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Biomedical subjects

H Antoun

Publications and source records attributed to H Antoun.

At least 19 recordsLinked to original sources
PubMed2002

Rock phosphate solubilization and colonization of maize rhizosphere by wild and genetically modified strains of Penicillium rugulosum.

Maize root colonization and phosphate solubilizing activity of the fungus Penicillium rugulosum were assessed in a greenhouse trial using soil-plant microcosms. The bacterial gene hph conferring resistance to hygromicin B was introduced by electroporation in the wild-type strain IR-94MF1 of P. rugulosum and one transformant, w-T3, was selected. Maize plants were grown for 5 weeks in a P-poor soil and fertilized with a Florida apatite mineral, with Navay, an apatite rock deposit from Venezuela, or with simple superphosphate. Inoculation treatments included strain IR-94MF1, transformant w-T3 and two IR-94MF1 UV-induced mutants with enhanced (Mps++) or reduced (Mps-) in vitro mineral phosphate solubilizing activity. In the absence of P fertilization, inoculation with any P. rugulosum isolate significantly reduced the size of the total and P-solubilizing bacterial community present in maize rhizosphere. The bacterial community significantly increased in maize inoculated with IR-94MF1 and w-T3 when P was added as apatites Navay or Florida. All P. rugulosum strains were able to stimulate the growth of maize plants as indicated by 3.6 to 28.6% increases in dry matter yields. In the presence of rock phosphate, P uptake by maize plants inoculated with the two mutants Mps++ and Mps- was not always in agreement with their P-solubilizing phenotypes. Strain IR-94MF1 and transformant w-T3 increased P assimilation by the plants fertilized with Navay rock phosphate by 26 and 38%, respectively. In this treatment, w-T3 showed its highest significant maize rhizosphere colonization. With the simple superphosphate treatment, w-T3 increased P uptake in plants by 8% over the uninoculated control and also decreased significantly the community size of total bacteria, total fungi, and P-solubilizing fungi in the rhizosphere.

Biological Transport↗
PubMed2001

A prospective randomized study comparing two techniques of bone augmentation: onlay graft alone or associated with a membrane.

Two techniques of ridge augmentation using onlay bone graft alone or associated with a non-resorbable membrane have been previously described. This prospective, randomized study compared these two techniques at 6 months, in terms of bone gain, resorption and quality obtained at edentulous sites. Osseous measurements were taken using stents, callipers and CT-scans. Membrane exposure occurred at one site, 4 weeks after placement. Endosseous implants were successfully placed at all grafted sites. The mean graft thickness for all subjects was 4.7 mm (range: 2.3-6.2 mm). Overall mean resorption was 1.5 mm (range: 0-4.6 mm) whereas overall mean width gain was 3.2 mm (range: 0.8-6.2 mm). Six months following surgery, the membrane group experienced significantly less bone resorption than the graft alone group (P<0.01). Width augmentation did not differ significantly between the two groups. In conclusion, combining a membrane with an onlay graft demonstrates less bone resorption with a minimal risk of complications. Longer follow-up is needed to confirm the benefits of using a non-resorbable membrane.

Adolescent↗
PubMed2001

Unusual methyl-branched alpha,beta-unsaturated acyl chain substitutions in the Nod Factors of an arctic rhizobium, Mesorhizobium sp. strain N33 (Oxytropis arctobia).

Mesorhizobium sp. strain N33 (Oxytropis arctobia), a rhizobial strain isolated in arctic Canada, is able to fix nitrogen at very low temperatures in association with a few arctic legume species belonging to the genera Astragalus, Onobrychis, and Oxytropis. Using mass spectrometry and nuclear magnetic resonance spectroscopy, we have determined the structure of N33 Nod factors, which are major determinants of nodulation. They are pentameric lipochito-oligosaccharides 6-O sulfated at the reducing end and exhibit other original substitutions: 6-O acetylation of the glucosamine residue next to the nonreducing terminal glucosamine and N acylation of the nonreducing terminal glucosamine by methyl-branched acyl chains of the iso series, some of which are alpha,beta unsaturated. These unusual substitutions may contribute to the peculiar host range of N33. Analysis of N33 whole-cell fatty acids indicated that synthesis of the methyl-branched fatty acids depended on the induction of bacteria by plant flavonoids, suggesting a specific role for these fatty acids in the signaling process between the plant and the bacteria. Synthesis of the methyl-branched alpha,beta-unsaturated fatty acids required a functional nodE gene.

Acyltransferases↗
PubMed2001

[Effects of inoculation with Rhizobium leguminosarum biovar trifolii on wheat cultivated in clover crop rotation agricultural soil in Morocco].

One hundred strains of Rhizobium leguminosarum bv. trifolii were isolated from roots of wheat cultivated in rotation with clover in two different regions of Morocco. The isolates were first screened for their effect on the growth of the cultivar Rihane of wheat cultivated in an agricultural soil under greenhouse conditions. After 5 weeks of growth, 14 strains stimulating the fresh or dry matter yield of shoots were selected and used in a second pot inoculation trial performed with two different agricultural soils. The results show that the strains behaved differently according to the soil used. In the loamy sand Rabat, strain IAT 168 behaved potentially like a plant growth promoting rhizobacteria (PGPR), as indicated by the 24% increases (P < 0.1) observed in wheat shoot dry matter and grain yields. In the silty clay Merchouch, no PGPR activity was observed, and 6 strains showed a significant deleterious effect on yields. These observations suggest that it is very important in a crop rotation system to choose a R. leguminosarum bv. trifolii strain that is effective with clover and shows PGPR activity with wheat to avoid deleterious effects on wheat yields.

Crops, Agricultural↗
PubMed2000

Physiological adaptation to low temperatures of strains of Rhizobium leguminosarum bv. viciae associated with Lathyrus spp.(1).

Strains of Rhizobium leguminosarum bv. viciae, isolated from the legume species Lathyrus japonicus and Lathyrus pratensis in northern Quebec (Canada), showed different capacities for growing at low temperature. In the present study, we investigated some mechanisms related to cold adaptation. Two cold-adapted strains (psychrotrophs) were compared to a poorly adapted strain and to a cold-sensitive strain (reference strain) for freezing survival, protein induction and fatty acid composition under low temperature. Following cold shocks (25 degrees C to 10, 5 and 0 degrees C), a common 6.1-kDa CSP (cold shock protein) was induced in all strains, but the total number of CSPs synthesized at 0 degrees C was higher in cold-adapted strains than in the cold-sensitive strain. The synthesis of CAPs (cold acclimation proteins) was observed under continuous growth at 5 degrees C in all three strains capable of growth at this temperature. Levels of survival after 24 h at -80 degrees C where higher in cold- (79%) and poorly adapted (64%) strains than in the cold-sensitive strain (33%), but a 2-h acclimation period at 5 degrees C before freezing doubled the survival of the cold-sensitive strain. Low temperature conditions affected similarly the fatty acid composition of all strains, regardless of their cold adaptation level. The proportion of unsaturated fatty acids increased significantly with the lowering of growth temperature from 25 to 5 degrees C, but showed a tendency to decrease after a cold shock from 25 to 5 degrees C. A specific unsaturated fatty acid, cis-12 octadecanoic acid, was produced during growth at 5 degrees C. The unsaturated cis-vaccenic acid was the principal component under all conditions. The cold adaptation trait was weakly reflected in symbiosis with the agronomic legume, Lathyrus sativus, with which one cold-adapted strain showed a slightly higher nitrogenase activity and shoot dry matter yield than a commercial strain under a sub-optimal temperature regime.

Journal Article↗
PubMed2000

The dnaJ (hsp40) locus in Rhizobium leguminosarum bv. phaseoli is required for the establishment of an effective symbiosis with Phaseolus vulgaris.

P121R25 is a Tn5-induced mutant of the effective Rhizobium leguminosarum bv. phaseoli strain P121R that is unable to use glutamate as the sole carbon and nitrogen source and is defective in symbiotic nitrogen fixation. Enzymatic analysis showed that three enzymes implicated in glutamate metabolism (glutamate dehydrogenase, 2-oxoglutarate dehydrogenase, and glutamate synthase) were affected by this mutation. Sequencing of the chromosomal locus bordering the Tn5 in P121R25 indicated the presence of the dnaK and dnaJ genes in an arrangement similar to that described in R. leguminosarum bv. viciae (GenBank accession number Y14649). The mutation was located in the dnaJ (hsp40) gene.

Chromosome Mapping↗
PubMed1999

Radiological analysis of hyaline membrane disease after exogenous surfactant treatment.

BACKGROUND: Exogenous surfactant treatment of hyaline membrane disease is known to modify the pattern of radiological changes on the chest radiograph. OBJECTIVES: To analyse and attempt to explain the radiological changes observed after exogenous surfactant treatment. Materials and methods. Thirty-nine premature infants with typical hyaline membrane disease. RESULTS: Transient asymmetrical clearing with better aeration of the right lung in the absence of malposition of the tip of the endotracheal tube was observed in nine cases (23 %). This asymmetry was patchy in one case. It was due to a complication of mechanical ventilation in three cases [pneumothorax (n = 2) and pneumomediastinum (n = 1)]. In the other six cases, asymmetrical clearing could be related to the anatomical position of the right main bronchus, which facilitates distribution of surfactant to the right lung. However, the course of these premature infants was similar to that of infants with symmetrical chest radiological findings after treatment. CONCLUSIONS: Asymmetrical clearing of chest radiographs, sometimes patchy, after surfactant treatment requires exclusion of pneumothorax or infection but has no influence on clinical outcome.

Biological Products↗
PubMed1999

Cerebellar atrophy: an important feature of carbohydrate deficient glycoprotein syndrome type 1.

We report three children, all younger than 2 years of age, presenting with cerebellar atrophy related to carbohydrate-deficient glycoprotein syndrome type 1, an autosomal recessive metabolic disease. One patient had multisystem disease; two others had mental retardation with ataxia. In all cases the cerebellar atrophy was diagnosed on magnetic resonance imaging and, in one case, confirmed by autopsy. The cerebellar atrophy predominantly affected the anterior lobe. Vertical orientation of the tentorium cerebelli from the neonatal period in two cases suggests antenatal onset of the disease. Biological tests confirmed the diagnosis in all cases.

Atrophy↗
PubMed1999

[Imaging in pediatric Herpes simplex virus type I encephalitis].

PURPOSE: The aim of this study was to describe radiological features of herpes simplex virus 1 encephalitis, rarely reported in children. PATIENTS AND METHODS: We analyzed imaging findings in 10 children with biologically proven herpes simples virus 1 encephalitis. RESULTS: Eight CT scans were performed before the second day of the clinical course, 6 CT and 6 MRI were performed after day 4. The initial CT scan was normal in half of the cases. Low densities and hemorrhagic lesions were seen in almost half of the cases. There was no abnormal contrast enhancement in this series. DISCUSSION: After 4 days of infection, hemorrhagic lesions were seen in all cases. Unilateral thalamic involvement was observed in half of the children, in correlation with clinical recurrence of encephalitis. The diagnostic, histological and therapeutic significance of these thalamic involvements remains to be elucidated.

Adolescent↗
PubMed1997

Sequence and mutational analysis of the 6.7-kb region containing nodAFEG genes of Rhizobium sp. strain N33: evidence of DNA rearrangements.

A 6.7-kb region upstream of nodBC genes in Rhizobium sp. strain N33 was shown to contain the nodAFEG genes and an open reading frame designated orfZ. The open reading frames for these genes contain 591, 282, 1209, 738, and 1,338 nucleotides respectively. Homologues of these genes were found in other rhizobia with the exception of orfZ, for which there was no counterpart found in the Genbank/EMBL database. Tn5 mutagenesis in nodEG and in the intergenic nodG-B region has shown a Nod+ phenotype on their temperate hosts Onobrychis viciifolia and Astragalus cicer. The nodules formed on O. viciifolia plants by these mutants were altered in shape and size. However, on A. cicer there was only a reduction in the number of nodules formed, compared with the wild-type strain. Sequence analysis of the orfZ-nodA and nodG-B intergenic regions indicates the presence of truncated nodD genes.

DNA Mutational Analysis↗
PubMed1996

Sequence and mutational analysis of the common nodBCIJ region of Rhizobium sp. (Oxytropis arctobia) strain N33, a nitrogen-fixing microsymbiont of both arctic and temperate legumes.

By heterologous hybridization, we have identified the common nodulation genes nodBCIJ of Rhizobium sp. strain N33 within a 8.2-kb PstI fragment. The nodBCIJ genes are located within a 4,620-bp region which also included a consensus nod box promoter. The four open reading frames coding for the nodBCIJ genes contain 657, 1,353, 915, and 789 nucleotides, respectively. We found that the nodA gene was not adjacent to the nodB gene, unlike the situation in many rhizobia. The DNA of the nodBCIJ genes of Rhizobium sp. strain N33 were found to be homologous to the corresponding genes of other rhizobia except for the 3'-coding region of the nodC gene. The deduced NodC protein was the longest of the rhizobia except Bradyrhizobium japonicum. Tn5 mutagenesis of the common nod region of strain N33 revealed that the nodBC genes were essential for nodulation on their temperate hosts Onobrychis viciifolia and Astragalus cicer. By contrast, mutations in the nodI and nodJ genes produced a Nod+ phenotype with a reduced number of nodules on the temperate hosts. Nodules formed on Onobrychis viciifolia by either nodI or nodJ mutants were approximately 10 times smaller than nodules formed by the wild type strain: this reduction in nodule size was not observed on Astragalus cicer.

Amino Acid Sequence↗
PubMed1996

Characterization and mutational analysis of nodHPQ genes of Rhizobium sp. strain N33.

We have shown, by sequencing the nodulation gene region of Rhizobium sp. strain N33 previously isolated from the Canadian high arctic, that the nodHPQ genes are located in a 4.8-kb region downstream of nodBCIJ. The open reading frames of nodHPQ are 747, 906, and 1941 nucleotides long, respectively. The strain N33 genome contains one copy of nodH and two copies of nodPQ that are homologous to those genes in Rhizobium meliloti. Tn5 insertions in the nodHPQ genes of strain N33 did not affect the formation of nodules on the two homologous hosts, Astragalus cicer and Onobrychis viciifolia. Since strain N33 contains the nodBCIJHPQ genes and the recently sequenced nodAFEG genes, we looked for similar host range with R. meliloti. Strain N33 and R. meliloti strains A2 and RCR2011 were shown to induce the formation of root nodules on plants of O. viciifolia. However, strain N33, compared with R. meliloti strains, was able to elicit a few, white, empty, root nodules on Medicago sativa. R. meliloti strains, compared with strain N33, were shown to induce only few nodules containing bacteria on A. cicer. Induction of nod genes transcription in strain N33 was shown to be induced by a variety of flavonoid compounds that are different from those inducing nod genes from R. meliloti.

DNA Mutational Analysis↗
PubMed1996

Classification of bacteria nodulating Lathyrus japonicus and Lathyrus pratensis in northern Quebec as strains of Rhizobium leguminosarum biovar viciae.

The diversity of two populations of rhizobia isolated from Lathyrus japonicus (30 strains) and Lathyrus pratensis (49 strains) growing in northern regions of Quebec, Canada, was determined on the basis of phenotypic characteristics, multilocus enzyme electrophoresis, DNA-DNA homology, and 16S ribosomal DNA sequencing. According to numerical analysis of phenotypic characteristics, strains were divided into four groups. Strains isolated from L. pratensis fell in groups I to III; the latter included reference strains of Rhizobium leguminosarum. All strains isolated from L. japonicus were included in group IV. All strains had nodulation characteristics similar to those of R. leguminosarum bv. viciae. Strains isolated from L. japonicus originating from an arctic region were usually able to grow at 5 degrees C and were more likely to be tolerant to copper (CuCl2.H2O, 100 micrograms/ml) and lead [Pb(CH3COO)2, 500 micrograms/ml] than strains isolated from L. pratensis from a boreal zone. However, both populations of Lathyrus strains were adapted to the cold in comparison to reference strains from temperate regions. Each population had similar genetic diversity (H = 0.45), determined by multilocus enzyme electrophoresis of the loci encoding eight enzymes, but the diversity obtained by analyzing all strains including the reference strains (H = 0.58) was higher. Representative strains of both populations showed high levels of DNA homology among themselves and with R. leguminosarum. Partial sequences of the 16S ribosomal RNA genes were similar to those reported for R. leguminosarum bv. viciae. We conclude that the strains isolated from L. japonicus and L. pratensis belong to R. leguminosarum bv. viciae but are distinguishable by growth at 5 degrees C, which is a characteristic related to their geographic origin.

Base Sequence↗
PubMed1996

Root colonization of maize and lettuce by bioluminescent Rhizobium leguminosarum biovar phaseoli.

Two strains of Rhizobium leguminosarum bv. phaseoli and three other plant growth-promoting rhizobacteria (PGPR) were examined for the potential of maize and lettuce root colonization. All of these strains were selected in vitro for their phosphate-solubilizing abilities. Maize and lettuce seeds were treated with derivatives of all strains marked with lux genes for bioluminescence and resistance to kanamycin and rifampin prior to planting in nonsterile Promix and natural soil. The introduced bacterial strains were quantified on roots by dilution plating on antibiotic media together with observation of bioluminescence. Rhizobia were superior colonizers compared with other tested bacteria; rhizobial root populations averaged log 4.1 CFU/g (fresh weight) on maize roots 4 weeks after seeding and log 3.7 CFU/g (fresh weight) on lettuce roots 5 weeks after seeding. The average populations of the recovered PGPR strains were log 3.5 and log 3.0 CFU/g (fresh weight) on maize and lettuce roots, respectively. One of the three PGPR was not recovered later than the first week after seeding in Promix. Bioluminescence also permitted visualization of in situ root colonization in rhizoboxes and demonstrated the efficiency of rhizobial strains to colonize and survive on maize and lettuce roots.

Lactuca↗