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Iron-Regulated Biofilm Formation in Staphylococcus aureus Newman Requires ica and the Secreted Protein Emp

Department of Genetics, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom,¹ Institute of Infection, Immunity and Inflammation, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom²

Received 10 December 2007/ Returned for modification 26 January 2008/ Accepted 30 January 2008

Staphylococcus aureus biofilm formation is induced in iron-restricted growth conditions in vitro. In this study, we showed that Emp and Eap play important roles in low-iron-induced biofilm formation of S. aureus Newman. Eap and Emp are secreted proteins which are non-covalently attached to the S. aureus cell surface and have previously been implicated in a number of aspects of S. aureus pathogenesis. We showed here that the transcription of these important virulence factors is induced by growth in low-iron medium, reflective of the in vivo environment. Our results show that iron regulation of Eap and Emp is Fur independent. However, Fur is required for full induction of eap and emp expression in low-iron conditions. In this study, we demonstrated that in addition to Fur, low-iron-induced biofilm formation requires Sae, Agr, and SarA. In iron-restricted growth conditions, Sae and Agr are essential for Emp and Eap expression and hence for biofilm formation, whereas SarA appears to have a less-significant role. We also showed that expression of the ica operon is required for biofilm formation in iron-restricted growth conditions. We demonstrated that in fact, ica is required for the expression of the important multifunctional virulence determinants eap and emp.

Published ahead of print on 11 February 2008.

Editor: A. J. Bäumler