Recombination and clonality in natural populations of Escherichia coli

Bacteria such as Escherichia coli have been commonly viewed as being primarily clonal organisms. As such, the genetic variation within clones was thought to be almost exclusively the result of the mutational process. This conclusion has recently been challenged by data from DNA sequencing studies of natural isolates that are incompatible with a primarily clonal structure. Molecular population genetic analyses of these data, including gene genealogical comparisons, have raised the possibility of a much more complex population structure that may encompass relatively frequent recombination, recurrent selective sweeps and extensive ecological population subdivision.     

Definitive Evidence for the existence of tight junctions in invertebrates

Extensive and unequivocal tight junctions are here reported between the lateral borders of the cellular layer that circumscribes the arachnid (spider) central nervous system. This account details the features of these structures, which form a beltlike reticulum that is more complex than the simple linear tight junctions hitherto found in invertebrate tissues and which bear many of the characteristics of vertebrate zonulae occludentes. We also provide evidence that these junctions form the basis of a permeability barrier to exogenous compounds. In thin sections, the tight junctions are identifiable as punctate points of membrane apposition; they are seen to exclude the stain and appear as election- lucent moniliform strands along the lines of membrane fusion in en face views of uranyl-calcium-treated tissues. In freeze-fracture replicas, the regions of close membrane apposition exhibit P-face (PF) ridges and complementary E-face (EF) furrows that are coincident across face transitions, although slightly offset with respect to one another. The free inward diffusion of both ionic and colloidal lanthanum is inhibited by these punctate tight junctions so that they appear to form the basis of a circumferential blood-brain barrier. These results support the contention that tight junctions exist in the tissues of the invertebrata in spite of earlier suggestions that (a) they are unique to vertebrates and (b) septate junctions are the equivalent invertebrate occluding structure. The component tight junctional 8- to 10-nm-particulate PF ridges are intimately intercalated with, but clearly distinct from, inverted gap junctions possessing the 13-nm EF particles typical of arthropods. Hence, no confusion can occur as to which particles belong to each of the two junctional types, as commonly happens with vertebrate tissues, especially in the analysis of developing junctions. Indeed, their coexistance in this way supports the idea, over which there has been some controversy, that the intramembrane particles making up these two junctional types must be quite distinct entities rather than products of a common precursor.     

Clinical and angiographic results with the ACS MULTI-LINK DUET trade mark Coronary Stent System - the DUET Study

BACKGROUND: The DUET Study is a multicenter prospective efficacy and safety evaluation of the ACS MULTI-LINK DUET coronary stainless steel balloon-expandable stent. AIMS: The primary objective was to determine the one-month incidence of MACE (major adverse cardiac events). The secondary objectives were the acute success rate, the restenosis and reocclusion rates (assessed by quantitative coronary angiography (QCA)) at six months and the occurrence of MACE in hospital and at six months. METHODS: Two hundred and ten patients were enrolled between February and June 1998 in 18 European centers. Successful stent placement was achieved in 209 patients. All patients were treated with ticlopidine 500 mg/day for one month and with aspirin >/=100 mg/day. To allow the investigators to gain familiarity with the stent system, the first one to three patients per center formed a separate lead-in population leaving an intention-to-treat population of 157 patients. The majority of the intention-to-treat population were male (79%); 28% had unstable angina, 69% had stable angina, 44% had had a previous myocardial infarction, 15% had had a previous percutaneous transluminal coronary angioplasty, and 3% had a history of stroke. The target vessel was 38.5% left anterior descending artery, 20.5% left circumflex artery and 41.0% right coronary artery. RESULTS: All but one of the intention-to-treat patients were effectively stented (17 required multiple stents). Six-month angiographic follow-up was available in 90% of the intention-to-treat population. Minimal lumen diameter (MLD) postprocedure was 2.61 +/- 0.33 mm, with a residual diameter stenosis of 16%. Six-month follow-up data showed an MLD of 1.87 +/- 0.56 mm with a residual diameter stenosis of 36%. The binary restenosis rate (>/=50% residual stenosis) was 15.6%. Up to one month following the procedure 94.9% of the population was MACE-free, with two subacute occlusions. At six months all patients were alive, of whom 82.8% were MACE-free, and 73% were free of anginal complaints. CONCLUSION: The results observed in the current DUET registry are comparable to data of other balloon-expandable-stent trials, with a low incidence of clinical events at follow-up.     

Genetic structure of Helianthus occidentalis (Asteraceae) in a preserve withfragmented habitat

We examined the spatial genetic structure of Helianthus occidentalis Riddell ssp. occidentalis Riddell (western sunflower) to determine whether this species is highly clonal and whether the distance between prairie patches influences genetic differentiation. In the Edge of Appalachia Preserve System, Ohio, this species is restricted to prairie patches that have a clumped distribution in the forest matrix. Data from this insect-pollinated forb with gravity-dispersed seed were compared to data from the same patches for Asclepias verticillata, an insect-pollinated species with wind-dispersed seed. Allozyme electrophoresis was used to collect genetic data from H. occidentalis samples from eight patches in four regions. Genetic data from three polymorphic loci indicted that this species is not highly clonal. Genetic differentiation was greater among patches within a region than among regions, suggesting that gene flow among patches is more limited in H. occidentalis than in A. verticillata. Founder effect may also have contributed to observed genetic differences among patches as some of these populations may have re-established after release from human use. As habitat fragmentation is increasing in the preserve, it is also likely that genetic differentiation may be increasing. Therefore, monitoring of genetic structure is necessary to further assess the effect of fragmentation.     

Fluorescent isotope-coded affinity tag (FCAT). I: Design and synthesis

A novel class of isotope-coded affinity tag is proposed possessing a fluorescent feature, referred to as fluorescent isotope-coded affinity tag (FCAT), to provide a new tool for quantitative proteomics. The label is designed to bind cysteine containing proteins or peptides. The FCAT reagent comprises four functional elements: a specific chemical reactivity group toward sulfhydryl groups; a linker that can incorporate the stable isotopes; a hydroxymethylbenzoic residue (base labile group) to cleave off a large part of the label before MS analysis; and a fluorescent tag for absolute quantification. The fluorescent part of the tag is also planned to be utilized to isolate the FCAT-labeled peptides via antibody based pull-down method. In this paper, we report on the solid phase organic synthesis of the light isotope containing FCAT molecule. The new labeling reagent showed good reactivity with model cysteine containing peptides. The fluorophore group was also effectively cleaved off from the labeled products to accommodate easier MS based analysis.     

Microbial Source Tracking in Adjacent Karst Springs

Modern man-made environments, including urban, agricultural, and industrial environments, have complex ecological interactions among themselves and with the natural surroundings. Microbial source tracking (MST) offers advanced tools to resolve the host source of fecal contamination beyond indicator monitoring. This study was intended to assess karst spring susceptibilities to different fecal sources using MST quantitative PCR (qPCR) assays targeting human, bovine, and swine markers. It involved a dual-time monitoring frame: (i) monthly throughout the calendar year and (ii) daily during a rainfall event. Data integration was taken from both monthly and daily MST profile monitoring and improved identification of spring susceptibility to host fecal contamination; three springs located in close geographic proximity revealed different MST profiles. The Giach spring showed moderate fluctuations of MST marker quantities amid wet and dry samplings, while the Zuf spring had the highest rise of the GenBac3 marker during the wet event, which was mirrored in other markers as well. The revelation of human fecal contamination during the dry season not connected to incidents of raining leachates suggests a continuous and direct exposure to septic systems. Pigpens were identified in the watersheds of Zuf, Shefa, and Giach springs and on the border of the Gaaton spring watershed. Their impact was correlated with partial detection of the Pig-2-Bac marker in Gaaton spring, which was lower than detection levels in all three of the other springs. Ruminant and swine markers were detected intermittently, and their contamination potential during the wet samplings was exposed. These results emphasized the importance of sampling design to utilize the MST approach to delineate subtleties of fecal contamination in the environment.