Involvement of potD in Streptococcus pneumoniae Polyamine Transport and Pathogenesis

Abstract

Polyamines such as putrescine, spermidine, and cadaverine are small, polycationic molecules that are required for optimal growth in all cells. The intracellular concentrations of these molecules are maintained by de novo synthesis and transport pathways. The human pathogen Streptococcus pneumoniae possesses a putative polyamine transporter (pot) operon that consists of the four pot-specific genes potABCD. The studies presented here examined the involvement of potD in polyamine transport and in pneumococcal pathogenesis. A potDdeficient mutant was created in the mouse-virulent serotype 3 strain WU2 by insertion duplication mutagenesis. The growth of the WU2⌬potD mutant was identical to that of the wild-type strain WU2 in vitro in rich media. However, WU2⌬potD possessed severely delayed growth compared to wild-type WU2 in the presence of the polyamine biosynthesis inhibitors DFMO (␣-dimethyl-fluroornitithine) and MGBG [methylgloxal-bis (guanyl hydrazone)]. The mutant strain also showed a significant attenuation in virulence within murine models of systemic and pulmonary infection regardless of the inoculation route or location. These data suggest that potD is involved in pneumococcal polyamine transport and is important for pathogenesis within various infection models.

Polyamine biosynthesis and transport mechanisms are crucial for fitness and pathogenesis of Streptococcus pneumoniae

“…Although the pneumococcal polyamine transporter has been implicated in both pneumonia and murine septicaemia, its role in nasopharyngeal colonization was unknown (Polissi et al, 1998;Ware et al, 2006). Similar to the cad deletion strain, a potABCD mutant was significantly attenuated in a murine respiratory tract colonization model (Fig.…”

“…Previous studies from our laboratory have shown that inactivation of potD in a mouse-virulent capsular type 3 strain significantly attenuates the progression of disease in systemic and pulmonary murine models, supporting a role for polyamine uptake in pneumococcal pathogenesis (Ware et al, 2006). We have also shown that polyamines may serve as functional analogues for choline molecules during in vitro growth, and a significant increase in PotD expression is seen when pneumococci are exposed to environmental stress and during murine septicaemia Ware et al, 2005).…”

Immunization with Polyamine Transport Protein PotD Protects Mice against Systemic Infection with Streptococcus pneumoniae

“…A putative pneumococcal polyamine transporter contains a lipoprotein, PotD, which is surface exposed and accessible to antibodies. PotD has been reported to be involved in virulence in both an animal model of sepsis and pneumonia (24,32). These studies were undertaken to investigate the role of PotD in protective immunity and to assess its potential as a vaccine candidate.…”

“…The pneumococcal genomes which have been sequenced contain homologues of known genes encoding enzymes which synthesize polyamines from ornithine and arginine. However, uptake of polyamines from the environment appears to be necessary for full expression of pneumococcal virulence (24,32). PotD is a putative polyamine-binding surface protein, and inhibition of its function with antibodies may alter intracellular polyamine levels to an extent which attenuates virulence.…”

“…However, flow cytometry and cell fractionation experiments have shown that PotD in pneumococci is surface exposed (27a). Previous studies have shown that a potD mutation in a mouse-virulent capsular type 3 strain significantly attenuates the natural history of infection in systemic and pulmonary murine models, indicating a role for PotD in pneumococcal pathogenesis (32).…”