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S Taghavi

Publications and source records attributed to S Taghavi.

30 records · Page 2Linked to original sources
PubMed1998

[Functional results and long-term outcome after bilateral lung transplantation for pulmonary hypertension].

Pulmonary hypertension (PH) signifies elevated blood pressure in the pulmonary circulation either due to clearly defined causes (cardiac, pulmonary-parenchymatous, systemic) or of idiopathic origin (primary PH, PPH). While conservative treatment is beneficial only for a small number of patients, lung transplantation represents a curative measure. The optimal form of transplantation [i.e. single lung (SLTX), bilateral lung (BLTX) or combined heart-lung transplantation (HLTX)] is still under discussion. This study is a retrospective analysis of 16 patients with different forms of PH who underwent BLTX from 1992 to 1996 in Vienna. Four patients had Eisenmenger's disease due to atrial septum defect, 3 had chronic thromboembolic PH and 9 had PPH. BLTX with cardiopulmonary bypass was the standard procedure in all patients. Acute retransplantation had to be performed in 3 patients. Mean pulmonary arterial pressure was reduced from 63 +/- 11 mmHg preoperatively to 23 +/- 5 mmHg on the second day postoperatively (p < 0.0001), while the cardiac index concomitantly improved from 2.1 +/- 0.5 to 3.9 +/- 1.2 l/min/m2 (p < 0.05). Echocardiography proved normalisation of right ventricular wall thickness and end-diastolic diameter within 12 months, while tricuspid insufficiency, present in all patients before transplantation, resolved completely. Perioperatively 4 patients (25%) died due to septic complications (n = 3) or therapy refractory rejection (n = 1). Follow-up of the remaining patients ranged from 6 to 51 months (mean 33 +/- 17). One patient died at 8 months due to fungal sepsis. Eleven patients (68%) are currently alive. Only 2 of them show functional signs of chronic allograft rejection (bronchiolitis obliterans syndrome). All patients are at present in NYHA functional class I or II. In conclusion, BLTX results in complete recovery of right ventricular function and morphology and offers good functional long-term results. Because SLTX correlates with a high incidence of reperfusion edema, and HLTX is seriously limited by the scarcity of donor organs, BLTX should be the method of choice for treating end stage PH.

Adult↗
PubMed1998

Effect of the siderophore alcaligin E on the bioavailability of Cd to Alcaligenes eutrophus CH34.

Alcaligin E, the siderophore of the heavy metal-resistant A. eutrophus strain CH34, was shown to interact with Cd and consequently affect its bioavailability and toxicity. The addition of alcaligin E markedly stimulated the growth in the presence of Cd of an alcaligin E-deficient CH34 derivative. Using bioluminescence assays, this effect could be assigned to a decrease in bioavailability of Cd in the presence of alcaligin E. However, Cd-uptake studies showed no influence of alcaligin E on the cellular concentration of Cd. Furthermore, by scanning electron microscopy, the morphology of precipitated Cd crystals was shown to be altered by alcaligin E. These data suggest that alcaligin E, besides its function in iron supply to the cell, provides a protection against heavy metal toxicity. A link between the A. eutrophus CH34 siderophore system and the czc-mediated Cd-efflux system is hypothesized.

Alcaligenes↗
PubMed1997

Genetic and physical maps of the Alcaligenes eutrophus CH34 megaplasmid pMOL28 and its derivative pMOL50 obtained after temperature-induced mutagenesis and mortality.

We describe the construction of restriction and genetic maps of plasmid pMOL28, which has a size of approximately 180 kb. To do so, partial BamHI-digested DNA of pMOL28 was cloned into cosmid pLAFR3, which can package up to 20-30 kb inserted DNA. Subsequently, a cosmid walking strategy, combined with BamHI or EcoRI restriction analysis and hybridization, was used to construct the restriction maps for both enzymes. On these maps, 35 BamHI fragments and 29 EcoRI fragments were placed, accounting for a total size of approximately 180 kb. We also analyzed several rearranged derivatives of pMOL28 that were obtained after a process of temperature-induced mortality and mutagenesis (TIMM), which is characteristic for Alcaligenes eutrophus CH34 and related strains. The restriction and genetic maps of pMOL50 (222 kb), an enlarged derivative of pMOL28 obtained after TIMM, were constructed. By comparing the pMOL28 and pMOL50 maps, at least two transposable elements were identified which participated in the formation of pMOL50 from pMOL28 during TIMM. These transposable elements were IS1086, which was recently sequenced, and a new element named IS1089, which is located on the 44-kb inserted DNA fragment in pMOL50. Partial sequencing of IS1089 revealed similarity of this element with IS1071 of the chlorobenzoate catabolic transposon Tn5271 of Alcaligenes sp. BR60.

Alcaligenes↗
PubMed1996

Identification of a partition and replication region in the Alcaligenes eutrophus megaplasmid pMOL28.

A 4.64 kb region of the 180 kb heavy metal resistance plasmid pMOL28 of Alcaligenes eutrophus CH34, previously shown to be able to replicate autonomously, was sequenced and analyzed. Three genes involved in plasmid maintenance were identified: parA28 and parB28 are involved in plasmid partitioning and stability, while repA28 encodes a protein required for replication. In addition to the par AB28 genes, a third locus, parS28, required in cis active partitioning was identified. The parABS28 locus of pMOL28 shows strong similarity in organization to the sop, par and rep regions, respectively, of the Escherichia coli F-factor, the E.coli P1 and P7 prophages and the Agrobacterium pTiB6S3 and pRiA4b plasmids. The ParAB28 proteins of pMOL28 also show similarity to the proteins encoded by two conserved open reading frames present in the replication regions of the Pseudomonas putida and Bacillus subtilis chromosomes. The functionality of the pMOL28 par region was examined by performing stability and incompatibility tests between pMOL28 and pMOL846 or pMOL850 which contain the 4.64 EcoRI replicon fragment of pMOL28, cloned in opposite orientations into pSUP202, which is itself unable to replicate in A. eutrophus. The RepA2 8 replication protein showed similarity to the RepL protein of P1, which is required for lytic replication of this E. coli phage. The replication origin of pMOL28, oriV28, seems to be located within the repA28 coding region, and pMOL28 replication may depend on transcriptional activation of oriV28.

Alcaligenes↗
PubMed1994

Plasmids for heavy metal resistance in Alcaligenes eutrophus CH34: mechanisms and applications.

Alcaligenes eutrophus CH34 is the main representative of a group of strongly related strains (mostly facultative chemolithotrophs) that are well adapted to environments containing high levels of heavy metals. It harbors the megaplasmids pMOL28 and pMOL30 which carry resistance determinants to Co2+, Ni2+, CrO(4)2-, Hg2+, Tl+, Cd2+, Cu2+ and Zn2+. Among the best characterized determinants are the cnr operon (resistance to Co, Ni) on pMOL28 and the czc operon on pMOL30 (resistance to Co, Cd and Zn). Although the two systems reveal a significant degree of amino acid similarity in the structural genes, the regulation of the operons is different. The resistance mechanism in both cases is based on efflux. The efflux mechanism leads to a pH increase outside of the cytoplasmic membrane. Metals are sequestered from the external medium through the bioprecipitation of metal carbonates formed in the saturated zone around the cell. This latter phenomenon can be exploited in bioreactors designed to remove metals from effluents. The bacteria are immobilized on composite membranes in a continuous tubular membrane reactor (CTMR). The effluent continuously circulates through the intertubular space, while the external surface of the tubes is in contact with the growth medium. Metal crystals are eventually removed by the effluent stream and collected on a glass bead column. The system has been applied to effluents containing Cd, Zn, Co, Ni and Cu. By introducing catabolic plasmids involved in the aerobic degradation of PCBs and 2,4-D into metal-resistant A. eutrophus strains, the application range was widened to include effluents polluted with both organic and inorganic substances. Biosensors have been developed which are based on the fusion of genes induced by metals to a reporter system, the lux operon of Vibrio fischeri. Bacterial luciferases produce light through the oxidation of fatty aldehydes. The gene fusions are useful both for the study of regulatory genes and for the determination of heavy metal concentrations in the environment.

Alcaligenes↗
PubMed1994

Electroporation of Alcaligenes eutrophus with (mega) plasmids and genomic DNA fragments.

Electroporation was used as a tool to explore the genetics of the heavy-metal-resistant strain Alcaligenes eutrophus CH34. A 12.9-kb A. eutrophus-Escherichia coli shuttle vector, pMOL850, was constructed to optimize electroporation conditions. This vector is derived from the E. coli plasmid pSUP202 and contains the replication region of the A. eutrophus megaplasmid pMOL28. Electroporation was used to transform A. eutrophus CH34 derivatives with megaplasmids (sizes up to 240 kb), and transformants were selected for resistance to heavy metals. Electroporation was also performed with endonuclease-digested genomic DNA. Transformation of markers affecting lysine biosynthesis (lysA194) and biosynthesis of the siderophore alcaligin E were observed. Transfer of the nonselected markers pheB332 and aro-333, linked to lysA194, confirmed the intervention of homologous recombination. However, during transformation of ale::Tn5-Tc, illegitimate recombination and transposition were also observed as an alternative for the inheritance of the Tn5-Tc markers.

Alcaligenes↗
PubMed1993

A new type of Alcaligenes eutrophus CH34 zinc resistance generated by mutations affecting regulation of the cnr cobalt-nickel resistance system.

Spontaneous mutants that were resistant to zinc were isolated from Alcaligenes eutrophus CH34 containing either the native plasmid pMOL28 or a derivative derepressed for its self-transfer, pMOL50. With the cured plasmid-free derivative of CH34, strain AE104, such mutants were not detected. The mutations, which were shown to be located in the plasmid, increased the level of the nickel and cobalt resistance determined by the cnr locus. The chromate resistance closely linked to the cnr locus was not affected by these mutations. In the Znr mutants, the resistance to zinc and nickel was constitutively expressed. Uptake studies showed that the zinc resistance in a Znr mutant resulted from reduced accumulation of zinc ions in comparison with that in the plasmid-free strain. Reduced accumulation of zinc was also observed to a lesser degree in the parental strain induced with nickel, suggesting that zinc interferes with the Ni2+ and Co2+ efflux system. A 12.2-kb EcoRI-XbaI restriction endonuclease fragment containing the cnr locus was cloned from plasmid pMOL28 harboring the mutation and shortened to an 8.5-kb EcoRI-PstI-PstI fragment conferring resistance to zinc, nickel, and cobalt. The 12.2-kb EcoRI-XbaI fragment was also reduced to a 9.7-kb BamHI fragment still encoding weak resistance to nickel and cobalt but not to zinc. Complementation studies demonstrated the recessivity of the cnr mutations with a Znr phenotype. Such mutations thus allow positive selection of mutants affected in the expression of the cnr operon.

Alcaligenes↗
PubMed1992

Cloning and sequencing of IS1086, an Alcaligenes eutrophus insertion element related to IS30 and IS4351.

A new insertion sequence (IS), designated IS1086, was isolated from Alcaligenes eutrophus CH34 by being trapped in plasmid pJV240, which contains the Bacillus subtilis sacB and sacR genes. The 1,106-bp IS1086 element contains partially matched (22 of 28 bp) terminal-inverted repeats and a long open reading frame. Hybridization data suggest the presence of one copy of IS1086 in the strain CH34 heavy-metal resistance plasmid pMOL28 and at least two copies in its chromosome. Analysis of the IS1086 nucleotide sequence revealed striking homology with two other IS elements, IS30 and IS4351, suggesting that they are three close members in a family of phylogenetically related insertion sequences. One open reading frame of the Spiroplasma citri phage SpV1-R8A2 B was also found to be related to this IS family but to a lesser extent. Comparison of the G+C contents of IS30 and IS1086 revealed that they conform to their respective hosts (46 versus 50% for IS30 and Escherichia coli and 64.5% for IS1086 and A. eutrophus). The pressure on the AT/GC ratio led to a very different codon usage in these two closely related IS elements. Results suggesting that IS1086 transposition might be activated by some forms of stress are discussed.

Alcaligenes↗