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PubMed2003

Phase variation of the 987P-like CS18 fimbriae of human enterotoxigenic Escherichia coli is regulated by site-specific recombinases.

The gene cluster of the CS18 (PCFO20) fimbriae of human enterotoxigenic Escherichia coli (ETEC) was found to include seven genes (fotA to fotG) that are similar to each of the seven structural and export proteins of the 987P fimbriae. However, no analogous gene to the fasH regulatory gene, which is located at the 3' end of the 987P gene cluster and encodes an AraC-like activator of transcription, could be detected. Surprisingly, two novel genes (fotS and fotT) encoding proteins similar to the site-specific recombinases of the type 1 fimbriae (FimB and FimE) were identified at the 5' end of the fot gene cluster. These genes were shown to be required for the catalysis of a 312 bp-inversion just upstream of fotA. The inversion determines CS18 fimbrial phase variation. FotS participates in inverting the 312 bp-segment in both the ON and OFF orientation, whereas FotT has a bias for the OFF oriented recombination. Similar regulators of fimbriation by phase variation were described in uropathogenic and commensal Enterobacteriaceae. In contrast, only AraC-like transcriptional activators were previously described as regulators of the intestinal colonization factors of human ETEC isolates. Thus, the CS18 and 987P gene clusters encode similar components for fimbrial biogenesis but different types of regulators for fimbriation. The combination of blocks of genes encoding similar structural products but different regulatory proteins underlines how modular DNA rearrangements can evolve by serving pathogen diversification. Acquisition of a phase variation module to regulate fimbrial genes is proposed to be beneficial for the adaptation and transmission of pathogens.

Amino Acid Sequence↗
PubMed1986

Primary structure of the gene encoding the bifunctional dihydrofolate reductase-thymidylate synthase of Leishmania major.

We have determined the nucleotide sequence of the dihydrofolate reductase-thymidylate synthetase (DHFR-TS) gene of the protozoan parasite Leishmania major (dihydrofolate reductase, EC 1.5.1.3 and thymidylate synthase, EC 2.1.1.45). The DHFR-TS protein is encoded by a single 1560-base-pair open reading frame within genomic DNA, in contrast to vertebrate DHFRs or mouse and phage T4 TSs, which contain intervening sequences. Comparisons of the DHFR-TS sequence with DHFR and TS sequences of other organisms indicate that the order of enzymatic activities within the bifunctional polypeptide chain is DHFR followed by TS, the Leishmania bifunctional DHFR-TS evolved independently and not through a phage T4-related intermediate, and the rate of evolution of both the DHFR and TS domains has not detectably changed despite the acquisition of new functional properties by the bifunctional enzyme. The Leishmania gene is 86% G+C in the third codon position, in contrast to genes of the parasite Plasmodium falciparum, which exhibit an opposite bias toward A+T. The DHFR-TS locus is encoded within a region of DNA amplified in methotrexate-resistant lines, as previously proposed.

Amino Acid Sequence↗
PubMed2004

Variable resistance patterns of integron-associated multidrug-resistant Acinetobacter baumannii isolates in a surgical intensive care unit.

Between 1998 and 2000, we characterized 91 nosocomial isolates of Acinetobacter baumannii by antibiotyping and genotyping. A total of 25 ribotypes were obtained among these 91 isolates. When the isolates from surgical intensive care units (ICUs) and other wards were compared, multiresistant A. baumannii isolates with the same ribotype 25 (R-25) were significantly more prevalent in nosocomial infections among the surgical patients. Further subtyping of the strains by pulsed-field gel electrophoresis confirmed that strains of the same ribotype in surgical ICUs and a few isolates from other wards were identical or clonally related. Different antibiotic resistance profiles were observed among these R-25 isolates. All R-25 isolates contained intI1 integrase, and two clusters of integron cassettes were found. These clusters of cassettes were encoded by an open reading frame (ORF) of -5'CS-aac(3)Ia-aadA1a-unknown or f-3'CS or 5'CS-aacA4-aadA1-catB8-3'CS, indicating the involvement of different resistant genes. Two isolates contained bla (IMP-1), which was acquired from a conjugatively transferable plasmid and did not involve integron-associated resistance. In conclusion, an epidemic of nosocomial infections associated with A. baumannii strains that have different resistance profiles was identified. Resistance profiles can change by a combination of plasmid- and integron-associated acquisition, especially in a unit with high antibiotic selective pressures. Infectious control personnel should be alert to the change in resistance profiles during routine monitoring.

Acinetobacter Infections↗
PubMed1992

Miles Technicon H.2 automated hematology analyzer.

Automated hematology analyzers are used in all large hospitals and most commercial laboratories, as well as in most smaller hospitals and laboratories, to perform complete blood counts (including white blood cell, red blood cell, and platelet counts; hemoglobin concentration; and RBC indices) and white blood cell differential counts. Our objectives in this study are to provide user guidance for selecting, purchasing, and using an automated hematology analyzer, as well as to present an overview of the technology used in an automated five-part differential unit. Specifications for additional automated units are available in ECRI's Clinical Laboratory Product Comparison System. We evaluated the Miles Technicon H.2 unit and rated it Acceptable. The information in this Single Product Evaluation is also useful for purchasing other models; our criteria will guide users in assessing components, and our findings and discussions on some aspects of automated hematology testing are common to many available systems. We caution readers not to base purchasing decisions on our rating of the Miles unit alone, but on a thorough understanding of the issues surrounding automated hematology analyzers, which can be gained only by reading this report in its entirety. The willingness of manufacturers to cooperate in our studies and the knowledge they gain through participating lead to the development of better products. Readers should refer to the Guidance Section, "Selecting and Purchasing an Automated Hematology Analyzer," where we discuss factors such as standardization, training, human factors, manufacturer support, patient population, and special features that the laboratory must consider before obtaining any automated unit; we also provide an in-depth review of cost issues, including life-cycle cost analyses, acquisition methods and costs of hardware and supplies, and we describe the Hemacost and Hemexmpt cost worksheets for use with our PresValu and PSV Manager CAHDModel software. Readers should also review the Clinical and Technical Overview and the articles "Miles Technicon H.2 Reports" and "Developing the Evaluation Reference Method."

Blood Cell Count↗
PubMed1980

The short-term and long-term amelioration of academic and motivational deficiencies among low-achieving inner-city adolescents.

56 low-achieving seventh-grade students in a predominantly black, inner-city junior high school were randomly assigned to one of four groups (SMART, PUSH, Standard Reading, or Nonintervention). The highly structured, school-based SMART program employed nonprofessional tutors to improve the academic skills and attitudes of the adolescents. The home-based PUSH program involved parents in restructuring the home environment to foster educational development. The Standard Reading group was the usual school reading class, and the Nonintervention group did not receive any special remediation. A battery of standardized educational and attitudinal tests was administered to each student (a) immediately before assignment to groups, (b) immediately after termination of the 10-week programs, and (c) at 6-month follow-up. Results from the 4 x 3 analysis of variance clearly demonstrated the short- and long-term efficacy of the SMART program and the long-term efficacy of the PUSH program. Each produced substantial increases in both the acquisition of fundamental academic skills and achievement motivation. Implications of these findings and directions for future research are discussed.

Achievement↗
PubMed1993

Relative effects of whole-word and phonetic-prompt error correction on the acquisition and maintenance of sight words by students with developmental disabilities.

We used an alternating treatments design to compare the effects of two procedures for correcting student errors during sight word drills. Each of the 5 participating students with developmental disabilities was provided daily one-to-one instruction on individualized sets of 14 unknown words. Each week's new set of unknown words was divided randomly into two groups of equal size. Student errors during instruction were immediately followed by whole-word error correction (the teacher stated the complete word and the student repeated it) for one group of words and by phonetic-prompt error correction (the teacher provided phonetic prompts) for the other group of words. During instruction, all 5 students read correctly a higher percentage of whole-word corrected words than phonetic-prompt corrected words. Data from same-day tests (immediately following instruction) and next-day tests showed the students learned more words taught with whole-word error correction than they learned with phonetic-prompt error correction.

Child↗
PubMedDate not supplied

Origins of theory of mind, cognition and communication.

There has been a revolution in our understanding of infant and toddler cognition that promises to have far-reaching implications for our understanding of communicative and linguistic development. Four empirical findings that helped to prompt this change in theory are analyzed: (a) Intermodal coordination--newborns operate with multimodal information, recognizing equivalences in information across sensory-modalities; (b) Imitation--newborns imitate the lip and tongue movements they see others perform; (c) Memory--young infants form long-lasting representations of perceived events and use these memories to generate motor productions after lengthy delays in novel contexts; (d) Theory of mind--by 18 months of age toddlers have adopted a theory of mind, reading below surface behavior to the goals and intentions in people's actions. This paper examines three views currently being offered in the literature to replace the classical framework of early cognitive development: modularity-nativism, connectionism, and theory-theory. Arguments are marshaled to support the "theory-theory" view. This view emphasizes a combination of innate structure and qualitative reorganization in children's thought based on input from the people and things in their culture. It is suggested that preverbal cognition forms a substrate for language acquisition and that analyzing cognition may enhance our understanding of certain disorders of communication.

Age Factors↗
PubMed1979

Dynamic spatial resolution.

The study of the dynamic behaviour of radiopharmaceuticals within a patient using a scintillation camera with data acquisition and processing facilities often presents analytical problems because of the limited data available. In the effort to maintain good spatial resolution sensitivity is often needlessly reduced producing further limitation in the statistical accuracy within regions of interest. It is shown that for a particular dynamic study and scintillation camera combination an optimum design of collimator exists, often of much greater sensitivity and poorer resolution than those used hitherto. A simple method is given for producing data for any system which will provide the basic information necessary to read off optimal collimator design parameters.

Mathematics↗
PubMed1996

Genetic organization and functional analysis of the otn DNA essential for cell-wall polysaccharide synthesis in Vibrio cholerae O139.

In 1992 a new Vibrio cholerae strain, designated V. cholerae O139 Bengal, emerged which has been responsible for large outbreaks of cholera in India and Bangladesh. Previously, we have shown that this strain arose from a V. cholerae O1 strain by the acquisition of novel DNA. Sequence analysis revealed that the novel DNA is flanked by two genes, rfaD and rfbQRS, which are also found in O1 strains. The mosaic structure of rfaDVCO139 indicated that it was one of the regions involved in recombination between donor and acceptor DNA. However, sequence divergence between the O1 and O139 rfbQRS genes indicated that the second recombination site between donor and O1-acceptor DNA is probably located downstream of rfbDVCO139. The DNA region between rfaDVCO139 and rfbQRSVCO139, designated otn, contained seven open reading frames (ORFs). Two ORFs, otnA and otnB, showed homology with genes involved in cell-wall polysaccharide synthesis. Mutations in otnA and otnB indicated that they are required for capsule synthesis but not lipopolysaccharide synthesis. The otn DNA is also found in V. cholerae O69 and O141 strains, and the organization of this DNA was essentially identical to that in the O139 strain. However, sequence divergence of the otnAB genes indicated that the O139 otn DNA region was not derived from the O69 or O141 strains. No antigenic relationship was found between the different V. cholerae serotypes carrying otn DNA, so the genes determining the antigenic specificity of the O antigen or capsule must be located outside the otn DNA. The O139 otn DNA contained a JUMPstart sequence, which is associated with polysaccharide-synthetic genes in several bacterial species. Furthermore, a repeat motif was observed in extragenic regions. A number of observations suggest that these sequences may facilitate gene flow between V. cholerae strains and the assembly of clusters of functionally related genes.

Antigens, Bacterial↗
PubMed2000

Molecular and evolutionary characterization of the cp32/18 family of supercoiled plasmids in Borrelia burgdorferi 297.

In this study, we characterized seven members of the cp32/18 family of supercoiled plasmids in Borrelia burgdorferi 297. Complete sequence analysis of a 21-kb plasmid (cp18-2) confirmed that the strain 297 plasmids are similar in overall content and organization to their B31 counterparts. Of the 31 open reading frames (ORFs) in cp18-2, only three showed sequence relatedness to proteins with known functions, and only one, a ParA/SopA ortholog, was related to nonborrelial polypeptides. Besides the lipoproteins, none of the ORFs appeared likely to encode a surface-exposed protein. Comparison with the B31 genomic sequence indicated that paralogs for most of the ORFs in cp18-2 can be identified on other genetic elements. cp18-2 was found to lack a 9- to 10-kb fragment present in the 32-kb homologs which, by extrapolation from the B31 cp32 sequences, contains at least 15 genes presumed to be unnecessary for plasmid maintenance. Sequence analysis of the lipoprotein-encoding variable loci provided evidence that recombinatorial processes within these regions may result in the acquisition of exogenous DNA. Pairwise analysis with random shuffling revealed that the multiple lipoproteins (Mlp; formerly designated 2.9 LPs) fall into two distinct homology groups which appear to have arisen by gene fusion events similar to those recently proposed to have generated the three OspE, OspF, and Elp lipoprotein families (D. R. Akins, M. J. Caimano, X. Yang, F. Cerna, M. V. Norgard, and J. D. Radolf, Infect. Immun. 67:1526-1532, 1999). Comparative analysis of the variable regions also indicated that recombination within the loci of each plasmid may occur independently. Last, comparison of variable loci revealed that the cp32/18 plasmid complements of the B31 and 297 isolates differ substantially, indicating that the two strains have been subject to divergent adaptive pressures. In addition to providing evidence for two different types of recombinatorial events involving cp32/18 plasmids, these findings underscore the need for genetic analysis of diverse borrelial isolates in order to elucidate the Lyme disease spirochete's complex parasitic strategies.

Amino Acid Sequence↗
PubMed2001

Genetic and biochemical analyses of a eukaryotic-like phospholipase D of Pseudomonas aeruginosa suggest horizontal acquisition and a role for persistence in a chronic pulmonary infection model.

Phospholipases D (PLDs) are virtually ubiquitous in eukaryotic organisms; however, they are relatively uncommon in prokaryotes. In this report, we demonstrate that the environmentally acquired, opportunistic pathogen Pseudomonas aeruginosa expresses PLD activity. A gene designated pldA was identified in the genomic database of P. aeruginosa PAO1 encoding a protein with significant homology to eukaryotic PLDs, but not to any prokaryotic PLDs. PldA is most homologous to PLDs from mammals and yeast. The pldA gene was cloned and shown to express an approximately 116 kDa protein with calcium-regulated PLD activity that is localized to the periplasm. Interestingly, not all strains of P. aeruginosa carry pldA. When present, pldA is always linked to an open reading frame (ORF), ORF4, and a gene (vgrA1) encoding a protein homologous to Vgr from Escherichia coli. Vgr proteins contain regularly repeated dipeptide motifs (valine-glycine repeats). In E. coli, genes encoding Vgr are associated with multicopy genetic elements designated Rhs (rearrangement hot-spots). P. aeruginosa PAO1 has 10 vgr homologues dispersed throughout its genome, but the copy number of these genetic elements varies considerably in different strains. Neither vgrA1 nor ORF4 is present in strains lacking pldA. Furthermore, sequences flanking vgrA1, pldA and ORF4 in the P. aeruginosa strains examined are highly conserved, suggesting a specific site of insertion. These and other data suggest that vgrA1, pldA and ORF4 constitute an approximately 7 kb mobile genetic element and that pldA was acquired horizontally, perhaps from a eukaryotic organism. Competition studies between a PldA knock-out mutant and the parental wild-type strain indicate that PldA contributes to the ability of P. aeruginosa PAO1 to persist in a chronic pulmonary infection model in rats.

Animals↗
PubMed1999

Analysis of the replication elements of the pMJ101 plasmid from the fish pathogen Vibrio ordalii.

Vibrio ordalii is a major cause of vibriosis in wild and cultured marine salmonids and carries pMJ101, a 30-kb cryptic plasmid that replicates in the absence of DNA polymerase I without producing single-stranded intermediates. A recombinant derivative harboring the pMJ101 replication region proved to be compatible with pJM1, a plasmid containing the iron acquisition system required for the virulence of V. anguillarum 775, another important pathogen that causes vibriosis. Sequence analysis of a 1.56-kb fragment harboring the pMJ101 replication region revealed the presence of typical features found in DNA origins including an AT-rich region, 11 dam-methylation sites of which 5 are within the putative ori region, and five copies of the 9-bp consensus sequence for DnaA binding. Gel retardation assays demonstrated that the latter replication element indeed binds DnaA purified from Escherichia coli. A potential open reading frame encoding a hydrophilic protein with a predicted pI of 10.3 and an M(r) of 33,826 was found adjacent to the ori region. Although these properties are typical of DNA-binding proteins, no significant homology was found between this predicted protein, named RepM, and other previously characterized proteins. Reverse transcriptase-polymerase chain reaction analysis of total RNA demonstrated the presence of repM mRNA in V. ordalii. The major initiation site of this mRNA was located 187 nucleotides upstream of the GTG initiation codon as determined by nuclease S1 protection assays. This transcription initiation site is preceded by putative -10 and -35 promoter sequences that control the expression of the repM replication gene. These results demonstrate that the replication region of pMJ101 shares some structural and sequence similarities with other DNA replication regions, which include DnaA binding and methylation sites and an open reading frame encoding a distinct protein required for its replication.

Amino Acid Sequence↗
PubMed2001

Names and words without meaning: incidental postmorbid semantic learning in a person with extensive bilateral medial temporal damage.

The authors describe a densely amnesic man who has acquired explicit semantic knowledge of famous names and vocabulary words that entered popular culture after the onset of his amnesia. This new semantic knowledge was temporally graded and existed over and above the implicit memory he demonstrated in reading speed and accuracy, familiarity ratings, and his ability to make correct guesses on unfamiliar items. However, his postmorbid knowledge was limited to verbal labels denoting famous people and words; he possessed virtually no explicit knowledge of the meaning of these words or the identities of these individuals, although there was some evidence that some of this information had been acquired at an implicit level. Findings are discussed in the context of a neural network model (J. L. McClelland, B. L. McNaughton, & R. C. O'Reilly, 1995) of semantic acquisition.

Amnesia↗
PubMed1998

Breath-hold MR cholangiography with snapshot techniques: prospective comparison with endoscopic retrograde cholangiography.

PURPOSE: To compare findings with magnetic resonance (MR) cholangiography with rapid acquisition with relaxation enhancement (RARE) and half-Fourier acquisition with single-shot turbo spin-echo (hereafter, half Fourier RARE) snapshot imaging techniques to those with endoscopic retrograde cholangiography (ERC). MATERIALS AND METHODS: Heavily T2-weighted thick-section (RARE) and thin-section (half-Fourier RARE) MR cholangiography were performed prospectively, on a 1.5-T imager, in the biliary tree of 61 consecutive patients before ERC. Findings at ERC were considered the standard of reference. The radiologist and endoscopist were blinded to each other's report. On- and off-site MR cholangiographic readings were performed to detect stones (n = 24), biliary dilatation (n = 34), or stenosis (n = 36). RESULTS: The sensitivity and specificity of MR cholangiography, respectively, calculated on a lesion-by-lesion basis, were 92.3% and 95.8% for cholangiolithiasis, 94.1% and 92.6% for duct dilatation, and 88.8% and 84.0% for stenosis. With snapshot MR cholangiography, on a patient-by-patient basis, differentiation between normal (n = 15) and abnormal (n = 46) results yielded a sensitivity of 92.4%, a specificity of 83.4%, and a positive predictive value of 95.6%. Pitfalls were caused by flow artifacts, compression by vessels, and low contrast between calculi and surrounding parenchyma. CONCLUSION: Snapshot MR cholangiography allowed noninvasive, accurate detection of biliary stones, strictures, and dilatation similar to that with ERC. Discrepancies regarding low-grade dilatation and strictures had no clinical relevance at retrospective review.

Bile Duct Diseases↗
PubMedDate not supplied

Breath-holding in healthy and pulmonary-compromised populations: effects of hyperventilation and oxygen inspiration.

Suspension of respiration during end-expiration often is recommended to minimize body organ displacement between sequential image acquisitions. The purpose of this report is to evaluate techniques for end-expiratory breath-holding applicable to a pulmonary-compromised population. Eighty-seven consecutive outpatients with chronic pulmonary diseases and 31 healthy nonsmoking volunteers were recruited for the study. All subjects were asked to hold their breath in end-expiration while in the supine position (29 after breathing room air, 29 after hyperventilating room air for six breaths, and 29 after breathing O2 from a portable oxygen tank via nasal cannula until pulse-oximeter readings stabilized or reached 100%). Each volunteer was tested with all three methods. The mean length of time for a breath-hole on room air without hyperventilation was 9.2 seconds for the patients and 31.7 seconds for the volunteers. A breath-hold after hyperventilation of room air was timed at 12.3 seconds for the patients and 41.2 seconds for the volunteers, and after O2 administration, the breath-hold was 22.4 seconds for the patients and 60.9 seconds for the volunteers. No adverse effects occurred. The pulmonary-compromised patient can suspend respiration most successfully after O2 administration (P < .0001), whereas hyperventilation seems to be less beneficial. Nonpulmonary-compromised volunteers can hold their breath for longer periods of time.

Adult↗
PubMed1995

Comparison of clinician judgment with digitized image analysis in the detection of induced optic disk change in monkey eyes.

PURPOSE: To compare the ability of clinicians to detect change in the photographic appearance of the optic disk with the performance of a system for digitized image analysis. METHODS: In 11 monkey eyes, a Topcon Imagenet System was used to acquire eight digitized image pairs and four stereoscopic photographs at an intraocular pressure of 10 mm Hg, and then, again, 45 minutes after intraocular pressure was increased to 45 mm Hg. We recently reported detection of global (ten of 11 eyes) and regional (11 of 11 eyes) change in the digitized images of these eyes by using two new statistical strategies for optic disk analysis. For the current study, we evaluated the ability of three clinicians (the authors) to detect a change within the stereoscopic photographs of these 11 optic disks. For each eye, the eight stereoscopic photographs (four at intraocular pressure of 10 mm Hg and four at intraocular pressure of 45 mm Hg) were developed as stereoscopic slides and arranged into four pairs (10/10, 45/45, 10/45, and 45/10 mm Hg). Thus, two pairs represented no change in intraocular pressure (10/10 and 45/45 mm Hg) and the other two pairs represented either an increase or a decrease in intraocular pressure (10/45 and 45/10 mm Hg). The 44 pairs of stereoscopic slides (four pairs for each of 11 eyes) were masked then randomly mixed. On two separate occasions, each clinician evaluated each pair of stereoscopic slides for the presence of absence of optic disk change. RESULTS: Reproducibility between the two readings of each clinician ranged from .50 to .64 (kappa statistic). Clinicians correctly detected change (as detected by image analysis) within 45% to 64% of the 10/45 and 45/10 pairs of stereoscopic slides. Clinicians correctly indentified no change within 86% to 100% of the 10/10- and 45/45-mm Hg pairs of stereoscopic slides. Clinicians correctly identified no change significantly more often than change (P < .01, chi 2 test). Change was not detected consistently by all three clinicians in any of the 11 eyes. CONCLUSION: In a controlled experimental setting, digitized image acquisition with extensive secondary statistical analysis more sensitively detected small short-term changes in the surface of the optic disks of monkeys than did three masked clinicians.

Animals↗
PubMed2004

Comparative analysis of a genome fragment of an uncultivated mesopelagic crenarchaeote reveals multiple horizontal gene transfers.

Marine planktonic crenarchaeota have escaped all cultivation attempts to date, all crenarchaeota growing in pure culture so far being hyperthermophiles. Here, we present a comparative genomic analysis of a 16S- plus 23S-rDNA-containing fragment of a crenarchaeote retrieved from an environmental genomic library constructed from picoplankton collected at 500 m depth in the Antarctic Polar Front. The clone DeepAnt-EC39 contained an insert of 33.3 kbp, which was completely sequenced. DeepAnt-EC39 appears to represent a lineage specific to deep-sea waters but widespread geographically, as revealed by the analysis of the 16S-23S-rDNA intergenic spacer region. A comparison with previously sequenced marine crenarchaeotal genomic clones also containing an rrn operon (74A4, 4B7 and Cenarchaeum symbiosum strains A and B) revealed a highly variable structure involving gene rearrangements and insertions/deletions. The surroundings of the rrn operon and the contiguous glutamate-1-semialdehyde aminotransferase gene appear hot spots for recombination. Phylogenetic analyses of all individual predicted proteins revealed the existence of several likely cases of horizontal gene transfer both, between the two archaeal kingdoms and between the two prokaryotic domains. The most frequent horizontal transfers appear to involve genes from mesophilic methanogenic euryarchaeota related to Methanosarcinales. We hypothesise that the acquisition of genes from mesophilic bacteria and euryarchaeota has played a major role in the adaptation of Group I crenarchaeota to life at lower temperatures.

Chromosomes, Archaeal↗
PubMed1995

Differential expression of two siderophore-dependent iron-acquisition pathways in Erwinia chrysanthemi 3937: characterization of a novel ferrisiderophore permease of the ABC transporter family.

In planta expression of a high-affinity iron-uptake system involving the siderophore chrysobactin in Erwinia chrysanthemi 3937 contributes greatly to invasive growth of this pathogen on its natural host, African violets. A previous study reported that global regulation by iron in this strain was mediated at the transcriptional level via the cbr locus which, when inactivated by insertional mutation, prevents the chrysobactin system from being tightly repressed by FeCl3. Herein, we report the nucleotide sequence of this locus and the functional analysis of its encoded products. Sequence analysis of a 4.8 kb genomic segment of a plasmid encompassing the cbr locus and characterization of the cognate translated products made it possible to uncover a system exhibiting similarity with prokaryotic transporters implicated in the transport of iron complexes. Accordingly, the CbrA product was shown to be the periplasmic component of a permease complex also including two integral membrane proteins, CbrB and CbrC, and the ATP-binding unit CbrD. This system allowed internalization of Fe(III) when supplied to bacterial cells as 59FeCl3 or 59Fe dicitrate, via complexation to a second siderophore recently detected in strain 3937. Most notably, we demonstrate that this second siderophore-mediated iron-acquisition system is operational in bacterial cells grown in the presence of FeCl3. The regulatory effect of cbr was further assessed on a lacZ chrysobactin operon fusion indicating that the transcriptional control exerted by cbr on expression of the chrysobactin system is of homeostatic nature. in conclusion, E. chrysanthemi provides an interesting model in which iron acquisition involves an inductive process resulting in differential expression of two siderophore-mediated pathways in relation to external iron accessibility.

ATP-Binding Cassette Transporters↗