Cell Wall Proteins of Staphylococcus aureus Responsive to Oxygen Tension and Iron Concentration

Lee, Seung Il; Lim, Yong; Shin, Sung Heui

Abstract

BACKGROUND: We previously reported that activity of iron-uptake systems (IUS) influenced on the growth of Staphylococcus aureus in laboratory medium and body fluids according to the iron and oxygen concentrations, which they are closely related each other in several microbial metabolism. In the present study, we tried to investigate the profiles of cell wall proteins of S. aureus according to the change of iron and oxygen concentrations. METHODS: SR-1 strain, whose IUS are defective, was isolated from the standard strain ATCC 6538 by repeated exposure against streptonigrin. These two strains were cultured under the aerobic, microaerobic and anaerobic conditions in the iron-sufficient BHI and iron-depleted BHI, respectively. Cell wall proteins were visualized by Coomassie staining after SDS-PAGE. RESULTS: Cell wall proteins of the both strains were expressed more than under the aerobic condition than under the anaerobic condition in the iron-sufficient medium as well as in the iron-deficient medium. However, expression of cell wall proteins of SR-1 strain was markedly inhibited compared to that of parental ATCC 6538 strain, especially in the iron-deficient medium. Among the proteins more expressed under the aerobic culture condition in the iron-deficient medium, about 88, 55, 39, 36, 35 and 33 kDa of proteins were iron-repressible and oxygen-inducible, and corresponded to the iron-repressible proteins which other researchers reported. CONCLUSION: Expression of cell wall proteins of S. aureus was affected by simultaneous and respective change of iron and oxygen concentrations. Activity of IUS influenced more on the expression of cell wall proteins of S. aureus in the iron-deficient environment than in the iron-sufficient environment. These results suggest the possibility that the iron-repressible and oxygen-inducible proteins mimic those (antigens) found commonly in clinical infections.