B-171. The Virulence Regulator Sae of Staphylococcus aureus: Promoter Activities and Response to Phagocytosis-Related Signals

T. Geiger, C. Goerke, M. Mainiero, C. Wolz;
Medical Microbiology and Hygiene, Tübingen, GERMANY.

The two-component system SaeR/S of Staphylococcus aureus is closely involved in the regulation of major virulence factors. However, little is known about the signals leading to saeR/S activation. A total of four overlapping transcripts (T1-T4) from three different transcription starting points are expressed in the sae operon. We employed a ß-galactosidase reporter assay to characterize the putative promoter regions within the saeR/S upstream region. The main transcript T2 is probably generated by endoribonucleolytic processing of the T1 transcript. Only two distinct promoter elements (P1 and P3) could be detected within the saeR/S upstream region. A weak P3 promoter upstream of saeR/S generates the T3 transcript and is preceded by a cis-acting enhancer element which is repressed by saeR/S. The most distal P1 promoter is strongly auto-regulated, activated by agr and repressed by sigma factor B. In strain Newman a mutation within the histidine kinase SaeS leads to a constitutively activated sae system. Evaluation of different external signals revealed that the P1 promoter in strain ISP479R and strain UAMS-1 is inhibited by low pH and high NaCl concentrations, but activated by hydrogen peroxide. The most prominent induction of P1 was observed at subinhibitory concentrations of α-defensins in various S. aureus strains, with the exception of strain ISP479R and strain COL. P1 was not activated by the antimicrobial peptides LL37 and daptomycin or by cell-wall-active antibiotics. In summary, the results indicate that the sensor molecule SaeS is activated by alteration within the membrane allowing the pathogen to react to phagocytosis related effector molecules.