oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 61 )

2019 ( 264 )

2018 ( 325 )

2017 ( 331 )

Custom range...

Search Results: 1 - 10 of 231806 matches for " Eric C Reynolds "
All listed articles are free for downloading (OA Articles)
Page 1 /231806
Display every page Item
Porphyromonas gingivalis and Treponema denticola Synergistic Polymicrobial Biofilm Development
Ying Zhu, Stuart G. Dashper, Yu-Yen Chen, Simon Crawford, Nada Slakeski, Eric C. Reynolds
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0071727
Abstract: Chronic periodontitis has a polymicrobial biofilm aetiology and interactions between key bacterial species are strongly implicated as contributing to disease progression. Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia have all been implicated as playing roles in disease progression. P. gingivalis cell-surface-located protease/adhesins, the gingipains, have been suggested to be involved in its interactions with several other bacterial species. The aims of this study were to determine polymicrobial biofilm formation by P. gingivalis, T. denticola and T. forsythia, as well as the role of P. gingivalis gingipains in biofilm formation by using a gingipain null triple mutant. To determine homotypic and polymicrobial biofilm formation a flow cell system was employed and the biofilms imaged and quantified by fluorescent in situ hybridization using DNA species-specific probes and confocal scanning laser microscopy imaging. Of the three species, only P. gingivalis and T. denticola formed mature, homotypic biofilms, and a strong synergy was observed between P. gingivalis and T. denticola in polymicrobial biofilm formation. This synergy was demonstrated by significant increases in biovolume, average biofilm thickness and maximum biofilm thickness of both species. In addition there was a morphological change of T. denticola in polymicrobial biofilms when compared with homotypic biofilms, suggesting reduced motility in homotypic biofilms. P. gingivalis gingipains were shown to play an essential role in synergistic polymicrobial biofilm formation with T. denticola.
Comparative transcriptomic analysis of Porphyromonas gingivalis biofilm and planktonic cells
Alvin W Lo, Christine A Seers, John D Boyce, Stuart G Dashper, Nada Slakeski, J Patricia Lissel, Eric C Reynolds
BMC Microbiology , 2009, DOI: 10.1186/1471-2180-9-18
Abstract: Approximately 18% (377 genes, at 1.5 fold or more, P-value < 0.01) of the P. gingivalis genome was differentially expressed when the bacterium was grown as a biofilm. Genes that were down-regulated in biofilm cells, relative to planktonic cells, included those involved in cell envelope biogenesis, DNA replication, energy production and biosynthesis of cofactors, prosthetic groups and carriers. A number of genes encoding transport and binding proteins were up-regulated in P. gingivalis biofilm cells. Several genes predicted to encode proteins involved in signal transduction and transcriptional regulation were differentially regulated and may be important in the regulation of biofilm growth.This study analyzing global gene expression provides insight into the adaptive response of P. gingivalis to biofilm growth, in particular showing a down regulation of genes involved in growth and metabolic activity.The gram-negative obligate anaerobe Porphyromonas gingivalis, in subgingival dental plaque, has been strongly implicated in the onset and progression of chronic periodontitis, a disease characterized by the destruction of the tooth supporting (periodontal) tissues [1,2]. There is increasing evidence that P. gingivalis is also associated with systemic diseases such as atherosclerosis [3,4] and preterm birth [4]. P. gingivalis is an asaccharolytic organism that relies on the catabolism of amino acids for energy production and growth [5]. An array of virulence factors has been associated with P. gingivalis pathogenicity, including proteases, adhesins, fimbriae and capsular polysaccharide [6,7]. The persistence of P. gingivalis in subgingival plaque for periods sufficiently long enough to elicit disease is inherently dependent on it surviving as part of a mature biofilm. Although mutational analyses have been employed to study genes associated with biofilm development by P. gingivalis [8-14], very little is known about the nature of P. gingivalis physiology and the crucial r
Characterization of hemin-binding protein 35 (HBP35) in Porphyromonas gingivalis: its cellular distribution, thioredoxin activity and role in heme utilization
Mikio Shoji, Yasuko Shibata, Teruaki Shiroza, Hideharu Yukitake, Benjamin Peng, Yu-Yen Chen, Keiko Sato, Mariko Naito, Yoshimitsu Abiko, Eric C Reynolds, Koji Nakayama
BMC Microbiology , 2010, DOI: 10.1186/1471-2180-10-152
Abstract: We observed that the hbp35 gene was transcribed as a 1.1-kb mRNA with subsequent translation resulting in three proteins with molecular masses of 40, 29 and 27 kDa in the cytoplasm, and one modified form of the 40-kDa protein on the cell surface. A recombinant 40-kDa HBP35 exhibited thioredoxin activity in vitro and mutation of the two putative active site cysteine residues abolished this activity. Both recombinant 40- and 27-kDa proteins had the ability to bind hemin, and growth of an hbp35 deletion mutant was substantially retarded under hemin-depleted conditions compared with growth of the wild type under the same conditions.P. gingivalis HBP35 exhibits thioredoxin and hemin-binding activities and is essential for growth in hemin-depleted conditions suggesting that the protein plays a significant role in hemin acquisition.Porphyromonas gingivalis has been implicated as a major pathogen associated with chronic periodontitis. The establishment of P. gingivalis at a periodontal site and progression of disease is dependent on the ability of the bacterium to utilize essential nutrients, of which iron (preferably in the form of heme) plays a crucial role. P. gingivalis lacks the majority of enzymes in the biosynthetic pathway for the porphyrin ring, hence it is unable to synthesize protoporphyrin IX, the precursor of heme [1-3]; and unlike other Gram-negative bacteria, P. gingivalis does not produce siderophores [3]. Although several studies have shown that P. gingivalis acquires heme from the host environment using gingipains, lipoproteins and specific outer-membrane receptors [3-5], the precise mechanisms by which P. gingivalis acquires heme are still unknown.The gene encoding the P. gingivalis outer membrane 40-kDa protein (OMP40) was first cloned by Abiko et al. [6]. As the recombinant OMP40 protein was demonstrated to exhibit hemin binding ability, and the molecular mass of the mature polypeptide determined by mass spectrometric analysis was 35.3 kDa, the protein
Porphyromonas gingivalis Type IX Secretion Substrates Are Cleaved and Modified by a Sortase-Like Mechanism
Dhana G. Gorasia?,Paul D. Veith?,Dina Chen?,Christine A. Seers?,Helen A. Mitchell?,Yu-Yen Chen?,Michelle D. Glew?,Stuart G. Dashper?,Eric C. Reynolds
PLOS Pathogens , 2015, DOI: 10.1371/journal.ppat.1005152
Abstract: The type IX secretion system (T9SS) of Porphyromonas gingivalis secretes proteins possessing a conserved C-terminal domain (CTD) to the cell surface. The C-terminal signal is essential for these proteins to translocate across the outer membrane via the T9SS. On the surface the CTD of these proteins is cleaved prior to extensive glycosylation. It is believed that the modification on these CTD proteins is anionic lipopolysaccharide (A-LPS), which enables the attachment of CTD proteins to the cell surface. However, the exact site of modification and the mechanism of attachment of CTD proteins to the cell surface are unknown. In this study we characterized two wbaP (PG1964) mutants that did not synthesise A-LPS and accumulated CTD proteins in the clarified culture fluid (CCF). The CTDs of the CTD proteins in the CCF were cleaved suggesting normal secretion, however, the CTD proteins were not glycosylated. Mass spectrometric analysis of CTD proteins purified from the CCF of the wbaP mutants revealed the presence of various peptide/amino acid modifications from the growth medium at the C-terminus of the mature CTD proteins. This suggested that modification occurs at the C-terminus of T9SS substrates in the wild type P. gingivalis. This was confirmed by analysis of CTD proteins from wild type, where a 648 Da linker was identified to be attached at the C-terminus of mature CTD proteins. Importantly, treatment with proteinase K released the 648 Da linker from the CTD proteins demonstrating a peptide bond between the C-terminus and the modification. Together, this is suggestive of a mechanism similar to sortase A for the cleavage and modification/attachment of CTD proteins in P. gingivalis. PG0026 has been recognized as the CTD signal peptidase and is now proposed to be the sortase-like protein in P. gingivalis. To our knowledge, this is the first biochemical evidence suggesting a sortase-like mechanism in Gram-negative bacteria.
Morphological evaluation of genetic evidence for a Pleistocene extirpation of eastern African impala
Sally C. Reynolds
South African Journal of Science , 2010, DOI: 10.4102/sajs.v106i11/12.325
Abstract: Palaeontology typically relies on fossil studies, in particular morphological differences, to reconstruct and interpret patterns of vertebrate evolution. However, genetic studies of population histories of extant species provide data about past population events (e.g. local extinctions, recolonisations) which are equally relevant to palaeontological questions. This study used morphological traits to evaluate a hypothesis based on genetic evidence that southern African impala (Aepyceros melampus) are the founder population for all other living African impala populations, after an eastern African extirpation event dating to around 200 000 years ago. Measurements of three horn metrics and the presence or absence of a particular dental trait were compared across four regional impala samples. Eastern African impala possess a unique combination of larger horns and a significantly higher occurrence of entostyles when compared to other impala populations. These traits are likely to have characterised a small group of founding impala which recolonised this region. This pattern appears consistent with the genetic evidence that a subset of the southern African impala gave rise to the eastern African populations. Other species with complex population histories, such as wildebeest, eland, topi and hartebeest may also therefore be expected to express variation in certain morphological traits in the fossil record because of similar patterns of recolonisations. The process of local extinction and subsequent repopulation over shorter timescales (102 – 103 years) may pass unnoticed in the fossil record, and lineages may appear uninterrupted. Instead, greater morphological variation within a species may be observed, which may be misinterpreted as reflecting a speciation event, or ecophenotypic variation. Combining data from genetic studies and palaeontology may provide further clues as to how faunal dispersals within Africa shaped the morphological variation in the fossil record, and how to best interpret such differences.
Nyctereutes terblanchei: The raccoon dog that never was
Sally C. Reynolds
South African Journal of Science , 2012, DOI: 10.4102/sajs.v108i1/2.589
Abstract: Fossils of the raccoon dog (genus Nyctereutes) are particularly rare in the African Plio-Pleistocene record, whilst the sole living representative, Nyctereutes procyonoides, is found in eastern Asia and parts of Europe. In southern Africa, only one fossil species of raccoon dog has been identified – Nyctereutes terblanchei. N. terblanchei is recognised from a handful of Plio-Pleistocene sites in South Africa: Kromdraai, Kromdraai–Coopers and Sterkfontein in Gauteng, as well as Elandsfontein in the Western Cape Province. The validity of this species identification was questioned on the basis of the rarity of southern African fossils assigned to Nyctereutes, that is, fewer than 10 specimens have been identified as Nyctereutes. This study examined this fossil sample of the raccoon dog from the Gauteng sites and compared dental and cranial metrics of the fossil with samples of modern canids and published data. Morphological traits used to distinguish Nyctereutes, such as the pronounced subangular lobe on the mandible and the relatively large size of the lower molars, were observed to be variable in all samples. Analysis showed that the size of the dentition of the southern African fossil samples was larger than that of living raccoon dogs, but fell well within the range of that of African jackals. These results suggest that fossil Nyctereutes cannot be distinguished from other canid species based on metric data alone, and may only be diagnosable using combinations of non-metric traits of the dentition and skull. However, based on the degree of morphological variability of the traits used to diagnose Nyctereutes, as well as the rarity of this genus in the African fossil record, these fossils are more likely to belong to a species of jackal or fox.
An X-ray spectral study of 24 type-1 AGN
C. S. Reynolds
Physics , 1996, DOI: 10.1093/mnras/286.3.513
Abstract: I present a study of the X-ray spectral properties of a sample containing 24 type-1 active galactic nuclei using the medium spectral resolution of ``ASCA''. The sample consists of 20 radio-quiet objects and 4 radio-loud objects. A simple power-law continuum absorbed by Galactic material provides a very poor description of the spectra of most objects. Deviations from the power-law form are interpreted in terms of X-ray reprocessing/absorption processes. In particular, at least half of the objects show K-shell absorption edges of warm oxygen (O vii and O viii) characteristic of optically-thin, photoionized material along the line-of-sight to the central engine, the so-called warm absorber. It is found that objects with significant optical reddening display deep O vii edges. Coupled with other evidence, this suggests the existence of dusty warm plasma. A radiatively driven outflow originating from the molecular torus is probably the source of this plasma. Rapid variability of the warm absorber also points to there being another component closer to the central source and probably situated within the broad line region. Spectral features at energies characteristic of cold fluorescent iron K$\alpha$ emission are common. Radio-quiet objects have iron emission well described as originating from either the inner regions of an accretion disk or, in a small number of cases, from the molecular torus. Two of the radio-loud objects (3C~120 and 3C~382) have a much broader feature which presents problems for the relativistic disk model. The presence of radio-jets may be important in forming this spectral feature.
Compton reflection and iron fluorescence in AGN and GBHCs
C. S. Reynolds
Physics , 1998,
Abstract: Any cold, optically-thick matter in the vicinity of an accreting black hole, such as the accretion disk, can intercept and reprocess some fraction of the hard X-ray continuum emission, thereby imprinting atomic features into the observed spectrum. This process of `X-ray reflection' primarily gives rise to a broad reflection `hump' peaking at 30keV and an iron emission line at 6.4keV. In this review, I briefly describe the physics of this process before reviewing the observations of these features in active galactic nuclei (AGN) and Galactic black hole candidates (GBHCs). In some AGN, Seyfert galaxies in particular, the iron line is found to be very broad and asymmetric. It is believed that such lines arise from the innermost regions of the accretion disk, with mildly-relativistic Doppler shifts and gravitational redshifts combining to produce the line profile. Hence, such lines give us a direct observational probe of the region within several gravitational radii of the black hole. The complications that plague similar studies of GBHCs, such as disk ionization and the possibly of inner disk disruption, are also addressed. I conclude with a discussion of iron line reverberation, i.e. temporal changes of the iron line as `echos' of large X-ray flares sweep across the accretion disk. It is shown that interesting reverberation effects, such as a definitive signature of extremal Kerr geometry, is within reach of high throughput spectrometers such as Constellation-X.
On the lack of X-ray iron line reverberation in MCG-6-30-15: Implications for the black hole mass and accretion disk structure
C. S. Reynolds
Physics , 1999, DOI: 10.1086/308697
Abstract: We use the method of Press, Rybicki & Hewitt (1992) to search for time lags and time leads between different energy bands of the RXTE data for MCG-6-30-15. We tailor our search in order to probe any reverberation signatures of the fluorescent iron Kalpha line that is thought to arise from the inner regions of the black hole accretion disk. In essence, an optimal reconstruction algorithm is applied to the continuum band (2-4keV) light curve which smoothes out noise and interpolates across the data gaps. The reconstructed continuum band light curve can then be folded through trial transfer functions in an attempt to find lags or leads between the continuum band and the iron line band (5-7keV). We find reduced fractional variability in the line band. The spectral analysis of Lee et al. (1999) reveals this to be due to a combination of an apparently constant iron line flux (at least on timescales of few x 10^4s), and flux correlated changes in the photon index. We also find no evidence for iron line reverberation and exclude reverberation delays in the range 0.5-50ksec. This extends the conclusions of Lee et al. and suggests that the iron line flux remains constant on timescales as short as 0.5ksec. The large black hole mass (>10^8Msun) naively suggested by the constancy of the iron line flux is rejected on other grounds. We suggest that the black hole in MCG-6-30-15 has a mass of M_BH~10^6-10^7Msun and that changes in the ionization state of the disk may produce the puzzling spectral variability. Finally, it is found that the 8-15keV band lags the 2-4keV band by 50-100s. This result is used to place constraints on the size and geometry of the Comptonizing medium responsible for the hard X-ray power-law in this AGN.
Observing the effects of strong gravity with future X-ray missions
C. S. Reynolds
Physics , 2000, DOI: 10.1063/1.1434647
Abstract: Spectroscopy of the broad iron iron with ASCA and BeppoSAX has up opened the innermost regions of accreting black hole systems to detailed study. In this contribution, I discuss how observations with future X-ray missions will extend these studies and all us to observationally address issues which are currently only in the realm of the theorists. In particular, high-throughput spectroscopy with XMM and, eventually, Constellation-X will allow the full diagnostic power of iron line variability to be realized. Instabilities of the inner accretion flow, the geometry of the variable X-ray source, and the black hole mass and spin will all be open to study. Eventually, X-ray interferometry will allow direct imaging of the black hole region in nearby active galaxies, thereby providing the ultimate probe of black hole astrophysics.
Page 1 /231806
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.