Published: October 2004

AbstractWe studied the response of glutathione‐ and ascorbate‐related antioxidant systems of the two tomato cultivars toPseudomonas syringaepv.tomatoinfection. In the inoculated susceptible A 100 cultivar a substantial decrease in reduced glutathione (GSH) content, oxidised glutathione accumulation and GSH redox ratio decline as well as glutathione peroxidase activity increase were found. The enhanced glutathione reductase activity was insufficient to keep the glutathione pool reduced. A transiently increased dehydroascorbic acid (DHA) content and ascorbic acid (AA) redox ratio decrease together with ascorbate peroxidase activity suppression were observed. Adversely to the progressive reduction in GSH pool size, AA content tended to increase but the changes were more modest than those of GSH. By contrast, in interaction with the resistant Ontario cultivar the glutathione pool homeostasis was maintained throughoutP. syringaeattack and no significant effect on the ascorbate pool was observed. Moreover, in the resistant interaction there was a significantly higher constitutive and pathogen‐induced glutathione‐S‐transferase (GST) activity. The relationship between GST activity and DHA content found in this study indicates that this enzyme could also act as dehydroascorbate reductase. These results reflect the differential involvement of GSH and AA in tomato‐P. syringaeinteraction and, in favour of the former, they clearly indicate the role of GSH and GSH‐utilizing enzymes in resistance toP. syringae. The maintenance of glutathione pool homeostasis and GST induction appear to contribute to tissue inaccessibility to bacterial attack.
Localized and Systemic Increase of Phenols in Tomato Roots Induced by Glomus versiforme Inhibits Ralstonia solanacearum
Authors: Zhu H. H. , Yao Q. 
Published: October 2004

Abstract Ralstonia solanacearum is an important plant pathogen in tropical and subtropical countries. Here, we describe the inhibition of R. solanacearum as a result of increased phenols induced locally or systemically by an arbuscular mycorrhizal (AM) fungus. In pot cultures, R. solanacearum populations in the rhizosphere, on root surfaces and in the xylem were decreased by 26.7, 79.3 and 81.7%, respectively, following inoculation of tomato plants (Lycopersicon esculentum Mill.) with Glomus versiforme Berch. Colonization of the plants by both R. solanacearum and G. versiforme increased the contents of soluble phenols and cell‐wall bound phenols in root tissue, but with different patterns. Whereas R. solanacearum preferably promoted the cell‐wall bound phenol content, G. versiforme preferably enhanced the soluble phenol content. Split root experiments revealed that R. Solanacearum was inhibited by G. versiforme, and that G. versiforme also increased the phenol content systemically, but to a lesser extent than locally.
Molecular Variability of Mycosphaerella graminicola as Detected by RAPD Markers
Authors: Razavi M. , Hughes G. R. 
Published: October 2004

AbstractA total of 90 isolates of Mycosphaerella graminicola, the cause of septoria tritici leaf blotch of wheat, were tested for DNA polymorphism using 15 decamer random primers. There was a high level of genetic variability among isolates. In 131 random amplified polymorphic DNA (RAPD) fragments, which were produced, 96% were polymorphic. Based on multilocus analysis, 40 different molecular phenotypes were detected. These molecular phenotypes were randomly distributed among sampling sites, suggesting that no clonal structure existed in the population. Cluster analysis showed that the maximum similarity value among isolates was approximately 81% and no identical isolates were detected, indicating that every isolate was a unique genotype. The high degree of DNA polymorphism, the large number of different molecular phenotypes, their random distribution and the results of the cluster analysis all suggested that sexual reproduction has a major role in the genetic structure of M. graminicola in western Canada. The presence of sexual reproduction provides the opportunity for development of new virulent genotypes in the population and suggests that the pathogen may adapt rapidly to any race‐specific sources of resistance. Therefore, when breeding for resistance to M. graminicola, emphasis should be placed on use of non‐race‐specific resistance.
Biocontrol of Rhizoctonia Damping‐off of Tomato by Bacillus subtilis Combined with Burkholderia cepacia
Authors: Szczech M. , Shoda M. 
Published: October 2004

Abstract Bacillus subtilis strain RB14‐C and Burkholderia cepacia strain BY were used in combination to control damping‐off of tomato plants caused by Rhizoctonia solani. Microcosm tests showed complete inhibition of R. solani growth on filter disks buried in soil added with the mixture of both bacteria. Single BY inhibited the fungus, but not completely, and RB14‐C had only slight inhibitory effect on pathogen growth. The efficacy of this combining treatment was checked in pot experiments, where bacteria were applied to the soil in several combinations: RB14‐C and BY together 4 days before seed planting, RB14‐C 4 days and BY 2 days before seed planting, RB14‐C 4 days and BY immediately before seeds. The effect of these treatments on population of R. solani in soil and infection of plants was compared with the activity of single application of each agent. All bacterial treatments significantly decreased damping‐off of tomato plants. The best control was obtained when BY was added 2 days after RB14‐C. In this treatment plant protection was significantly higher than that obtained in other combined applications and obtained by single strains, except BY added to the soil 4 days before seed planting. The lowest suppression indicated BY introduced to the soil before seed planting. RB14‐C only slightly decreased number of R. solani in the soil. In contrast, BY drastically reduced population of the pathogen. However, there was not a clear relation between decrease of pathogen density in soil and the rate of plant infection. The results show that combination of B. subtilis RB14‐C with B. cepacia BY can lead to greater damping‐off suppression than biocontrol exhibited by these strains used separately, but the effect of combining bacterial agents was clearly related to the order in which both agents were introduced.