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Biomedical subjects

C E Barber

Publications and source records attributed to C E Barber.

16 recordsLinked to original sources
PubMed2000

A two-component system involving an HD-GYP domain protein links cell-cell signalling to pathogenicity gene expression in Xanthomonas campestris.

The synthesis of extracellular enzymes and extracellular polysaccharide (EPS) in Xanthomonas campestris pv. campestris (Xcc) is regulated by a cluster of genes called rpf (for regulation of pathogenicity factors). Two of the genes, rpfF and rpfB, have previously been implicated in the synthesis of a diffusible regulatory molecule, DSF. Here, we describe a screen of transposon insertion mutants of Xcc that identified two DSF-overproducing strains. In each mutant, the gene disrupted is rpfC, which encodes a hybrid two-component regulatory protein in which the sensor and regulator domains are fused and which contains an additional C-terminal phosphorelay (HPt) domain. We show that rpfC is in an operon with rpfH and rpfG. The predicted protein RpfG has a regulatory input domain attached to a specialized version of an HD domain, previously suggested to function in signal transduction. The predicted protein RpfH is structurally related to the sensory input domain of RpfC. We show that RpfC and RpfG act positively to regulate the synthesis of extracellular enzymes and EPS, but that RpfC acts negatively to regulate the synthesis of DSF. We propose that RpfGHC is a signal transduction system that couples the synthesis of pathogenicity factors to sensing of environmental signals that may include DSF itself.

Amino Acid Sequence↗
PubMed2000

The grandmother role as experienced by lesbian women.

This study explores the grandmother role as experienced by a nonrandom sample of nine lesbian women. It examines how they define the grandmother role, and the behaviors and actions through which they enact the role. During individual interviews each woman was asked to talk about what makes a woman a good grandmother, memories of her own grandmothers, and the relationship she has with one or more of her grandchildren. The effect of her sexual orientation on the relationship was not explored. These women define the grandmother role as providing emotional support to their grandchildren, providing varied experiences for their grandchildren, and providing support for the parents of their grandchildren.

Adult↗
PubMed1998

The rpfA gene of Xanthomonas campestris pathovar campestris, which is involved in the regulation of pathogenicity factor production, encodes an aconitase.

Xanthomonas campestris pv campestris (Xcc) is a plant pathogenic bacterium that controls the production of pathogenicity factors in part by a cluster of genes designated rpf (regulation of pathogenicity factors). Sequence analysis of one of these genes (rpfA) revealed an open reading frame with amino acid sequence similarity to aconitases from other bacteria. Aconitase activity was lower in cellular extracts of an rpfA::Tn5 mutant than in those from the wild type. A zymogram of aconitase activity after native gel electrophoresis showed the presence of two distinct aconitases in Xcc; the major aconitase was absent in the rpfA::Tn5 mutant. This mutant also had reduced levels of extracellular enzymes and extracellular polysaccharide (EPS). Supplying rpfA in trans to the rpfA::Tn5 mutant restored both the major aconitase activity and the synthesis of these pathogenicity factors. The transcription of the genes for two extracellular enzymes (prtA, encoding a serine protease, and engXCA, encoding endoglucanase) was reduced in the rpfA mutant background. Because some eukaryotic aconitases are also involved in iron regulation, we explored a possible connection between rpfA and iron metabolism. Intracellular iron levels in the mutants were lower than in the wild type as assessed by sensitivity to the iron-activated antibiotic, streptonigrin. Wild-type bacteria grown in iron-deficient conditions had a similar sensitivity to streptonigrin as the aconitase mutant. Overall, these results suggest that a prokaryotic aconitase can also act as a regulator of gene expression and that the regulation is possibly related to changes in intracellular iron levels.

Aconitate Hydratase↗
PubMed1998

Entry of Xanthomonas campestris pv. campestris into hydathodes of Arabidopsis thaliana leaves: a system for studying early infection events in bacterial pathogenesis.

Xanthomonas campestris pv. campestris (Xcc) is a vascular pathogen of cruciferous plants that normally gains entry to plants via hydathodes. In order to study the basis of the preference for this protal of entry we have developed an Arabidopsis thaliana model with attached or detached leaves partially immersed in a bacterial suspension. Entry of bacteria into leaves, assessed by resistance to surface sterilization, could be detected after 1 h. Dissection of leaves and histochemical staining for beta-glucuronidase produced by the bacteria indicated that they were located in hydathodes. In contrast, similar experiments with the leaf-spotting pathogen X. campestris pv. armoraciae gave patterns of localized staining dispersed over the leaf area, indicative of entry through stomata. A survey of 41 A. thaliana accessions showed that they fell into three classes distinguishable by total numbers of Xcc that entered under standard conditions and by preference for hydathode colonization. Previously isolated Xcc mutants affected in pathogenicity were tested for hydathode colonization: an hrp mutant behaved indistinguishably from the wild type, and rpf regulatory mutants gave 10-fold reduced colonization, whereas with rfaX mutants with altered lipopolysaccharide, few if any viable bacteria were recoverable from hydathodes. This fact, together with the rapid induction of superoxide dismutase in the bacteria located in hydathodes, suggests that an early defense reaction is mounted in the hydathode.

Arabidopsis↗
PubMed1997

A novel regulatory system required for pathogenicity of Xanthomonas campestris is mediated by a small diffusible signal molecule.

Mutations in the seven clustered rpf genes cause downregulated synthesis of extracellular enzymes and reduced virulence of Xanthomonas campestris pathovar campestris (Xcc). The phenotype of mutants in one of the genes, rpfF, can be restored by a diffusible extracellular factor (DSF) produced by all Xcc strains tested, apart from rpfF and rpfB mutants. DSF accumulates in early stationary phase (when synthesis of enzymes is maximal), but levels decline subsequently. Addition of DSF to exponentially-growing wild-type bacteria does not cause precocious enzyme synthesis. rpfB and rpfF are expressed throughout growth, but the rate increases in early stationary phase. RpfB is predicted to be a long-chain fatty acyl CoA ligase, and RpfF shows some relatedness to enoyl CoA hydratases. The properties of DSF suggest that it may be a fatty-acid derivative, and certain lipid preparations possess DSF activity at higher concentrations. These include lipid extracts and acid-hydrolysed lipoplysaccharide and lipid A from Xcc, and purified dodecanoic and hydroxydodecanoic acid. DSF production is confined to certain xanthomonads. We propose a model for the DSF system, which represents a novel mechanism for regulating virulence factor synthesis in response to physiological or environmental changes.

Diffusion↗
PubMed1997

Olfactory acuity as a function of age and gender: a comparison of African and American samples.

A frequently reported finding in age-related sensory impairment is that olfaction shows consistent and uniform decline with age. In most studies, discerning whether loss in olfaction is due to aging per se or to factors extrinsic to the aging process (e.g., smoking, chemical exposure, head injury) is difficult. Moreover, studies of olfaction have generally relied on data collected from samples drawn primarily from Western societies. As such, little is known regarding differences in olfaction involving non-Western cultures. Using international data from the 1986 National Geographic Smell Survey, responses of 19,219 American respondents and 3,204 respondents from Africa were analyzed. All respondents were screened for factors negatively affecting olfaction. Measures of olfactory acuity included odor detection, identification, intensity, and quality. The odor of interest was androstenone, a scent produced by bacteria on the human body and appearing in sweat. The results indicate that some measures of olfactory acuity tend to decline across age groups, but that this decline is less marked than reported in previous studies. The most important finding is that loss of olfaction is not consistent or uniform between geographic regions of America or Africa, between male vs. female respondents, or among the four measures of olfactory acuity. African respondents (both men and women) had significantly higher percentages of detection than did American respondents, women generally reported higher levels of olfactory functioning than did men, and some measures of olfaction were stable across age groups, or were higher among older respondents (e.g., odor identification).

Adolescent↗
PubMed1991

Genetic and molecular analysis of a cluster of rpf genes involved in positive regulation of synthesis of extracellular enzymes and polysaccharide in Xanthomonas campestris pathovar campestris.

The cosmid clone pIJ3020 containing DNA from the plant pathogenic bacterium Xanthomonas campestris pathovar campestris has previously been shown to complement a non-pathogenic mutant defective in synthesis of extracellular enzymes. The DNA cloned in pIJ3020 was analysed by mutagenesis with Tn5 and Tn5lac and by nucleotide sequencing. The results indicate that this region of the genome contains a cluster of genes, mutation in any of which results in failure of the enzymes and extracellular polysaccharide to be synthesized. The designation rpf (regulation of pathogenicity factors) is proposed for these genes. The nucleotide sequence of one gene (rpfC) predicts a protein product with homology to conserved domains of both sensor and regulator proteins of prokaryotic two-component regulatory systems, which are usually involved in regulating gene expression in response to environmental stimuli.

Amino Acid Sequence↗
PubMed1990

Advances in screening protocols for the detection of early bladder cancer.

Bladder cancer screening faces several obstacles, including low yield, numerous false-positive results, and the absence of a single effective screening test. We present a model of a screening program that (1) targets an occupational cohort exposed to a putative carcinogen, to increase the detection of disease, (2) uses four screening tests in parallel to maximize case detection, and (3) defines a diagnostic protocol that minimizes the number of invasive procedures by utilizing both flexible and rigid cystoscopy. In a hypothetical cohort of 1000 men aged 45 to 74 years potentially exposed to a bladder carcinogen, the model would find eight of the nine detectable cancers, with a sensitivity of 89% and a specificity of 78%. In addition, the model allows the sensitivities, specificities, and predictive values of the individual screening tests to be compared and evaluated in a single cohort.

Aged↗
PubMed1990

A Xanthomonas campestris pv. campestris protein similar to catabolite activation factor is involved in regulation of phytopathogenicity.

A DNA fragment from Xanthomonas campestris pv. campestris that partially restored the carbohydrate fermentation pattern of a cya crp Escherichia coli strain was cloned and expressed in E. coli. The nucleotide sequence of this fragment revealed the presence of a 700-base-pair open reading frame that coded for a protein highly similar to the catabolite activation factor (CAP) of E. coli (accordingly named CLP for CAP-like protein). An X. campestris pv. campestris clp mutant was constructed by reverse genetics. This strain was not affected in the utilization of various carbon sources but had strongly reduced pathogenicity. Production of xanthan gum, pigment, and extracellular enzymes was either increased or decreased, suggesting that CLP plays a role in the regulation of phytopathogenicity.

Amino Acid Sequence↗
PubMed1987

Transformation of Xanthomonas campestris pathovar campestris with plasmid DNA.

Procedures for the introduction of plasmid DNA into Gram-negative bacteria have been adapted and optimized to permit transformation of the plant pathogen Xanthomonas campestris pathovar campestris with the cloning vector pKT230 and other broad-host-range plasmids. The technique involves CaCl2-induced competence and heat shock and is similar to that routinely used for Escherichia coli. Wild-type X. c. campestris strains appear to restrict incoming unmodified DNA, so that plasmid DNA for transformation must be prepared from X. c. campestris (into which it has previously been introduced by conjugation). To overcome this disadvantage a restriction-deficient mutant has been isolated.

DNA, Bacterial↗
PubMed1980

Response format and coding procedures in research on time perspective: a methodological commentary.

The dimension of time perspective for extension of personal future was examined as it may be affected by response format and coding procedures. A total of 75 undergraduate students responded to a questionnaire containing one of three formats for reporting anticipated future life-events, varying in the structure imposed on responding. Temporal estimates of life-event occurrence were coded using two procedures, each of which permitted a near and a far value. Analyses suggest that the greatest degree of caution should occur in considering the representativeness of far estimates of extension provided under an open-event format. While coding procedures each produced a significant near/far difference, cross-procedure comparisons were not as impressive, despite also being significant. Questions can therefore be raised regarding techniques for obtaining time perspective data and preparing them for analysis.

Adult↗
PubMedDate not supplied

Xanthomonas campestris contains a cluster of hrp genes related to the larger hrp cluster of Pseudomonas solanacearum.

All Xanthomonas campestris pathovars tested contain DNA which hybridizes to the large hrp gene cluster of Pseudomonas solanacearum (C.A. Boucher, F. Van Gijsegem, P.A. Barberis, M. Arlat, and C. Zischek, J. Bacteriol. 169:5626-5632, 1987). Clones carrying these sequences were isolated from genomic libraries of X. campestris pvs. campestris and vitians. Mutagenesis of the corresponding genomic regions of both pathovars gave strains defective in both pathogenicity and hypersensitive response induction. X. c. pv. campestris contained a hrp gene cluster covering about 25 kb, which was homologous and colinear over a continuous 19-kb DNA region with the P. solanacearum hrp cluster. Cross-complementation showed that X. c. pv. vitians and X. c. pv. campestris hrp sequences are functionally interchangeable, but the source of the hrp genes did not determine the compatibility-incompatibility of the host-pathogen interaction. One X. c. pv. campestris Hrp- mutant was "complemented" by specific subclones of the P. solanacearum hrp cluster, suggesting the existence of some functional homology between the clusters of the two species. Expression of hrp genes (studied by lacZ fusions) was repressed in rich medium, and in minimal medium the level of expression depended on the carbon source supplied to the cells. Transcription of hrp genes was not regulated by genes that control the synthesis of extracellular enzymes, which are required for pathogenicity. In addition X. campestris Hrp- mutants produced wild-type levels of these extracellular enzyme activities. These results suggest the existence of two independent sets of pathogenicity genes that are regulated differently.

Chromosome Mapping↗
PubMedDate not supplied

Interaction of Xanthomonas campestris with Arabidopsis thaliana: characterization of a gene from X. c. pv. raphani that confers avirulence to most A. thaliana accessions.

Infiltration of leaves of Arabidopsis thaliana accession Columbia with Xanthomonas campestris pathovar campestris leads to bacterial growth and disease symptoms reminiscent of those incited in Brassica plants inoculated under the same conditions. A search among A. thaliana accessions for variation in the reaction phenotype to strains of X. campestris pathovars campestris, aberrans, and raphani showed that there were no clear differential responses between plant accessions to the individual bacterial strains tested. X. c. pv. raphani strain 1067 was avirulent to all A. thaliana accessions tested. A gene was cloned from X. c. pv. raphani 1067 which, when transferred into the virulent X. c. pv. campestris strain 8004, strongly reduced symptom development and bacterial growth in A. thaliana Columbia plants but did not affect virulence to Brassica plants. The gene (denoted avrXca) interacted with all A. thaliana accessions tested except one, Kas-1, which developed disease symptoms and supported growth of the transconjugant to levels similar to those with X. c. pv. campestris 8004 alone. Sequence analysis of avrXca revealed a probable open reading frame encoding a protein of 66,566 Da that has no homology with other known sequences. A sequence motif conserved among hrp genes was identified in the 5' noncoding region of avrXca, and features characteristic of a signal peptide were found in the N-terminal portion of the presumed AvrXca protein. DNA from different phytopathogenic bacteria contained sequences hybridizing with avrXca in related X. campestris pathovars but not in Erwinia or Pseudomonas strains.

Amino Acid Sequence↗
PubMedDate not supplied

Use of health services before diagnosis of head and neck cancer among Boston residents.

One hundred thirty incident cases of head and neck cancer in Boston between September 1, 1985, and March 31, 1988, provided interview or medical record review data on the use of health services in the 24 months preceding the diagnosis of cancer. One hundred twenty-four subjects were able to recall whether and how often they visited health care sites in this period, reporting a median number of 10.5 visits; 94% recalled at least one visit. Eighty-nine medical record reviews indicated a median of seven visits. For the most part, these visits were to providers whom subjects considered their regular source of care--sources that provided care in a broad range of locations. These data support a strategy of integrating screening for head and neck cancers into existing health care services.

Adult↗
PubMedDate not supplied

Molecular biology of spiroplasma plasmids.

With one exception, all spiroplasma strains examined contained extrachromosomal DNA, most of which was in the form of covalently closed circular plasmids. One plasmid, pIJ2000, carried by Spiroplasma citri strain ASP-1, was purified and characterized and used to probe for related plasmids in other strains. Unsuccessful attempts were made to clone pIJ2000 into Escherichia coli using the vectors pAT153 and pBR322. However, spiroplasma chromosomal DNA fragments could be cloned without difficulty.

Cloning, Molecular↗