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The NADH oxidase of Streptococcus pneumoniae : its involvement in competence and virulence[Note 1. Part of this work has been presented at the ...]
Author(s) -
Auzat Isabelle,
ChapuyRegaud Sabine,
Le Bras Gisèle,
Dos Santos Delphine,
Ogunniyi A. David,
Le Thomas Isabelle,
Garel JeanRenaud,
Paton James C.,
Trombe MarieClaude
Publication year - 1999
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1999.01663.x
Subject(s) - biology , virulence , oxidase test , nadph oxidase , mutant , superoxide , streptococcus pneumoniae , microbiology and biotechnology , gene , biochemistry , nox , genetics , enzyme , bacteria , chemistry , organic chemistry , combustion
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 O 2 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 O 2 . 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 O 2 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 O 2 in the regulation of pneumococcal transformability and virulence.