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

Abstract

SummaryA 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 þ 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.

Relationship between codon biased genes, microarray expression values and physiological characteristics of Streptococcus pneumoniae

“…Taken together, these data suggest that defence against oxidative species is highly developed in S. pneumoniae, possibly as a consequence of its ability to colonize and persist in the nasopharynx, where partial oxygen pressure is high. Consistent with this hypothesis, nox, sodA and psaA, which are essential for infection (Auzat et al, 1999;Yesilkaya et al, 2000;Tseng et al, 2002) also appeared to be transcribed at high levels (11 200,5630 and 12 987 FU,respectively). In spite of the anaerobic metabolism of S. pneumoniae, one of the highest CAI and fluorescence values (0?738 and 11 683 units, respectively) corresponded to the pyruvate oxidase gene, spxB, which is one of the more abundant polypeptides of the transparent variants of S. pneumoniae .…”

Role of the dpr Product in Oxygen Tolerance in Streptococcus mutans

“…3A). From mid-log phase (A 660 of 0.2), the increase in cell mass would lead to increased production of H 2 (29), and their deduced amino acid sequences showed 75.4 and 57.1% identity, respectively, with that of S. mutans Dpr. To date, nonheme peroxidases (30, 31), a pseudocatalase (20), and oxidases (2, 10, 16, 34) of lactic acid bacteria, including streptococci, have been reported to substitute for catalase, which is present in other aerotolerant bacteria but not lactic acid bacteria, and some of them, including SOD, were proven to play a role in aerotolerance (9,10,21,27,33).…”

Pyruvate Formate Lyase Is Required for Pneumococcal Fermentative Metabolism and Virulence

“…Therefore, in vivo fitness is determined to a large extent by the processes governed by sugar metabolism. Accumulating evidence suggests that there is a direct link between pneumococcal virulence and sugar metabolism (6,16,20,21,50). This is not limited to proteins involved in polysaccharide degradation, transport, and regulation (16, 31) but also includes those involved in redox metabolism, such as NADH oxidase (Nox) (6), and in pyruvate metabolism (42,50).…”

“…Accumulating evidence suggests that there is a direct link between pneumococcal virulence and sugar metabolism (6,16,20,21,50). This is not limited to proteins involved in polysaccharide degradation, transport, and regulation (16,31) but also includes those involved in redox metabolism, such as NADH oxidase (Nox) (6), and in pyruvate metabolism (42,50). For example, mutation of nox caused diminished virulence in a systemic infection model, and this was attributed to a probable change in the NADH/NAD ϩ ratio or the increased sensitivity of S. pneumoniae to oxidative stress (6).…”

“…This is not limited to proteins involved in polysaccharide degradation, transport, and regulation (16,31) but also includes those involved in redox metabolism, such as NADH oxidase (Nox) (6), and in pyruvate metabolism (42,50). For example, mutation of nox caused diminished virulence in a systemic infection model, and this was attributed to a probable change in the NADH/NAD ϩ ratio or the increased sensitivity of S. pneumoniae to oxidative stress (6). Mutation of spxB (pyruvate oxidase) led to a reduction in virulence in both pneumonia and sepsis models with mice, which was linked to a decrease in acetyl phosphate levels and downregulation of adhesive proteins (45,50).…”