The NADH oxidase of Streptococcus pneumoniae : its involvement in competence and virulence

Authors

  • Isabelle Auzat,

    1. Laboratoire d'Enzymologie et de Biochimie structurale du Centre National de la Recherche Scientifique, 91198 Gif-sur Yvette, France.,
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  • Sabine Chapuy-Regaud,

    1. Laboratoire de Génétique et Physiologie Bactérienne, Centre Hospitalo Universitaire de Rangueil, Université Paul Sabatier, 31403 Toulouse cedex France.,
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  • Gisèle Le Bras,

    1. Laboratoire d'Enzymologie et de Biochimie structurale du Centre National de la Recherche Scientifique, 91198 Gif-sur Yvette, France.,
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  • Delphine Dos Santos,

    1. Laboratoire de Génétique et Physiologie Bactérienne, Centre Hospitalo Universitaire de Rangueil, Université Paul Sabatier, 31403 Toulouse cedex France.,
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  • A. David Ogunniyi,

    1. Molecular Microbiology Unit, Women's and Children's Hospital, North Adelaide, South Australia 5006, Australia.
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  • Isabelle Le Thomas,

    1. Laboratoire de Génétique et Physiologie Bactérienne, Centre Hospitalo Universitaire de Rangueil, Université Paul Sabatier, 31403 Toulouse cedex France.,
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  • Jean-Renaud Garel,

    1. Laboratoire d'Enzymologie et de Biochimie structurale du Centre National de la Recherche Scientifique, 91198 Gif-sur Yvette, France.,
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  • James C. Paton,

    1. Molecular Microbiology Unit, Women's and Children's Hospital, North Adelaide, South Australia 5006, Australia.
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  • Marie-Claude Trombe

    1. Laboratoire de Génétique et Physiologie Bactérienne, Centre Hospitalo Universitaire de Rangueil, Université Paul Sabatier, 31403 Toulouse cedex France.,
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Marie-Claude Trombe. E-mail trombe@CICT.fr; Tel. (+33) 561 322 974; Fax: (+33) 561 322 620.

Abstract

A soluble flavoprotein that reoxidizes NADH and reduces molecular oxygen to water was purified from the facultative anaerobic human pathogen Streptococcus pneumoniae. The nucleotide sequence of nox, the gene which encodes it, has been determined and was characterized at the functional and physiological level. Several nox mutants were obtained by insertion, nonsense or missense mutation. In extracts from these strains, no NADH oxidase activity could be measured, suggesting that a single enzyme encoded by nox, having a C44 in its active site, was utilizing O2 to oxidize NADH in S. pneumoniae. The growth rate and yield of the NADH oxidase-deficient strains were not changed under aerobic or anaerobic conditions, but the efficiency of development of competence for genetic transformation during growth was markedly altered. Conditions that triggered competence induction did not affect the amount of Nox, as measured using Western blotting, indicating that nox does not belong to the competence-regulated genetic network. The decrease in competence efficiency due to the nox mutations was similar to that due to the absence of oxygen in the nox+ strain, suggesting that input of oxygen into the metabolism via NADH oxidase was important for controlling competence development throughout growth. This was not related to regulation of nox expression by O2. Interestingly, the virulence and persistence in mice of a blood isolate was attenuated by a nox insertion mutation. Global cellular responses of S. pneumoniae, such as competence for genetic exchange or virulence in a mammalian host, could thus be modulated by oxygen via the NADH oxidase activity of the bacteria, although the bacterial energetic metabolism is essentially anaerobic. The enzymatic activity of the NADH oxidase coded by nox was probably involved in transducing the external signal, corresponding to O2 availability, to the cell metabolism and physiology; thus, this enzyme may function as an oxygen sensor. This work establishes, for the first time, the role of O2 in the regulation of pneumococcal transformability and virulence.

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