Plasmid content and localization of the genes encoding the denitrification enzymes in two strains of Rhodobacter sphaeroides

Authors

  • Carole Schwintner,

    1. CEA–Cadarache/DEVM/Laboratoire de Bioénergétique Cellulaire, Bât. 156, 13108 Saint Paul lez Durance Cedex, France
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    • 1

      Laboratoire de Génétique Moléculaire de la Recombinaison (UMR144), Institut Curie, 26, rue d'Ulm, 75248 Paris cedex 05, France.

  • Monique Sabaty,

    1. CEA–Cadarache/DEVM/Laboratoire de Bioénergétique Cellulaire, Bât. 156, 13108 Saint Paul lez Durance Cedex, France
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  • Bénédicte Berna,

    1. CEA–Cadarache/DEVM/Laboratoire de Bioénergétique Cellulaire, Bât. 156, 13108 Saint Paul lez Durance Cedex, France
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  • Sandrine Cahors,

    1. CEA–Cadarache/DEVM/Laboratoire de Bioénergétique Cellulaire, Bât. 156, 13108 Saint Paul lez Durance Cedex, France
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    • 2

      CEA–Cadarache/DEVM/Laboratoire du Métabolisme Carboné, Bât. 156, 13108 Saint Paul lez Durance Cedex, France.

  • Pierre Richaud

    Corresponding author
    1. CEA–Cadarache/DEVM/Laboratoire de Bioénergétique Cellulaire, Bât. 156, 13108 Saint Paul lez Durance Cedex, France
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*Corresponding author. Tel.: +33 4 42 25 35 70; Fax: +33 4 42 25 47 01; E-mail: richaud@kebbi.cad.cea.fr

Abstract

Plasmid content and localization of the genes encoding the reductases of the denitrification pathway were determined in the photosynthetic bacterium Rhodobacter sphaeroides forma sp. denitrificans by transverse alternating-field electrophoresis (TAFE) and hybridization with digoxigenin-labeled homologous probes. Two large plasmids of 102 and 115 kb were found. The genes encoding the various reductases are not clustered on a single genetic unit. The nap locus (localized with a napA probe), the nirK gene and the norCB genes encoding the nitrate, nitrite and nitric oxide reductases, respectively, were found on different AseI and SnaBI digested chromosomal DNA fragments, whereas the nos locus (localized with a nosZ probe), encoding the nitrous oxide reductase, was identified on the 115-kb plasmid. Furthermore, the genes encoding two proteins of unknown function, one periplasmic and the other cytoplasmic, but whose synthesis is highly induced by nitrate, were found on a different chromosomal fragment. For comparison, the same experiments were carried out on the well-characterized strain Rhodobacter sphaeroides 2.4.1.

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