Jean-Pierre Magnin
Centre national de la recherche scientifique
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Featured researches published by Jean-Pierre Magnin.
Microbiology | 1985
John C. Willison; Gabriel Ahombo; Jacqueline Chabert; Jean-Pierre Magnin; Paulette M. Vignais
Summary: The mutant R plasmid pTH10 was used to construct a circular linkage map of the Rhodopseudomonas capsulata B10 chromosome. Mutations affecting nitrogen fixation (nif mutations) were dispersed in several groups on the chromosome. Biochemical analysis of nif mutants allowed identification of the structural gene for the nitrogenase component II or Fe protein (nifH) and a putative regulatory gene, possibly nifA. These two genes appeared closely linked in conjugation experiments, but represented two distinct linkage groups in crosses mediated by gene transfer agent. Other mutants were affected in the synthesis and/or stability of the nitrogenase component I or MoFe protein; synthesis of component II was also affected, but to a lesser extent. In two of these mutants, nitrogenase activity and the content of component I was increased five- to sixfold by the addition of 1 mM-molybdate to the growth medium.
Molecular Genetics and Genomics | 1990
Annette Colbeau; Jean-Pierre Magnin; Béatrice Cauvin; T. Champion; Paulette M. Vignais
SummaryAn hydrogenase-deficient (Hup−) mutant of Rhodobacter capsulatus was obtained by adventitious insertion of IS21 DNA into an hydrogenase structural gene (hup) of the wild-type strain 1310. The resulting Hup− mutant, strain JP91, selected by its inability to grow autotrophically (Aut− phenotype) together with other Hup− mutant strains obtained by classical ethyl methane sulphonate mutagenesis were used in R plasmid-mediated conjugation experiments to map the hup/aut loci on the chromosome of R. capsulatus. The hup genes tested in this study were found to cluster on the chromosome in the proximity of the his-1 marker. A cluster of hup genes comprising the structural genes was isolated from a gene bank constructed in the cosmid vector pHC79 with 40 kb insert DNA. The clustered hup genes, characterized by hybridization studies and complementation analyses of the R. capsulatus Hup− mutants, span 15–20 kb of DNA.
Biotechnology Letters | 1998
Agnès Boyer; Jean-Pierre Magnin; Patrick Ozil
Thiobacillus ferrooxidans removed copper ions at pH 1.4 with a specific uptake capacity of 0.7 g Cu 2+ g -1 dry weight. A 0.6 M copper ion tolerant T. ferrooxidans was isolated after successive subcultures on ferrous sulphate oxidation without loss of production, 52 mg protein (mol Fe 2+ oxidised) -l . This adaptation lead to a decrease in copper ion uptake to 0.09 g Cu 2+ g -1 dry weight.
Electroanalysis | 1998
Margarita Stoytcheva; Vencislava Sharkova; Jean-Pierre Magnin
An acetylcholinesterase amperometric sensor is used to register the current of oxidation of thiocholine, the product of the acetylcholinesterase catalyzed hydrolysis of acetylthiocholine. The decrease of the value of the signal obtained in presence of arsenate(III) is interpreted as due to the diminution of the quantity of the generated thiocholine because of the inhibition of the immobilized acetylcholinesterase on the surface of a graphite electrode. The experiments were performed varying the concentrations of the inhibitor and of the substrate, as well as pH. The kinetics of the inactivation of the immobilized acetylcholinesterase by arsenate(III) was investigated. Obtained results could be employed for the quantitative determination of AsO33− based on the inhibition of the immobilized acetylcholinesterase on the surface of a graphite electrode, using an electrochemical approach.
Ultrasonics Sonochemistry | 2010
Abeer Al Bsoul; Jean-Pierre Magnin; Nadine Commenges-Bernole; Nicolas Gondrexon; John C. Willison; Christian Pétrier
Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical and chemical effects on microorganisms. The aim of this study was to investigate the effect of ultrasound on the destruction of Mycobacterium strain 6PY1. Ultrasound waves (20 kHz or 612 kHz) were used to treat aqueous suspensions of Mycobacterium at different volumes, initial bacterial concentrations, and power densities. At the same power density and the same exposure time, sonication at high frequency resulted in a lower destruction of Mycobacterium sp. 6PY1 (35.5%) than sonication at low frequency (93%). The percentage of removal was not significantly affected by the volume of the irradiated suspension (150-300 ml) or the initial cell concentration (2.15 x 10(-3)-1.4 x 10(-2)mg protein L(-1)). At low frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density, with a constant level reached after a certain power density. At high frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density. The mechanism of cell killing was investigated by examining the effects of OH() radical scavengers such as sodium carbonate. At high frequency the presence of sodium carbonate suppressed the removal process. However, at low frequency the removal process was not affected, thus indicating that OH() radicals have a negligible role in this case. The latter result was supported by ten times H(2)O(2) production at high frequency greater than that at low frequency.
Biotechnology Letters | 1998
Francis Baillet; Jean-Pierre Magnin; A. Cheruy; Patrick Ozil
Thiobacillus ferrooxidans tolerates Cr 3+ up to 75 mM during growth on ferrous sulphate without modification of its bacterial activity (53 μg protein mM -1 Fe 2+ oxidised). At pH 1.4 and in the presence of Cr 2 O 3 , a maximal uptake capacity of 509 mg.g -1 dry weight was obtained with biomass harvested in the middle of the exponential growth phase. Cr 6+ uptake by T. ferrooxidans resulted in the precipitation of a chromium-rich compound on the surface bacterial cells, as observed by transmission electron microscopy.
Archives of Microbiology | 1987
John C. Willison; Jean-Pierre Magnin; Paulette M. Vignais
Phodobacter capsulatus (formerly Rhodopseudomonas capsulata) strain B10 was found to contain a single plasmid of molecular weight 86×106. Strains lacking this plasmids were isolated by various methods from strains containing the mutant R plasmid, pTH10. With the exception of two strains, which were found to contain chromosomal insertions of R plasmid DNA, strains lacking the endogenous plasmid appeared to be unaffected in any of the following metabolic or genetic functions: photosynthetic, autotrophic, diazotrophic, and dark, anaerobic growth; the production of bacteriocin; homologous recombination; the restriction of foreign DNA; and the production of gene transfer agent. DNA-DNA hybridization experiments confirmed that the plasmid had been eliminated from these strains and not become integrated into the chromose. However, sequences homologous to those of the endogenous plasmid were found to be present in the chromosome of R. capsulatus B10. This suggests, among other possibilities, that the endogenous plasmid may have originated in the chromosome, and might serve to duplicate certain chromosomal functions.
Biosensors and Bioelectronics | 2009
Margarita Stoytcheva; Roumen Zlatev; Jean-Pierre Magnin; Marcela Ovalle; Benjamin Valdez
A novel electrochemical biosensor integrating the strictly autotrophic bacterial strain Leptospirillum ferrooxidans as a recognition element and a Clark type oxygen probe as a transducer was designed, metrologically and analytically characterized and applied for the specific Fe(2+) determination. The bacterial Fe(2+) oxidation involves O(2) consumption, thus the quantification was performed registering the decrease of the oxygen reduction current. The limit of detection was found to be 2.4 micromol L(-1) and the sensitivity of the determinations-3.94 nAL micromol(-1). The response time of the biosensor is 18s for Fe(2+) concentrations of 10(-5) to 10(-4) mol L(-1). The biosensor was applied as well for the indirect determination of Fe(2+) oxidizing species such as Cr(2)O(7)(2-), reaching a sensitivity of 2.47 nAL micromol(-1). The transducer characteristics were evaluated and optimized to obtain short response time and high sensitivity. The analytical performances of the biosensor subject of the present work were found to be similar to that of the At. ferrooxidans based one developed by the authors earlier, avoiding however the sulfur compounds interference, because of the substrate specificity of the applied bacterial strain.
Canadian Journal of Microbiology | 2014
Jean-Pierre Magnin; Nicolas Gondrexon; John C. Willison
This paper presents the first report providing information on the zinc (Zn) biosorption potentialities of the purple non-sulfur bacterium Rhodobacter capsulatus. The effects of various biological, physical, and chemical parameters on Zn biosorption were studied in both the wild-type strain B10 and a strain, RC220, lacking the endogenous plasmid. At an initial Zn concentration of 10 mg·L(-1), the Zn biosorption capacity at pH 7 for bacterial biomass grown in synthetic medium containing lactate as carbon source was 17 and 16 mg Zn·(g dry mass)(-1) for strains B10 and RC220, respectively. Equilibrium was achieved in a contact time of 30-120 min, depending on the initial Zn concentration. Zn sorption by live biomass was modelled, at equilibrium, according to the Redlich-Peterson and Langmuir isotherms, in the range of 1-600 mg Zn·L(-1). The wild-type strain showed a maximal Zn uptake capacity (Qm) of 164 ± 8 mg·(g dry mass)(-1) and an equilibrium constant (Kads) of 0.017 ± 0.00085 L·(mg Zn)(-1), compared with values of 73.9 mg·(g dry mass)(-1) and 0.361 L·mg(-1) for the strain lacking the endogenous plasmid. The Qm value observed for R. capsulatus B10 is one of the highest reported in the literature, suggesting that this strain may be useful for Zn bioremediation. The lower Qm value and higher equilibrium constant observed for strain RC220 suggest that the endogenous plasmid confers an enhanced biosorption capacity in this bacterium, although no genetic determinants for Zn resistance appear to be located on the plasmid, and possible explanations for this are discussed.
Advances in Botanical Research | 2013
John C. Willison; Jean-Pierre Magnin
Abstract Endogenous plasmids are found in most strains of Rhodobacter sphaeroides , Rhodobacter capsulatus and Rhodospirillum rubrum , but appear to be less common in other species of purple non-sulphur bacteria. They have also been found in some species of green and purple sulphur bacteria. Until recently, there was little conclusive evidence for the functions of these plasmids, and most were considered to be cryptic. The advent of whole genome sequencing has enabled predictions of possible plasmid functions that can then be tested experimentally. In addition, transcriptomic and proteomic studies in R. sphaeroides 2.4.1 have shown that plasmids play an active role in genome function and may code for essential metabolic processes. This chapter summarises experimental and genomic evidence for plasmid function in the anaerobic anoxygenic phototrophs, with particular emphasis on photosynthetic metabolism, nitrogen oxide reduction, cell wall biosynthesis and heavy metal resistance, and new experimental evidence is presented for the role of the endogenous plasmid in the R. capsulatus strains B10 and SB1003. The evolution of these plasmids will also be considered, and insights from nucleotide sequence comparisons will be combined with those from phylogenetic analysis of plasmid replication modules in the Roseobacter clade of the α- Proteobacteria , which includes aerobic anoxygenic phototrophs.