124,683 research outputs found
HB27
No full textThe mesophile Acinetobacter sp, strain BD413 and the extreme thermophile Thermus thremophilus HB27 display high frequencies of natural transformation. In this study we identified and characterized a novel competence gene in Acinetobacter sp, strain BD413, com;l, whose product displays significant similarities to the competence proteins ComA and ComEC in Neisseria and Bacillus species, Transcription of comA correlated with growth phase-dependent transcriptional regulation of the recently identified pilin-like factors of the transformation machinery. This finding strongly suggests that comA is part of a competence regulon, Examination of the genome sequence of T, thermophilus HB27 led to detection of a comA/comEC-like open reading frame (ORF) which is flanked by an ORF whose product shows significant similarities to the Bacillus subtilis competence protein ComEA. To examine whether these two ORFs, designated comEC and comEA, are implicated in natural transformation of T, thermophilus HB27, both were disrupted by using a thermostable kana-mycin resistance marker, Natural transformation in comEC mutants was reduced 1,000-fold, whereas in comEA mutants the natural transformation phenotype was completely eliminated. These results strongly suggest that both genes, comEC and comEA, are required far natural transformation in T, thermophilus HB27, Several transmembrane cr-helices are predicted based on the amino acid sequences of ComA in Acinetobacter sp, strain BD413 and ComEC in T, thermophilus HB27, which suggests that ComA and ComEC are located in the inner membrane and function in DNA transport through the cytoplasmic membrane
comB, a novel competence gene required for natural transformation of Acinetobacter sp BD413: identification, characterization, and analysis of growth-phase-dependent regulation
No full textHere we describe five tandemly arranged and converging ORFs in Acinetobacter sp. BD413, namely lytB, orfY, orfX, comB, and orfZ, located upstream of the previously identified competence gene comC. The N-termini of the deduced proteins OrfY and ComB exhibit the conserved endopeptidase cleavage motifs Of prepilin proteins; the deduced protein ComB is similar to type IV pilins. LytB is similar to the Escherichia toll LytB, which has been implicated in the stringent response. No homologues of OrfX, OrfY and OrfZ could be identified. A mutation in orfY or orfZ led to 100-fold reduced transformation frequencies and a mutation in comB resulted in a noncompetent phenotype. Disruption of lytB did not affect the natural transformation phenotype. Complementation studies clearly demonstrated that comB is involved in natural transformation, whereas the transformation-deficient phenotypes of orfY and orfZ mutants were due to polar effects on comB and comC, respectively. Analyses of the twitching motility phenotype and of the ultrastructure of the noncompetent comB mutant suggested that the competence gene comB is not essential for the biogenesis of type IV pill and expression of the type IV pill-associated property of twitching motility. Transcriptional fusions between comB and a promoter-fire lacZ gene were constructed, and analysis of growth-phase-dependent transcription revealed increased expression of comB during prolonged exponential and stationary phases
Pilin-Like Proteins in the Extremely Thermophilic Bacterium Thermus thermophilus HB27: Implication in Competence for Natural Transformation and Links to Type IV Pilus Biogenesis
No full textThe extreme thermophile Thermus thermophilus HB27 exhibits high frequencies of natural transformation. Although we recently reported identification of the first competence genes in Thermus, the molecular basis of DNA uptake is unknown. A pilus-like structure is assumed to be involved. Twelve genes encoding prepilin-like proteins were identified in three loci in the genome of T. thermophilus. Mutational analyses, described in this paper, revealed that one locus, which contains four genes that encode prepilin-like proteins (pilA1 to piLA4), is essential for natural transformation. Additionally, comZ, a new competence gene with no similarity to known genes, was identified. Analysis of the piliation phenotype revealed wild-type piliation of a pilA1-pilA3Deltakat mutant and a comZ mutant, whereas a piLA4 mutant was found to be completely devoid of pilus structures. These findings, together with the significant similarity of PilA4 to prepilins, led to the conclusion that the T. thermophilus pilus structures are type IV pili. Furthermore, the loss of the transformation and piliation phenotype in the pilA4 mutant suggests that type IV pili are implicated in natural transformation of T. thermophilus HB27
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The thin pili of Acinetobacter sp strain BD413 mediate adhesion to biotic and abiotic surfaces
No full textTwo structurally different appendages, thin and thick pili, are found in members of the genus Acinetobacter. The presence of pilus structures correlates with different phenotypes, such as adherence to surfaces, a trait not only observed in pathogenic Acinetobacter species, as well as motility. However, their distinct individual roles were unknown. To characterize the role of different pili in the physiology of Acinetobacter, we isolated the thin pili from the cell surface of Acinetobacter sp. strain BD413 (recently recognized as representative of Acinetobacter baylyi), a soil bacterium that rapidly takes up naked DNA from its environment. Electron microcopy revealed that the pilus has an external diameter of 2 to 3 nm for single filaments. The filaments are packed into right-handed bundles. The major protein constituting the pilus was purified, and the encoding gene, acuA, was cloned. AcuA was found to be weakly related to the structural subunit of F17 pilli of Escherichia coli. Analyses of the acuA flanking DNA region led to the identification of three closely associated genes, acuD, acuC, and acuG, whose deduced proteins are similar to chaperone, usher, and adhesin of F17-related pill, respectively. ;Transcriptional analyses revealed that acuA expression is maximal in the late-stationary-growth phase. Mutation of acuA led to a loss of thin pili and concomitantly loss of adhesion to polystyrene and erythrocytes but not loss of competence. Therefore, thin pili of Acinetobacter sp. strain BD413 are suggested to be assembled by the chaperone/usher pathway and are involved in adherence to biotic and abiotic surfaces
ComP, a pilin-like protein essential for natural competence in Acinetobacter sp strain BD413: Regulation, modification, and cellular localization
No full textWe recently identified a pilin-like competence factor, ComP, which is essential for natural transformation of the gram-negative soil bacterium Acinetobacter sp, strain BD413, Here we demonstrate that transcription and synthesis of the pilin-like competence factor ComP are maximal in the late stationary growth phase, whereas competence is induced immediately after inoculation of a stationary-phase culture into fresh medium. Western blot analyses revealed three forms of ComP, one with an apparent molecular mass of 15 kDa, which correlates with the molecular mass deduced from the DNA sequence, one 20-kDa form, which was found to be glycosylated, and one 23-kDa form. The glycosylation of ComP was not required for its function in DNA binding and uptake. The 20-kDa form was present in the cytoplasmic membrane, the periplasm, and the outer membrane, whereas the 23-kDa form was located in the outer membrane and might be due to a further modification. Immunological data suggest that ComP is not a subunit of the pilus structures, Possible functions of ComP in the DNA transformation machinery of Acinebacter sp. strain BD413 are discussed
Molecular analyses of the natural transformation machinery and identification of pilus structures in the extremely thermophilic bacterium Thermus thermophilus strain HB27
No full textThermus thermophilus HB27, an extremely thermophilic bacterium, exhibits high competence for natural transformation. To identify genes of the natural transformation machinery of T. thermophilus HB27, we performed homology searches in the partially completed T. thermophilus genomic sequence for conserved competence genes. These analyses resulted in the detection of 28 open reading frames (ORFs) exhibiting significant similarities to known competence proteins of gram-negative and gram-positive bacteria. Disruption of 15 selected potential competence genes led to the identification of 8 noncompetent mutants and one transformation-deficient mutant with a 100-fold reduced transformation frequency. One competence protein is similar to DprA of Haemophilus influenzae, seven are similar to type IV pilus proteins of Pseudomonas aeruginosa or Neisseria gonorrhoeae (PilM, PilN, PilO, PilQ, PilF, PilC, PilD), and another deduced protein (PilW) is similar to a protein of unknown function in Deinococcus radiodurans R1. Analysis of the piliation phenotype of T. thermophilus HB27 revealed the presence of single pilus structures on the surface of the wild-type cells, whereas the noncompetent pil mutants of Thermus, with the exception of the pilF mutant, were devoid of pilus structures. These results suggest that pili and natural transformation in T. thermophilus HB27 are functionally linked
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Complete nucleotide sequence and genetic organization of the 210-kilobase linear plasmid of Rhodococcus erythropolis BD2
No full textThe complete nucleotide sequence of the linear plasmid pBD2 from Rhodococcus erythropolis BD2 comprises 210,205 bp. Sequence analyses of pBD2 revealed 212 putative open reading frames (ORFs), 97 of which had an annotatable function. These ORFs could be assigned to six functional groups: plasmid replication and maintenance, transport and metalloresistance, catabolism, transposition, regulation, and protein modification. Many of the transposon-related sequences were found to flank the isopropylbenzene pathway genes. This finding together with the significant sequence similarities of the ipb genes to genes of the linear plasmid-encoded biphenyl pathway in other rhodococci suggests that the ipb genes were acquired via transposition events and subsequently distributed among the rhodococci via horizontal transfer
In vivo synthesis of monolysocardiolipin and cardiolipin by Acinetobacter baumannii phospholipase D and effect on cationic antimicrobial peptide resistance
No full textAcinetobacter baumannii is an opportunistic pathogen, which has become a rising threat in healthcare facilities worldwide due to increasing antibiotic resistances and optimal adaptation to clinical environments and the human host. We reported in a former publication on the identification of three phopholipases of the phospholipase D (PLD) superfamily in A. baumannii ATCC 19606T acting in concerted manner as virulence factors in Galleria mellonella infection and lung epithelial cell invasion. This study focussed on the function of the three PLDs. A Δpld1-3 mutant was defect in biosynthesis of the phospholipids cardiolipin (CL) and monolysocardiolipin (MLCL), whereas the deletion of pld2 and pld3 abolished the production of MLCL. Complementation of the Δpld1-3 mutant with pld1 restored CL biosynthesis demonstrating that the PLD1 is implicated in CL biosynthesis. Complementation of the Δpld1-3 mutant with either pld2 or pld3 restored MLCL and CL production leading to the conclusion that PLD2 and PLD3 are implicated in CL and MLCL production. Mutant studies revealed that two catalytic motifs are essential for the PLD3-mediated biosynthesis of CL and MLCL. The Δpld1-3 mutant exhibited a decreased colistin and polymyxin B resistance indicating a role of CL in cationic antimicrobial peptides (CAMPs) resistance
- …
