Longitudinal ruptures of polyester knitted vascular prostheses.
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AIM: The purpose of the study was the characterization of a type of rupture occurring on warp-knitted polyester vascular prostheses. MATERIALS AND METHODS: We studied 20 cases of warp-knitted polyester vascular prostheses that were explanted from humans that showed a longitudinal rupture as a part of a collaborative retrieval program. All the prostheses were immediately fixed in a 10% formaldehyde solution after their explantation in the operating room. The clinical data of these cases were recorded. The explants were photographed, washed to eliminate the surrounding tissues, and photographed again. The ruptures were characterized with macroscopic examination, optical stereomicroscopy, and scanning electron microscopy. RESULTS: The mean duration of implantation of the prostheses was 16.0 +/- 3.3 years (range, 9-20.7 years). The prostheses were Cooley Double Velour (n = 15) and Microvel Double Velour (n = 5). There were 16 aortobifemoral bypass grafts, 1 aorto-biiliac, 1 aorto-aortic, 1 iliofemoral, and 1 axillobifemoral. The longitudinal ruptures occurred on two specific parts of the prostheses: the guide line (6 cases) and the remeshing line (11 cases). In three cases both lines were affected. Scanning electron microscopy showed major degradation of the trilobar filaments of the velour and gradual ruptures of the flat filaments of the remeshing and guide lines. CONCLUSIONS: In this study, we have identified a specific mechanism of late (9-20 years) longitudinal rupture of knitted polyester prostheses consisting of degradation of the polyester filaments along the remeshing and guide lines that run the length of the graft. (+info)
Role of fatty acid de novo biosynthesis in polyhydroxyalkanoic acid (PHA) and rhamnolipid synthesis by pseudomonads: establishment of the transacylase (PhaG)-mediated pathway for PHA biosynthesis in Escherichia coli.
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Since Pseudomonas aeruginosa is capable of biosynthesis of polyhydroxyalkanoic acid (PHA) and rhamnolipids, which contain lipid moieties that are derived from fatty acid biosynthesis, we investigated various fab mutants from P. aeruginosa with respect to biosynthesis of PHAs and rhamnolipids. All isogenic fabA, fabB, fabI, rhlG, and phaG mutants from P. aeruginosa showed decreased PHA accumulation and rhamnolipid production. In the phaG (encoding transacylase) mutant rhamnolipid production was only slightly decreased. Expression of phaG from Pseudomonas putida and expression of the beta-ketoacyl reductase gene rhlG from P. aeruginosa in these mutants indicated that PhaG catalyzes diversion of intermediates of fatty acid de novo biosynthesis towards PHA biosynthesis, whereas RhlG catalyzes diversion towards rhamnolipid biosynthesis. These data suggested that both biosynthesis pathways are competitive. In order to investigate whether PhaG is the only linking enzyme between fatty acid de novo biosynthesis and PHA biosynthesis, we generated five Tn5 mutants of P. putida strongly impaired in PHA production from gluconate. All mutants were complemented by the phaG gene from P. putida, indicating that the transacylase-mediated PHA biosynthesis route represents the only metabolic link between fatty acid de novo biosynthesis and PHA biosynthesis in this bacterium. The transacylase-mediated PHA biosynthesis route from gluconate was established in recombinant E. coli, coexpressing the class II PHA synthase gene phaC1 together with the phaG gene from P. putida, only when fatty acid de novo biosynthesis was partially inhibited by triclosan. The accumulated PHA contributed to 2 to 3% of cellular dry weight. (+info)
Isolation of poly(3-hydroxybutyrate) (PHB)-degrading microorganisms and characterization of PHB-depolymerase from Arthrobacter sp. strain W6.
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Microbial degraders of poly(3-hydroxybutyrate) (PHB) were isolated from soil. Arthrobacter sp. strain W6 used not only PHB as a carbon source, but also PHAs such as poly(3-hydroxybutyrate-co-[5%]3-hydroxyvalerate), poly(3-hydroxybutyrate-co-[14%]3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-[22%]3-hydroxyvalerate). PHB-depolymerase was purified to homogeneity from the culture broth of Arthrobacter sp. strain W6 by a procedure involving DEAE- and butyl-Toyopearl column chromatographies. The Mr of the enzyme was estimated to be about 47,000 by SDS-polyacrylamide gel electrophoresis. The enzyme was most active at pH 8.5 and 50 degrees C, and was inhibited by phenylmethylsulfonyl fluoride, Hg2+, Ag+, and Pb2+. (+info)
A new type of thermoalkalophilic hydrolase of Paucimonas lemoignei with high specificity for amorphous polyesters of short chain-length hydroxyalkanoic acids.
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A novel type of hydrolase was purified from culture fluid of Paucimonas (formerly Pseudomonas) lemoignei. Biochemical characterization revealed an unusual substrate specificity of the purified enzyme for amorphous poly((R)-3-hydroxyalkanoates) (PHA) such as native granules of natural poly((R)-3-hydroxybutyrate) (PHB) or poly((R)-3-hydroxyvalerate) (PHV), artificial cholate-coated granules of natural PHB or PHV, atactic poly((R,S)-3-hydroxybutyrate), and oligomers of (R)-3-hydroxybutyrate (3HB) with six or more 3HB units. The enzyme has the unique property to recognize the physical state of the polymeric substrate by discrimination between amorphous PHA (good substrate) and denatured, partially crystalline PHA (no substrate). The pentamers of 3HB or 3HV were identified as the main products of enzymatic hydrolysis of native PHB or PHV, respectively. No activity was found with any denatured PHA, oligomers of (R)-3HB with five or less 3HB units, poly(6-hydroxyhexanoate), substrates of lipases such as tributyrin or triolein, substrates for amidases/nitrilases, DNA, RNA, casein, N-alpha-benzoyl-l-arginine-4-nitranilide, or starch. The purified enzyme (M(r) 36,209) was remarkably stable and active at high temperature (60 degrees C), high pH (up to 12.0), low ionic strength (distilled water), and in solvents (e.g. n-propyl alcohol). The depolymerase contained no essential SH groups or essential disulfide bridges and was insensitive to high concentrations of ionic (SDS) and nonionic (Triton and Tween) detergents. Characterization of the cloned structural gene (phaZ7) and the DNA-deduced amino acid sequence revealed no homologies to any PHB depolymerase or any other sequence of data banks except for a short sequence related to the active site serine of serine hydrolases. A classification of the enzyme into a new family (family 9) of carboxyesterases (Arpigny, J. L., and Jaeger, K.-E. (1999) Biochem. J. 343, 177-183) is suggested. (+info)
Introduction of bacterial metabolism into higher plants by polycistronic transgene expression.
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Multiple-gene transformation is required to improve or change plant metabolisms effectively; but this many-step procedure is time-consuming and costing. We succeeded in the metabolic engineering of tobacco plants by introducing multiple genes as a bacteria-type operon into a plastid genome. The tobacco plastid was transformed with a polycistron consisting of three bacterial genes for the biosynthesis of a biodegradable polyester, polyhydroxybutyrate (PHB). Accumulation of PHB in the leaves of the transgenic tobacco indicated that the introduced genes were polycistronically expressed. This "phyto-fermentation" system can be used in plant production of various chemical commodities and pharmaceuticals. (+info)
Model system for studies of microbial dynamics at exuding surfaces such as the rhizosphere.
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An autoclavable all-glass system for studying microbial dynamics at permeable surfaces is described. Standard hydrophobic or hydrophilic membranes (46-mm diameter) of various pore sizes were supported on a glass frit through which nutrient solutions were pumped by a peristaltic pump. The pump provided a precisely controlled flow at speeds of 0.5 to 500 ml of defined or natural cell exudates per h, which passed through the membrane into a receiving vessel. The construction allowed a choice of membranes, which could be modified. The system was tested with a bacterium, isolated from rape plant roots (Brassica napus L.), that was inoculated on a hydrophilic membrane filter and allowed to develop into a biofilm. A defined medium with a composition resembling that of natural rape root exudate was pumped through the membrane at 0.5 ml/h. Scanning electron microscopic examinations indicated that the inoculum formed microcolonies embedded in exopolymers evenly distributed over the membrane surface. The lipid composition and content of poly-beta-hydroxybutyrate in free-living and adhered cells were determined by gas chromatography. The bacterial consumption of amino acids in the exudate was also studied. (+info)
Leeds-Keio artificial ligament: a new concept for the anterior cruciate ligament reconstruction of the knee.
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The features of the Leeds-Keio artificial ligament, which was developed as a collaborative project between the University of Leeds in the UK and Keio University, are introduced. The ligament is made of polyester, and has a mesh structure. The diameter of the polyester fibers is 22 microns. The ligament has a tensile strength sufficient for anterior cruciate ligament (ACL) reconstruction, and fatigue tests have shown satisfactory durability of the ligament. The stiffness of the Leeds-Keio artificial ligament is about 200 N/mm, which is similar to the natural ACL. A combination of a bone plug and stapling is used for the bone fixation, taking into consideration the strength in both the initial mechanical fixation and the long term fixation. From an animal study, it was shown that fibrous tissue was induced around the artificial ligament, and the collagen fibers became aligned in the longitudinal direction of the ligament. For the clinical experience, one-hundred and thirty five cases were reviewed. The Lachaman sign disappeared in 87.4%, and the pivot shift sign disappeared in 88.1%. Side-to-side difference of anterior displacement of the knee, measured with a KT-2000 knee arthrometer at 30 degrees of flexion, was less than 3 mm in 85.9%. More than 90% of the patients experienced full range of motion. Thus, from the clinical results, it can be concluded that reasonable stability was obtained with the operation. If the Leeds-Keio artificial ligament may not be the perfect substitute for the ACL, both experimental and clinical studies indicate that it represents a major forward step in the history of knee ligament surgery. (+info)
Polyhydroxyalkanoate-accumulating bacterium isolated from soil of a sugar-cane plantation in Brazil.
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Strain IPT101T, isolated from the soil of a sugar-cane plantation in Brazil, was analysed in a polyphasic taxonomic study. The strain produces polyhydroxyalkanoates from sucrose and other carbon sources. Morphological, physiological and biochemical data as well as 16S rDNA, whole-cell protein and fatty acid analyses indicated that strain IPT101T represents a new species in the genus Burkholderia. The name Burkholderia sacchari sp. nov. is proposed, with strain IPT101T (= LMG 19450T = CCT 6771T) as the type strain. (+info)