Iron-regulated biofilm formation in Staphylococcus aureus Newman requires ica and the secreted protein Emp

Dept. of Genetics, University of Leicester, University Road, Leicester LE1 7RH, UK; Institute of Infection, Immunity and Inflammation, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD

^* To whom correspondence should be addressed. Email: jam26{at}le.ac.uk.

	Abstract

S. aureus biofilm formation is induced in iron-restricted growth conditions in vitro. In this study we show 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 show 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. In this study we demonstrate that, as well as 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 biofilm formation, whereas SarA appears to have a less significant role. We also show that expression of the ica operon is required for biofilm formation in iron-restricted growth conditions. In fact we demonstrate that ica is required for the expression of the important multi-functional virulence determinants, eap and emp.