Transferrin Binding Protein of Staphylococcus aureus is not Essential for Iron-uptake from Transferrin in vitro

Park, Sang Kee; Lim, Yong; Shin, Sung Heui

Abstract

BACKGROUND
Staphylococcus aureus produces siderophore and expresses transferring-binding protein for uptake of iron essentially required for multiplication under the iron-restricted conditions. We investigated which of the two iron-uptake systems is dominant or essential for S. aureus growth. METHODS: Streptonigrin-resistant mutant (SR-1) of S. aureus, isolated by repeated exposure to streptonigrin, was used in this study. SR-1 strain produced less amount of siderophore than the parent strain and did not express the transferring-binding protein. Growth and iron consumption of the two bacteria were compared during cultivation in the media containing various concentrations of iron, by measuring optical densities of the culture fluids at 600 nm and residual iron concentrations of the culture supernatants. RESULTS: Growth of the two bacteria in the iron-sufficient media containing various sources of iron was more active than in the iron-deficient media, in which iron concentration was 0.2 microgram/dL. Growth of SR-1 strain was markedly inhibited in the iron-deficient media with/without apotransferrin (0.5 mg/mL). However, growth of SR-1 strain did not show any difference in the iron-sufficient media containing FeCl3 (0.2 micrometer) and hemoglobin (0.5 mg/mL) as compared with that of the parental strain. Moreover, growth of the two bacteria did not show any difference in the media containing holotransferrin (0.5 mg/mL). There was no difference in iron consumption between the parental and mutant strains, evidenced by the residual iron concentration of the culture supernatants. CONCLUSION: Siderophore production is thought to be dominant or essential iron-uptake system for in vitro growth of S. aureus. The pathogenetic role of multifunctional transferring-binding protein, including transferring-binding activity and glycolytic enzyme activity, is expected to be established through further continued studies.